Download Electron Paramagnetic Resonance Study of the Copper(II

Diss. ETH No. 12669
Electron
Paramagnetic
Resonance
Copper(II) Complexation with
Study of the
Carbonate
Solution and at Calcium
Ligands in Aqueous
Carbonate Surfaces
DISSERTATION
submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY
ZURICH
for the
degree
of
Doctor of Natural Sciences
presented by
Paul Michel Schosseler
Dipl.
born
Chem. ETH
April 3,1969
citizen of
accepted on the
Prof. Dr. A.
Luxembourg
recommendation of
Schweiger,
examiner
Prof. Dr. B. Wehrli, co-examiner
1998
Fier meng Elteren
Table
of Contents
Table of Contents
i
Summary
v
vii
Zusammenfassung
1
1. Introduction
2. Basic
Concepts
of CW and Pulse EPR
2.1 One Electron in the
Magnetic
5
Field
5
2.1.1 Electron Zeeman Interaction
2.1.2
Crystal-Field Splitting
2.1.3 g
9
2.2.2 TheS= 1/2,/=
Spins
1/2system
Matching Range
2.3.2 Nuclear
Experiments
Splitting
Quadrupole
Summary
2.4 EPR of Cu2+
3.
18
Complete Spin Hamiltonian
2.3.1 Zero-Field
2.3.3
15
and Exact Cancellation
2.2.5 Combination Lines in ESEEM
2.3 The
13
Strong Coupling
2.2.3 Weak and
of
Energy
22
23
25
25
Interaction
25
Terms
26
Complexes
27
31
Methodology of EPR
3.1 CW and Pulse EPR
3.2 MW Pulses and
7
12
Interaction
Hyperfine
2.2.4
Spin-Orbit Coupling
Anisotropy
2.2 Interaction with Nuclear
2.2.1
and
5
Spin Dynamics
31
34
ii
3.3 Relaxation Times and Linewidths
35
3.4 Pulse EPR
37
Experiments
3.4.1 Two-Pulse ESEEM
4.
39
3.4.3 ID Four-Pulse ESEEM
40
3.4.4 HYSCORE
41
3.4.5 ENDOR
44
Aqueous Chemistry
4.1
37
3.4.2 Three-Pulse ESEEM
Cu2+
of Cu2* and Carbonates
47
and Carbon Dioxide
4.1.1 Coordination
48
Chemistry
of
Cu2+
48
4.1.2 Carbon Dioxide
4.1.3
Complexation
of
49
Cu2+by
Carbonate
Ligands
4.2 The Solid Calcium Carbonates
50
4.2.1 Structural Characteristics
4.2.2
Crystal
50
Growth and Dissolution
4.2.3 Interactions with Trace Metal Ions
4.3 Chemical
4.3.1
Equilibrium
5.
Calculations
ChemEQL
4.3.2 Surface
52
54
56
56
Complexation
Model
57
4.3.3 The
C02/H20 system
58
4.3.4 The
Cu2+/H20 system
59
Cu2+/C02/H20 system
The CaC03(s)/Cu2+/H20 system
4.3.5 The
60
4.3.6
61
Copper
Carbonate
Complexes in Aqueous Solution.
5.1 Introduction
5.2
49
69
Experimental Section
5.2.1
5.2.3
70
Sample Preparation
5.2.2 Glass
Forming
69
70
Additives
71
Equipment
72
Manipulation
73
5.2.5 EPR and ESEEM Simulations
74
5.2.4 Data
5.3 Results
5.3.1
75
Optical Spectra
5.3.2 EPR
75
Spectra
5.3.3 ESEEM and ENDOR of
76
13C
5.3.4 ID and 2D ESEEM of Protons
5.4 Discussion
79
84
91
iii
5.4.1
Optical Spectra
5.4.2 EPR
91
Spectra
92
5.4.3 ESEEM and ENDOR of
13C
93
5.4.4 ID and 2D ESEEM of Protons
95
5.4.5 Structure
Proposals
97
5.4.6
Effects
98
Freezing
5.5 Conclusions
6. Interactions of
100
Cu2+ with Solid Calcium
Carbonates
6.1 Introduction
6.2
101
101
Experimental
Section
102
6.2.1
Sample Preparation
102
6.2.2
Equipment
105
6.2.3 Data
Manipulation
105
6.2.4 EPR and HYSCORE Simulations
106
6.3 Results
106
6.3.1 AAS Measurements
106
6.3.2 EPR
106
Spectra
6.3.3 Two-Pulse ESEEM
6.3.5
113
13C
116
ID Four-Pulse ESEEM of Protons
123
6.3.4 HYSCORE of
6.4 Discussion
123
6.4.1 AAS Measurements
6.4.2 Structural
Assignment of the
6.4.3 Mechanistic
123
Observed
Interpretation
6.4.4
Summary
6.4.5
Application to
of the
Copper Species
124
130
Experimental
Results
other Metal Ions
6.5 Conclusions
133
136
139
APPENDIX A
141
Hamiltonian
A.l
Spin
A.2
Density Operator
141
Formalism
A.3 Calculation of CW and Pulse EPR
142
Spectra
143
145
APPENDIX B
B.l Two-Pulse ESEEM Formula
145
B.2 Three-Pulse ESEEM Formula
146
B.3 Four-Pulse ESEEM Formula
146
APPENDIX C
C.l
Equilibrium
149
Constants
149
iv
C.2 EXCEL
Input Matrices
References
Symbols
and Abbreviations
for
ChemEQL
152
155
163
Acknowledgement
167
Curriculum Vitae
169
Summary
The interactions between trace metal ions and the
minerals
are
of interest both for environmental chemists and
ation with carbonate and bicarbonate ions in solution
speciation
in many
surfaces and
reactivity
a
central role in trace metal
coprecipitation
at
calcium carbonate
reactions influence the distribution of the ions
as
well
as
the
of the minerals.
(EPR) techniques
2+
plays
carbonate
geologists. The complex¬
aquatic environments. Furthermore adsorption
In this thesis continuous
Cu
widespread calcium
with carbonate
wave
applied
are
ligands
to
(CW) and pulse Electron Paramagnetic
investigate
the
complexation
Resonance
of the transition metal ion
in aqueous solution and at the surface of the two
CaC03
modifications, vaterite and calcite. From the detailed structural and electronic informa¬
tion obtained for the
structure of
metal ions
CaC03
copper-carbonate complexes general
minerals and
adsorption
C-labeled carbonate
ligands
try of the copper complexes
electron with the
from water
The small
or
13
conclusions about the surface
coprecipitation reactions
of other trace
derived.
are
The first part deals with the
13
and
ligand
in aqueous solution.
are
followed
through
field and nuclei of
hydroxyl ligands
C
pH dependent complexation
13
Changes
the interactions of the
C-labeled carbonate
observed in the
pulse
2+
and
in the coordination geome-
in the first and second coordination
hyperflne coupling
between Cu
unpaired
2+
Cu
ligands and protons
spheres of the cation.
EPR spectra in frozen solution
and at pH 5.5 is assigned to weak, monodentate coordination of carbonates to the Cu
2+
vi
ion. The
C
large
hyperfine coupling
ligands
nation of carbonate
the four-membered
per
complex
mono-
ring.
leads to
and is
found at
explained by
an
elongation
a
higher covalency
complexation
The carbonate
and bidentate coordination at
6.5 and 8 arises from bidentate coordi¬
pH
in the
of the
bonding
%
equatorial plane
of the cop¬
of the axial water bonds. The observation of both
pH
by pulse
6.5 and 8
contradiction to the calculated concentrations of
EPR in frozen solution is in
copper-carbonate complexes
temperature. Although equilibrium shifts during the freezing of the samples
excluded, the basic mechanisms of
zen
solution
The
expected to apply
are
investigation of the Cu
in the second part of the thesis
2+
mono-
and
C and proton
solution. Atomic
adsorption
uptake by
gives insight
ions
on
by rapid dehydration.
or
Cu
ions
effect.
on a
molecular level into
assignment is based
and
The
integrated
resulting
square-planar
crystal growth
or
on
carbonate surface, covered
information obtained for Cu
2+
metal ions like Fe
range 8.5 to 9
reac¬
the EPR parameters
lattice
binding
comparable
,
Co
2+
,
by
2+
Ni
a
by
they
are
thin, structured surface
provides
2+
and Zn
a
2+
better
within
a
few min¬
is due to monodentate
chelate
to a
CW EPR,
and dissolution.
distortions
EPR results show that the
copper
can
complex¬
complexes
explain
the inhi¬
Upon recrystallization the
exhibit
a
dynamic
expected
solid solution. The results support the concept of
CuxCa,1_X)C03(s)
pH
square-pyramidal
into the calcite lattice where
local
pulse
The strong surface
surface sites like kinks and steps, revealed
are
be
observed in fro¬
complexation
nearly complete
four carbonate surface ions,
bition of calcium carbonate
2+
vaterite and calcite in the
the mineral surface,
ation in solution. The formation of
exposed
can not
also in aqueous solution at ambient temperature.
absorption spectroscopy (AAS)
coordination to three
at
at room
hyperfine couplings observed for the copper-carbonate complexes in
of the Cu
utes, is followed
complexation
and bidentate
tions at the mineral surfaces. The structural
13
in
layer.
understanding
to
a
Jahn-Teller
destabilize
dynamic
the
calcium
The detailed structural
of the interaction of other
with calcium carbonate minerals.
tMHtih
Die
ist
von
Wechselwirkungen zwischen Spurenmetallen
groBem
Interesse fiir Umweltchemiker und
Carbonat- und Bicarbonationen in
tallen in naturlichen Gewassern.
lungsreaktionen
beeinfiussen
und Calciumcarbonatmineralien
Geologen.
bestimmt oft die
Losung
Adsorption
Komplexbildung
Speziierung
von
mit
Spurenme¬
Calciumcarbonatoberflachen und Fal-
an
Verteilung
sowohl die
Die
der Metallionen als
auch die
Reaktivitat der Mineralien.
Gegenstand
der
vorliegenden
Ubergangsmetallions
ftachen der beiden
(CW)
und
Cu
2+
CaCOj
gepulster
mit
Arbeit ist die
Carbonatliganden
Paramagnetischer
Elektron
SchluBfolgerungen beziiglich
Adsorptions-
und
C markierten
Fallungsreaktionen
Carbonatliganden
dem ungepaarten Elektron des
markierten
ersten
in der
EPR
Carbonatliganden
und zweiten
in
anderer
Komplexbildung
Losung und
Resonanz
an
des
den Ober-
Losung
und Protonen
Die kleine
Temperatur
(EPR). Aus den geometri-
von
und
dem
Wasser- oder
sowie
13
und
zwischen
C-Kernen
Hydroxylliganden
von
in der
geben AufschluB liber Anderungen
C-Hyperfeinkopplung,
pH 5.5
2+
zwischen Cu
Wechselwirkung
Ligandenfeld
Rations
13
allgemeine
Spurenmetalle abgeleitet werden.
untersucht. Die
von
konnen
CaC03 Mineralien und
pH-abhangige Komplexbildung
Koordinationssphare des
bei tiefer
der
Kupfercarbonatkomplexe
Kupferions mit
Koordinationsgeometrie.
Spektren
wasseriger
der Oberflachenbeschaffenheit
In einer ersten Studie wird die
13
in
Modiflkationen Vaterit und Calcit mittels 'Continuous Wave'
schen und elektronischen Strukturen der
der
Untersuchung
welche in den Puls-
beobachtet wird, kann einer
einzahnigen
viii
{Coordination zwischen
Hyperfeinkopplung
bei
pH
6.5 und 8 weist auf eine
hinweist und kann durch die hohere Kovalenz der
den. Die Carbonatkoordination in der
axialen
der
kung
Wasserbindung.
zweizahniger Bindung
im
Widerspruch
atkomplexe.
zu
Obwohl
ausgeschlossen
Losung
Die
der berechneten
man
auch fur ein-und
an
der
13
C-und
gibt
weniger
und
und
gefrorener Losung
steht
von
Kupfercarbon-
der
grundsatzlichen
Vaterit und Calcit im
in
wasseriger
oder Ecken
und Puls-EPR
werden. Die
Tellereffekt. Die lokalen
C03(s) Mischphase.
zeigen,
dass die
Treppenabsatzen
Cu
Der Nachweis
zu
an
von
zeigen
einer
Diese Resultate unterstiitzen das
,
,
und Zn
in
an
der
durch
Losung,
quadratisch-
Die bei der Umkristallisa-
einen
dynamischen
Konzept
einer
CaC03
mit
der
Jahn-
Cu^Ca^.^
dynamischen,
mit
Oberfiache. Die fur
erhaltenen Strukturinformationen vertiefen das Verstandnis der
Ni
Kupferio-
Oberflachendefekten wie
Destabilisierung
einer dunnen, strukturierten Oberflachenschicht bedeckten
Co
m
mittels CW EPR erklart die Hem-
-auflosung.
Ionen
Verzerrungen fiihren
anderer Metallionen wie Fe
der EPR
einzahnige Komplexbildung
vergleichbar mit einer Chelatbindung
Calziumcarbonatkristallwachstums und
Kristallgitter eingebauten
Komplexbildungsre-
praktisch voUstandigen Adsorption
Oberflachenbindung.
von
pH-Bereich 8.5
Kupfercarbonatkomplexe
der
quadratisch-pyramidalen Kupferkomplexen
Treppenabsatzen
Cu
einer Strek-
Strukturzuordnung erfolgt aufgrund
Minuten
dehydratisiert
ist verantwortlich fur die starke
2+
zu
ein-
auf molekularer Ebene Einblick in
drei bis vier Oberflachencarbonationen,
ins
fiihrt
wer¬
beim Einfrieren der Proben nicht
Protonenkopplungskonstanten
Mineraloberflache rasch
tion
Viererring erklart
zweizahnige Komplexbildung
Kupferaufnahme durch
den Mineraloberflachen. Die
nach der innerhalb
mung
Carbonatkoordination
doch annehmen, dass die
Losung. Atomabsorptionspektroskopie (AAS)
von
C-
Raumtemperatur gelten.
Parameter und
planaren
6.5 und 8 in
pH-Werten
Gleichgewichtsverschiebungen
bis 9 in einer zweiten Studie
nen
Jt-Bindung
im
pH-abhangigen Verteilungen
werden konnen, kann
Untersuchung
aktionen
zweizahnige
gleichzeitige Beobachtung
Die
grofie
werden. Die
equatorialen Komplexebene
bei den hoheren
Bindungsmechanismen
bei
zugeordnet
und Carbonat
Kupferion
Wechselwirkung
CaCQ3 Mineralien.
Introduction
chapter 1
Chemical processes at the surfaces of minerals,
organisms
are
of outmost
water interfaces act as
importance
catalysts
leading
e.g. to the
degradation
tion of
inorganic
material
The
complexation
regulates
and the formation of surface
metals in the
aquatic
Carbonates
atmospheric
and
aquatic chemistry.
for redox reactions and promote
of toxic
organic
with
in
organic particles and biological
organic
the basic
and
The solid-
photochemical
reactions
substances. The dissolution and
precipita¬
inorganic composition
inorganic ligands
precipitates considerably
of natural waters.
in solution and at solid surfaces
influence the distribution of trace
environment [1,2].
among the most reactive minerals found at the earth's surface [3].
are
The dissolution of calcite and dolomite represents about 50% of the chemical denudation
of the continents. The
reservoir of
C02.
As
natural waters with
tems trace
metal
a
hydrosphere
result
typical
speciation
2+
Ca
,
links the carbonate minerals with the
Mg
2+
and
HC03
is controlled
by carbonate
of trace metal
are
not
of calcite,
only important
for the
aquatic
and bicarbonate ions. The
the other hand,
scavenging by adsorption of metal
coprecipitation during crystal growth
These processes
on
atmospheric
the most abundant ions present in
concentrations in the millimolar range. In many
tation of carbonate minerals in lakes and oceans,
pathways
are
aragonite
sys¬
precipi¬
provides important
ions at the mineral surface
or
and other carbonate minerals.
bio-availability
of toxic metals such
as
2
1 Introduction
copper and cadmium.
in
aquatic systems by
A better
2+
Cu
and Cd
They
understanding
2+
can
also be used to extract information
analysis
the
of
sedimentary
ligands
a
e.g. [5-10] and references
in solution and the
adsorption
and surface functional groups,
Published
are
mainly
interpretation
cal
bonding
tool for the
on
therein)
requires
at surfaces
,
Fe
more
goal
knowledge about
chemical
bonding
2+
,
sur¬
spec¬
of the
the
com-
between solute
geometrical and
electronic
constants for carbonate
complexes
solubility experiments and often lead to contradictory
and structures is obtained from
investigation
of electronic
spectroscopic investigations.
configurations
ligands
on a
a
can
be
species,
distinguished [12,13].
complexes
A convenient
in solution is
the methods most
com¬
and bidentate
coor¬
mono-
The number of
spectroscopic
characterization of surface structures under environmental
molecular scale is restricted
calcite surfaces have been
of metal
spectroscopies,
for the characterization of carbonate
that allow for
description
2+
of the molecular structures [5,9]. More detailed information about chemi¬
monly adopted
A
by
stability
stochiometries and
titration and
dination of carbonate
conditions
Mn
thermodynamic and
and is also the
characterization of the
UV/Vis spectroscopy [11]. With IR and Raman
techniques
as
complexes.
complex
based
changes
[4].
number of
large
present investigation. From the chemical point of view,
structures of the metal
chemical
in aqueous solution and at carbonate mineral
faces has therefore been the motivation for
plexation
on
of the interactions between metal ions such
and carbonate
troscopic studies (see
records
imaged
down to
of chemical structures and
[14]. With atomic force microscopy (AFM)
microtopographic
bonding
X-ray photoelectron spectroscopy (XPS)
at
and molecular scales
calcite surfaces
can
[15].
be obtained
by
and low energy electron diffraction (LEED)
[16,17].
Although
these
they do not allow
techniques
for the
(EPR) [18-20].
a
of chemical
geometrical
in solution and at surfaces
EPR is
given deep insight
investigation
Detailed information about the
plexes
have
can
bonding
at individual
be obtained from electron
species with unpaired electrons like radicals
absorption sites.
and electronic structures of the metal
powerful spectroscopic
filled rf-orbitals. The non-destructive
into calcite surface processes
or
technique
tool for the
com¬
paramagnetic resonance
investigation of chemical
transition metal (TM) ions with
allows the in-situ
study
partially
of structures and
3
dynamics
of such
species involved
of EPR
applications
In
approach
our
numerous
chemical and biochemical reactions. The
thus very diverse and range from
are
material sciences and
in
geology
to
biology
chemistry
physics
2+
spin
of the Cu
ion with its
coordinative environment to obtain structural and electronic information about the
plexation
tinuous
(CW)
wave
and
pulse
spheres
EPR methods the
ligand exchange
of the metal ion
are
interaction with the solid carbonates. From the
well suited for this
tion,
the
so
that axial and
investigation
equatorial
[1]. Mechanism like the
eral surfaces which
keep
complex
tive carbonate surfaces
ity
highly
complexation
[22,23].
and the
investigation
challenging [24].
It is also
bonate surface is
CW and
pulse
given
ferent
topics
a
expected
general
EPR
to
are
are
explained
illustrated with
The fundamental
new
insights
given
2+
even
or at
ion low
chemistry
in small
are
very
important
concen¬
and min-
algae
of the metal
in
more
of EPR
theory
in
important
ion,
on
of CW and
four-pulse
electron
pulse
2
chapter
detail in
highly reac¬
by adsorption
resonance
chapters
study are
spin
echo
and
car¬
at the car¬
spectroscopy
described. The
are
methodology
description
spectroscopies.
of
is
The dif¬
copper-carbonate system
5 and 6
the
summarized in
and
2 and 3. The
related to the
results in
EPR
complexes
theory
the
chapters
magnetic
are
the
to note that both the reactiv¬
be influenced
about the copper
examples closely
chapter
In
into the mechanisms of inhibition.
in this
experimental
EPR schemes used in this
three- and
plants
material
quantum-mechanical concepts underlying
experimental aspects
pulse
give
introduction
that the discussion of the
description
easily distinguishable [21].
and
of its interaction with the
can
precipitation. Knowledge
reader who is not familiar with
for
to a Jahn-Teller distor¬
subject
organic
The carbonate
the
complexes
of metal ions. The copper ion, e.g., is known to inhibit the calcium
bonate dissolution and
After the
algae
with
and structure of the carbonate surfaces
coprecipitation
so
since the 3d ion is
toxic for
during
view of EPR copper
the concentration of the free Cu
and should be well understood
other hand, is rather
point of
con¬
reactions in the first and
followed in solution and
coordination sites become
environment copper is
aquatic
trations
com-
of carbonate ions in solution and at the vaterite and calcite surfaces. With
second coordination
are
over
and medicine.
the interactions of the electron
we use
and
more
can
be followed.
phenomenological
Appendix
presented
A. In
chapter
3
and the different
analytical formulae
of the two-,
envelope modulation (ESEEM) experiments
in
4
1 Introduction
B
give insight into
Chapter
4 summarizes the
Appendix
the
advantages
and limitations of the different
pulse
sequences.
which the
interpretation
of the
important aspects
spectroscopic
carbonate minerals vaterite and calcite
surface reactivities
are
The second part of
chapter
presented
with
are
a
of copper and carbonate
discussed. Current theories about the mineral-
focus
on
4 is dedicated to the
ChemEQL [25] using
the
complexation
calculations of the distribution of surface ion
developed by
ation model
used for the
are
the interaction with trace metal ions.
speciation
calculations for copper and
son
preparation
computed predictions
of the
complexation models
In
chapter 5
as
and 6,
shown in
with the
chapter
in solutions is the
solid calcium carbonates in
Cu
2+
to the
copy
as
integration
the spectra
first coordination
From the
are
analysis
results
2+
are
13
with
chapter
of the
chapters
results
complete
presented
5 and 6. A
helps
to
compari¬
refine surface
and discussed. In
pulse
a
first
EPR
(chapter 5). The
and electronic structures obtained for the
study
for the
of the interaction of copper with
adsorption of
within minutes. The fate of the Cu
into the lattice bulk
are
easily followed by
complexes
is detected with
2+
ions at the
CW EPR spectros¬
changes. Ligand
substitution in the
pulse
EPR
techniques.
C spectra of labeled carbonate ions in solution and at the cal¬
cium carbonate surface differences between solution and surface
Comparison
complex¬
speciation calculations
6. AAS measurements show that the
of the copper
13
the surface
on
C. The
C-labeled carbonate ions in aqueous
very sensitive to the symmetry
sphere
in
experimental
geometrical
starting point
mineral surface is
surface and the
is based
UV/Vis spectroscopy and CW and
detailed information about the
complexes
complexes
Appendix
the pro¬
4.
finally, experimental
investigated by
constants tabulated in
samples investigated
part the pH dependent complexation of Cu
solution is
performed with
Schindler et al. [26]. The results of the
of the
on
data is based. The structures of the calcium
carbonate ions in solution and at the calcium carbonate surfaces,
gram
chemistry
with other TM ions allows for
a more
tion results and the calcium carbonate surface
complexes are deduced.
general interpretation
properties.
of the
adsorp¬
Concepts of
Basic
chapter 2
CW and Pulse EPR
In this
and the
the theoretical concepts
chapter
terminology
lowing chapters
understanding
mation is obtained
spins
by
CW
complexes
pulse
or
is discussed in
more
2.1.1
Electron Zeeman Interaction
For the discussion of the
any
magnetic
oriented and the
netic field
BQ
be oriented
magnetic
two energy
results in
parallel
or
a
are
outlined
discussed in the fol¬
of the interactions between
examples
detail at the end of the
of EPR
centre with
in each section the
chapter.
an
we
start with the
electron
spin
S
=
simple
levels
are
degenerate.
The
application
of the two energy levels
anti-parallel
to the
magnetic
quantum-mechanical
as
of
spin,
an
the electron
field vector. The
nature of the electron
energy of this system is derived from the classical
expression
case
of
a two-
1/2. In the absence of
moment, associated with the electron
splitting
energy levels is due to the
EPR
Magnetic Field
principles
paramagnetic
field the
topics
of the
EPR. In addition to the
One Electron in the
a
pulse
and their environment determines whether the relevant infor¬
2.1
level system for
CW and
magnitude
is introduced [18-20,27]. The
electron and nuclear
EPR of copper
necessary for the
underlying
is
randomly
external mag¬
spin S
can
quantization
spin.
The
only
of the
potential
for the energy of
a
mag-
6
2 Basic
netic
dix
dipole
in a
magnetic field and
A), expressed
*
where
Bohr
=
in
frequency
T
by the
splitting
and
by the
spin Hamilton operator
is
(2 1)
)
and h the Planck constant
are
then given
=
the
by
(J s), B0is given
eigenvalues
Tesla
denotes the
(T) The
Eq (2 1)
ener
and charac
SeTBoms
(2 2)
between the two energy states
proportional
to
the
magnitude of B0,
EPR experiment
electromagnetic radiation
as
illustrated
by
A£
=
Figure
in
E(ms
=
+1/2)
could imagine involves the
one
field of variable
called electron Zeeman interaction
is
given
is
Se|fi0(mHz)
simple
in
of Km
(3e
1/2,
±
=
difference between the two Zeeman states
The most
(Appen¬
units
spin quantum numbers ms
£(ms)
(EZI)
described
is
ge= 2 0023, the dimensionless g value of the free electron,
Magneton (J
The
of CW and Pulse EPR
SejSB0
gies for the two spin states
tenzed
Concepts
frequency
v to
2-1 The energy
E(ms= -1/2)
application
of
4
hv
^r
Transitions between
energy levels induced
-1/2
ma
Free Electron
microwave
with spin S= 1/2
Splitting
of
Spectrum
in
A
magnetic field B0
Electron Zeeman Effect
hv
8e
2-1
Illustration of the Zeeman
external magnetic field
Zeeman states
occurs
splitting for
B0
if the
For
a
a
S
=
1/2
system with
given irradiation
resonance
condition
is
frequency
fulfilled
one
Mo
unpaired electron
v a transition
(see inset)
f.
=
sn
Fig
by
irradiation
EPR
energy levels
an
this system If the energy of the
ms=1/2
A Energy
=
in an
between the
2.1 One Electron in the
Magnetic
Field
7
radiation field matches the energy gap AE, transitions between the two
induced, i.e. the spin
onance
From
=
CW EPR
a
however, the microwave frequency is usually held
experiment
and the
res¬
case
discussed
can
fields
exerted
are
complications
be described
are
terms in the
levels in
rf-electrons
states. If the
and fields
(up
or
a
by
very
a
simple
to five
observed
than
one
Eq. (2.1)
depending
case
magnetic
In many
or
Fe
)
2+
or
on
Mn
2+
the
and electric
cases
further
or
organic
molecules
they
can
be described
by
moments
additional
splittings of the energy
be much
larger than the electron
the interactions
can
the nature and the symmetry of the chemical environment of
only
frequency
the lowest energy levels
(K).
In this
case
EPR
may be to small to excite all the
are
populated
spectra
can
only
with electrons if the
constant
be observed in the
(J-K" )
and T
ground
state
paramagnetic system.
For TM ions in the condensed
are
most cases,
magnetic and electric
energy splitting is much larger than kT, where k is the Boltzmann
manifold of the
Mo(V). In
around
and will lead to further
the energy of the MW
transitions. Furthermore
the temperature
resonances
electron, e.g. for TM ions with
Mn
high-spin
number of para¬
2-1.
For TM ions like VO
the ion. In this
in
or
additional
as
smaller than the electron Zeeman term,
Figure
Ti(III)
as
98
unpaired electron.
more
for
are a
two-level system with
TM ions such
are
one, there
interactions between the different
spin Hamiltonian
Zeeman term,
far is
so
the environment of the
by
linearly (cf. chapter 3).
field is swept
Spin-Orbit Coupling
and
arise from the presence of
unpaired
triplet
magnetic
con¬
B0 and ge are inversely proportional.
complicated spectra
more
tings
the
(2.3)
2, e.g. free radicals in solution
however,
in
reasons,
centers that
magnetic
several
case
ge-±B0.
=
Crystal-Field Splitting
Although the
-
orientation to the other. In this
flipped from one
it follows that
Eq. (2.3)
2.1.2
g
v
experimental
For
in
be
states can be
condition is fulfilled:
hE
stant
can
spin
phase
crystal-field (CF) splitting
the interactions
and the
responsible
for the
spin-orbit coupling (SOC).
large split¬
The
com-
2 Basic
8
bined effect of these two interactions
for most TM
orbital
angular
momentum
The effect of
Figure
energy
removes
completely, leaving
ions
(quenching
on
splitting
in
the
case
TM
a
angular
ion
of octahedral symmetry
given
is
by
zero
9)
the first part of
in
schematically
drawn
hgands
momentum, p
illustrated
is
energy levels
state, often with
non-degenerate ground
a
2-2 with the arrangement of the
degeneracy of the
the orbital
of the orbital
octahedral CF
an
of CW and Pulse EPR
Concepts
in
the inset
The
A
EPR
UV/Vis
44.2,2 (B1g)
•-AL
dz2 (A1g)
..#
free
ion
^^dX2,dyz(Eg)
'2g
degenerate
with 5
dxy(B2g)
energy levels
splitting
in
an octahedral
Jahn-Teller
crystal field
Fig
2-2
Illustration of the effect of
resulting
energy
Teller effect
splitting
through
an
an
octahedral CF
A The
is
with axial
elongation
on
degeneracy
the energy levels of
of the orbitals
of the axial bonds
In the
not
special
affected
by
case
splitting of the ground level (Bj )
of the id
ion in
An
the SOC and the Jahn Teller theorem
shown
tions
in
elongation
Figure
to
the
optical
schematically
indicated
in
by
a
applies
a
Jahn
transitions
shown
in
the
the small shaded box
The orbital
displacement
The
ion
by
of the
term is
degeneracy
is
the
z-
hgands
on
of the coordination octahedron leads to the energy level scheme
2-2 with the
Vj, V2 and V3
is
3<T TM
a
further lifted
symmetry, the degeneracy of the E
Oh
lifted and the energy of the system lowered
axis
is
is
leading
Vj, v2 and v3 The geometrical arrangement of the hgands
inset The Zeeman
splitting
elongation
are
unpaired
indicated
by
electron
arrows in
in
the
the
dx2
large
i
orbital The electronic transi¬
shaded
area
One Electron in the
2.1
Field
Magnetic
splitting imposed by
The measurement of EPR spectra is limited to the Zeeman
external field
in
area
on
the
Figure 2-2)
spin Hamiltonian
has
unpaired
and
in
one
electron in the
Eq. (2.1)
with S
spin through
molecules has
ing (e.g. radicals)
or
large
of the electric CF's
ence
precisely the
to the electron
result the
ment. As a
depends
external
on
TM
the electron
Generally
g-factor
is
no
nian is
field. The effects of the
for the
spectrum and does
e.g. the
on
case
for the Cu
2.1.3
g
When
has to be
of the
crystalline
environ¬
of the Zeeman levels
anisotropy
of the EZI
the EPR spectra will
on
necessarily
2+
ground
which
state
of
a
paramag¬
strongly depends
on
the individual ion and its environment. The influ¬
a
number of parameters such
as
the g matrix
or
the
the number of energy levels involved in the EPR
refer to the true electron
ion. However, this has
spin
no
spin quantum
influence
and true electron
on
spin
the
number
theory
in the
and
no
as
it is
differ¬
following.
Anisotropy
dealing
aware
sample in
different
splitting
which
ground state
(for S>l/2). The spin operator 5 used in the spin Hamilto¬
will be made between effective
ence
to the
and the orientation of the system in the
of the EPR spectra in the
spin, reflecting
not
thus have
state and excited states,
sensitive to its
the
chemical bond¬
g-factor should
ground
spin Hamilton operator is introduced
tensor D
"effective"
-
the
on
state of most
to first order and the influ¬
angular momentum
spin
the
chapter.
description
"effective"
splitting
an
The
longer isotropic
of the environment is included in
zero-field
spin negligible.
ligand field
the involved energy terms and thus
ence
zero
and make the electron
ground
quenching by
the SOC is
ions)
amounts of orbital
spin
be discussed in the next
an
on
(e.g.
the symmetry of the
magnetic
netic ion,
CF's
by
non-degenerate and
state is
field can, however, act
ligand
momentum due to the
angular
be described
can now
ground
free-electron value. Interaction between the
however, admixes small
couple
1/2 since the
=
an
orbital (small shaded
a
second order effects of the SOC. Since the
orbital
zero
spin system
momentum. The
only associated spin angular
electron
non-degenerate dx2
could think that the
9
with
magnetic moments
that the CW and
the
in
a
crystalline
pulse EPR spectra may
with random orientation
molecular environment
either
depend on
one
the orientation
superpositions
of many
(e.g. powder samples).
In solu-
magnetic field B0 (e.g. single crystals)
single crystal spectra
or
or are
10
2 Basic
Concepts
of CWand Pulse EPR
tion rotational and translational motion of the molecules often averages out the aniso¬
tropic
interactions. Due to short relaxation times
performed
at low
are
qualitatively identical
sotropy is of importance and
external
example
magnetic
EPR measurements have to be
temperatures where molecular motion is frozen. These 'frozen solu¬
tions' EPR spectra
In the first
pulse
field
the
B0
we
to
powder spectra.
will discuss the
only magnetic
and the
spin
field
anisotropy
Thus the concept of ani-
of the EZI in
experienced by
the electron
oriented either
vector S was
more
parallel
spin
or
lel to
BQ.
As shown above additional inner fields, transmitted to the electron
SOC,
are
present in molecular systems which may be
fields
are
related to the symmetry of the molecule, e.g. to the CF of
tive field
is
a
Bem experienced by
superposition
the electron
spin in
larger
of the external and internal fields. For
an
was
the
antiparal-
spin by
the
than the external field. These
molecular
a
detail.
or
a
TM ion. The effec¬
crystalline
environment
anisotropic system Eq. (2.1)
is written
X
8eTBeffS
=
In the second part of
splitting
is
expressed by
=
Eq. (2.4)
(3x3)
a
the orientation
the
orthorhombic and is
dependent
variation of the Zeeman
g interaction matrix. The information about the symme¬
try of the inner fields is thus transferred to
by determining
(2-4)
TBoSS-
principal values
a
g matrix and
of this matrix. In
expressed in its principal
axes
can
be obtained
general
experimentally
the g matrix will be
system (PAS) by
8x
g
=
(2.5)
gy
Si
where
one
of the
(x,y,z)
is the PAS and g^
principal axes,
field is obtained
gy
the electron
by inserting
the
and
spin
gz
are
the
vector is
principal
quantized along BQ
corresponding principal
arbitrary orientation of B0 the expression for the resonant
the
values of g. For
following expression into the resonance condition:
value into
B0 along
and the resonant
Eq. (2.3).
field is obtained
by
For
an
insertion of
One Electron in the
2.1
2
where
lx,
2.2
2,2
I
and
lz
are
Magnetic
Field
11
2,2
(2.6)
the direction cosines between
and the three
B0
principal
axes
(x,y,z).
To illustrate the effect of g
case
tetragonal distortion
ters
along
the
z
on
(e.g.
the EPR spectrum
a
In this
axis).
we
consider the
special
TM ion in octahedral coordination with
case
the EZI is described
by
two
a
parame¬
g± and gH given by
Sx.
Eq. (2.6)
tor
anisotropy
where the CF has axial symmetry
Sx
z
Figure
and the line
ber of
2
2-3
shape
a
single angle 6 between the magnetic
an
9
2
+
2-3
field
vec¬
2
gHcos 9.
(2.8)
axial g matrix with
gu
>
g±, represented by
of the corresponding EPR spectrum
are
is
typical
for
a
Schematic
packets with
shape
ellipsoids
a
ellipsoid,
large
num¬
with respect to
For
a
given
Peg(6)
drawings
line
rotational
powder sample.
ellipsoid
powder
a
drawn, assuming
systems with random orientation of their g
magnetic field B0. This situation
g
Fig.
2
g±sin
paramagnetic
the static
be rewritten with
axis.
*(er
In
(2.7)
=
can now
and the
BQ
=
of the axial
g-ellipsoid
and the
results from the contributions of
different
resonance
corresponding
a
EPR
spectrum. The
large number of individual spin
positions (some examples
are
shown).
12
2 Basic
magnetic field strength fl0,
all
spins
for which
the spectrum and
B0
makes
cally exemplified
in the
powder spectrum
are
that for gn
>
tributing
The
angle
an
powder
obtained
to the spectrum is much
case
9 with the z-axis of the g
<
spin packets
Figure 2-3. The
in
and gx into the
ellipsoid,
hv/Pefl^
in the
typical
xy-plane
than
schemati¬
ground
or a
and
spin packets
B0.
con¬
the z-axis.
2+
for the Jahn-Teller distorted Cu
of the
of the
condition. Note
resonance
along
i.e.
contribute to
are
positions
extreme
due to the fact that the number of
elongation
an
These
=
B0(g±) due to the inverse proportionality of g
degeneracy
by
field is removed either
spin packet.
shape
larger
discussed above is
octahedral symmetry. The
a
by inserting gn
mainly
is
shape
line
line
Brfgu)
gx one obtains
asymmetric
The
spins fulfilling the resonance condition g(8)
all
considered to form
are
of CW and Pulse EPR
Concepts
complex
in
state in the octahedral coordination
compression along
the z-axis. The axial
symmetry of the g matrix thus reflects the symmetry of the ligand field.
2.2
Interaction with Nuclear
So far the interaction of the electron
EPR spectrum with
one
single
spin
(/
=
1/2)
or
nitrogen
is associated with
electron
the
spin
unpaired
will
a
0
are
atoms
(/
magnetic
now
analogy
=
1).
considerably
The intrinsic
the local
spin angular
magnetic
interaction
the electron
resulting in
the nuclear Zeeman
interaction
(NZI)
is
spin
field
yields
anisotropy.
increased if nuclei with
fields built up
spin
spin,
momentum
moment. In addition to the external
experience
hyperfine
to
magnetic
found in the environment of the electron
electron. The interaction of the electron
moments is called
In
>
with the external
line which may be broadened due to the g
information content of the EPR spectrum is
quantum number /
Spins
as
a
an
The
spin
e.g. protons
of these nuclei
magnetic field BQ the
by
the nuclei close to
with these nuclear
magnetic
(HFI).
the nuclear
splitting
spin
/ is
of the nuclear
quantized
spin
in
a
magnetic
field
states. The nuclear Zeeman
expressed by
Here gn is the dimensionless nuclear
g-factor,
a
constant
depending
on
the type of
2.2 Interaction with Nuclear
Pn the
nucleus, and
splitting
nuclear
magnetic spin quantum
the EZI
with gn
energy levels is
(2/+1)
into
the ratio
(e.g.
=
5.58)
fields set up
gpe/gnPr|
and the small
the nuclear
by
entation of the nuclear
This results in
2.2.1
a
(J-T ).
nuclear magneton
observed, each level being characterized by
660 for
an
is
anisotropy
spins through
unpaired
of each electron
electron with g
usually neglected
spin
respect
state into
=
2 and
in EPR. The local
the HFI at the electron
moment with
Two mechanisms with different
between electron and nuclear
cal
a
a
spin depend
to the external
(2/+1)
proton
a
magnetic
on
the ori¬
magnetic
field
.
levels.
Interaction
Hyperfine
between the
nuclear quantum number /
given
a
13
number m,= I, I-l,..., -I. The NZI is much smaller than
=
magnetic
splitting
For
Spins
magnetic
physical origin
contribute to the
can
The first mechanism is the
spins.
moments of the electron and nuclear
dipolar interaction between magnetic moments.
dipole-dipole
spin
analogy
in
coupling
interaction
to the classi¬
The energy of this interaction is writ¬
ten as
31"
=
^T:^eSnK\si--2(Sr)(Ir)l
r
where
(p-,
d-
The second mechanism becomes
tron
spin
the vector
by
at the nucleus. This
is the
magnetic
r.
Note that the
hyperfine
fields exerted
the nuclear hyperfine fields.
important
case
quantized along
electron
the external
spin through the
discussed in
more
by
=
r
the distance
in space
spin
is located in
(point
interaction
dipole-dipole
anisotropic.
a
are
the electron
field
spin
molecular
1/2, /
=
1/2 system
of the elec¬
contributions of .s-orbitals to the
contact
interaction is
at the nucleus are much
exceed the NZI. In this
B0but along
spin density
an
case
(section 2.2.2).
given by
stronger than
the nuclear
effective field set up
HFI. The consequences of the weak and strong
detail for the S
) and
single point
The
if there is finite
if there
They may easily
magnetic
a
2
N-A
or/-orbitals).
molecular orbital. The energy term of this so-called Fermi
1.
-1
moments and is thus
e.g. if the electron
expected
nod at the nucleus
a
(47tl0
vacuum
the relative orientation of the
Purely dipolar
orbital with
and connected
interaction is
(2.10)
J
r
considered to be located at
spins (in m),
dipole approximation)
depends
<-
n0 is the permeability of the
between the two
on
h
spin
is not
mainly by
the
hyperfine coupling
are
14
2 Basic
*comact
Here
l*P(0)l
(f) jrf.g.ft.ll'Wfsi
=
the
is
probability density
Fermi contact interaction
unpaired
electrons
the nucleus
ization
In
isotropic and
or/-orbitals
by
electron
unpaired
encountered also
is
hke 7t-radicals
mechanisms like
or
TM
configuration
HFI will be anisotropic due to the
general the
following
anisotropic part
the s-orbital The
in
systems with then-
in
density
The spm
ions
interactions or spm
at
polar¬
where the
is
2+ 2
irradiation)
resulting
Aws
matrix
A
is
given
)
=
(2 13)
the second, traceless matrix
hyperfine coupling
illustrated for the
The
coupling
± 1 and
simple
state into 4 levels
Am;=
case
on
the energy level
The NZI of the Cu
(>0
m
ions is
Figure 2-4)
of isotropic EZI and HFI for
0
(only
MW irradiation
the electron spin
are
shown
in
is
affected
by
however
the
neglected
in
a
in a
causes transitions
and
spin
split¬
between
microwave
diagram
The
split by also
The
the energy level
much smaller than the HFI and thus
is
diagram
between the electron and nuclear spin results
The four allowed transitions
ms manifolds
solution)
interaction matrix A and the
EPR spectrum consists of four lines centered about glso and
sign of g„
in
by
purely dipolar part is expressed by
ting of each electron spin
levels with
hyperfine
motion
la,so +
2-4 the effect of the
Cu
(e g by molecular
(212)
=
the EPR spectrum
(eg
interaction, except for sys¬
S\I,
=
PAS The
Figure
out
then combined to form the
are
hyperfine interaction
A
in its
averaged
is
dipolar
added to the spin Hamiltonian
term is
*v
2
of the
(2 11)
[28]
Both mechanisms
7=3/2
is
p-, d-
then induced
is
tems where the
In
in
Concepts ofCW and Pulse EPR
the
important for the order of the ml states
drawing
in
The
the different
2 2 Interaction with Nuclear
i
Spins
Energy
15
m
-I/O
j
7ig=1/2
mF1/2
iL
-
iV
mf 1/2
mF-3/2
1'
Free Electron
ms=
with spin S= 1/2
m,-3/2
1/2
^f
-
mF-1/2
mF1/2
i'
EZI
1
Hyperfine
Interaction
with nucleus /
B0
mF3/2
mpt/2
m=3/P
'
=
3/2
m^-1/2 m^-3/2
A" 533,.
EPR
Spectrum
I
"
Bo
BQ(gmo)
Fig
2-4
Energy
level
5=1/2 and
diagram
and
nucleus /
a
=
EPR spectrum for
resulting
a
spin system with
3/2 with isotropic electron Zeeman
(gu0)
and
one
electron
hyperfine (auo)
interactions
transitions are labelled
by
hyperfine
powder
interactions
their nuclear magnetic spin quantum numbers For anisotropic
line
shapes
cussed for the g amsotropy (see also
2.2.2
The S
=
111,
For the theoretical
sider the
complete
electron spin
this
axis can
is
be
I
=
plete
tensor
as
dis
4)
1/2 system
spin Hamiltoman For
determined
by
EPR spectra it
an
5
=
is
often
not necessary to con¬
1/2 system the quantization
axis
of the
the EZI and the influence of the nuclear spins
on
neglected (high field approximation) Furthermore the coupling between
the different nuclear spins, most important
large coupling
2
section
description of pulse
mainly
observed for the individual lines
are
of the nuclei to the
space into
subspaces
in
NMR,
unpaired electron
It
can
is
be
then
neglected compared
possible
to
to
divide the
which contain the interactions between the spin S
the
com¬
=
1/2
2 Basic
16
and
single nuclear spin
a
by
spectrum is obtained
fictitious spin S'
=
1/2
Concepts of CWand Pulse
subspaces
I. This
assigned
be
can
mostly
is
The
mental
=
analytical
The
and
the
than the excitation bandwidth of the
be
same treatment can
applied
=
dimensionality of the Hamiltonian
13
1/2 nuclei like
formulae
understanding
magnetic
field
a
mw
for the calcula¬
often allows
presented
of
pulse
B0.
experi-
C and H to be discussed in terms of
that it
in this section
are
can
a
be treated
also of importance for
sequences. For the derivation of the formu¬
is considered to be
Combination of Eq. (2.9) and Eq. (2.12)
quantized along
yields
a
nuclear
Hamiltonian for each ms manifold [30]
*«,p
-VB°/+<S>«.PA/-
=
(5)a_ p
In this notation
equal
states,
expressed
B0
and the
1/2
>
electron transition if the energy dif¬
anisotropy is neglected and the electron spin S
the external
spin
larger
given
complete
[29]).
EPR spectra of /
development
lae g
e.g.
are
to the
spin
and the
systems with S
1/2,1=1/2 system. This system has the major advantage
analytically.
the
case)
possibility to reduce
pulse
simple S
the
(see
tion of the spectrum
separately
the combination of the results. For
ferences between the transitions
pulses (which
be treated
can
EPR
=
to
in
B0[0 0
loss of
ms
the
ll
generality
=
is the
±1/2 in
laboratory
is taken
expectation value
simple
our
the
case.
the
of the
spin
spin
static
a/P
electron
Hamiltonian
magnetic
field
spin
can
be
vector
Furthermore it is assumed without
laboratory z-axis.
that the nucleus lies in the
of
The nuclear
where
frame,
along
(Z14)
*z-plane
of the coordinate system. In the
resulting expression
*«. P
Vj is given by
=
V, + ms(AIz + BI*)
-gn$nB0/h;
secular parts of the HFI,
oratory frame.
the nuclear
are
=
Au
functions of
DiagonaUzation
frequencies [31]
A
=
Vj/, ±
and B
\(AIZ
I
=
hyperfine
2~
2
JA^
matrix
+
(2.15)
BIX),
+
Azy, the
secular and
pseudo-
elements, expressed in the lab¬
of this Hamiltonian yields the
following expressions
for
2.2 Interaction with Nuclear
17
Spins
W^
In first
approximation,
often treated in the
to be
located at
a
the
(2.16)
coupling
between the electron and the nuclear
point dipole approach,
single point
delocalization to the
in space
ligand nuclei.
where the electron
(e.g.
The
on
spin density
the central atom of
hyperfine
a
matrix A is then
TM
spin
is
is considered
nucleus) without
expressed
in its PAS
by
A{
A
A±
=
A2
=
=
lauo
Aj_
A3
where the second matrix in
symmetric
-
(2.17)
+
IT
A(
Eq. (2.17), representing the dipolar coupling,
is
axially
with
H(Ageg„PA
m
The
the vector
matrices
r
are
matic
limit
z-axis)
to
isotropic
g the
2
9
A^cos
2
/4||Cos
B
=
(An-Ajjsinecose
angle
The
=
between the
field vector
laIJO/2+71,
A± (8
+
B0.
In
frequencies va
see
=
=
«lso
in die
+r(3cos8 -1)
principal
Figure
and
values of these
(2.19)
and
axis of the
(2.20)
dipolar coupling
2-5 these parameters
Vq are
along
coupling
3rsin8cose.
section 2.2.3). The
90°, B0
principal
is found
Eq. (2.16) by
2
9
=
gn factor and the elec¬
largest dipolar coupling (27)
electron and nucleus. The
A
drawing.
(Vj
r.
connecting
magnetic
>
For
related to the parameters A and B in
Here 9 is the
and the
constant T is a function of the nuclear
dipolar coupling
tron-nuclear distance
(2.18)
hrJ
are
matrix
shown in
centered about Vj in the weak
coupling
equatorial plane).
varies from
Au (8
=
a
(A,,)
sche¬
coupling
0°, B0 along
the
18
2 Basic
2-5
Fig.
drawing
Schematic
Concepts
of the distribution of the basic
axial HFI matrix, indicated
It has
magnetic fields,
by
the electron
spectra it is
set up at
through
quantized along
the
by
the
ellipsoid
the
the
to
e.
two terms
coupling
which
by far exceed
one
whereas the strong
coupling
situation is
CW EPR spectra. In the third case, the
are
of
equal size.
called
so
This situation is found for the
nated in
a
2.2.3
Weak and
tized
high
along
field set up
field
an
isotropic glso-value
is valid
approximation
the direction of the
by
up to
the NZI.
sphere
of the
for most
matching
as
coupling
coupling
is found
copper-hexaaquo
couplings
or
com¬
observable in
range, the two contributions
shown in
so
magnetic
and
coupling
we
chapters
5 and 6.
are
obtained
spins,
field vector
by setting B
=
consider
again
isotropic coupling aK0
that all
0 in
>
an
0. We
electrons and nuclei,
B0,
the HFI at the nucleus is therefore directed
levels of this system
depends
hyperfine coupling (e.g.
Strong Coupling
For the discussion of the weak and strong
that the
will be
C nuclei of the carbonate ions coordi¬
bidentate fashion to the copper nucleus
/= 1/2 system with
The NZI
one.
has to consider the weak
typical
spin
interpretation of the
discussed in the next section. Weak
are
an
(first term) and
The nuclear
of these two contributions. For the
the dominant interaction
case
va and Vg for
field B0
know which contribution is the dominant
g. for the water protons in the first coordination
plex
magnetic
and is in the range of several MHz. The
on
features
in this Hamiltonian describe
hyperfine coupling (second term).
500 MHz for the copper atom) may thus
Depending
frequency
the inset.
the nucleus by the external
resulting
important
gn-factor
strong
m
already been mentioned before that the
the
on
of CW and Pulse EPR
5
=
1/2,
assume
are
quan¬
taken
along
along
the z-axis. The energy
Eq. (2.15).
z.
The
magnetic
2 2 Interaction with Nuclear
Spins
NZI
+
Energy
19
HFI
m,v,
+
m^m,S'"laiso
a,
m,=-1/2
A
\rrR\
m)
+1/2y
|CHX)
I
I
m,=+1/2
m,=-1/2
|pp>
^
ms=-1/2
^
|(3a>
m,=+1/2
Effective fields
in
+a,so/2
the
A
ms= +1/2 manifold
V
"eff
i!
3eff
+a,sc/2
Fig
2-6
(top) Energy
case
level scheme for
drawing
pling
are
Figure
case
indexed
It
assumed that v,
=
1/2 system
in
the weak and strong
=
<
and
magnetic field In
the energy levels
|(3fi),
0 and aK0
where
general mt
since
by
coupling
(bottom) Schematic
the superposition of the
+1/2 manifold
are
>
drawn for the weak and the strong
|a>
is not a
and
|p>
commonly designated by
refer to the two spin states
good quantum number for
the quantization
axis
cou¬
0 The electron and nuclear Zeeman levels
their magnetic quantum numbers
ms and m, and
|aa), |a(5) |fia)
tion
1/2, /
2-6 the energy level schemes
is
by
=
electron and nuclear spin transitions
of the effective magnetic fields set up at the nucleus
NZI and HFI for the ms
In
5
an
together with the possible
in
the external
the characterization of
of the nuclear spin deviates from the direc¬
of the external magnetic field due to the HFI For this
reason a new
numbenng
of the
Concepts
20
2 Basic
levels is introduced,
namely |1), |2), |3)
weak and strong
coupling
In the weak
coupling
spin is given
tor
diagram
put up by
in first order
arrow, is
quantization
by
decreases the energy
In the strong
Figure
the
to the effective field.
numbering
the direction of
2-6 for the ms
along
drawn
=
(Vj
case
hyperfine
Again
is illustrated in the
+1/2 manifold. The
magnetic
opposite
fields
directions.
by the bold
the nucleus and indicated
field
hyperfine
vec¬
slightly
the NZI.
by
also/2)
<
of the nuclear
quantization
the z-axis and have
experienced by
caused
of the levels in the
figure.
the addition of both contributions. The
splitting
by
are
vector,
coupling
is determined
spin
The
by the external magnetic field B0. This
at the bottom of
obtained
(Vj > also/2)
case
|4).
and
is shown in the
case
the NZI and the HFI
The effective
of CW and Pulse EPR
field
the direction of
«1S0/2.
the fields act in
The NZI
opposite
quantization of
gives only
a
the nuclear
small contribution
directions in the ms
-
+1/2 mani¬
fold.
In the ms= -111 the nuclear Zeeman and
coupling.
both weak and strong
increased
We
nian
as can
now
cause
ms to another. This has
four level system
as a
Figure
2-6 the six
axis to deviate from the z-axis. This is e.g. the
case
when the
weak and strong
no more
tron
o
case
valid and
0).
As
S% and
result not
a
effects
in the ms
probability
coupling
of the electron
flip
general
important
possible
(Ams
=
S have to be considered
only
on
spin
arrows.
magnitude
changed
frequencies
forbidden
transitions between the four levels
case.
=
0)
are
when
or
of the effective
going
from
spin
state of the
are
indicated both for the
involving only
a
zero
transition
spins flip (&ms=±l, Am7= ±1)
example with isotropic coupling
probability.
spin
indicated by full arrows, the forbidden elec¬
The hollow arrows represent the nuclear transitions which take
our
one
observable in the
transitions increases. In
The allowed electron transitions,
±1, Am,
when
state can now also affect the
of the so-called
within the ms manifolds. Note that in
transitions have
the
the transition
transitions where both the electron and the nuclear
dashed
2-6.
Hamilto-
change
nucleus. The transition
diagram in Figure
nucleus but also the direction is
experienced by the
direction for
spin
coupling is anisotropic (B
field
by
is
same
between the Zeeman states is thus
where additional terms in the
more
quantization
high-field approximation
the
splitting
The
be inferred from the energy level
consider the
the
hyperfine fields act in the
place
the forbidden
2.2 Interaction with Nuclear
EPR
21
Spins
spectra
V13
V24
"24
'13
1>
<<]
'
V„
NMR
V14
"23
'14
V23
spectra
vp
*a
v
v
v
va
2v,
^W2
0
weak
Fig.
2-7
(top) EPR stick spectra observed
and strong
coupling
strong coupling
coupling
case
for the energy level schemes
respectively.
solid and dashed lines,
in
Figure 2-6 for the weak
The allowed and forbidden electron transitions
The nuclear
differences between the electron transitions,
frequencies
are
are
indicated
(bottom) Corresponding
NMR
drawn
as
as
energy
spectra with
positive frequencies only
The EPR and NMR spectra, obtained for the energy level schemes in
in
schematically
drawn
Figure
2-7 for the weak and strong
coupling
case.
spectrum allowed (solid lines) and forbidden (dashed lines) transitions and
around glso. The
with
v
ences
ues
=
E,
numbering
of the
frequencies
-E. The nuclear transition
positive frequencies
tered around
frequencies V12
are
frequencies va and
v» are
They
are
shown
given by
and V34. In the NMR spectrum in
the strong
coupling
2
1
2
T|
are
as
energy differ¬
the absolute val¬
Figure
2-7
only
are cen¬
are
given by
2
and
v«vp
centered
case.
The intensities of the allowed and forbidden electron transitions
COS
In the EPR
observed therefore with the consequence that Va and Vg
also/2 and separated by 2v: in
are
is taken from the energy level scheme
between the allowed and forbidden transitions.
of the transition
2-6
Figure
(2.21.a)
22
Concepts of CWand Pulse EPR
2 Basic
'-4V+
2
/,
sin T|
=
f
(2.21.b)
:
v„v
avp
where
angles
v+
=
+
and
v34
between the external
nucleus in the
two
Hamiltonian in
the levels in
intensity
2.2.4
v_
an
the
Eq. (2.15) and has
to be chosen as
-45°
2-6 to be correct. More detailed
Figure
can
be
that for T)
seen
of the forbidden transitions is
rj
are
(all fields along
increase of the
one
point
or
a
to the
by
strong coupling
effective
frequency
magnetic field, experienced by
zero
come
at this
point.
very close
We consider
section 2.2.2
decrease of the
a
in the ms
coupling
(they are
as
again the
in
and
Figure 2-6)
magnetic
=
+1/2 manifold
S
1/2, /
=
=
shown in
to the one shown in
mirrored about the
/
already
ISO
,
cross).
Figure
In this situation the
which
1/2 system with the
are
of
Figure
anisotropic
and
becomes
HFI discussed in
importance for the nuclear frequency
2-5. In the strong
the bottom of
angle r\
|1)
intensity.
The NMR spectrum for such
(«.«>-r)
also/2)
2-6 the energy levels
Figure
a
system in the weak
coupling
case
2-7. The broad va
origin so that the line shape is inverted. The matching
rp
=
frequency
1/2 system defined in section 2.2.2 is
2
hyperfine split¬
the nucleus, and thus also the nuclear
not allowed to
=
(vx
field and thus
field. The
the cancellation effects
case was
analogous
1/2,
[32]
of
hyperfine
In the energy level scheme in
(NMR) spectra of disordered systems.
=
of the
is caused either
situation is reached where the
45° and allowed and forbidden transitions have equal
is
z as
the
numbering
found in
case
leads to the exact cancellation of the nuclear Zeeman field and the
|2)
on
zero.
coupling
hyperfine coupling
of the NZI. At
is twice the nuclear Zeeman
vais
acting
procedure
45° for the
descriptions
0
=
<
<
of the
sum
Matching Range and Exact Cancellation
magnitude
ting
tj is the half
angle
The
.
field and the effective field vectors
magnetic
The transition from the weak
by
v^-v^
=
ms manifolds. It is obtained by the diagonalization
From these formulae it
[33].
the
v12
given
by the
the situation
powder
line is
range for the S
following conditions [34,35]
(2.22)
2.2 Interaction with Nuclear
Spins
23
Matching range
boundary
conditions:
<«».-7)
•
v,
=
+
T
V",so
+
T)
Exact cancellation
Fig.
2-8
Schematic illustration of the
matching
range with the
functions of als0 and T, both assumed to be
narrows
These
Vj
=
boundary
l(2also+T)/4l
singularity
to an
5
=
1/2,
conditions
are
illustrated
/
=
have
1/2
frequency
given
as
va line
in
or
v_
In
are
of the
angle
Figure
2-8.
line
point
a
9 and
an
For
shape
isotropic
| T.
only discussed
system.
combination lines v+
broad and show
schematically
independent
is induced for the va manifold,
we
conditions
exact cancellation the
isotropic peak.
Combination Lines in ESEEM
So far
boundary
the exact cancellation condition is reached. At this
line is observed at the
2.2.5
positive. At
the basic
two-pulse
and
Experiments
frequencies va
four-pulse
and
ESEEM
v»
observed in the
experiments
observed. In disordered systems the basic
rapidly decaying signals
spectrometer deadtime of typically 100
ns.
which may be
The
sum
frequencies
completely
combination
also
peak V+
are
hidden in the
shows
a
much
Concepts
2 Basic
24
narrower
frequency
of ON and Pulse EPR
distribution and useful information
can
be extracted from its
shape
[36-38].
This is illustrated in
two-dimensional
drawn
as a
the basic
plot
function of
two-dimensional
plot
Figure
with two
ture
2-9. The
singularities.
1/2,
=
the
frequency
line
powder
sum
=
1/2 system with axial HFI. In the
as
=
scaling
axis with
shape yields
peak clearly
For 6
well
as
the
sum
peak v+
are
shows
0°/90° the
the
a
of the
frequency
much
frequency
intensities
distribution shown at the
frequency
narrower
peak frequency v+ equals 2vj.
sum
by
solely governed by
the
distribution
The
depar¬
anisotropic part
hyperfine interaction. At the frequency position given by
(v„ + vft)
v
a
/
and vB
frequencies va
from this value for intermediate 9 values is
of the
sum
S
9, using Eq. (2.16) and defining v+ as (va + vB). Projection of the
on
sinG to account for the
top of
Figure 2-9 for the
a
turning point
peak.
2-9
=2v, +
1
9
T2
(2.23)
——
Ig
v
is observed which
The maximum shift
90"
Fig.
p'max
An
yields
9
=
another
T2
——
16 v,
singularity
in the
lineshape
of the
from the twice the nuclear Zeeman fre-
-
Illustration of the 8
combination
the
dependence
peak v+ (bottom).
frequency
axis
yields
The
the line
of the basic
projection
shapes
frequencies v„ and Vg and
of the orientations
shown in the upper
part.
the
sum
weighted with sinfl
on
quency is observed at
a
2.3 The
Complete Spin
9 value of
approximately
to 0°/90° vanish in the ESEEM
peak
row
the
at
experiments
turning point remains, giving
The
2.3.1
Zero-Field
origins.
ent
we
For systems with
included in the
five
unpaired
zero-field
written
the strong
spin
narrow
a
slowly decaying
position
of this
dipolar coupling
depth
time
peak
for 9 close
factor k the
nar¬
which
sur¬
signal
with respect to the
constant T can be calculated.
Hamiltonian
case
more
for
than
3
.
electron
one
one
electron
spin
spin (5
in
>
magnetic
1/2)
an
fields of differ¬
additional energy
interactions between the electrons, has to be
dipole-dipole
Hamiltonian
d-electrons
Examples
for such systems
2+
(e.g. high-spin Mn )
spin triplets
or
are
in
TM ions with up to
organic molecules.
term, which is active also in absence of the external
splitting
peaks
Splitting
have discussed the
reflecting
term,
frequency
Complete Spin
2.3
So far
2vz the
45°. While the
25
due to the modulation
vives the spectrometer deadtime. From the
double nuclear Zeeman
Hamiltonian
magnetic field,
(2.24)
where D is the traceless zero-field interaction
interaction
can
field and the
be much
coupling
Nuclear
a
nuclear
3.
NQI
fine structure tensor. The zero-field
depending
on
the symmetry of the
ligand
spins.
spin Hamiltonian that will
spin quantum number / >
gradient
nucleus. The
or
Quadrupole Interaction
action of the electric
This field
larger
than the EZI,
of the electron
The last term in the
with
is
as
tf^=SDS,
2.3.2
The
is
quadrupole
arises from
1/2. The
physical origin
moment of these
uneven
be considered here is found for nuclei
of this term is the inter¬
nuclei with the electric field
distributions of electric
charges
gradient.
around the
given by
The D tensor may also contain second-order correction terms ftom the
spin-orbital coupling.
*nqi
where
in the
Q
same
and the term
(2.25)
/Q/,
=
is the traceless nuclear
as
way
can
of CW and Pulse EPR
Concepts
2 Basic
26
the ZFS. It's
often be
quadrupole tensor.
impact
the EPR
on
The
NQI
can
be
formally treated
spectrum is, however, much smaller
neglected.
As for this thesis, systems with S
>
1/2, /
>
1/2
are
of minor
importance,
we
will not
extent the discussion of these terms any further.
2.3.3
Summary
of
Energy Terms
The energy terms introduced in the
tions of the electron and nuclear
be added to form the
Xsp
Depending
on
and their relative
S
=
1/2).
extended
+
SDS
magnitudes
+
SAI
by adding
the
to more
appropriate
including the magnitude of the
-
terms.
gajlB0
+
neglected (e.g.
than
one
nuclear
in the next
chapter
for Cu
tools
2+
.
can
(2.26)
Knowledge
spin,
of the
of the
interacting ions
the zero-field
splitting
the Hamiltonian
complete spin
can
for
be
Hamiltonian
interactions and the relative orientations of PAS's of the
interaction matrices allows for the calculation of the CW and
appropriate mathematical
the interac¬
1Q1.
spin quantum numbers
terms can be
coupled
describing
among themselves and with their environment
the electron and nuclear
If the electron is
sections and
Hamiltonian:
complete spin
|fl0gS
=
spins
preceding
are
presented
in
Appendix
pulse
A. The
EPR spectra. The
procedure
is illustrated
2.4 EPR of Cu2+
2.4
The
EPR of Cu
Complexes
spin Hamiltonian
for
weakly coupled
with
13
(e. g.
C nuclei and
XsP
=
a
spin system consisting
ligands
nuclei from
protons)
can
be written
JBoSS + SACuI
+
expressed by A
and A
matrices
made between the two copper
in
experimental
which
are
obtained
small
tion of the spectrum
a
states. The 2D
angle
6
larger
JiN
last term and
those for
3/2)
spheres
hyperfine coupling
axially symmetric
is
and
to the
neglected. The
g
distinction is
no
simplifying assumptions are often justified
describes the
13
treating
plot
in
B0).
Figure
a
u
g and A
the copper
C and proton interactions
hyperfine interaction
The EPR spectrum is described
axially elongated
an
copper
copper-hexaquo complex
powder line shapes
In
large
2-3
as
the
by
by
the
complex
as
dis¬
2-10a. The parameters chosen for the simula¬
are
which
with gn
usually
can
be
angle
g±and A||
>
recorded
as
the
splitting
linewidths whereas the gK and
A[t
in the g±
values
Ay.
assigned to the different »t;
as a
function of the
between the z-axis and the external
experimental spectra
>
first deriva¬
is shown. The spectrum is
shows the contributions of the different m, states
Figure
e.g.
matrices.
corresponding absorption spectrum
of four axial
resolved due to
than the
quadrupole interaction
modulation CW EPR spectra
2-10b the
(defined
field vector
These
EPR spectrum for
are
amplitude
superposition
=
(2.27)
perturbation theory (Appendix A).
Figure
1/2, /
first and second term. The CW EPR spectrum is then
to the
cussed in section 2.1.2 is shown in
tives. In
=
compared
typical powder
Due to the
ion (S
term
principal values gK, gx, An, Aj_ of the
A
Cu
work. The third
by neglecting the
second order
isotopes.
a
XN.
assumed to be coaxial and
are
2+
of
follows:
as
The copper
.
27
in the first and second coordination
The electron Zeeman interaction is much
copper nucleus,
Complexes
can
region
usually
magnetic
is often not
be determined
without difficulties.
The interactions of the electron
described
by 9(N
are
usually
tigated by applying pulse
spin
with the
weakly coupled
not resolved in the CW EPR
spectra and
7=1/2 nuclei,
can
EPR. Due to the limited bandwidth of the MW
only
be inves¬
pulses only
a
2 Basic
28
a)
b)
H
EPR spectrum
0
EPR
(first derivative)
EPR spectrum
h
Concepts of CW and Pulse
(absorption spectrum)
l
m,=3/2
Fig. 2-10(a)
mj=V2
m^-1/2
CW EPR spectrum for
same
spectrum drawn
an
m,=-3/2
axially elongated
absorption spectrum
as
transitions as a function of the
angle
Bn
copper
with
a
2D
complex (first derivative), (b)
plot showing
small part of the EPR spectrum calculated from the Hamiltoman
The dashed lines
pulse
in
Figure
EPR experiment
in
Eq (2 27)
2-10b indicate the excitation bandwidth
performed
at
the
B0 position
indicated
by
the
spectrum The
by treating
pulse
EPR spectra of the
the spin Hamiltonian
tem More accurate
results
are
as
described
obtained
13
in
can
C nuclei and protons
section 2 2 2 for the S
by including
the g anisotropy
excited
is
(-50 MHz)
arrow
position spin packets from different m7 states with different 9 values
to the
the different mI
8
m
a
given
a
B0
thus contribute
can
=
At
for
be calculated
1/2, /
=
1/2 sys¬
the computation
2.4 EPR of Cu2+Complexes
[39,40]. Diagonalization
copper
hyperfine
of the EZI while
interaction has
no
neglecting
direct influence
29
the second term in Eq. (2.27)
on
the nuclear
frequencies
as
the
leads to
the two nuclear Hamiltonians
*«. e
where the
Xf-nr v,+<s>„, pA,'/,l
hyperfine interaction
Diagonalization
magnitudes
=
matrix
of these Hamiltonians
A,'
yields
and relative orientations of the
is
now
(2.28)
expressed
the nuclear
magnetic
frequencies
the g
anisotropy
are
given
in
[42].
as
functions of the
field and the g and
[41]. Explicit expressions for the nuclear frequencies va and
ing
in the PAS of the EZI.
Vo
for /
=
A,'
matrices
1/2 nuclei includ¬
30
2 Basic
Concepts ofCW and Pulse
EPR
Methodology of EPR
chapter 3
preceding chapter
In the
interpretation
we
of both CW and
mental aspects of CW and
have introduced the theoretical framework used for the
pulse
EPR spectra. In this
chapter
we
EPR and introduce the different
pulse
focus
on
pulse
EPR schemes
the
experi¬
used in this work.
3.1
CW and Pulse EPR
EPR spectra
can
be recorded in different
being S-band (2-4 GHz), X-band (8-10 GHz),
GHz).
can
The
magnetic
field
be deduced from the
strengths
resonance
thesis have been done at X-band
approximately
A
typical
320 mT at g
v
condition
(Eq. (2.3)).
frequencies,
and
fulfilled. In the
are
which
recorded
by putting
sweeping the
rectangular cavity),
important
and W-band (-90
appropriate Zeeman splitting
Most of the
corresponds
applications
to a
magnetic
in this
field of
2.
=
experimental
the most
Q-band (-35 GHz)
necessary to obtain the
X-band CW EPR spectrum of copper
CW EPR spectra
frequency
frequency regions,
external
a
was
magnetic
sample
Figure
2-9.
sample into a MW irradiation field of constant
field
B0 until
the
set-up the MW field is build up in
into which the
shown in
already
resonance
a
resonator
condition is
(typically
a
tube is introduced. The MW irradiation is pro-
32
Methodology of EPR
3
vided
by
a
klystron and transferred
critically coupled which
resonator
Additional
to
the cavity
that the incident power
means
absorption by
sample dunng
the
the resonator and the reflection of MW power The
as a
function of the magnetic field
of the magnetic field with
(S/N)
ratio
excitation
considerably
In
is
field
is
BQ
at
found
pulse
neously
yields
frequency
of
typically
with
e
maximum
g
in
200 mW
is
single high-power
The relation between
3 1 The excitation
A
100 kHz
is
absorbed
leads to
by
the
detuning
a
of this reflected MW power
Amplitude
the
increases
modulation
signal-to-noise
of the spectra The
shape
MHz) and the
detailed treatment of the
experimental
(approximately
recorded
MW
pulse
pulse length
profile of the pulse
by exciting
is
of given
a
large frequency
frequency
obtained
in
range simulta
v at a constant
and excitation bandwidth
is
shown
magnetic
in
Figure
the limits of the linear response the
CW MW irradiation
of excitation
frequency
v
MW pulse
Excitation bandwidth
of
in
length t obtained by am
plification of a segment of the
the
frequency
domain obtained
Fourier Transformation of the MW
by
pulse
CW irradiation
Fig
3-1
The
length
of the MW
determines the
the shaded
of
2
very small
more
resonator is
[43]
EPR the spectrum
a
recording
for the derivative
responsible
is
completely
is
resonance
the CW EPR spectrum
bandwidth of the MW irradiation
MW power
aspects
a
and
through waveguides The
pulse
excitation
area
of width
obtained
by amplifying
bandwidth of the
l/r„
a
segment of the CW irradiation
pulse Homogeneous
excitation is
expected
in
CW and Pulse EPR
3.1
ory
(
by
sin^c
Fourier Transformation of the
)
for
rectangular pulse
a
from the central
approximately
Figure
where the first
frequency are given by
in the shaded
MHz is thus obtained for
in
pulse shape
area
10
a
pulse,
ns
2-9. Reduction of the
lit
by
pulse length
single EPR pulse, which
a
length of the pulse
containing
allow for
a
the
sample
rapid dissipation
pulse. Immediately after the
MW
high
pulse
power in the resonator and
deadtime of the spectrometer
range of 100
ns.
depends
By increasing
corresponds
sensitivity
Most EPR
and
as
compared
applications
interpretation of pulse
more
to the
advanced theoretical
pulse methods
the low
other hand
can
power
sequences of MW
brought
1.
as
compared
inal
The
CW EPR. The
of the CW EPR
one
into the resonator
is not
use
of continuous
cavity
A
by
the MW
protected
from the
possible.
wave
methods
significant advantage
This so-called
can
be
responsible
for
as
the
recording
that
large
pulses explains
can
pulse
EPR
for TM ions. CW EPR spectra
number of
spin systems, including
weakly coupled
90°
also
be obtained
by manipulating
however the efforts put into the
the
spins
development
of
of forbidden transitions [46]
(see below)
a
the
on
radicals
nuclei and relaxation
are
examples
with
new
or
the
for such
strongly non-linear behav¬
assumption of a linear response is only valid for weak excitation by soft pulses with
<
are
the short relaxation of the transverse magne¬
pulse experiments, especially
a
a
of CW EPR with respect
A further limitation of
of correlations via 2D spectroscopy
flip angles
to
spectra requires sophisticated technical equipment and
Under the excitation of MW pulses the electron spin systems shows
ior.
to
resonator is however also
pulse methods (see e.g. [44,45]). The enhancement
establishing
illustrated
the bandwidth of the resonator and is in the
higher sensitivity.
spin system
as
to CW EPR.
be recorded at RT for
of the
the
signal recording
and TM ions. The additional information about
properties
2
to excite the whole spec¬
the sensitive detector must be
measuring temperatures imposed by
tization involved in
=
the bandwidth of the resonator the dead time
background.
is the
given
of the excitation. The bandwidth of the
larger than
on
still make
EPR
to 3 mT at g
impossible
limitations
reduced. The large bandwidth of the pulse EPR
the lower
of the sine function away
leads to broader excitation range. Due to
selectivity
is much
of the
to a sine function
1/2/_. An excitation bandwidth of 100
v
cases
a severe
thus determines the
resonator
high MW
is
corresponds
crossings
zero
by
which
technical limitations it is, however, in most
trum
This
Uniform excitation is considered to be
.
delimited
.
33
nom¬
34
Methodology of EPR
3
manipulations.
Nevertheless CW and
cation of both
gives
applied
because of the
high
determination of small
3.2
rotating frame
coupling
spin
pulses
moments in
distributed and
a
an
net
given sample
a
magnetic
external
volume. The
perturbation, the magnetic
is observed
magnetization (Mz)
xy
components
only along B0
are ran¬
in the Boltz-
equilibrium.
In the
rotating frame the
axes
rotates with the
system
frequency v,^
frequency
frequency
v, obtained from the resonance condition in
frequency v,^.
excitation
reduced
The
large
It is the interaction of Af with the
which
case
single
rotating
frame
magnetic
Jt/2
are
pulse,
(v
=
In
application
of
a
perturbing magnetic
field
the
by
flip angle
strength
the
on
of
a
the
MW
pulse (e
amplitude.
phase of the pulse
g. 90
The
axis
°
for
a
Eq. (2.3), from the
considerably
fields and the detector
3-2 the most
MW
during
pulse
spins
the
of
simple pulse experi¬
under this
pulse
in the
frequency vMW leads
to
precess about the resultant of
pulse.
strong MW it/2 pulse applied along y the magnetization M
Tie
and
v-vMW of the
thus appears to be
magnetization
field component Bl±B0 and the electron
the static and the
=
vMW).
Figure
and the behavior of the
illustrated. The
BQ
the offset il
applied electromagnetic
gives observable pulse EPR spectra.
a
given by
static field
for the on-resonant
or even zero
spins
is
of the MW
time-independent
true resonance
2
of the mag¬
B0 (taken along the z-axis) being out-of-
field
for the electron
a
for the
up the contri¬
precession
resonances
ment,
allowing
given spin system.
on a
excitation about the z-axis. In this frame the excitation becomes
the
pulse
appli¬
EPR is
Spin Dynamics
to describe the effects of MW
magnetic
the
first introduce the concepts of macroscopic magnetization and
we
in the absence of
mann
-
only
system. In this work
constants.
netic moments about the external
domly
and
complementary
are
macroscopic magnetization M of a sample is obtained by adding
-The
bution of all
phase
EPR
of the
structural resolution in disordered systems,
MW Pulses and
In this section
pulse
picture
reliable
a
is
n/2 pulse) depends
Under the influence of
rotated to the *-axis
on its
2
.
This
length tp and amplitude,
about which the magnetization vector
is
rotated
is
a
given
3.3 Relaxation Times and Linewidths
Pulse
experiment
35
ji/2 pulse
FID
of
frequency
il
Behavior of M
Mk
Bo
Boltzmann
equilibrium
magnetization vector M
aligned along the static
the
is
field
Fig.
fig
3-2
Illustration of the
behavior of the
its
zero.
pulse
by 90'
After the MW
Relaxation
under the per-
zation processes with Q back
turbation
B,
to its
simplest pulse experiment with
case
pulse
equilibrium position along
z,
after the pulse the magneti-
in the
xz-plane
magnetization
is shown for the on-resonant
field is
MWn/2
M is tilted
in
vector
M in the
Figure 3-2,
a
single
rotating
MW jt/2
frame
thereby precessing
which
oscillating components Mx
can
be recorded
In this
chapter
S
induction
magnetization
frequency
paragraph.
The
£2
.
This
precession
vector in the
after the MW
resulting
vector moves back to
with the offset
magnetization
decay (FID)
discuss the effects which
we
equilibrium position.
consider
an
free
and M of the
and the
xy-plane
pulse.
Relaxation Times and Linewidths
3.3
its
as
pulse (top)
(bottom).
where the z-component of the
is switched off the
behavior is called relaxation and will be discussed in the next
leads to
equilibrium position
=
For this purpose
we
bring
the
switch back to the
again the single magnetic moments contributing
1/2 system the
netic field and
a
spins
can
be oriented
perturbation (e.g. pulse)
magnetization
parallel
or
to
vector back to
microscopic view and
the overall
anti-parallel
magnetization.
to the
In
external mag¬
induces transitions between the two energy lev-
36
Mz magnetization in equilibrium
els. The
their
to
quantization
given by
induced e.g.
in-phase precession
by
a
MW
spin-lattice
T2, respectively.
spin
Tx
is related
energy and time
taken
a
or
spin-lattice
broad
tronic
resonance
ground
through
on
the other hand
moments about the external
line.
of
a
smearing
values
separated
spin
changes
relaxation time
Tx
field,
is restored and the transversal
in
magnetization
and the
spin-spin
are
associated
relaxation time
of energy via the thermal vibration of the
to the linewidth of an
Large T,
states, well
Mz magnetization
are
spin packet.
of the energy levels
usually
written in terms of
caused
sample. T2
is
the resultant linewidth of
a
A small
(large Aw)
T,,
and thus
found for systems with isolated elec¬
from the lowest excited states. The
spin flips
in the
out
individual
by dipolar
usually
and
spin-spin
single spin packet
to a
relax¬
exchange interactions
much shorter than
the dominant contribution to the linewidth. The two contributions
by relating
spins parallel
involves reorientation of the
Heisenberg uncertainty principle,
the
for At, leads to
assembly
of
relaxation relates to the characteristic lifetime of the
ation is concerned with the mutual
between the
magnetic
by the dissipation
(AwAr > hllit),
as a measure
surplus
magnetization Mx and M
vanish. These
longitudinal
state and is determined
lattice.
small
Mz magnetization
of the
the Boltzmann
The
a
pulse.
magnetic components Mx and M
with the
is the result of
moments. Transversal
an
Upon relaxation
the
Changing
axis.
microscopic magnetic
is
Methodology of EPR
3
are
Tx
and thus
often summarized
relaxation time
T2 given
by
\
T2
T2
=
±12
+
^r.
2I
(3.1)
l
is the relaxation time which is of
magnetization generated
and observed in
dependent
and determines the
tion metal
complexes T2
importance
pulse
EPR
homogeneous linewidth
in connection with the transverse
experiments. T2
of
values in the range of several jts
temperatures. Among the various effects influencing T2
centrations
shortening
or
clustering
a
of
paramagnetic molecules
of the relaxation time.
is temperature
single spin packet.
liquid
are common at
we
only
mention
which may lead to
For transi¬
helium
high spin
a
con¬
considerable
3.4 Pulse EPR
3.4
37
Experiments
Pulse EPR
importance of spin
The
Experiments
in
experiments
echo
pulse
lines encountered in solid-state EPR which make the
EPR is
of FID's often
recording
ble. Due to the short relaxation times of transition metal ions
pulse
have to be recorded at
and
liquid
tions like the g matrix
or
helium temperatures in most
B0 mhomogeneities
the EPR line. As illustrated in
by
the contribution of many
fields. Unlike the
Figure 2-3
lead to
an
the broad
explained by
cases
EPR
impossi¬
experiments
anisotropic
interac¬
inhomogeneous broadening
of
inhomogeneously broadened line is obtained
an
spin packets, subject
to
static
slightly differing
homogeneous linewidth, the inhomogeneous linewidth
magnetic
is not related to
any relaxation time.
3.4.1
Two-Pulse ESEEM
An
of the
important
effect of the
inhomogeneous broadening is, however,
FDD, obtained after the excitation of
contributing
Q,. The
the
magnetization
vector have
an
now
already during
a
rapid vanishing
slightly
by
Jt/2
a
different
of the transversal
pulse
of double
netic moments
ent
by 180°
length. Applied
in the
jry-plane.
after
a
magnetic field distri¬
echo
simple spin
time interval
As the order of the
Figure
pulse, leading
3-3 where
ior of the
me
to an
pulse
magnetization
observable
vectors. Both
deadtime (~ 100 ns) is indicated
typically
spin
sequence of the
as
in the range of several tenths of
eral Jis, in steps of 10
Echo
or
20
area
ns
are
moments is reversed
i
this
pulse flips
while
%
the
by
a
the mag¬
with differ¬
at time t after the
echo). This is illustrated in
applied along
after the first
occurs
experiment,
experiment is shown together with
pulses
striped
often
spins, processing
(primary
echo
rapid decay
spin packets
precession frequencies
velocities, is also reversed the in-phase magnetization is restored
second
All
magnetization, which
the spectrometer deadtime. In the most
two-pulse ESEEM experiment, the dephasing of the magnetic
second
pulse.
under the action of the
dephasing of the magnetic moments
bution leads to
EPR line
the
pulse.
-x.
the behav¬
The spectrometer
The
pulse lengths
is incremented from
-
100
are
ns to sev¬
ns.
envelope modulation. The
FID itself does not contain much information for
a
system with large inhomogeneous broadening. The importance of this ESEEM methods
stems from the fact that due to
the coupling of the electron
spins
to
nearby
nuclei the
38
Methodology of EPR
3
TC/2
Fig.
3-3
71
Defocusing
Refocusing
of the magnetization af-
of the
ter the n/2
ter the
pulse
Illustration of the two
pulse
packets during the evolution
ESEEM sequence
time T
pulse
the first time
spin echo
a
is
observed
modulation due to the
amplitude
If the echo intensity
For
5
=
1/2,
/
The basic
Appendix
The echo
tem
to
B the
decay
reversed
by the
Incrementation of the tune
T2
in
depends
recorded
For N nuclei
is
is
as a
on
of the
pulse
At the time 2t after the first
T
yields
the echo
characterized
by
the
to an
unpaired
T a
envelope
T
v_
is
between the two
modulation pattern results
frequencies va
was
the absence of effects like
coupled
decay
after the first
area
the time interval
function of
by the product of the
given
individual spin
to the
to the nuclear spins
of this modulation effect
envelope decay
pulse
k
ESEEM modulation formula
two-pulse
modulation pattern
is
(indicated by the striped
(sum combination frequency) and
theory
the relaxation time
faster
is
(top) and behavior of the
1/2 system it contains the nuclear
=
combination lines v+
quency)
coupling
of the electron spin echo
pulses
an
period
af¬
(bottom) The dcphasing leading
FID within the spectrometer deadtrme
along) during
magnetization
n pulse
and Vg
as
well
as
(difference combination fre¬
given
by Rowan
given for
a
S
phase-memory
spectral
=
et
al
1/2, /
time
[39]
=
TM
In
1/2 sys¬
identical
diffusion which lead to
electron the overall echo
a
envelope
N individual modulation patterns
[30]
N
Emod(x)
n<""^)
=
i
=
This property of the modulation pattern
tions
by
(3 2)
l
division of time traces
can
(cf chapter 5)
be used to eliminate unwanted modula¬
Pulse EPR
3 4
Experiments
For anisotropic systems with broad basic
modulation
be much faster than the
can
the modulation pattern
lope
pulse) leads to
peak
severe
may be of
3.4.2
and vR the
envelope
as
the spin echo then refocuses
distortions of the spectra In these
decay
of the
itself The truncation of
of the echo
enve
the deadtime of the second
m
analysis of the
cases
narrow sum
advantage
Three-Pulse ESEEM
The three
is not
frequencies va
of the
by the spectrometer deadtime (the first points
be recorded
can not
decay
39
pulse ESEEM experiment
extensively
other important
pulse
The
experiment
used
application
the
in
three-pulse
The first two
tl
on resonant
to evolve
spin
during
first introduced
by
section we want to
Mims
sequence
pulses
packets)
as
well
the evolution
is
time t
create
as
shown
in
(typically
electron
[30] Although
discuss it here
sequences like Mims ENDOR and HYSCORE
pulses separated by the fixed delay
able time
was
Figure 3-4
are
in
based
on
polarization along
The third MW
pulse
this
the
z axis
van
( Mz for the
allowed
is
converts the electron
polar
ization and nuclear coherence to observable electron coherence which manifests itself
stimulated electron spin echo
an
echo
depends
!j while
on
keeping
modulation In
is
given for
an
x constant
Appendix
5
at
the time T after the last
the evolution time r.
=
1/2, /
Jt/2
yields
B the
=
a
Recording
analytical formula
of the three
amplitude
amplitude
pulse
as a
function of
two-pulse ESEEM
ESEEM modulation
It/2
delay ^
|
(incremented)
I
time f
Fig
3-4
Three
pulse ESEEM sequence
with three ic/2
pulses separated by the
(fixed) and t] (incremented) The stimulated echo
MW
pulse
is
as
of this
1/2 system
t
(fixed)
The
modulation pattern similar to the
71/2
delay
pulse
of the echo
it
as
It consists of three ir/2
several hundreds of ns) and the
nuclear coherence The nuclear coherence
period tl
detail
observed at time
time
x
intervals
t
after the third
Methodology of EPR
3
40
The main differences between the two formulae
lines in the
three-pulse ESEEM,
occurrence
of
[1
blind spots
for the
cos(2itvBt)]
-
tion
and va,
v»
and the
as
two-pulse experiment.
observed for much
magnetization
is
envelope decays
primary
[1
For
and the
cos(27tvaT)]
-
1
k/8)
vs.
with
=
and
n
0,
-
va/p
basic frequencies do not contrib¬
stored
with
The stimulated echo
times than the
longer
respectively.
corresponding
the
the evolution time tv the echo
in the
depth (k/2
amplitude factors
the
to
modulation. Furthermore,
during
TM decay
due
zero
the absence of combination
the shallower modulation
frequencies
1, 2,... these factors become
ute to the
are
echo
(«j
can
as
Tx
electron
as
polariza¬
to the
compared
therefor in
be
general
intervals of several tenths of
Us).
The choice of the time intervals in the
ited
by
ESEEM
the deadtime after the third 7t/2
be recorded from
tx
=
0
on.
produced by
the artifacts
This
requires
undesired
The modulation
pulse.
however extensive
two-pulse spin
pattern
can
phase cycling
echoes due to the
in
to
(t+i,)
is
principle
get rid of
non-ideality
of the
ID Four-Pulse ESEEM
As
have
we
affected
seen
in the
preceding chapter,
the spectrometer deadtime and the first
by
points
broad lines with
ter 2
that the
rapidly decaying time signals.
sum
tropic systems.
peak
obtained in
In this section
described, which yields
T; decay
ESEEM
3.
As
of the echo
experiment.
are
of the modulation pattern
can
narrow
envelope.
at
stimulated echo if /,
inated
on
the
a narrow
is
inverted
three-pulse
ESEEM sequence
This is the one-dimensional version of the
pulse. Upon
traces
(HYSCORE)
four-pulse
is described in the next
second and third
increasing t, this primary echo will
overlap the
with the
phases 0 and B for the first Jt/2 pulse The phase of
by these procedure while the primary echo is not affected and the
primary echo will be eliminated
of
line, also for aniso¬
equals t and gives a peak in the modulation pattern. This artifact can be elim¬
by subtracting two tune
the stimulated echo
case
combination lines and has furthermore the benefit of
The two-dimensional version
the time (j after the third
in the
already been demonstrated in chap¬
ESEEM is
experiment based
especially
example for such an artifact consider the two-pulse echo generated by the
an
pulse
an
two-pulse
It has
pulse
ESEEM
both two- and three-
therefore not be recorded. Considerable information may be lost
an
is also lim¬
pulses [47].
3.4.3
is
experiment
the spectrometer deadtime. The shortest value for the variables T and
given by
7t/2
three-pulse
by
the subtraction
3 4
Pulse EPR
Experiments
41
n
nil
7i/2
1
(fixed)
time increments
sum
*-
peak
HYSCORE
Fig
3-5
Four
tc/2
m
t1
t1
\
tj
t2
|
pulse ESEEM sequence
peak experiment
*-
with the time increments for the
one
dimensional
sum
and the two dimensional HYSCORE
section
pulse sequence of the four pulse ESEEM
The
pulse
7t/2
sequence
pulse
first time
is
extended
The nuclear coherence created
period tl
is
is
refocused
by
pulse
experienced by
The
analytical
+
Vjj)f[
Cc{%)
is
is
given
in
transfer echo
is
period
formed which
3.4.4
formula for the four
its
Figure 3 5 The three
in
between the second and the third
pulses and evolving during the
same
in
change
detected
is
Appendix
as in
derived
was
B The
the three
sum
=
t2
this
pulse
At time
amplitude
after the third Jt/2
x
by
inhomogeneous
pulse
7t
as an
£'lna by setting t{
blind spot behavior
and the
after the
pulse experiment
corrected form [37]
obtained from the contribution
leads to the
shown
the nuclei thus
of the stimulated electron spin echo formed at time
[47] and
is
the first two
the second evolution
during
nuclear coherence
strong
n
transferred between the two ms states of the electron
The local magnetic fields
HFI
by inserting
a
2tl
modulation
pulse [48]
by Gemperle
peak
The
a
et al
modulation
amplitude
(v
factor
pulse experiment
HYSCORE
The two dimensional
duced
by
copy
reflecting
version
of the four
pulse
Hofer et al [49] HYSCORE stands for
ESEEM experiment
hyperfine
the transfer of nuclear coherence
by
3
first intro
sublevel correlation spectros
the
ji
manifolds In the HYSCORE experiment the two time intervals
independently (see Figure
was
5) Founer Transformation of the
pulse
11
between the
and t2
two time
are
ms
incremented
domains
yields
a
42
Methodology of EPR
3
3-6
Fig.
Simulated HYSCORE spectra for
showing
the
the
and the
peaks
a
cross-peaks between the
coupling
can
weakly coupled, isotropic
5
nuclear
v..
be determined from the
two-dimensional spectrum with the frequency
In
Figure
frequencies va
3-6 HYSCORE spectra for
a
axes
and
projection
1/2, /
=
=
1/2 system,
The exact location of
onto the
(Vj,v2)-plane.
Vj and v2.
weakly coupled
S
=
1/2,
/
=
1/2 system
are
shown.The evolution of the nuclear coherence in the two time intervals
/, and t2 with dif¬
ferent
frequencies va
quencies (va,
about the
Vp)
and
and
Vp (cf.
(Vp, va)
diagonal (V[
=
term
£IIIa in Appendix B) yields cross-peaks
in the 2D spectrum. This
v2),
indicated
between the two ms manifolds is not
peaks (va, va)
obtained
and
HYSCORE has
expansion
tra
considerably
peaks
solid line in
complete (k pulse
into
a
a
as
of the 2D spectrum
few
on
major advantages
second dimension
cross-peaks
can
nucleus. Furthermore HYSCORE is
only
nuclear
frequencies
as
3-6. If the transfer
The ID ESEEM spectrum is
v2.
compared
particularly
placed symmetrically
strong enough) additional
the
to
the other ESEEM methods:
interpretation
be observed between
pically
observed
as
or
simplifies
broadened ESEEM lines due to the
are
Vj
are
Figure
not
(Vp, Vp) will be observed on the diagonal.
by projection
the
by
a
at the fre¬
useful for the
refocusing
of
complicated
frequencies
investigation
action of the
7t
of the
spec¬
same
of anisotro-
pulse.
coherence transfer echoes the ESEEM lines
As the
are
free
3.4 Pulse EPR
from dead-time distortions. Weak and strong
positive
and
negative phase
coupling
coupling features
in the
easily distinguished
is
factors in the relevant terms
strong coupling, peaks will be observed in the
weak
43
Experiments
Emi and E^, respectively.
tude and
positions
(v1( v2) quadrant [48,50].
shown. The
(Vj
45°,
=
a
of the
Avmax
ridges information
coupling [42,51-53].
S
1/2,
=
leads to
dipolar coupling
2Vj-v2).
a
The maximum shift
dipolar coupling
=
/
=
In
can
Avmax
constant T by
be extracted about
magni¬
3-7
typical
a
HYSCORE
g and axial HFI is
isotropic
ridges
from the
ridges.
Figure
1/2 system with
curvature of the
correlation
as
away from the
anti-diago¬
observed for 8
anti-diagonal,
cated in the
figure.
The end
tations 0
0, 90°
are
can
points
found
on
(3.3)
be estimated from the
of the
the
ridges
which
anti-diagonal.
separation
correspond
of the
to
ridges
as
indi¬
the canonical orien¬
Due to their weak
intensity they
are
however often difficult to observe.
Frequency v, [MHz]
Fig.
3-7
HYSCORE spectrum for
anisotropic,
two
a
weakly coupled,
disordered S
=
1/2, /
axial HFI. The dashed lines indicate the nuclear Zeeman
frequency
axes.
-
[42]
V2(^)=V2Amax.
isotropic coupling
=
of these
weakly coupled
is related to the
The
shapes
orthorhombicity
spectrum for
nal
and
For
(Vj, -v2) quadrant, well separated from the
In disordered systems the broad ESEEM lines will appear
From the
due to the
=
1/2 system with
frequencies
on
the
44
Methodology of EPR
3
3.4.5
ENDOR
In the ESEEM
experiments discussed
spins whereas the
tron
nuclear
spins
ESEEM effect is thus observed for
where the
anisotropy
is
averaged
so
excited
are
isotropic
out
far the
applied
indirectly via
systems
by molecular
or
for the
manipulation of
tively [54]. Many ENDOR experiments
are
Mims [55] and Davies [56], shown in
by
echo
are
amplitude
is measured
fixed. The RF
pulse
as a
induces
spin flips
transitions lead to
spin
tron
changes
arrows
a)
nil
covers
the
polarization
which
spins,
respec¬
pulse
the RF
spin
All time intervals
frequency
range of
Figure 2-6). Nuclear
are
observed via the elec¬
is small
(< 1 MHz) the whole
frequency through
the spectrum.
delay f,
(variable)
nil
1
delay f;
RF
both MW and
nil
1
MW
RF
pulse
frequency.
nil
i
use
sequences introduced
in the two ms manifolds in
by sweeping
in solution
3-8. In both schemes, the electron
echo. As the excitation range of the RF
NMR spectrum has to be recorded
HFI. No
electron and nuclear
of the nuclei if it
in the electron
anisotropic
techniques
function of the variable RF
the nuclear transition, (cf. hollow
the elec¬
paramagnetic species
based on the two
Figure
the
act on
motion.
The ENDOR (Electron Nuclear Double Resonance)
radio-frequency (RF) pulses
pulses
MW
n
x
x
(variable)
time t
Fig.
3-8
Illustration of the Mims (a) and Davies
fixed. The electron
frequency.
spin
echo
(b) ENDOR
amplitude
is
pulse
recorded
as
sequences. All time
a
delays
are
function of the variable RF
3.4 Pulse EPR
Recently methods
have
Experiments
45
to increase the effective bandwidth of the RF
emerged
pulses
(eg. [57]).
Only
Mims ENDOR spectra
three-pulse experiment
between the HFI
"t
=
a
of
a
subject
and is
Blind spots
experiment.
presented in
are
to a similar
nucleus and the time
with
blind-spot
in the spectrum if die
occur
-,
this thesis. The method is based
=
n
delay
on
following
relation is fulfilled
v.
0,1,2,...
(3.4)
a
This
blind-spot
behavior
recorded with different
Finally
nucleus
depends
and
an
partially eliminated by addition
be
on
the nuclear
of nuclei like
ENDOR effect.
practical
limitations
13
C
gn-factor.
as
and
length
relaxation
enhancement which
a
by
can
be
a
from
of the RF
time).
effect is
originates
flip angle of the
If the
partially
RF
or
longer pulses
pulses
are
coupling
is
for
frequency [54].
are
subject
a
given
to
needed to
technical
large enough (e.g.
counterbalanced
modulation of the internal
the electron at the nucleus, with the RF
pulse
considerable drawback for the
much stronger RF fields
Strength
(e.g. T,
This
strongly coupled nitrogen nuclei) this
duced
of several spectra,
values.
it should be noted that the effective
investigation
observe
i
can
the
behavior than the ESEEM
by
the
hyperfine
magnetic field,
pro¬
The addition of exter¬
nal RF and internal fields leads to an increase of the ENDOR effect.
46
3
Methodology of EPR
Aqueous Chemistry of
chapter 4
and Carbonates
Cu
In the first part of this
The coordination
chapter the
chemistry
carbon dioxide and the
chemical
protagonists of this thesis
of copper is reviewed
geochemistry
as
well
as
are
the aqueous
chemistry
in
on
Cu
2+
.
chapters 5
This
compilation
is the basis for the discussion of the
investigation
are
equilibria
presented.
or
The
tion and at the surface, calculated from the
as
again
with
experimental results
and 6.
In the second part chemical
tems under
of
of solid calcium carbonates. Furthermore the inter¬
action between trace metal ions and calcium carbonate minerals is discussed
focus
introduced.
expected
speciation
5 and 6 and
discrepancies
calculations
are
are
for the
compared
discussed.
distributions of
thermodynamic stability
starting points for the preparation of samples
tions of the
for the various sys¬
speciation calculations
experimental
to the
complexes
constants,
in solu¬
are
studies. The
spectroscopic results
in
used
predic¬
chapters
Aqueous Chemistry of Cu2+
4
48
and Carbon Dioxide
4.1
Cu
4.1.1
Coordination
2+
Chemistry of Cu
configuration
The Cu
coordination
is the most stable valence state of copper in water and the
of Cu
chemistry
2+
shows
coordination group consists of four
completing
a
a
(4+2) coordination,
indicating
a
stronger
a
(dz2, dM and dyz)
lowering
2.0
A
effect. This is the
transitions
plexes
one
case
same
or
lowering
2+
making
a
differences
are
for stabilization of the
[21], Kt and K2 for x
Figure
Elongation
=
1,2
of the axial
pointing along
2-4
on
the z-axis
page 15.
there may be several stable
resulting
in
a
a
rapid
con¬
intercon-
dynamic Jahn-Teller
in solution. External factors such
sphere
subject
as
may result in the stabi¬
complex.
to a static
Such
com¬
Jahn-Teller effect.
by the ligand geometry
complex by distortion. This point
is
copper-ethylenediamine (en) complexes
are
much
higher than K3 since in the
equatorial plane,
thus
allowing
of the axial water molecules. Formation of the
coordination of two (en) molecules both at
Jahn-Teller distortion difficult.
equatorial,
the
distances for the equato¬
static distortion of the
the formation constants of
through displacement
a
complex
coordination takes place in the
plexes requires
ligands
axes can occur
and induce
2+
is the stabilization of the
the coordination geometry is fixed
possibilities
[Cufcn^HjO)^]
two cases the
sphere
in the second coordination
bond-length
chelating ligands
clearly illustrated by
longer than
in overall energy. In this case
2+
ligands
A, respectively.
with identical
Cu(H20)6
H-bonding
configuration
which limits the
tion
for the
with measurable
For
about 12%
the Jahn-Teller effect [21].
version between the different distortion
lization of
being
and 2.2
two distant axial
copper-hexaaquo complex Cu(H20)6
of the energy of the metal d-orbitals
symmetrical complexes
the
one or
equatorial ligands. Typical
of the
are
with
observed
frequently
most
distorted octahedron [24]. The six water
shown in the energy level scheme in
as
figurations producing
phase
or
of the
sphere
configuration through
bonds leads to
For
coplanar ligands
for the distortion of the coordination
reason
electronic 3d
great diversity. The
the axial bonds
bonding
rial and axial Cu-0 bonds
The
a
tetragonal pyramid
distorted
molecules in the first coordination
show
and Carbonates
equatorial
for
x
and axial
a
=
first
distor¬
3
com¬
positions
4.1
In solution copper has
plexes
in the presence of
The dimeric salts
pronounced tendency
bridging ligands
as
the solution
because of their
widely investigated
4.1.2
well
as
a
Cu2+ and Carbon Dioxide
such
as
49
form dimeric and
to
OH", carbonate
interesting magnetic
carboxylic
com¬
acids.
compounds have been
of the later
complexes
or
polymeric
behavior
(e.g. [58]).
Carbon Dioxide
Although the atmospheric reservoir
is of primary
importance
sedimentation and
number of
a
geochemical
photosynthesis [1,3].
sphere in large deposits
produced through
in
of carbon dioxide
A
is rather small, the gas
and biochemical processes such
major part
of calcium carbonate
(C02)
of
C02
is buried in the
(CaC03), mainly calcite.
Such
hydro¬
deposits
sedimentation in freshwater and marine environments with
as
are
bio¬
high
logical productivity.
Dissolution of
Carbonic acid
(H2C03).
bonate
2_
(C03 ) ions.
C and the
acidity
in water leads to the formation of the
can
undergo dissociation
The constants that govern these
constant
given for carbonic
=
C02(aq)
+
acid is the
H2C03.
about 0.3% of the dissolved
C02
so
equilibria are
called
carbonic acid
diprotic
to form bicarbonate
pH dependent distribution of the three species
species H2C03
only
C02
(HC03)
tabulated in
is illustrated in
car-
Appendix
chapter
composite acidity
and
4.3. The
constant for the
This formulation takes into account that at 25 °C
is present
as
carbonic acid, able to
undergo
disso¬
ciation.
Extensive work has been done
[12,13]. The
occurrence
of
mono-
the coordination behavior of carbonate
on
and bidentate coordination has been confirmed
spectroscopy through investigation of the C-O chromophores and by X-Ray
determination. Detailed studies of cobalt-carbonate
into
complexation
4.1.3
mechanisms such
Complexation
The
diversity
CuHC03
complexation
in the
+
,
of Cu
2+
as
2+
between Cu
CuC03
tabulated [13,60]. At
or
Cu(C03)2
high pH
2
,
ring
by
liquid and solid phase.
0
ligands
complexes
and carbonate
a
structure
given insight
Ligands
ligands
number of
complexation
values mixed
IR
closure and substitution effects.
Carbonate
For
[59] have
by
is known to show
a
large
copper-carbonate complexes
constants
like
have been determined and
hydroxocarbonates
are
expected
to form
and
50
Aqueous Chemistry of Cu2+
4
precipitate
from solution. The most
minerals malachite
important
oxysalts
as
copper-carbonate compounds
(Ci^CO^OH^) and azurite (Cu3(OH)2(C03)2) [61].
is not stable at ambient temperature under
well
solid
and Carbonates
like
Na2Cu(C03)2
•
3
atmospheric
H20
and
bidentate
or
ligand, bridging
3D framework structures
ers or
metal atoms to form finite
The Solid Calcium Carbonates
4.2.1
Structural Characteristics
Carbonate rocks represent about one-sixth of the
than 90% and
bonate
as
are
it is the
high
found: calcite,
aragonite
thermodynamic
pressures and is
stable
at
frequent
following
occurrence
Mg
to
2+
organisms.
(e.g.
of calcium
It
Aragonite
is stabilized
seawater).
It is also found
frequently
occurs
however
alternating planes
as
the carbonate
planes
of all carbonates with
2+
The Ca
ure
Mn
2+
2+
,
a mean
ion in calcite is
4-1) with
Fe
,
a
Cd
Ca
2+
,
of
C03
depicted
are
2-
in
2+
and Ca
[62,63]. In aqueous solutions
Figure
ions, perpendicular
4-1. The
or
C03
<(OCO) angle of 120° and
6-coordinated, forming
2+
as a
calcite within 24 hours.
-O distance of 2.38
Zn
as
with respect to cal¬
calcium carbonates in this work [64,65]. The rhombohedral calcite structure
alized
e.g.
by
that the mineral may well be
supersaturation
in natural waters
car¬
polymorph
only marginal importance
speculated
as
in
Of the
discuss the structures of calcite and vaterite, the relevant
only
we
mass.
account for more
polymorphs
conditions.
Vaterite has
Some authors
vaterite undergoes recrystallization
In the
ordinary
component of lake precipitates
a
CaMg(C03)2
In nature three
in presence of
organisms.
product of artificial precipitation.
cium carbonate is
complexes, chains, lay¬
and vaterite. Calcite is the most abundant
tissue of fractured cells of certain
a more common
as
for the
ton can act as mon-
global sedimentary
and dolomite
origin.
phase
precipitated
in the skeletal parts of certain
repair
CaC03
calcite
of maritime
mostly
are
compounds
[24].
4.2
rock-forming carbonates,
CuC03
Na2Cu(C03)2 provide examples
different coordination structures with carbonate ions. The carbonate
odentate
The salt
conditions. These
the
are
Co
2+
are
A.
A
a
variety
known to form
be visu-
to the c-axis. Two of
group is the fundamental unit
a mean
slightly
can
C-O distance of 1.28
distorted octahedron (cf.
of divalent cations such
calcite-type
as
A.
Fig¬
Mg +,
carbonates with struc-
4.2 The Solid Calcium Carbonates
Fig.
4-1
Schematic
drawing of the coordination sphere of a calcium ion
planes indicated by
the shaded
area
perpendicular
51
in calcite with two carbonate
to the c-axis.
rural variations due to the differences in ionic radii of the metals.
The
hexagonal
structure of vaterite is more
Unlike in calcite the carbonate ions
surrounded in
Ca
+-0
a
first coordination
distance of 2.59
rounded
by
dron and
a
A.
In
6 oxygens at 3.05
trigonal prism
a
or
to calcite
(Km
=
8.48)
parallel
an
2+
Ca
ions with
which
an
c
axis. The Ca
the Ca
sphere
a
explains
and the lower
+
ions
an
density
A forming
are
either
are
3
g/cm (vs.
a
sur¬
elongated
almost
regular
an
respectively.
higher solubility {Km
2.54
ions
octahe¬
molar ratio of 2:1,
the
2+
octahedral fashion with
intermediate between
6 oxygens at 3.55
by
and less well established.
the
to
6 oxygens in
second coordination
A forming
loosely packed
vaterite structure is
oriented
sphere by
octahedron. This leaves two sets of
compared
are
complicated
=
g/cm
2.71
3
The
7.9)
as
for cal¬
cite) [3].
The
morphologies
for the two
Figure
4-2. Calcite often forms
vaterite
particles
are
typically a few
large
aggregates of a
crystal morphologies
are
polymorphs
are
2
m
large
responsible
are
also
rhombohedral
quite
crystals
number of small
to up to 30 m
as can
whereas the
crystallites
for the differences in
/g for calcite compared
different
<
50
/g
for vaterite
seen
in
spherulitic
nm
specific surface
2
be
[63]. The
areas
[66,67].
which
52
Aqueous Chemistry of Cu2+ and Carbonates
4
Fig.
4-2
SEM image of
The vatente
clearly
vatente
a
spheruhtes
shown
in
4.2.2
urn
shape.
Crystal
supersaturated
(inset) Some particles
are
shapes
This
solution
is more
intergrown with calcite crystals
The white scale bar at the bottom of the SEM image
corresponds
to
Growth and Dissolution
their abundance
are
they
among the
most reactive
minerals
at the earth
surface Due
often control composition and chemical properties of natural
waters. The dissolution and
numerous
a
(Foto Prof Giovanoh, Univ Bern)
Carbonate minerals
to
from
aggregates of small crystals of variable
the TEM image
of rhombohedral
1
sample prepared by precipitation
are
precipitation kinetics of calcite have been the subject of
investigations (see e.g. [68-70] and references therein) Three different
reac¬
tion mechanisms have been identified
CaC03(s)
+
CaC03(s) +
CaC03(s)
The dissolution at
H+
^ Ca2+
*-i
H2C03* ^
*
==^
Ca2+
high degrees
+
HC03"
Ca2+
+
2HC03"
(4 1)
(4.2)
2
+
C02
(4.3)
of undersaturation is described in terms of the fol-
4 2 The Solid Calcium Carbonates
lowing rate
law with contributions from the three forward reactions
*/
where
the dissolution rate far from
Rj- is
the second term at
pH (< 5),
and the third term at low
pC02 (<
supersaturation calcite
precipitated
described
Rb
where k
is
terms of the
in
plex by
the
Ca
ions
2+
The
,
etal
C03
2
m
and
idea
same
tion of calcite
high pC02 (>
in
k-2"Ca^2HCOi
+
terms of
Eq (4 5)
CaC03(s)
was
atm)
0 1
first order
kt are
and
in
Eq (4 4)
is
high pH (> 6)
Close to saturation
or
at
from solution and the overall backward reaction
+
Inskeep
involves the formation of
with
forwarded
a
[69] have
et al
Brown et al
specu¬
surface activated
activation energy due to the
an
by
<4 5>
k-3aCa^C0\
second and third order rate constants
lated that the last reaction
],
s
The first term
atm) and high pH (> 7)
0 1
1
2
m
individual reaction steps
k-^c^aco,
=
are
t
equilibrium [mol
and a, activities of the dissolved species
effective at low
is
(4 4)
*lV + *2«HiCO; + *3.
=
rate constants
rate
53
com-
dehydration
of
[71] who explained the precipita¬
the surface reaction/molecule integration mechanism of Chiang
[72]
More
msight
into
the mechanisms of calcite dissolution and precipitation
the detailed kinetic expressions of Arakaki et al
plexation
model of Van
presented
above In this
Cappellen
approach
[73]
is
given
who combined the surface
by
com-
al [6] (section 4 3 2) with the mechanistic models
et
the
macroscopically
observed reaction rates
are
linked
to
the distribution and reactivity of chemical species at the calcite surface The existence
of
hydration
and
H20
sites
>C03H and >CaOH at the
C02 both
in air
and
in water was
spectroscopic techniques by Stipp
et al
tance of dissolved
as
CaC03
species
by
the reaction with
experimentally with
surface-sensitive
calcite surface, formed
shown
[16]
Arakaki et al
great similarity
mam
difference
mvestigated by Kralj
between their results
following directly
stress the impor¬
'precipitation agents'
The dissolution and precipitation kinetics of vatente
into calcite have been
[73] also
an
et al
as
well
as
the transformation
[63,74,75] These
the dissolution and
growth
from the different solubilities
authors noticed
a
kinetics of calcite, the
Aqueous Chemistry of Cu2+
4
54
The kinetic studies mentioned
far do not take into account the
so
activated surface sites such
additional
for
new
growth
nuclei may form
directly
on
the surface which
spectroscopic techniques [77].
The AFM
pictures
starting points
then
are
This processes have been visualized with AFM
crystal layers.
nature of
[2], At higher supersaturation
steps and kinks
as
microtopography
and dissolution of material
precipitation
of the carbonate surface. Close to saturation
occurs at
and Carbonates
[15,76] and
other
highly dynamic
have also revealed the
the calcite surface. Some authors [15,16] have concluded that the calcite-water
interface is ordered and
amorphous hydrated
crystalline
surface
layer,
and that
a
few
evidence is found for
no
in
monolayers
depth,
as
a
disordered
postulated by
or
Davis et
al. [78].
4.2.3
Interactions with Trace Metal Ions
So far
of
ence
we
have
impurities
only considered the reactivity
this
reactivity
be
can
of pure calcium carbonate. In the pres¬
altered. Here
considerably
limit the discus¬
we
sion to the effects of trace metal ions.
The interaction of trace metal ions such
calcium carbonate has been the
[7,79-81]).
often
uptake
adsorption,
CaC03(s)
separate
called
so
followed
solid-solution.
MeC03(s) phase
lattice sites
Following
or
by
surface
on
large
on
adsorption
surface-exchange
Strong adsorption
+
Mn
Me
,
Zn
number of
high affinity
precipitation
precipitation
via
and Ni
Co
,
with
investigations (see
e.g.
for the carbonate surface and
or
recrystallization
in most
cases
and formation of
the molar ratio Ca
occurs
by complexation
Ca(surface)
,
the calcium carbonate may
the concept of McBride
stants of the
rather
Cd
coprecipitation reaction proceeds
Depending
It is unclear whether
tural)
a
a
of the metal ion is observed upon
cium carbonate. This
initial
subject
Most metal ions show
of
as
2+
:Me
2+
the
a
of cal¬
via
rapid
MeC03(s)-
precipitation
of
a
occur.
exchange
2+
with Ca
in
exposed (struc¬
to carbonate groups at the solid-water interface.
[8], Zachara
et
al. [81] determined
equilibrium
con¬
reaction:
2+
(aq)
=
Me(surface)
2+
+
Ca
(aq).
is observed for metal ions with ionic radii smaller than Ca
(4.6)
that
4.2 The Solid Calcium Carbonates
form
a
solid carbonate with calcite structure (e.g. Cd
thanCd
2+
The
like Zn
higher hydration energies
ions with
and Mn
2+
which show limited
of
application
techniques
has also
coprecipitation
high-resolution,
2+
,
Co
2+
Sr
at
provided
lattice structural sites. Based
et al.
nism for the
uptake
uptake
2+
of Cd
calcite surface;
mechanism. The
analysis
by calcite.
[77]
et al.
surface-sensitive
on
calcite surfaces not
sites
on
ences
only
crystal
solution
In their XPS
a
are
a
large
importance
of
Cu
wave
2+
eluded that Cu
tions. At
high
by
EPR
ions
2+
Cu
are
(XSW)
mecha-
sorption at the cal-
and
as
ions
by
the
relevant metal
X-ray reflectivity
fraction of adsorbed Pb
the
2+
the interaction of Cu
sorption
reaction is
adsorption
of Cu
of Cu
2+
2+
Ca
2+
ions
ions.
occurs
Paquette
ions.
et al.
compositional
complete
2+
on
Strong
differ¬
faces.
with calcium carbonates.
within minutes.
Papa-
calcite in terms of surface-solid
of Franklin et al.
for the calcite surface and also
inhibition of the calcite
solution is also observed for the metal ions Fe
vaterite to calcite
of the Co
which leads e.g. to
2+
[87]. Nassrallah-Aboukais
important
crystallographically nonequivalent
investigated
high affinity
by
et al.
of the metals but also the geometry of the active
properties
explained
the calcite dissolution
Pingitore
2+
an
2+
study
CvijCaj.jCOj, in accordance with the results
al. [80] found
and
sorption
substitution of Ca
layer of calcite where they replace the
sectors grown from
al. [86]
microscopic
XPS, LEED and Auger electron spectroscopy
revealed that
Franklin et al. [10] found that the
et
desorbed
showed however that for the interaction of trace metals with
the
Several authors have
dopoulos
on
to demonstrate the
excluded, however, solid-state diffusion
[84]
the calcite surface
for
and
spectroscopic
calcium carbonate minerals.
synchrotron X-ray standing
[85]
easily
are more
2+
in the surface atomic
and Reeder
above). Metal
see
-
[83] observed rapid incorporation of the Co
they
of Sturchio et al.
primarily
Zn
[17] concluded that solid-state diffusion is
cite-water interface Xu et al.
dynamic
and Ni
,
2+
atomic-scale structural information about
processes of trace metals
(AES) data Stipp
Mn
,
sorption reversibility [81].
[82] used X-ray absorption spectroscopies (XAS)
by
2+
55
2+
and Zn
,
a
[10]. Compton
et
strong inhibition of
precipitation
and dis-
weaker inhibition for
2+
Mg
[66,67], finally, have investigated the transformation of
through
the interaction of Cu
incorporated
concentrations
they
observed mixtures of vaterite, calcite,
as
2+
with the carbonates.
They
con-
clusters in the calcite bulk at low concentra-
found inhibition of the vaterite dissolution and
aragonite
and malachite.
56
4
Aqueous Chemistry of Cu2+
and Carbonates
4.3
Chemical Equilibrium Calculations
4.3.1
ChemEQL
The
speciation
2+
of Cu
with
the calcium carbonate surface
ChemEQL [25]. The stability
hydroxyl
was
calculated
constants
taken from the literature [13,60], In the
of the setup of the EXCEL
For the
from
ate
in
a
computation
input
and carbonate ions in aqueous solution and at
following
complexes
tions and the
a
equations
mass
action
species expressed
sponding K values.
expressions
as
products
This is illustrated in
[CuHC03+]
=
short
description
are
expressed
2+2
equilibrium
are
as
and H
C03
,
in solution. The formalism and the
C.l. The
speciation
species
stants are
added in
+
formation of
for the
according
documented
to
these equa¬
of the involved components and the
Eq. (4.7)
for the
•
CuHC03 complex.
•
(4.7)
Kn
the
an
additional column. The total
or
speciation
con¬
free concentrations of the compo¬
the columns. The matrix is
input
calculations
data the concentration of the
Newton-Raphson
method. The
guess of component concentrations
ponents. From the
finally
written in
presented below
errors
are
species
compared
of the material balance
species
are
EXCEL
an
are
given
species
concentrations. This
more
details
see
e.g.
procedure
[88].
is
calculated
iteratively
concentrations obtained from
to the total
equation
an
in
improved
a
com¬
guess for the
refined
fol¬
first
a
concentrations of the
centration of the components is derived which is then used for
filled. For
Eq. (4.7))
C.2.
From these
the
corre¬
form the lines and the components the columns. The formation
sheet. All matrices used for the
lowing
species
copper-carbon¬
constants are
then written
[Cu2*]1 [COj]1 [ff+]1
nents are added at the end of
Appendix
were
of the program and
A matrix is set up with the stoichiometric coefficients (bold exponents in
where the
program
given.
minimum number of components, e.g. Cu
Appendix
the chemical
of the complexes used in the calculations
matrix is
the chemical
using
con¬
computation of
repeated until the iteration criteria
are
ful¬
4 3 Chemical
4.3.2
Surface
In the surface
Complexation
complexation
Uon is descnbed as chemical
exposed
at the
model [6,26]
bonding
mineral surface In the
nation sites In the
and
equilibria
experimentally
by
take
stability
constants
and the values given
are
independent
or,
the
exposed
hydrated
precisely, chemisorp-
at the
hsted
are
Km for
surface
surface
in
have free coordi¬
ions
and>C03H
water
corresponding
Appendix
C 1
[16] These
sites can
equilibria
rough
and
anionic
surface sites The chem¬
C l/TableC3
complexes
are
are
evidence has been given
Furthermore coordination of
surface
Appendix
in
ions
ions are written as
species >CaOH
Spectroscopic
reactions
place
in
more
CaCOj these
of
the carbonate surface
comparison with the solution
These values
equilibria
can
for the surface species
The intrinsic
obtained
on
deprotonation
and cationic solution species
ical
case
and dissociation of water
for the formation of hydrated sites
undergo protonation
adsorption
between dissolved species and lattice-bound
presence of water primary
by adsorption
57
Model
>C03 Compared to the lattice ions,
>Ca and
formed
Equilibrium Calculations
not
be determined
estimates taken from
fitting
of surface coverage and surface
can
to
surface
charge
In
charge
[6],
data
practice, surface
have therefore to be descnbed with conditional formation constants
Kc,
which
account for the non-ideal behavior of the surface species due to the coulombic interac¬
tion with an average surface
related
potential
Intnnsic and conditional formation constants
are
through
Ke
where
z is
potential (V),
=
Kmt eRT
formally equal
and F is
(4 8)
to
Faraday's
the
constant
For the definition of the surface
model, the
so
charge
of the surface
=
¥
is
the surface
(96'485 C/mol)
potential *P
the
called constant capacitance model,
«F
complex,
is
simplest electnc
double
layer (EDL)
used [1]
E
(4 9)
K
where p
is
the surface
2
charge (C/m )
The EDL capacitance K
2
(F/m ) depends
on
the
58
Aqueous Chemistry of Cu2+and Carbonates
4
ionic
strength / and
k
a constant
a, related to the dielectric
properties of the EDL
^
=
(4 10)
a
For the computation of the surface
species and die electrostatic term,
ponents
are
formally
to the stochiometnc matrix
calculated from
a
number of
the matrix These parameters
surface sites (in
mol/g),
are
equilibria with ChemEQL die primary surface
treated
(cf Appendix
as a
concentration,
expenmental parameters which
the
specific
are
added
as com¬
C) Concentrations of surface species
surface
(in
area
and die concentration of the solid
are
added at die end of
2
m
/g), the number of active
(in g/1) Ionic strength and
capacitance finally allow for die calculation of the surface potential
4.3.3
The
COj/HjO system
For the presentation of die results obtained with
ple example
for
a
die
C02/H20
closed system (no
centration
out the
cT
=
chapter
0 05 M
system In Figure 4-3 die pH
exchange
are
ChemEQL
wuh the
we
dependent
atmospheric C02)
widi
a
start out widi a sim¬
carbonate
equilibna
total carbonate
dlustrated In dus representation which wdl be used
die activities of the different species
are
drawn
on a
through¬
loganthmic
-0-
-&-o-
con¬
scale
H2C03"
HC03
C032
pH
Fig.
4-3
pH dependent carbonate equilibna
concentration cT
=
0 05 M
in
H20
in
a
closed system with
a
total carbonate
4.3 Chemical
against
the
Equilibrium Calculations
59
pH.
*
with
H2C03,
/C03
are
is
depedence
of the
curves
pH
of the
phase
Figure
Cu
a
species Cu(OH)2
2+
ligands
and
the
(~pK2), respectively.
neglecting
ion is the dominant
sum
of
C02(aq)
HC03"
and
The linear
or
is reflected in the
activity
,
species
Cuj
=
the
Cu(OH)3",
etc.
illustrates the
complex
presence of
bridging ligands.
concentrations (see also
6
In the
pH
5-10
formation of
pH
M. At
<
qua¬
slopes
pH
a
solid
7. This is shown in
9 the coordinated
>
to the formation of the
hydroxo
range 7 to 9 the appearance of the
pronounced tendency
The dimeric
possible
in water at
stepwise deprotonated leading
Cu2(OH)2
5
as
species H2C03 /HC03"
the proton
on
total copper concentration
water molecules are
2+
defined here
Cu2+/H20 system
hydrated
4-4 for
,
pK values.
In the absence of other
the
and 10.1
species activities
between the
The
(~pKj)
6.3
=
H2C03
activities for the
deprotonated. Equal
found at
dratic
4.3.4
the carbonic acid
increasing pH
With
complexes
2+
of Cu
to form clusters in the
2+
are
less dominant at lower Cu
[89]).
8
7
9
11
10
-X-
Cu2+
-o-
CuOH+
-o-
Cu(OH)2°
-A-
Cu(OH)3
-o-
Cu(OH)42"
-*-
Cu2(OH)22+
12
pH
Fig.
4-4
Copper-hydroxo species
concentration
Cu^
=
510
in the Cu
M.
/H20 system
as
a
function of
pH
for
a
total copper
Aqueous Chemistry of Cu2+
4
60
In
.2+
The
4.3.5
Cu
system
/C<VH20
4-5 the copper
Figure
and Carbonates
speciation
in the presence of carbonate
aqueous system is shown. The total copper concentration CuT is
total carbonate concentration 0.05 M. An ionic
for the effect of the
activities of the
respect
to
rite
CuO(s)
chite
as a
are
closed,
1 M is assumed to account
=
hydrated Cu(H20)6
the
complexes CuC03
relevant in the considered
the mixed
at
5-10
a
M and the
charged species.
and the bidentate carbonate
are not
again
in
glass forming agent (cf chapter 5) which considerably influences the
The dominant species in this system
species
strength
/
ligands
0
Cu(C03)2
and
2-
at
+
pH
>
hydroxocarbonate malachite Cu2C03(OH)2(s) (and
higher pH)
function of pH
log[C«2+]
is
obtained
This function is drawn
as a
supersaturation.
the oxide teno-
solubility
The
by rewriting equation 16 of Appendix
diffuse line in
5.7
Hydroxo
of mala¬
C. 1:
-2.9-pH~\og[Co\']
=
x—x—:
5.7.
<
the system is unstable with
pH range. However,
due to considerable
pH
ion at
(4.11)
Figure
4-5. Malachite is
'
<^
»
expected
to pre-
1
1
1
-X-
Cu2+
-+-
CuHC03+
1
5
-•-*-
M
1
1
-D-
.
1
1
\
i
h
-6
3
4
6
5
CuCO30
Cu(C03)22Cu(OH)2°
7
9
8
10
PH
Fig.
4-5
Copper species
ionic
strength
/
in a
=
closed aqueous system with
Citj
1 M. The diffuse line indicates the
pH according to Eq. (4.11).
=
5 10
solubility
M and cT
=
0 05 M and for
of malachite as
a
a
function of
4.3 Chemical
cipitate
plexes
at
are
pH
4.5.
>
Experimentally
Equilibrium
61
finds, however, that the copper-carbonate
one
stable for several hours at high carbonate concentrations
inhibition of the malachite
Samples
indicating
com¬
kinetic
a
precipitation.
for the EPR measurements
were
concentration of the assumed monodentate
with
Calculations
Cu(H20)6
Cu(C03)2
should dominate.
CuC03
pH
8
pH
8. The distribution of the
at
and 8. A maximum
pH 5.5,6.5
CuHC03 complex
is
expected
dominant species, however. At pH 6.5
and
as
prepared
Copper-hydroxo species
amount
pH
at
CuC03
only
to about 2% at
in % of the total copper concentration
complexes
5.5
and at
Cu^ is
in Table 4-1.
given
copper-carbonate complexes in solution at
pH (given in % of total copper concentration
C«r=510"4 M) as calculated with ChemEQL [25] for an
Concentration of
Table 4-1
different
ionic
strength /
Cu(H20)62+
CuHC03+
CuC03°
Cu(C03)22"
60
7
33
-0
pH6.5
5
2
83
10
~0
~0
17
81
CaCO^syCv^/HJO system
The
4.3.6
chapter
In this
analogy
(
1 M at 25 °C.
pH5.5
pH8
13
=
to the
C-labeled)
the second
experimental
and calcite
in solution is
given by
case
2+
two situations for the
are
the
studies in
CaC03(s)/Cu /H20
chapter
dissolution of the solid
the solid carbonate is added to
=
0.05 M. In
a
a
solution with
third part of the
ation constant for copper is derived which renders
lations and the
For the
computation
strength
lems with
presented
in
the carbonates vaterite
a
phase ( cT
=
0
M). In
13
a
given total ( C-labeled)
chapter
a
surface
complex-
better agreement between the calcu¬
experimental results.
strength resulting from
ionic
case
are
mixed with pure water and the total carbonate concentration
pH dependent
carbonate concentration cT
6. In the first
system
of the surface
complex
concentrations the differences in ionic
the different carbonate concentrations have to be considered. The
is not fixed
experimentally by
background signals
discussed in
addition of
chapter
an
5 for the
inert salt to avoid the
glass forming
prob¬
agents. In both
4
62
the ionic
cases
the
Aqueous Chemistry of Cu2+
strengths
range 8 to 10 and
pH
are
estimated from the concentrations of the solution
average value is taken for the surface
an
The small amounts of counter-ions K
to
adjust pH
are
neglected.
and Carbonates
For the
and
cT
0.05 M system
one
high pH
values
typical
are
calculation.
prepared
measurements were
of K ions from
equivalent
the base used to prepare the carbonate solution is included in the ionic
tion, however. Samples for the EPR
in
from base and acid added to the solution
N03
=
speciation
species
at
strength
pH
estima¬
8.5 and 9 since
for natural waters in contact with carbonate minerals
[1].
Calculations for cT =0M:
The parameters used for the calculations
taken from the literature: surface
This value is calculated from the
mol/g.
cleavage plane
2
F/m
7
=
.
30
area:
The
of calcite (5 sites/nm
is calculated
capacitance
0.003 M and
a
=
2
0.006
m
(M)
2
,
density
cies
M
(a)
(b)
as
are
well
as
better
comparison.
direct
equilibrium
The
same x-
activity
are
and
same a
value
CuC03 complex
by the
concentrations of
y-scales
are
for
used in all
be
used
ionic
by
Van
HC03" ions
up to
(10T4)
9
value
Cappellen
solid
et
car¬
>CaC03"
build-up
of
a
and
species
complexes
>C03Ca+
large
surface
seen
that the copper surface
it is
=
5-10"
allow for
to
a
given through
protonated
the carbonate is
decreasing carbonate
>CaOH2+
are
are,
and
shown in
>C03\
The com¬
Figure 4-7 (a) and
as
the low
capacitance
does not
The concentration of these
C03
complexes
are
and
species.
however, counterbalanced by high
complexes
potential.
concentration at
become the dominant
calcium and carbonate surface ions
of these
pH
as
CuT
increase in solution. The dominant copper
9. With
pH
representations
is constant
vaterite. At lower
2+
can
was
an
closed system with
a
CaC03 complex
exceeds the solution concentrations of Ca
and it
with
high capacitance typical for the
complexes
phase
and
(b), respectively. The charges
allow for the
on a
strength
At the vaterite surface the dominant
formed
exposed
Eq. (4.10)
to
higher pH hydroxides (represented here by Cu(OH)2 )
plexes
lattice sites
-4
activities of the calcium and carbonate solution spe¬
of the
with the solid
and the activities of the Ca
species
of surface sites: 2.5-10
g/1; capacitance:
/F. The
the different copper
shown. The
the
2+
or
solution interface.
Figure 4-6 the pH dependent
In
of Ca
experimentally
[6]); concentration of solid: 26
al. [6] for rodochrosite and calcite to obtain the
bonate-aqueous
density
/g [64];
m
according
1/2
either determined
were
2
2
are
ions. From
of minor
Figures
species
4-6 and 4-7
importance.
4.3 Chemical
Fig. 4-6
Solution
M.
phase; (b)
pH dependent
lated for the calcite
1
m
for the closed
CaC03(s)/Cu
+/H20 system with Citj.
=
510" M and cT
=
0
(a) Calcium and carbonate species given by pH dependent dissolution of the solid
vaterite
The
species
63
Equilibrium Calculations
/g; density
copper
species
distribution of solution and surface
experiment
in
chapter
of surface sites: 8.3-10"
per and carbonate concentrations
tance and ionic
in solution and at the vaterite surface.
strength
are
the
Ciij
=
6 with the
complexes
was
following parameters:
mol/g; concentration
of solid: 45
1.4-10" M and cT
0 M,
same as
in the vaterite
=
also calcu¬
surface
g/1;
area:
total cop¬
respectively. Capaci¬
experiment.
The results of the
64
Aqueous Chemistry of Cu2+
4
-*^
h
+
1-
y
and Carbonates
l^
!
/
'
S5
"4
s
/
5
/\
b
/
7
<?
y
/
'
.
log(c[M])
?
' •
t
1
•
-X-
>CaOH°
-+-
>CaOH2+
-*"
>CaHC03°
"""
>CaC03
^
><^
—
j
-x;
>co3
>CO,H°
n
^
X1
>
^
•
-7
-
A
10
11
12
pH
Fig. 4-7 Surface
species for the
surface ions,
same
(b) complexes
system
as in
formed
by
Figure
4-6 (a)
complexes
formed
the carbonate surface ions
by
the calcium
including
the copper
complex
calculations
are
very similar to those shown
in
Figures 4-6
concentrations of the surface and copper species and are,
and 4-7 except for the smaller
therefore,
not given
explicitely
4.3 Chemical
Calculations for cT
Equilibrium Calculations
0.05 M:
=
The parameters used for the calculations of the surface
bonate concentration cT
/
=
0.05 M
solution
resulting
are now
in
Cu(C03)2 complex
at
is illustrated in
complex
dominates at
erably reduced.
capacitance
by
calcite
by
analogous
one
.
with
a
Figure
4-3. As
2+
a
result the free Ca
with
a
major
The surface
>C03Ca
higher potentials
is
again
by
at the vaterite surface.
small. In the
pH range 7
are
to
9 it is
in solution. This situa-
2+
at
2+
and
pH
>9
in solution.
2+
constant for Cu
analogy to the
>CaC03
Zachara et al. for the interaction between Co
modified surface complexation
complexation
com¬
concentration is consid¬
copper-carbonate complexation
found
Co(C03)2 species
librium in solution, in
con¬
contribution of the
carbonate concentration the
while the
allows for
2-
a
strength
of vaterite, is reduced. The distribution
high
complexes
car¬
The activities of the carbonate ions in
[81]. These authors explained the unexpected decrease of adsorbed Co
Calculations with
total
above except for the ionic
Figure 4-5
in
(Figure 4-8a)
8
>
to the one
the formation of
tions
37 F/m
4-8. Due to the
the strong
by
=
solubility product
The concentration of copper surface
tion is
K
large capacitance
The
further diminished
2
speciation
9. The situation for the calcium and carbonate surface
Figure
pH
same as
to those shown in
the
pH
the
are
is similar to the
species
2_
plexes
a
0.05 M
=
analogous
centration, determined
of the copper
65
constant for Cu
is derived from the
:
corresponding equi¬
Cappellen et al. [6].
treatment of Van
The two equa¬
given below:
H2C03
+
>CO3H0
Cu2+
+
=
Cu2+
CuHC03+ + H+
=
>C03Cu+ + H+
The formation constant of the
[CuHCO*3][H*]
[H2C03][Cu2+]
The constant is calculated with the
et
al.
is
given by
[CuHCO*3]
[HC03][H+]
[HCO'3][Cu2+]
[#2C03]
~
=
Cappellen
(4.13)
CuHC03 species in Eq. (4.12)
~
CuHC0>
(4.12)
compared
the
acidity
pK
101'8 10"3,8
•
=
10"2
(4.14)
value of the true carbonic acid
HjCC^ (Van
sites to the
microscopic
constant of the
>C03H
66
Aqueous Chemistry of Cu2+
4
Fig. 4-8
Surface
cT
=
for the closed
species
0.05 M.
constant of
If
we
Eq. (4.13)
carbonic acid,
take K
we
=
CaC03(s)/Cu2+/H20
(a) Complexes formed by
the carbonate surface ions
10
_2
including
Eq. (4.14)
tribution of the copper
show strong surface
species.
bonding
=
as a
find that the copper surface
system with
the calcium surface
the copper
log(KH co 12)
from
and Carbonates
=
510"5
M and
complex.
-4.1).
starting point
complexes
are
for the
pH range
8.5 to
equilibrium
of minor
This is in contradiction to the
in the
Cu^
ions; (b) complexes formed by
constant of
importance in
experimental
9, independent
the dis¬
results which
of the total carbonate
4.3 Chemical
Equilibrium
Calculations
concentration. The EPR results indicate that the Cu
ions
67
bound to 3
are
or
4 carbonate
groups at the vaterite/calcite surface.
The
overall
complexation
complexation
of
a
Cu
2+
74.
Cu2+ + n1/
The overall
binding strength
to reaction 12 in
surface
Pn
,)
Figure 4-8).
K,ot
=
species
equilibrium
in the
0
For the
cT
pH
the
log(P])
C and thus
1.8.
=
Pn
decrease of 20% for
Generally
the
n
to the
com¬
corresponding
The
log(K „_„*)
=
1.5
•
copper-carbonate surface complexes and the
with the overall
complex Cu(C03)2
higher pH
2as
species
complexation
0.05 M
=
constant the copper surface
complex
from the
copper-amino
ligands.
from Eq. (4.14) is then
range 8 to 9. At
in solution and the surface
(4.15)
[Cu2+][L]
5.3 for four bicarbonate
0 M system this carbonate
=
—n—
=
to the situation observed for
species, calculated
the carbonate solution
activity
analogy
Km
1-5, for the vaterite system with cT
With this
the dominant
by
values of n, e.g. due to sterical constraints, which
we assume a
constant derived
copper solution
=
be described
can
The first step for the monodentate bicarbonate
4-9 shows the distribution of the
log(AT
by
in
end up with
complexation
Figure
major
we
L
Kt(X is the product of the equilibrium constants Pn
Appendix
higher
values. If
(n+l) complexation step,
plexes [90],
ligands
[Cu(L)2~n]
constant
decreases with
is reflected in lower
identical
with
Cu(L)n2n
complexation steps.
ligand corresponds
n
,,
=
complexation
of the individual
ion with
reaction
be
(to
compared
complexes
the surface
found for Co
24-
by
constant
now
complex
appear
by
the
as
is rivaled
Zachara et al. [81].
is not observed due to the low
is rivaled
with
C03
2-
hydroxo-complex Cu(OH)2
atpH9.5.
Although
the
mental results it is
speciation
calculations are
important
to note that
face should also affect the surface
1.
In this derivation the
not the
case
constant
n
carbonate
for surface ions
given
above is thus
or
a
a
now
complexation
ligands
are
carbonate
lower limit
layer
in
a
surface
experi¬
at the calcium carbonate
constants of the Ca
considered to be
ligands
as
in better agreement with the
carbonate
and
C03
sur-
ions.
statistically independent which is
layer.
it does not include
The surface
possible
complexation
chelate effects.
68
4
Aqueous Chemistry of Cu2+ and Carbonates
'
—
:
s
\
>C03Ca+
>C03Cu+
-^Cu(C03)22
Cu(OH)2°
-*-
>
/
-7
-+-
*?
X
-Si
-
>co.
^
-a-
X
-
9
10
11
12
PH
Fig. 4-9
Carbonate surface
M and cr
The reduced fractional
pH
<
complexes
0.0S M,
=
sorption
8 is not found for Cu
to calcite is
assuming
sorption
for the closed
including
2+
in
a
our
governed by Eq. (4.6)
calculations. As the
description
model.
possible
than in
to reevaluate all the
Spectroscopic
evidence
presented
by
sorption
the data of Zachara et al.
stronger surface complexation for Ca
data it is not
+/H20 system with
observed for all metal ions
2+
Cappellen
Citj.
=
510
our
Zachara et al.
of the
can
only
in
chapter
complexation
foreign
be
[81]
at
metal ions
reproduced by
model. With
complexation
of the metal ion coordination to the calcite surface
should be used which take into account the
ligands.
CaC03(s)/Cu
the major copper solution species
our
limited
constants of the Van
6 indicates that for the
complexation
to several
constants
carbonate surface
Copper Carbonate
Complexes in
chapter 5
Aqueous Solution.
5.1
Introduction
In this
plexation
are
the results of the first part of this
chapter
of Cu
2+
13
with
presented (cf. [91]).
The electronic and
magnetic
ion. The
moments of
pH dependent
followed. The
tate
based
Cu(H20)6
The results
are
copper-carbonate complexes
calculations in section 4.3.5. The
for
a
in
The
chapter
13
niques. Two-pulse
coupling
com-
structures
of the
the
carbonate
hyperfine couplings
complex
compared
to
as
experience
complexes
2+
by
sphere
ion and the
of the metal
ligands
a
can
thus be
single crystal
the concentrations of
and the results
are
of the axial and equato-
determined in
pH
pH,
mono-
obtained from the
gathered
in this
CW
and biden-
speciation
study
allows
of the EPR spectra obtained for the surface
com¬
6.
C interactions
in the
on
2+
in solution at different
straightforward interpretation
plexes
investigation of the
electron of the Cu
substitution of water molecules
interpretation is
study [92],
the
C and proton nuclei in the first coordination
rial water protons in the
ENDOR
geometric
unpaired
deduced from the interactions between the
13
study,
C-labeled carbonate ions in aqueous solution at different
were
ESEEM
matching
determined with
proved particularly
two-pulse
ESEEM and ENDOR tech-
useful for the
investigation of a large
13
C
range whereas ENDOR allowed the observation of smaller
70
Copper Carbonate Complexes
5
interactions with broad basic
frequencies.
The proton
water molecules were observed with ID and 2D
the contributions
are
well
separated
Aqueous Solution.
in
signals
four-pulse
equatorial
of the
techniques,
ESEEM
where
of the
cou¬
C03 (Sigma,
98%
magnitude
due to the differences in the
and axial
plings.
Section
5.2
Experimental
5.2.1
Sample Preparation
For the
enriched)
tube to
solved
a
preparation
suspended
was
13
by
pH
closed
N2-saturated
13
following
recovered with this
aliquot of
centration of cT
=
was
adjusted
10 ml of the
added, resulting
ring,
the
pH
was
the vessel. With
the second vessel and bubbled
error
a
was
eral
was
hours
transferred to
total Cu
2+
HN03
an
ionic
a
strength
CuT=
was
the aqueous
70% of
a
5-10
estimated
at
a
13
COz
were
total carbonate
vessel
equipped
of 1.5 M. The
10
-4
_2
degassed C02 partially
in the
a
build-up
loss of
pH 5.5. This
pH adjustment the
taken. At
the
pH
8
solution
precipitation
solution
was
and the
of
was
pH
a
solu-
solution
was
loss
of pressure in
approximately
was
was
13%
smaller than the
redissolved in the solution at
stirring
with
pH of the
Cu(N03)2
M
con¬
M. After five minutes of stir¬
Degasing of COz resulted
was
glass
closed
and 0.5 ml of
concentration
taken after five minutes of
as
in
determined by
was
of the total carbonate concentration and therefore considered to be
M KOH. After each
sample
dis-
trapped
procedure
through
BaCOj. Approximately
gas volume of ~1 ml in the closed vessel
ble. Furthermore the
sample
was
added to obtain
lowered to 5.5.
a
was
in this
trapped
gas not
teflon
slowly
was
from the solution
C-labeled carbonate solution with
to 6.5 with 1 M
of carbonate from the solution
titration
13
0.06 ± 0.01 M
in
C02
C03
a
procedure.
pH electrode. NaN03 was
tion
distilled water. Ba
13
remained constant. The carbonate concentration
titration with KOH and back-titration with
An
13
13
glass vessel connected through
C02 degasing
addition of KOH. The
balloon
a
until the
a
concentrated HC1 and
by adding
collected in
C-labeled carbonate solution, Ba
in water in
second vessel filled with
the second vessel
phase
of the
negligi¬
higher pH.
A
raised to 6.5 and 8 with 1
stirred for five minutes and another
blue-green
material
highly supersaturated
with
was
observed after
respect
to
sev¬
malachite
(Cu2C03(OH)2).
The
diately transferred
sample
1.5 M with
sample tubes
prepared by adjusting
was
liquid N2.
and frozen in
strength
the ionic
of
a
with and without
samples
13
Cu(N03)2
in the
EPR spectra in the
pulse
same
frequency
range
mation upon
influences the
water are due to the
density
tetrahedral structure and the
completely
especially
with OH"
difficulty
can
lead to
true for the Cu
or
to
structure are
2+
an
present also in
foreign
with its
upon
clusters
freezing
interactions and thus fast
on
of
liquid
(up
[24].
water
to form
this effect is
struc¬
to 130 mole¬
greatly
20 K for structural
phases.
bridged
com¬
enhanced due
ions in the ice structure. The temperature
complexes by pulse EPR.
phases
crystalline
result the
pronounced tendency
the copper carbonate
per ions in separate
a
of solutes into separate
aggregation
polydentate ligands. Upon freezing
include
As
melting and large
T2 requires temperatures below
dipolar
tedious and
dipolar character of the H20 molecule
of the relaxation time
tron
more
melting and boiling temperatures
hydrogen bonding.
broken upon
pseudo-crystalline
The cluster formation
to the
EPR measurements
pulse
°C and the high
at 4
for strong inter-molecular
ture of ice is not
plexes
promote glass for¬
Forming Additives
The maximum
cules) with
to
signals (see
C
complexation equilibria (lower Af-values).
Glass
This is
it makes the
freezing although
13
the
as
NaN03 that
from
nitrogen signals
below). The addition of NaN03 to the sample solution is required
allowing
solution to
C02 were prepared under iden¬
C-labeled
tical conditions to eliminate the strong sodium and
5.2.2
copper-hexaaquo
The
M
5-10
imme¬
were
NaN03.
Two series of
occur
precipitation,
which did not show any visible
samples,
to EPR
71
Section
Experimental
5.2
dependence
investigation of
The concentration of paramagnetic cop¬
the other hand leads to strong electron-elec¬
dipolar relaxation, making pulse EPR experiments
impossible.
It is well known that the formation of
vented
by the addition
salts [93]. The
the lower
of
a
down of ice
glass forming agent
lowering of the
melting points of
crystal
large crystalline
to
the
diffusion rate due to the
the
resulting
nucleation and
solvent
sample
such
As
a
as
higher viscosity
eutectic mixtures lead to
growth.
phases
result
an
homogeneous
be pre¬
can
alcohols
or
inert
of the additive
inhibition
or
disordered
or
slow
phases
72
of
Copper Carbonate Complexes in Aqueous Solution.
5
non-crystalline glass
However
tate
glycerol
of weak
one
can
organic
bility
has to be
that
aware
freezing.
glass forming agents
coordinate to transition metal ions.
complexes
suitable glass
formed upon
are
with
ligands
forming agent
They severely
C02
or
lead to the
was
major problem
a
in this
precipitation
an
tration of 1.5 M
problems
ei nuclei
5.2.3
were
used. The
the
polyden-
disturb the formation
evaluation of different
caused
by
study.
the
phases.
the solu¬
The best results
possibilities
magnetic
a
Alcohols and other
complexation, decreased
of solid carbonate
obtained with inert salts. After
was
or
like the monodentate carbonate ion. The choice of
solvents either inhibited the weak bicarbonate
of
like ethanol
a
NaN03
moment of
were
concen¬
the Na and
already mentioned.
Equipment
The UV/Vis spectra
Lambda 6
spectrophotometer
In addition to the
NaN03
were
copper-carbonate samples,
solution and 0.1 M
tion of the
with the
KHC03
solution
copper-carbonate spectra
C03
2-
and
observed due to
bubbling
of
were
liquid nitrogen cryostat.
recorded
on a
quency
were
electronic
modulation
with
a scan
a
speed
Perkin Elmer
of 300 nm/min.
reference spectra of pure water, of 1.5 M
were
recorded to allow for base-line
350 nm). At
pH
correc¬
5.5 base-line distortions
Bruker ESP 300 spectrometer
Solution spectra at
of 9.776 GHz
measured at 130 K and 9.483 GHz with
a
temperature with
nm
were
C02.
(MW) frequency
of 0.5 mT and
room
and to exclude interference of the copper spectra
N03 chromophores (<
Cw EPR spectra
microwave
measured at
between 200 and 900
frequency
measured with
a
a
room
temperature spectra
using
a
with
a
measured at
a
equipped
were
flat cell. Frozen solution spectra
MW power of 5 mW,
of 100 kHz. The
a
magnetic
modulation
frequency counter, respectively.
was
amplitude
field and the MW fre¬
Bruker NMR Gaussmeter ER 035M and
The accuracy
were
checked with
a
HP 5248M
a
N,N-diphe-
nylpicrylhydrazyl (DPPH) reference.
Two-pulse
band
pulse
ESEEM and ENDOR
EPR spectrometer
experiments were
[94]. The four-pulse ESEEM
BRUKER ESP 380E spectrometer and
[33]. All
measurements were
carried out with
a
home-built X-
traces were recorded on a
home-built S-band
carried out at 14 K
a
pulse
EPR spectrometer
using cooling equipments
from Oxford
Experimental Section
5.2
Cryogenics,
and
The
repetition
at a
two-pulse
rate of 1 kHz.
ESEEM time traces
were
Tt-T-echo, with pulse lengths of 20 and 40
intensity was
echo
of 10
ns.
tive MW n/2
were
was
spin
pulses
applied during
and x
20
echo sequence
and
the time interval
ns
and 30 |xs,
respectively.
respectively,
processing.
pulse lengths
the Jt/2 and the
of four
pulse, respectively.
were
incremented
Four-step phase cycles
were
AVgp
ns
pulse
for the jc/2 and the
the echo
intensity
was
(16
to
ns
independently from 48
sum
of 16
recorded with
ns
pulse,
To avoid
were
added
to 4096 ns in
steps
experiments recorded
were
pulse lengths
employed
20 and 8
experimental
values of 385, 445, 505 and 565
independently from
employed
ns.
steps)
7t
measured
in
contributions [47].
The spectrum shown in the
x
50 kHz
experiments the echo intensity was measured
steps). Four-step phase cycles
were
=
sequence n/2—
ns
ns
experiments
was set to
values from 96 to 576
In the 2D HYSCORE
(16
of the MW and RF
in steps of 8
spectra measured with
intervals tj and t2
ns.
x
frequency vw
ns
to eliminate unwanted echo
7t
of variable
recorded with the
ns
stim¬
used, with nonselec¬
4480
t2, incremented from 48
ns
experiments the
was
distortions due to blind spots.
24 and 16
combination-peak experiments
S-band HYSCORE
sum
signal
The two-dimensional spectra represent the
experiments
the
the RF increment
The
incremented in steps
t1 (Mims-ENDOR). The lengths
with
with x values from 96 to 352
all
frequency (RF) pulse
function of times tl and t2, incremented
ns.
ns.
sequence Jt/2-t-
pulse, respectively.
For the ENDOR
were
=
pulse
inter-pulse delay t,
four-pulse ESEEM experiments
In the ID
k
n/2-T-n/2-f;-Jt/2-T-echo
blind spots 30 spectra recorded with
as a
150
the
using
for the tc/2 and
avoid
function of time tj
of 16
ns
ns to
T-Jt/2-/7-Jt-f2-7t/2-T-echo,
after data
was
selective radio
a
recorded
function of the
varied between 200 and 800
X-band
as a
as a
The spectrometer dead time
ulated electron
pulses
measured
73
in all
200
ns to
3400
ns
ns.
ns
for
section is
The time
in steps of 40
experiments to eliminate unwanted
echo
contributions.
5.2.4
Data
Data
Manipulation
processing
was
done with BRUKER software
(The MathWorks, Inc.). The time
one
or two
dimensions with
a
(WBMEPR) and MATLAB
4.2c
traces of the ESEEM data were baseline corrected in
fifth-degree polynomial
function and
apodized
with
a
74
Copper Carbonate Complexes
5
Hamming
window.
Zero-filling
in
performed prior
was
Aqueous Solution.
All fre¬
to Fourier transformation.
quency domain results represent absolute-value spectra.
The modulations in the
nuclei from the inert salt
nuclear gD factors of
13
two-pulse
NaN03
C and
23
Na
Q»n
0.404)
senting only
the
12
C
occur at
lower
are
13
(natural isotope ratio)
are
in the
and
C nuclei
dure eliminates the modulations of
Na,
frequency
less
disturbing.
are
13
14*
T"J
use
respectively,
same
were
and the 98%
23
by making
1.405 and 1.478,
frequencies
the contributions of
eliminated
were
combination lines of these two nuclei
=
ESEEM patterns of the sodium and
obtained
are
Eq. (3.2).
The
T*J matrix lines
ESEEM spectra repre-
by dividing
and H which
nitrogen
and both matrix and
range.
C-labeled carbonate
1
of
the time traces of
samples. This
proce-
identical for the two
sam¬
ples.
In the ENDOR
from the 98%
to scale the
5.2.5
13
the sodium
spectra. Both procedures
are
is eliminated
intensity
illustrated in
by subtracting
of the proton
Figure
5-5
on
signals
the
was
12
C
used
page 79.
EPR and ESEEM Simulations
refined
"-values
obtained from the
by simulations performed with
PAR, strain effects
can
be considered
metric with
coinciding principal
Two-pulse
were
these simulations electron Zeeman and
of 50 MHz
was
ns was
m,"
homogeneous linewidth
prior
the program COMPAR [95]. With COMdifferent linewidths for the four
m7
matrices
were
assumed to be
axially
simulated with the program MAGRES
hyperfine
interactions
-states to the ESEEM
assumed for the MW
introduced
u
CW EPR spectra at 130 K
-
sym¬
axes.
ESEEM spectra
the contributions of the four
experimental
by using
transitions. For the simulations the g and A
of 150
signal
C-labeled carbonate spectra. The
The g- and A
were
experiments
pulses.
to the
of 0.3 MHz
was
In
spectra. An excitation bandwidth
Time traces
processing
were
[96].
considered to include
were
computed
and
a
dead time
of the data with MATLAB 4.2c. A
used to account for relaxation effects.
5.3 Results
5.3
Results
5.3.1
Optical Spectra
The UV/Vis spectra of the
6.5 and 8
are
values of
810, 780,
shown in
Figure
Cu(H20)6
and the
respectively.
increase, indicating
that
a
observed. In agreement with the literature [97]
bidden d-d transitions
the
following by v2 and v3 (cf. Figure
unpaired electron
tronic
configuration
is located in the
for the
spectra (see below)
at
pH 5.5,
At
higher pH
superposition
we
have
the
intensity
Xmax
and the
of at least two bands is
assigned
these bands to the for¬
dx2.y2 (Blg) <-> d^ (B2g) and djj (Blg) <-> dM, d^ (Eg), labeled in
2-2
vibrational and rotational motion of the
the
copper-carbonate samples
5-1. The spectra consist of weak, broad bands with
760 and 750 nm,
width of the bands
2+
75
are
on
page
8). The bands
complexes.
dj
2
For the
orbital [92], and
are
not resolved due to
copper-hexaaquo complex
we assume
copper-carbonate complexes since
the
optical
the
same
elec¬
and CW EPR
very similar. The estimated values for v2 and v3
are
given
Table 5-1.
500
600
700
800
A.(nm)
Fig.
5-1
Optical absorption spectra
of the
aqueous solution at different
pH
copper-hexaaquo
and at RT.
and the
copper-carbonate samples
in
in
76
Copper Carbonate Complexes
5
Table 5-1
Electronic transition
in
Aqueous Solution.
energies estimated from the optical spectra.
v2(cm ±100)
Cu-hexaaquo
12200
13500
Cu-carbonate
pH
5.5
12700
14300
Cu-carbonate
pH
6.5/8
13300
15400
5.3.2
EPR
Spectra
The solution EPR spectrum of
of
one
100)
±
v3 (cm
broad line centered at g
four transitions
g-values
are
=
2.19
2+
measured at
(Figure 5-2).
approximately
pH 5.5,
6.5 and
5 mT for all carbonate
slightly with increasing pH, leading
to a
Figure
For the
temperature consists
copper-carbonate samples
5-3. The
principal
simulations of these spectra
distorted octahedral
are
complexes
fields with
8, respectively. The splitting of the
complexes.
same
The linewidth decreases
samples
values of the g and A
given
higher
higher resolution.
The frozen solution CW EPR spectra of the
shown in
room
resolved and the centre of the spectrum is shifted to
of 2.16, 2.16 and 2.15 for
four lines is
Cu(H20)6
u
ligands [98],
are
matrices obtained from the
in Table 5-2. These values
with six oxygen
measured at 130 K
the
are
typical
parallel
for
axially-
direction
being
Cu(H20)6'
pH8
290
310
Magnetic
Fig.
5-2
330
field
Room temperature CW EPR spectra of the
samples
in aqueous solution at the different
350
Bq [mT]
copper-hexaquo
and the
copper-carbonate
pH. The dashed line marks the g
=
2
position.
5.3 Results
77
Cu(H20)6'
280
260
300
Magnetic
Fig.
5-3
aqueous solution
defined
A
u
by
region
small
(130 K). The inset for the pH 5.5 spectrum shows
illustrate the presence of several
to
are
quite
orthorhombicity
Table 5-2
Sq [mT]
species
at this
the distortion axis.The fits obtained for the
matrices
340
spectra of the copper-hexaquo and the copper-carbonate samples in frozen
CW EPR
g.
field
320
poor
as can
be
seen
for these matrices
EPR parameters of copper
an
enlarged
pH
8 spectrum with axial g and
from the simulation shown in
can
Figure
therefore not be excluded. With
complexes
5-4. A
increasing
measured at 130 K.
.Cu\
Cu-hexaaquo
view of the
pH.
,Cu\
8±
*ll
(± 0.001)
(±0.001)
(MHz ±10)
(MHz ±10)
2.403
2.076
425
25
Cu-carbonate
pH 5.5
2.370
2.068
445
35
Cu-carbonate
pH
6.5
2.336
2.059
470
40
Cu-carbonate
pH
8
2.328
2.056
480
50
78
Copper Carbonate Complexes
5
280
260
in
Aqueous Solution.
300
320
340
Magnetic field Sq [mTj
Fig.
5-4
Comparison
between
The simulation
pH,
a
decrease of the
leading
minor
to the
species
g-values
development
are
A
arising
and
of
at
lency
four oxygen
-values
plane
2
a ,
carbonate
water
ligands bound
giving only
the four
only
weak
Pj
2
lent and sp
a
are more
in Table 5-2 and the
and
|J
[99].
2
inset in
pH
5.5
pH 6.5
Figure 5-3.
distribution of g- and
responsible
pronounced
be calculated
can
These parameters
plane
been done for the
in
a
pH
can
form
8
for the
for the cop¬
Jt
can
for the
ion and
Values close to 0.5
xy-plane
frequencies
expressions
are measures
the z-axis. In this
and
the
using
cova-
a
set of
correspond
a
with
case
complex
axially
the
with two
coordinated
ligand orbitals
all be considered to be
bonds with the 3d, 4s and
the metal ion.The values obtained for the different parameters
of
complete ionic bonding.
sample, assuming
oxygen atoms
a
transition
bonds between the Cu
bidentate fashion in the
perturbations along
hybridized. They
optical
whereas values close to 1 indicate
directly coordinated carbonate
2
At
and
region.
slightly varying geometries
-states and are
equatorial plane, respectively.
complete covalent bonding
The calculation has
given
and the 7C-out of
in the
8.
is observed,
hexaaquo
as
enlarged
strains lead to
fields. The strain effects
and Maki et al.
ligands
in the g±
be identified
in the four m;
pH
hexaaquo complex.
parameters
of the o, Jt-in
can
geometrical
differently
higher
From the g- and A
[98]
hyperfine couplings
A* hyperfine pattern
an
at
in table 5-2.
EPR spectra. This is shown in the
per carbonates than for the
Kivelson et al.
copper-carbonate samples
from the presence of complexes with
values which cancel
out of Table 5-1
given
increase of the
an
observed for all spectra. These
-
increasing linewidth
to
with the parameters
contribute to the spectrum which
species by comparing the
Strain effects,
and simulation for the
experiment
performed
was
are: a
=
equiva-
4p orbitals
0.84,
pj
of
=
of
0.84
5.3 Results
and
P
free
2+.
Cu
ion
=
5.3.3
All
79
0.66. Numerical values used for the calculations like the SOC constant for the
Xq are taken from
[98].
ESEEM and ENDOR of
13
C spectra
is illustrated in
in this section
presented
in section 5.2 to eliminate the
Figure
13C
were
subjected
to the
procedure
described
sodium, nitrogen and proton contributions. The procedure
5-5 for the
pH
5.5
case.
After division of the two ESEEM time
carbonate
Time
(^sec)
6
8
10
Frequency (MHz)
Fig.
5-5
Elimination of the sodium
illustrated
field
by
signal
the spectra of the
position, (a) ESEEM
pH
for
5.5
time traces of
ratio) sample together with the division
samples (t
=
0.22
(is).
The
two-pulse
sample.
13
a
ESEEM
All spectra
C carbonate and
of the two traces,
C spectrum is obtained
(a) and Mims ENDOR (b)
are
12
(b)
recorded at 14 K at the g,
C carbonate
ENDOR
spectra of the
by subtraction of the
-
(natural isotope
two
spectra.
same
5
80
traces
ate
Copper Carbonate Complexes
(Figure 5-5a)
samples
a
modulation
positions
prominent
MHz
(g||)
Zeeman
C combination
g,,
(gj. They
C carbon-
frequency
the
is left
corresponding
Figure
shifted
are
the
recorded at different
were
5-6a and b ESEEM and ENDOR
(256 mT) and g± (314 mT)
are
13
analogous result.
features in the ESEEM spectra
and 6.9 MHz
13
Figure 5-6b). Subtraction of
in die range from g,, to g±. In
spectra for the observer position
The
an
the
to
ESEEM and Mims ENDOR spectra
pH 5.5. Two-pulse
field
is shown in
(Figure 5-5b) yields
Aqueous Solution.
C carbonate (natural abundance) and
corresponding mainly
(the corresponding spectrum
ENDOR spectra
12
obtained for the
in
13
by about
C
sum
are
shown, respectively.
combination lines at 5.65
0.2 MHz from twice the nuclear
frequency 2vc, calculated from the B0 field values and indicated by
260
mT
dashed lines
320
ESEEM
ENDOR
ESEEM
ENDOR
0
4
2
6
8
Frequency (MHz)
Fig.
5-6
Two-pulse
pH 5.5 sample recorded
ESEEM and Mims ENDOR spectra of the
observer field
position
g..
(a)
and gL
(b), indicated by
arrows
spectrum (inset). The nuclear Zeeman frequency vc of carbon and the
frequency 2vc
measurements
are
are
indicated
0.28
Other parameters: MW
temperature T
=
14 K
us
(a)
by
dashed lines.
and 0.20 (is
frequency v,^
=
(b). The
9.10 GHz
The
t
arrows
at the
in the echo-detected EPR
values
used
sum
combination
for
the ENDOR
indicate the blind
spot positions.
(ESEEM), v,^
=
9.27 GHz (ENDOR);
5.3 Results
in the
The basic
figures.
from 1 to 5 MHz,
however, clearly
5-6
positions
truncated
are not
with different
considerably
are
by
Vc
truncated
by
broad features in the range
as
the spectrometer deadtime.
as
calculated from
the blind spots
was
region.
They
The
confirmed
peaks with
MHz, centered round the
13
maxima at 2.5 and 4.5
C nuclear Zeeman
frequency
range of the ENDOR
ESEEM and ENDOR spectra, recorded at field
arrows
by measurements recorded
frequency
3.44 MHz. At lower observer fields the S/N ratio is very poor and the va
truncated due to the limited
are,
Eq. (3.4). That the spectral features in
values. The spectra show two broad
T
MHz and linewidths of about 1
=
Vn, observed
revealed in the ENDOR spectra recorded in the g±
indicate the blind spot
Figure
frequencies vaand
81
positions
peak
is
amplifier (2-30 MHz).
between
g^
to
g± do not reveal
additional information.
pH 6.5/pH 8.
pH
8
Figure
samples
5-7 and
The
ESEEM and Mims ENDOR spectra of the
two-pulse
recorded at different field
sample measured
at
are
very similar
together.
the gj_ field
i
1
0
2
Figure
In
6.5 and
illustrated
as
5-8c. The results obtained from these measurements
Figure
treated and discussed
positions
pH
are
therefore
5-7. ESEEM and ENDOR spectra of the
position
are
1
4
compared.
The
1
1
6
8
by
pH
features in the
prominent
r
10
Frequency (MHz)
Fig.
5-7
Two-pulse
position.
ESEEM and Mims ENDOR spectrum of the
The dashed lines indicate the nuclear Zeeman
combination
frequency 2vc.
The
arrows
pH
(ENDOR).
sample recorded
at the
frequency vc of carbon
indicate the blind spot
value for the ENDOR spectrum: 0.23 us, T= 14 K, v^,
GHz
8
=
positions.
9.12 GHz
8
£±-field
and the
sum
Parameters:
(ESEEM), v,^
=
x
9.34
82
Copper Carbonate Complexes
5
ESEEM spectrum
the nuclear Zeeman
at
the
are
peaks
2.7 and 4.2 MHz of width 1.2
=
6.6 MHz is observed at
at
peak is expected
in the
to occur
being close
one
to twice
6.76 MHz. The ENDOR spectrum shows two
MHz, centered round vc
ENDOR features observed for the
peak
Aqueous Solution.
6.8 MHz, the latter
at 1.5 and
frequency 2vc
in
pH
higher pH.
spectral
An additional ENDOR
sample (Figure 5-6b).
5.5
If
we
assign
this
peak
range 0 to 1 MHz and
ENDOR spectrum. However, the 6.6 MHz line
peaks
3.38 MHz, similar to the
=
feature, the va
to a Vn
can not
be observed in the
be associated with the 1.5 MHz
can
peak
found in the ESEEM spectrum. Both the ESEEM and ENDOR spectra thus reveal the
13
presence of at least two different
Besides
a
weakly coupled
found with
MHz at
gu
Consequently
the
Figure
recorded at different
(Figure 5-8b)
visible
as narrow
can
spin packets
with
row
peaks
are
very
are
positions,
are
weakly coupled
13
C
nucleus
ESEEM spectra of the
as
a
Vo are
Figure
13
the
in
the basic
weakly coupled
13
C nuclei.
position (b)
(Figure 5-8)
were
discussed in section 5.4.3.
as a
by
peak, clearly
sum
dip
in the broad
position (Figure 5-8a). Here, only
axis contribute to the spectrum and
selectivity. The
Vq, and the combination
interactions A
C
condition
performed
nar¬
upper bar in
frequencies,
corresponding frequencies
(#,,)
of 0.8 MHz and 9 MHz
weakly and strongly coupled nucleus,
coupling
v»
the dominant features
spectra in Figure 5-8b and
C nuclei, the lower bar the
Hyperfine
sample,
5-8 (inset). At field
ESEEM
frequencies, va and
13
6.5
indicated by
C nucleus, hidden
therefore centered round A 12 and
with MAGRES
C is
are
result of this orientation
The latter fulfills the strong
va and
13
range from 5.6
pH
shown. The observer fields
be observed at the g,, field
obtained from the spectrum for the
tively.
are
two-pulse
BQ approximately along the g,,
strongly coupled
2vc
of the va peak at 1.6 MHz increases and the
nicely
observed
v+ and v_, of the
6.5 and 8.
stronger coupled
a
feature at 6.8 MHz in Figure 5-8c, appears
Figure 5-8a indicates
of the
field
stronger coupled
Figure 5-8c,
pH
condition is fulfilled (cf section 2.2.4). The effect is
5-8, where
The features of the
of the
at
gL.
intensity
the
pH 5.5,
Numerical values for
2vc.
in the echo-detected EPR spectrum in
arrows
complexes formed
observed at
close to
matching
B0
C nuclei in the
already
C
hyperfine coupling
a
to 6.9 MHz at
illustrated in
peak.
13
(2v:« A );
split by 2vc.
the basic
respec-
frequencies
Simulations carried out
with the parameters
given
inTable 5-3 and
5.3 Results
83
mT
260
320
Experiment
Simulation
Experiment
Simulation
Experiment
Simulation
10
6
4
Frequency [MHz]
Fig.
5-8
Experimental
and simulated
two-pulse
field positions 258 mT
(a), 288
detected EPR spectrum
(mset)
combination
frequency 2vc
simulation parameters
frequencies, va and
are
mT
ESEEM spectra of the
(b)
and 313 mT
The nuclear Zeeman
are
given
marked
in
by
13
C nuclei MW
frequency vMW
=
sample, measured
arrows in
The upper bar
me sum
The
(a) indicates the basic
in
v_,
of the
corresponding frequencies
9 10 GHz, temperature T
at
the echo-
of carbon and
frequency vc
frequencies, v+ and
C nuclei at the g»-position, the lower bar the
coupled
6 5
dashed hnes for each pair of spectra
Table S 3
Vq, and the combination
pH
(c), indicated by
=
14 K
weakly coupled
of the
strongly
84
5
Copper Carbonate Complexes
Hyperfine
Table 5-3
mono-
in
matrices of the
Aqueous Solution.
C carbonate nuclei for
and bidentate coordination, obtained from the
MAGRES simulations.
bidentate
monodentate
\A^\
(MHz)
|Aj|
(MHz)
\Aj\
(MHz)
a.
The
principal
respect
c
b. Aj
5.3.4
coordination
0.1 ±0.3
4.0 ±0.1
0.1 ±0.3
6.9 ±0.1
3.5 ±0.3
9.0 ±0.1
axis A
c
and A2 lie in the g_L
separation
on
portional
of
signals
the maximum shift
c
in the ID
75 ± 5
degrees
with
is coaxial to the g,, axis.
In
four-pulse ESEEM spectra.
Figure
5-9
et different field
four-pulse
depending
protons
B0
field
position.
2Vj (cf.
Tx -decay
to
or
protons of
from 1.2 MHz (d) to 1.5 MHz
0.5 MHz from
2vH
(b).
arrows
three
water
positions.
tons may also
be contribute to the
This
2.2.5),
peaks
is
which is pro¬
observed both
are
copper-hexaaquo complex, recorded
peaks,
spectrum)
At lower
2vH arises
largest
from
weakly coupled
shift from
assignment
fields
mainly
this
an
additional
be
equatorial
values range
peak
shifted
by
from the protons of water coordi¬
is however not
lineshape in
2vH can
molecules coordinated in the
magnetic
are
which show additional shoulders
largest hyperfine couplings [92], Attmx
is observed, which arises
nated in axial
section
peak' spectra
in the echo-detected EPR
The feature close to
since these protons show the
'sum
of the stimulated echo.
of the solvent molecules. The broad line with the
unambiguously assigned
or
constant T. Sum
ESEEM spectra of the
positions (indicated by
the
from
ESEEM
A better resolution is however obtained in the ID
due to the
shown. The spectra consist of two
on
four-pulse
dipolar coupling
four-pulse ESEEM experiments
~
by
plane, A3
Amm of the peaks
to the square of the
in two- and
plane
is tilted
3
to the g,, axis.
ID and 2D ESEEM of Protons
The
based
coordination
unambiguous
as
equatorial
frequency region (see below).
pro¬
5.3 Results
85
OH2 (al)
I
H2Oz,
CU
H20
->OH2 (equatorial)
J
OH2
OH2
22
26
24
28
30
MHz
Fig.
5-9
Four
pulse ESEEM spectra
of the Cu
hexaaquo complex (lower inset), measured
at field
positions 272 mT (a), 290 mT (b), 310 mT (c) and 330 mT (d), indicated by
arrows in
echo detected EPR
signal traces,
spectrum (upper inset) The spectra represent the
measured with 1 values between 96 and 576
twice the
proton Zeeman frequency
2vH
(16
ns
ns
steps)
sum
of 30
the
The dashed lines indicates
Other parameters MW
frequency Vj^
=
9 709
GHz, temperature T= 14 K
The distinction of
tra
Cu
can
2+
equatorial
and axial proton
signals
in the
four-pulse ESEEM
spec¬
be used to determine the number of water molecules coordinated to the central
at different
the three
pH Four-pulse
sum
copper-carbonate samples
peak spectra
are
recorded at 14 K and at the observer field
of the
compared
position
in
copper-hexaaquo complex
Figure
5-10. The spectra
310 mT, indicated
by
an arrow
and
were
in the
86
Copper Carbonate Complexes
5
in
Aqueous Solution.
i
1
1
1
1
1
25
26
27
28
29
30
Frequency [MHz]
Fig.
5-10 Four-pulse proton
different
ESEEM
spectra of the copper hexaaquo and the copper-carbonate
pH, recorded
samples
at
arrow in
the echo detected EPR spectrum
14
K) The spectra represent the
and 576
(16
ns
The shaded
equatonal
ns
area
steps)
sum
sponds
signals
of 30
signal
which
can
5
sample (viMW
traces, measured with
be
twice
t
=
by
an
9 72 GHz, T
=
values between 96
the proton Zeeman
frequency 2vn
unambiguously assigned
to
protons of
water molecules
position (c)
in
pH
Figure 5-9,
rated. In the presence of carbonate
decreases with
magnetic field position 310 mT, indicated
(inset) of the pH 5
The dashed line indicates
marks the
echo-detected EPR spectrum of the
to the
at the
pH (cf. shaded
5 5
in
This observer field
where the different contributions
ligands,
area
sample (inset)
the
signal intensity
of the
are
corre¬
well sepa¬
equatorial protons
Figure 5-10), assuming that the intensity of the
5.3 Results
matrix line at
vanished and
same
for all
signal
a new
already mentioned,
As
by
the
next to the matrix line
proton peak
pletely
2vH is
axial protons
by
equatorial protons
and
recorded at the observer field 310 mT. Two different
aaquo spectrum
weakly coupled
(Vj
quency
cross-peaks
nuclei
v2
=
shown in
are
are
contributions of axial and
diagonal (Vj
The
peak.
=
5-1 la and b
along
observed
13.2 MHz, matrix line
=
away from the
of the matrix
Figure
-v2
+
diagonal.
the
2vH), respectively.
shifted
second dimension. Therefore
a
representations
(only
diagonal,
one
of the
were
copper-hex¬
quadrant). Cross-peaks
of
close to the nuclear Zeeman fre¬
protons). Stronger hyperfine couplings shift the
shifted
are
peak
to the
copper-carbonate samples
In the HYSCORE
equatorial protons
ridges
com¬
Unambiguous assignments for the
the spectra into
spectra of the copper-hexaaquo
HYSCORE
of the
shape
0.3 MHz from the matrix line is observed.
be excluded.
can not
and
pH 8 the equatorial proton peak has
At
change.
shifted
by spreading
obtained
are
samples. Simultaneously, position
contributions from the
0.5 MHz from the matrix line
87
appear
well
separated ridges
to both sides
0.35 MHz and 0.85 MHz from the anti-
by
The
as
spectra in Figure 5-1 la and b the
peak
at
(15.6, 15.6) MHz is
a
spectrometer
artifact.
The spectrum of the
copper-hexaaquo complex
pH
HYSCORE spectra of the
Figure
5-12a and b,
Figure
5-1 lb, scaled
and the
signal
respectively.
by
indicating
a
change
anti-diagonal,
rial and axial protons have
man
Eq. (3.3)
frequency
it
can
be
pH
seen
at a
At
pH
shown
plot
in the
5.5 the
hyperfine coupling
as
levels
compared
contour
intensity
is illustrated in
Figure
to
plots
chosen
were
as
the
in
in
of both the axial
peak the shape of the
of the axial protons. At
two shoulders with a maximum shift of
as
5-12b. All
8 spectrum is obtained at S-band
a
magnetic
detected EPR spectrum in
intensity.
that the maximum shift
V] is lowered for
spectrum recorded
samples,
same contour
be
pH
approximately
ridges
from equato¬
disappeared.
Better resolution of the
From
8
now
has decreased. Close to the matrix
8, the matrix line is broadened by
0.2 MHz from the
The
the matrix line
equatorial proton ridges
is altered,
pH
5.5 and
can
A,^
given dipolar coupling
field of 136.5 mT
Figure 5-13a)
and
a
frequencies (2-4 GHz).
increases if the nuclear Zee-
T. In
Figure 5-13b a HYSCORE
(indicated by
frequency
an arrow
in the echo-
of 3.713 GHz is shown. A vE
value of 5.81 MHz is calculated for this field value. The spectrum reveals two main fea-
88
Copper
5
Carbonate
Complexes
12
in
14
Aqueous Solution.
16
18
Frequency V[ [MHz]
Fig.
5-11 HYSCORE spectra of the
the
sum
copper-hexaquo complex
of 16 spectra, recorded
352
ns
the
spectral
(16
ns
steps), (vMW
features
to
=
frequency
9 72
matrix
molecules, (b) corresponding
at
The
two
dimensional
the field position 310 mT with
GHz,
protons
contour
T
=
14
(vH)
plot.
T
plots represent
values between 96 and
K) (a) Surface plot with the assignment of
and axial
(HM)
and
equatonal (H )
water
The dashed lines indicate the proton Zeeman
5.3 Results
89
Frequency vt [MHz]
Fig.
5-12 HYSCORE spectra of the
levels
as
from the
Figure
in
Figure
antidiagonal
5-11.
pH
5.5
5-lib. For the
(a) and the pH 8 (b) sample with the
pH 8 spectrum,
is indicated
by
the maximum shift
same contour
Av^^of the
the two solid lines. All parameters
are
the
plot
shoulders
same as
in
90
5
tures,
a
Avmax
~
broad
Copper Carbonate Complexes
asymmetric peak
0.35 MHz from the
in
Aqueous
at the nuclear Zeeman
anti-diagonal.
The
Solution.
frequency
ridge
can
and
a
ridge
shifted
by
be related to the shoulders
observed in the X-band spectrum whereas the shoulders found close to the matrix line
here arise from protons in the second
Cu
an
third coordination
sphere (>
4
A
away from the
ion).
110
100
120
130
Magnetic
field
140
150
B0 [mT)
N
X
5
c
0
3
Frequency V! [MHz]
Fig.
5-13 S-band spectra of the pH 8 sample (a) Echo-detected EPR spectrum recorded with
ns
two-pulse sequence (v^
represents the
of 4
sum
arrow in
(a)) with
Zeeman
frequency,
t
=
3.713 GHz, 7"
spectra, recorded
at
=
a
Avmax.
ns
20/40
K). (b) The HYSCORE spectrum
the field position 136 5 mT (indicated
values 385, 445, 505 and 565
the solid lmes the shift
14
by
an
The dashed lines indicate the proton
5.4 Discussion
91
Discussion
5.4
The
different
experimental
presented in the preceding section confirm the formation of
results
copper-carbonate complexes
as a
the results and propose structures for the
function of
complexes
In the
pH.
following
we
combine
in agreement with the coordination
chemistry of copper [24] and carbonates [12,13].
Optical Spectra
5.4.1
The coordination of carbonate to the Cu
energies v2/v3,
manifested
by
2+
hypsochromic
a
ions leads to
shift (to
an increase
of the
higher frequencies)
spectra (Table 5-1). Since carboxylic acids induce weaker ligand fields than
hydroxyl ions [21]
bathochromic shift is
a
increase in energy can, however, be
explained by
Jahn-Teller distorted octahedral copper
primarily
solved
affects the Vj transition
v2/v3
a
2-2
on
complexation.
The
stronger tetragonal elongation of the
complexes [11].
(cf. Figure
result of the
as a
optical
water or
An
8).
page
elongation
of the axial bond
The broad band of the
unre¬
transitions will however also be shifted to the blue because of the raise in
dx2
energy of the
spectra with
expected
splitting
in the
^^
level and the stabilization of the
2
=
675
nm
(-14800 cm" )
are
orbitals. Similar electronic
djZ,d
observed, for example, for Cu(oxalate)2
complexes [100].
The increase in
breakdown of the
intensity
by
oxalate: 1) monodentate
complexation
an
axial
in the
position
possibility
is
plane.
higher pH
this breakdown is related to the
ligand
are
equatorial plane
and
at
mixing
distinguish
2+
as
it
equatorial
partial
a
or
bidentate
at an
equatorial and
equatorial plane.
The last
considerable restriction of the axial elon-
in section
mono-
non-
like carbonate
positions, 2)
3) bidentate complexation
requires
example
between
a
of d- and p- orbitals
chelating ligands
and axial
in addition to scheme 2, which defines the
highly improbable
indicates
orbitals [101].
conceivable for
complexation
gation (cf. [Cu(en)x(H20)6_2x]
not allow to
bands at
the forbidden character of d-d transitions. For
covalent bonding with the
Different coordination schemes
or
absorption
Laporte rule stating
centrosymmetric complexes
induced
of the
4.1.1).
bidentate
The
optical spectra
complexation
do however
in the
equatorial
Copper Carbonate Complexes
5
92
5.4.2
EPR
solution like
is
given by
[102-104].
For the
Cu(H20)6
without resolved copper
the
hopping
As
a
hyperfine
hyperfine
hyperfine anisotropics
values obtained at
interconversion of the Jahn-Teller distortion
or
ion, fast relaxation leads
m," -dependent
equally
are not
and 6.5
a
are
further slow-down of the
explained by
the broad
2+
Cu(H20)6
dination of
a
resonance at
cies, confirmed
by
similar, the resolution of the m,
tumbling rate.
out for the four
These
5.5. The
pH
m7
-states. The g
"
-pattern is
smaller linewidth at
findings
in
are
pH
The spectra at
Cu(C03) complex
complexes.
observed since the g and
are
very
pH
8
good agreement
5.5 and 6.5
be
can
with considerable contribution of
changes at pH
at
pH
5.5
are
8
are
then due to the
coor¬
tions of the geometry
be reflected
might
orthorhombicity
therefore
7t
bonding
-
are
lent in- and out-of plane
well
seems to
complexes
increasing
the
pH
as
the
pH
8 spe¬
occurrence
predictions
complex¬
5.5 spectrum also
clearly
pH. Smaller
at this
strain effects at
of
of the spe¬
influence the
parameters
can
be related to
an
varia¬
and
higher pH
increase of the
between the carbonate ions and the Cu
bonding parameters
these values
of different
by
as
6.5 and
pH
of the g matrix.
The variations of the g- and A
of the o and
of the
similarity
this issue is addressed in section 5.4.6. The
occurrence
is frozen. The g and copper
in contradiction to the
freezing procedure
illustrates the simultaneous
reflected in the
complexes
EPR measurements. This result
species
ciation calculations. The
equilibria;
in Table 5-2 show the
pulse
the
further well defined
Although
resonance
second carbonate molecule.
hyperfine parameters given
alency
widths
of the
mobility
averaged
At 130 K the molecular motion of the copper
the small
broad
to one
well
speciation (section 4.3.5).
the formation of the
hyperfine anisotrop¬
interaction. Complexation of carbonate ions hinders
lines with
pH 5.5
with the calculated
ation
of the g and
higher at pH 6.5. The slightly lower g-value and die
indicates
a
the CW EPR spectra recorded at
of the distortion axis and decreases the rotational
result four
however
spin rotation and modulation
of the molecules
through tumbling
axis
complex formation
temperature. Various relaxation mechanisms govern the EPR linewidth of copper
complexes in
ics
Aqueous Solution.
Spectra
Further evidence for
room
in
only rough
a
,
Pj
and
estimates
7t-bonding between
P
they
2+
calculated for the
seem
the metal and
cov-
ion. This trend is
pH
8
sample.
to indicate considerable cova-
ligand
orbitals. The
high
cov-
5.4 Discussion
alent
bonding
complexes
through
ion
for the derealization of electron
high pH, allowing
at
the
rt
the formation of bidentate carbonate
explained by
character may be
93
system of the carbonate.
ESEEMandENDORof13C
5.4.3
The presence of mono- and bidentate coordination at different
by
the results of the
5.5
only
tropic
a
13
small
g and axial
coupling
C
pulse
hyperfine coupling
is observed.
Using Eq. (2.23)
c
hyperfine matrices,
an
single
a
monodentate
the
coupling
6.5
sample
isotropic coupling aisg
can
complex plane
complex [105];
ligand
our
A,
planar
it
can
be
carbonate
A, obtained
estimated from
explained
n
ligand
,
which show the
spin density
C HFI is
same
either
ligand
by
can
(Eq. (2.18)),
r
models
(rCu.0
hyperfine coupling
=
2
of the
connectivity (M-O-H)
13
observed for the
to the carbonate
ligand
is
C
as
higher
do not allow for
Bidentate coordination of carbonate
8 and is reflected
by
have been observed
the observation of
by
Eaton et al.
ligands
large
to the
13
of
C
C
a
axis of
pH
only
hydro¬
sphere
substitute for
or
a
equatorial
is smaller than the dis¬
A,
rc_Q
=
equatorial
A, angle
1.3
13
C
coupling
water
protons
the carbonate C-atoms
15
.
that the dereali¬
than to the water
Ugand
and that
The broad lines observed in
a more
Cu
0.2
13
to a
intramolecular
coupling suggests
expected to be orthorhombic rattier than axial.
orientationally disordered systems
=
found e.g. in the
was
system is twisted out of the
from
geometrical
to the orthorhombic
larger isotropic component
13
A^^
principal
120°, assuming sp hybridization of the O atom). The small
=
compared
zation of
degrees
pH
iso-
dipolar
a
equatorial plane
of the
2
Cu(H20)6
the
if the
The Cu-C distance of 2.6
2+
The
assuming
between carbonate and water molecules in the first coordination
tance of 2.85
be
and
At
is obtained from the simulations of the
data. A similar tilt of the monodentate carbonate
smaller water
(Cu-O-C)
ligands.
spectra and the shift
A tilt of 15 + 5
sterical constraint considerations: the carbonate
plane.
clearly revealed
(see also Table 5-3). We assign this coupling
copper-carbonate complex.
[Co(C03)2(H20)4]
is
=1.2 MHz and
carbonate/bicarbonate ion coordinated in the
matrix out of the
gen-bonding
pH
C-labeled carbonate
7= 1.1 MHz is estimated from the ENDOR
nucleus of
of
13
EPR measurements with
MHz in the ESEEM spectra
by
2+
from the Cu
density
detailed
ion takes
interpretation.
place at pH
hyperfine couplings.
Such
6.5 and
couplings
[106] in their investigation of the interaction between
94
5
Copper Carbonate Complexes
C-labeled carbonate and
complexation of
to direct
not
are
based
on
the carbonate to the metal
principal
that the observed
value of the
the spectra is obtained
carbonate
ligand
two
Fig.
C
hyperfine matrices
5-14 Illustration of the
coupling
along
only
mono-
bonding
sp
cases are
indicated
hybridization
13
3dx2_y2 and the
ion. The
n
copper
C
ij
system (shown by lobes) which
bonding of the
carbonate
%
bonding between
2pz
oxygen orbital leads to
from the Cu
2+
Overlap
can
the 3d
between the
(c) out-of-plane
ion
can
take
place
via
(a)
a-
sp oxygen orbital. Stabilization of the coordination
not involved in the C-0 bond.
it
+
2
and the
The
monodentate
C.
for the oxygen atoms, coordination
through (b) in-plane
density
a
by ellipsoids (not scaled). The
spin density to the
orbital,
electron
largest
ion; each of them involves different ligand and metal orbitals [98]. If
between the
is obtained
if the
the orientation of the PAS's of the
Three different mechanisms may contribute to the covalent
we assume
g anisot-
arrangement used for these
and bidentate coordination of carbonate to the Cu
allows for the delocalization of
2
detailed
described in Table 5-3.
matrices for the two
to the metal
a
large
reproduced
be
geometrical
d, and the oxygen and carbon 2p orbitals constitute the
ligands
For
is
in
the g,, axis. Further refinement of
Figure 5-14, together with
as
(see Figure 5-8).
in the simulations the contribution of
equatorial plane.
simulations is illustrated in
13
matrix is taken
The
analysis
have to be taken into account. The anal¬
-states
can
by including
in the
detailed
assigned
large hyperfine coupling given
spectral features
hyperfine
a
of the MW excitation, the
selectivity
ropy and contributions of up to four ml
ysis reveals
ion; however
simulations of the ESEEM spectra
of the spectra the orientation
analysis
Aqueous Solution.
and lactoferrin and have been
copper(II)-transferrin
in this work. Our parameters for the
given
Table 5-3
in
7t
and the second sp oxygen
3dxz and
bonding.
be delocalized
Via the
through
3d
metal orbitals
2pz oxygen orbital
the carbonate
system of monodentate carbonate ligands is tilted with respect
n
system.
to the 3d orbitals of
5.4 Discussion
the metal due to intramolecular
making
at the
13
orbital
overlap
C nucleus
by
and
the
large
about 5% of the
A
rough
ion
(at
13
spin density
of about 0.3% in the
allows
on
of bidentate
From the
is found
on
complexation
each of the four
reproduce
C atom
ring systems, leading
to
to
explain
large isotropic
13
8 MHz, observed for
bis-(diethyl-dithiocarbamate)).
attribute the
isotropic coupling
however, yields
a
or a
it is known that
spin density
1.3
[92],
water oxygens
A)
and
a
on
2+
the Cu
spin density
A, point of maximum electron den¬
of the
large
hyper-
orthorhombic
Other mechanisms such
the
C
have favored the CI mechanism for the
approximately
z.
[107]
mechanism
[28] have been proposed
0.3
for the
and for the orthorhom-
equatorial
with 80% of
anisotropic part
largest coupling along
C(2s) "transannular overlap"
(at
density
2pz orbital yields explanations
copper-hexaaquo complex
point-dipole interactions,
the
xy-plane,
difficult. Polarization of the electron
in the carbon
2pz orbital of the
one to
fine matrix with the
anism
case
more
and steric hindrance in the
A), 5% spin density on each of the four oxygens (at
2.3
sity [21])
in the
coupling.
C
model based
bonding
spin density
higher isotropic coupling
bicity of the
%
hydrogen-bonding
95
as a
Cu^c-^.^)
configuration-interaction (CI)
spin density
at the
couplings. Kirmse
explanation
of
an
13
mech-
C nucleus in similar
et al.
[108], for example,
isotropic
13
C
coupling
of
symmetric Cu/Ni^dtc^ complexes ((et^dtc^
Without detailed
to the different
convincing explanation
MO
calculations
mechanisms.
for the
-
it
is
difficult
=
to
Spin density derealization,
anisotropic part
of the
large
13
C
cou¬
pling.
5.4.4
ID and 2D ESEEM of Protons
13
The
8 and
an
C
couplings
reveal monodentate coordination of carbonate at
additional bidentate carbonate coordination at
plexation
of carbonate
ligands
in the first coordination
pH
6.5 and
sphere
pH
pH 5.5,
2+
of the Cu
the removal of water molecules, the measurement of the proton
other mechanisms
can
contribute to
couplings
copper-hydroxo complexes,
tion of 5-10
tion
4.3).
_4
and
Above this
pH the
are
not
by
yield
carbon¬
couplings, (a) depro-
higher pH, leading
to the formation of
(b) geometrical
M, hydroxo complexes
may
of the proton
changes
tonation of coordinated water molecules at
com-
ions leads to
additional information about the coordination shell. Besides the substitution
ates two
6.5 and
8. Since the
rearrangements. At
expected
formation of binuclear
Cu2(OH)2
2+
copper concentra-
a
to form below
pH
6
[89] (cf.
complexes
sec-
leads to
a
96
Copper Carbonate Complexes
5
decrease of the EPR
We
four-pulse
cules
peak and
combination
by carbonate ions.
due to
a
ment is
The
change
bonate oxygens whereas at
Hydrolysis
are
in agreement with the
bonate ions in the
and the
pH
coordination
pH 6.5 contributions of
can not
C results since
equatorial plane
replaced by
8
equatorial
equatorial protons
at
positions
maximum
sample A,,,^
car¬
one
H20/OH" are
still
case.
The proton spectra
involves at least three coordination
positions.
car¬
At
pH
that at the most two water molecules
shifts of 0.5 and 0.3 MHz
and
occupied by
are
and bidentate coordination of two
mono-
carbonate ions. In the combination
couplings, respectively,
mainly
are
unambiguous assign¬
an
be ruled out in this
equatorial proton signal suggests
5.5 the strong
have been
13
observed in the
observed for the axial protons
spectral changes
complexes
of the
ligands.
HYSCORE spectra to the substitution of water mole¬
8 where all
pH
at
Solution.
Aqueous
equatorial proton signal intensity
in the coordination. For the
possible
visible.
in the absence of other
intensity
the decrease of the
assign
in
were
corresponding shifts Avmax
peak spectra
of
Cu(H20)6
observed for the axial proton
of 0.35 and 0.2 MHz
were
obtained from the X-band HYSCORE spectra. The better resolved S-band HYSCORE
spectrum yields
A
tances of 2.8
2.7
A,
(rCu-o
Avmax value
A
=
sample,
2-2
^>
which
suggested by
ro-H
A
like
this
then estimate
Cu(H20)6
8
sample.
From these results dis¬
to an
an
al.
=
[92]
109°,
for
me
good agreement with
copper-hexaaquo complex
sp3 hybridization).
From the Cu-H
axial Cu-O distance of about 2.5
elongation of 0.3
A
A
for the
pH
8
of the axial Cu-O bond. The idea of
equatorial plane,
rough estimation, is supported by the optical spectra. The view is fur¬
by
the
change
hydroxyl ligands
positions
in the
in the
length
axial
=
of the axial Cu-O
2.36
A)
for
ligand is
or
example,
is
bond, observed in
Cu(OH)64" (rCu.0
equatorial plane [24].
is not considered since it is
complex by NH3 ligands
K5 for an
pH
due to coordination of carbonate ions in the
copper-amino complexes,
2+
et
h angle (Cu-O-H)
Na2Cu(C03)2-3 H20 (rCu.0
carbonate and
ions at axial
we
*
corresponds
ther corroborated
pounds
=
elongation
axial bond
stant
of 0.35 MHz for the
be calculated. The first distance is in
can
obtained from the data of Atherton
distance of 3.2
an
a
and 3.2
=
2.81
A)
com¬
with
Coordination of carbonate
thermodynamically
unfavorable: for
the substitution of four water molecules of the
straightforward,
400 times smaller and
whereas the
K6 has
not been
complexation
reported [90].
con¬
5.4 Discussion
5.4.5
In
Structure
Figure
Proposals
5-15 structure
for the
proposals
pH 5.5,6.5
and 8 in frozen aqueous solution,
species
to be
are
atoms drawn in
not
possible
expected
parentheses
rather than
in
are
given.
As discussed
at
before, mixtures of
This is taken into account
by
Figure 5-15, indicating that unambiguous assignments are
arguments supporting
pH
copper-carbonate complexes, present
single species.
a
from the EPR data and that
structures. The
97
our
equilibria
proposals
5.5
may allow for the presence of both
can
be summarized
as
follows:
OH2
I
H02CO,,
,^OH2
H20
^OCOaH
|
OH2<OH*>
pH
6.5
OH2
'
02CO,
,^0,
^cu> ,c=o
o
H<2)Cr
,
^
(-o2co)
PH8
0=C,
I
02CCT
Cux
I
/C=0
o
0H2
0H2
I
o=cs
o
\
^Cu
i
/C=o
o
y
OH?
Fig. 5-15 Structure proposals
pH,
as
for
copper-carbonate complexes
deduced from the
equilibria
with
complexes
experimental
possible contributions
with two bidentate
rings
of both
can
in frozen aqueous solution at different
results. Features
species
to the
not be excluded.
given
in
parentheses
indicate
spectra. At pH 8 the presence of
98
Copper Carbonate Complexes
5
-
At
pH
5.5
bonate in the
water
only
a
C
small
protons
are
carbonates,
is observed for
as
bonates based
position.
on
well
-
At
pH
Distinction between
the ESE modulation
larger covalency
of the
-At
ligands.
water or
pH
species
8 all the
Internal
equatorial
H-bridging
equatorial
non-bound carbonate
the
elongation
show
with
one or two
a
mixture of
large
13
C
of the Cu-O
coordinated
no
can
not be excluded.
at
axial
of carbonate ions at the central Cu
bonds leads to
an
elongation
of the axial Cu-
to the coordination of one
equatorial plane.
are
occupied by
with axial water molecules
positions
torial and axial
For the
Elongated axial
pH
positions
as
is
well
mono-
and bidentate carbonate
stabilize monodentate
can
2+
Cu-O bonds
are
simultaneous
the presence of
car¬
equa¬
postulated.
approximately equal
complexation
One could argue that similar spectra
species.
amounts of bidentate
At
pH 8 this
Cu(C03)2
are
would
and
mon¬
"
odentate
Cu(C03)4
unlikely,
even
complexes.
under
The simultaneous formation of these
non-equilibrium
different CW EPR spectra due to the
5.4.6
rings between
and bidentate
mono-
obtained from mixtures of purely monodentate and bidentate
require
ligands
due to the Jahn-Teller stabilization.
samples
ion is
coor¬
observed. The coordination of
the formation of four-membered
unlikely,
6.5 and pH 8
of carbonate ions at the Cu
as
proper
evidence for
dination of carbonate ions. The presence of species with two bidentate carbonate
bonate
car¬
species.
couplings gives
strongly coupled protons point
equatorial positions
three
is difficult because there is
contains
complexation
hydroxyl ligand in
or
[Co(NH3)4C03H20] complexes
already
depth [109]
sample
and bidentate
mono-
O bond. Contributions from
remaining
and
6.5 the observation of both small and
simultaneous
ion. The
as
[Co(C03)2(H20)4]
reference system available and the
of two
steric hindrance favor the trans-coordination of
with two carbonates may
([59],[105]). Species
bond at the axial
as
hyperfine couplings
hydrogen-bonding between
observed. Internal
oxygens and coordinated water
Aqueous Solution.
to monodentate coordination of car¬
coupling, assigned
and strong
equatorial plane,
in
Freezing
conditions. Furthermore
pronounced difference
in
we
complexes
expect them
is
to show
bonding covalency.
Effects
The structure proposals deduced from the low temperature EPR results stress the
importance
of the monodentate coordination at all
pH
and suggest
higher
coordination
5.4 Discussion
numbers than the
expected
ones
investigations
EPR
complexation
perature
are
is therefore
commonly accepted complexation
from
are more
in better agreement with the
to
keep
in mind that the
copper-carbonate complexation
rium shifts between
lowered due to the
room
pulse
speciation
of the ion
responsible
calculations. It
are
performed in
product
of water
for considerable
CuC03
decreases at lower temperatures. The
has been observed for the formation constants of
upon
dependence
the temperature
authors have called attention to the
can occur
CaHC03
changes
freezing [112,113].
in
of the
complexation
complexation
Orii et al.
[113] have
of solute concentrations
during crystallization.
and solution
acid-catalyzed ring opening [13], thereby increasing
ate
ligands.
Carbonate concentration
could account for the formation of
gradients
Cu(HC03)x
in
are
pH
thus
Several
composition
drops
pH
in
due to inho-
can
lead to
an
the number of monodentate carbon¬
in the
"x
drop
can
constants.
observed local
A
effect
CaC03 complexes
and
of up to 3 units for sodium carbonate-sodium bicarbonate buffers which
mogeneities
equilib¬
same
[111]. The high coordination numbers observed in the frozen aqueous solutions
that
[1]
effect of the inert salt. Soli et al. [110] showed however
cryoscopic
explained by
tem¬
room
temperature and the freezing point of the solution which is
that the formation constant of
not be
the
macroscopic
recorded at
EPR measurements
dependence
may be
spectra
from the
predictions
frozen aqueous solutions. The temperature
and of the
given by
reliable than those calculated from the
constants. On the other hand the CW EPR
important
constants for
One could argue that the detailed structures
copper-carbonate complexes.
pulse
99
freezing sample
"
and
Cu(C03)x
*
on
the other hand
complexes
with
S
x
"
2. In 1 M
KHC03
solutions
Cu(HC03)4
complexes
reports suggest that the number of coordinated
ligands
have been
reported [12].
may have been increased
These
by
the
freezing procedure.
On the other hand there is
complexation
direct evidence that
freezing
induces
mechanism of monodentate and bidentate carbonate
ion. Therefore it
Cu(HC03)
no
and
seems
Cu(C03) complexes
aquatic chemistry
the dominant
important only
safe to conclude that
we
ligands
complexation model
to the
pH
or
in the
2+
Cu
is also valid for the
in aqueous solution. From the view
point of
notice that bidentate coordination of carbonate to the Cu
complexation
at low
our
changes
2+
ion is
form whereas monodentate coordination should become
at
high
carbonate concentrations.
100
5
Copper Carbonate Complexes
The combination of different
tion about the
bonate
13
geometrical
complexes
spectroscopic methods
and electronic structures of
at different
pH.
dipolar interaction matrix,
hyperfine coupling
of
provided
mono-
Although
we
unpaired
describe the
isotropic coupling also
larger coupling
explained by
through
the
possible by
a
n
between the
unpaired
that the
of the
bonding
and
the
narrow
a
13
analysis
in the
large
are
typical
is in contradiction to the
calculations based
surements at room
changes
At
ate to die Cu
ligands
are
bidentate
the
be
discrepancies
an
The observa¬
that have been
on
con¬
investigated
published equi¬
between the CW EPR
mea¬
temperature and in frozen solution indicate that pH and concentration
due to non-ideal
ing freezing.
speciation
as
for
leads to
equatorial plane
pH values
of
can
a
spin density
tion of monodentate carbonate coordination at all
well
leads to
HFI is made
ligands coordinated at axial positions.
as
is
of the
increase of the bond
predictions
with
derealization of
Complexation
librium constants. This result
axial
matrix
C carbon which
ditions close to exact cancellation.
for water
an
comparison
coupling
features observed in the ESEEM spectra that
length
ion and the
equatorial plane
electron and the
system of the carbonate ion. A detailed
is reflected
bonding
1 MHz and the
>
equatorial protons suggest
higher covalency
and bidentate copper-car¬
hyperfine coupling by
orthorhombic rather than axial. Bidentate coordination in the
much
detailed informa¬
electron of the Cu
Q
an
has
The weakness of the monodentate
the small interaction observed between the
C nucleus of the carbonate.
the
Aqueous Solution.
Conclusions
5.5
by
in
pH
glass
formation
might be responsible for equilibrium
5.5 and low temperature
ion is found whereas at
complexation observed
only monodentate coordination of bicarbon¬
higher pH
coordinated in the equatorial
plane.
in the frozen
both
mono-
and bidentate carbonate
The basic mechanisms of
samples
mono-
and
should also be valid in aqueous
solution at ambient temperature. Bidentate coordination is
coordination form at ambient temperature.
shifts dur¬
expected
to
be the dominant
Interactions
chapter 6
of Cu
2+
with Solid Calcium
Carbonates
6.1
by
in
Introduction
In this
chapter
CW and
pulse
chapter
the interaction of Cu
EPR. The
5 for the
chapter:
Which
are
the
interpretation
of the spectra is based
in solution. The
complexes adsorb
How do copper
formed at the surface? and How
are
investigated
the results obtained
on
following questions
surface?
to the mineral
the metal ions
are
integrated
into
crystal lattice?
The
majority
of the
experiments performed
the calcium carbonate mineral vatente.
environment, this mineral has
investigations considerably:
areas
of calcite
are
typically
tration of surface bound Cu
important
in
pulse
EPR
a
its
a
2+
ions
2
m
/g).
performed
surface
to an
13
simplifies
up to 30 m
a
are
a
first
approaches
on
the
spectroscopic
2
/g (specific surface
much
improved sensitivity
with vaterite. Two
based
in the natural
higher
which is
pulse EPR measurements involving
C-labeled carbonate ions into the system. In
with
area
questions
importance
Vaterite thus allows for
leading
All
these
of minor
property which
high specific
few
to answer
Although
significant
experiments.
carbonate ions have been
13
with solid calcium carbonates is
copper-carbonate complexes
addressed in this
complexes
2+
are
experiment (1)
concen-
especially
13
C-labeled
used to introduce
a
C-labeled carbonate ions is added to unlabeled solid vaterite. In
copper solution
a
second
experi-
6 Interactions of Cu2+with Solid Calcium Carbonates
102
ment
(2)
copper solution is added to
a
these two
experiments
the surface
are
all
possible
13
C
a
suspension
couplings
considered. The fate of the Cu
2+
to the different
C02:Ca C03(vat) and
C-labeled vaterite. With
fully
C03(vat) throughout
The structure and other
of vaterite
properties
this
as
during the
and
(3), labeled
CaC03(calc),
tions in this
experiment are
The
13
where Cu
apply
2+
ions
to
well
adsorbed
lution of the
techniques. Two-pulse ESEEM spectra
are
interaction while detailed
copper-vaterite
proton signals of the equatorial and axial
question,
whether
third
experiment
powder.
The condi¬
a
water
13
are
observed with ID
used to follow the time
C
evo-
coupling parameters
Specific
are
information about the
molecules is obtained with the ID four-
ESEEM method.
6.2
Experimental
6.2.1
Sample Preparation
Section
(A) Preparation of vaterite:
chemicals and double distilled
pared by pouring
Na2C03
100 mL of
solution at
room
from 11.5 to 10 and
[114],
was
stirring
|im),
under
high
this
formed
a
preparation
a
0.4 M
pH
of vaterite
was
CaClj solution
temperature. The
white
during
For the
N2-saturated water
analytical reagent grade
used. Unlabeled vaterite
into the
of the stirred
same
volume of
NajCOj
precipitate
CaC^ solution.
procedure
a
pre¬
0.4 M
dropped
solution
was
collected
The solution
on a
for 24 hours
showed that the
.
room
The XRD
analysis
of the fine white
precipitate
consists
mainly
aged by
was
Buchner filter
washed with 30 mL of double distilled water and dried at
vacuum
was
gel-like precipitate, probably hydrated amorphous CaCOj
the addition of the
for five minutes and the
10-16
by
labeled
chosen to compensate for the low copper concentrations.
extracted from simulations of the HYSCORE spectra.
pulse
calcite
on
C and proton interactions in the different experiments
and 2D-ESEEM
are
less.
similarities and differences
as
calcite is addressed in
are
(2)
or
chapter, respectively.
between vaterite and calcite have been discussed in section 4.2. The
the results obtained with vaterite also
transfor¬
within 24 hours
completed
preparation procedures experiments (1)
Ca
in solution and at
ligands
ions is then followed
mation of vaterite to calcite in water, which is
According
of
to carbonate
(porosity
temperature
powder
obtained
of vaterite. REM and TEM
Experimental Section
6.2
pictures
Figure 4-2
(<
tals
spherulitic particles
showed
on
50 nm,
52). These particles
page
[63]),
which
Nassrallah-Aboukai's et al.
same
M
procedure by
with
explains
[66,67].
the
13
a mean
are
high enough
\im)
pulse
mixing
2+
of two Ca
Wray
temperature this
[118]
the solutions
1
areas <
or
2
m
tion of fine
/g,
according
same
too
a
2-
specific
than
large
procedure
solutions
depends
surface
size
crystal
few
a
areas
during
2
m
/g (crystal
various conditions
on
[118,119]. Precipitation
from
highly supersat¬
number of small calcium carbonate crys¬
results in the formation of vaterite, whereas at
leads to the formation of
small for
grained
to the
volume of 0.2
reproduce
the results of
who found pure calcite at temperatures around 40 °C. Slow
aging
the mill and the
higher
areas
is obtained. We were, however, not able to
aragonite
et al.
/g, observed by
m
obtained
with
grained calcite
C03
etc.
urated solutions is necessary to obtain
70 °C pure
was
CaCl2 solution to the
surface
and
supersaturation, temperature, pH,
room
2
of up to 30
however, rarely achieved. Which calcium carbonate polymorph is
are,
formed upon the
tals. At
number of small crys-
EPR studies with adsorbed copper. Due to the industrial
precipitation [115-117]. Specific
sizes 0.5-1
like
large
5 Jim (cf
in section 5.2.1.
also made to prepare fine
allow for
approximately
of calcite several studies have dealt with the control of
importance
calcite
were
a
areas
C-labeled vaterite
13
to
surface
addition of 30 mL of 0.2 M
K2 C03 solution prepared as described
Attempts
diameter of
aggregates of
high
103
high
experiments.
our
calcite from
coarse
during
pressures
large calcite crystals
An alternative
procedure
material is mechanical
the
grinding
with
grinding.
mixing
specific
of
surface
for die prepara¬
Abrasion from
process may however
considerably
alter the surface.
(B) Adsorption experiment
labeled carbonate solution with
obtained
by dilution
N2-saturated double
to a
HNO3
2+
total Cu
and 1.5 ml of
drying
0^
methods like
efficiency of the
=
a
a
prepared
aliquot
as
a
first
experiment
13
a
10
.3
5
M
Cu(N03)2
M. The
pH
N2(g).
The
solution
was
C-
was
described in section 5.2.1, with
of 29 mL of this solution
balloon, filled with
5-10
heating
mineral.
In
total carbonate concentration of cT= 0.05 ± 0.01 M
distilled water. An
concentration
Other
tion
12
C02:Ca C03(vat):
of the stock solution,
closed vessel connected to
with 1 M
1.
a
13
pH
were
was
was
transferred
adjusted
to 7
added, resulting in
a
raised to 9 with 1 M KOH and the
the vaterite up to 100 °C
were
found to diminish the
adsorp¬
6 Interactions of Cu2+ with Solid Calcium Carbonates
104
solution stirred for five minutes. The solution
slurry
vaterite
in
second vessel, obtained
a
vaterite in order to obtain
kept
under
with
a
was
an
syringe
a
then added under
by addition
homogeneous suspension.
N2 atmosphere. Samples
and
was
of several
This
of water to the
drops
resulting suspension was
of 2 mL were taken at different time
cellulose nitrate filters of
passed through
to 0.8 g of a
stirring
porosity
0.1 p,m. The filtrate
washed with 1 mL of double distilled water and the rolled moist filters
duced into
an
EPR tube and frozen in
liquid nitrogen. Samples
also
intervals
taken
were
were
intro¬
immediately
after the addition of the carbonate solution, after 10, 30, 60 minutes and 2, 3, 6 and 24
hours. Bare filters treated with
affinity
2+
for the Cu
aqueous 10
an
_3
M
13
was
under
added in
kept
HN03
and 0.5 mL of
2+
a
total Cu
a
a
10
_3
concentration
M
In
a
second
closed vessel to 20 mL of
N2 atmosphere.
water,
a
solution did not show any
ions.
(C) Adsorption experiment Ca C03(vat):
labeled vaterite
Cu(N03)2
resulting pH of 10
The
Cu(N03)2
Ciij. 2
-5
2.5-10
solution
M.
were
Samples
experiment 0.25
to
the
procedure described
added under
of 3 mL
stirring, resulting
were
taken
calcite
high-vacuum
(Merck, suprapur)
Mn
EPR
signals.
tilled water in
was
solution
were
Samples
a
surface
areas
The washed calcite
closed vessel,
kept
tested in this
was
under
added under
of 25 mL
were
(porosity 10-16 p.m),
in form of
compressed
(puriss)
(E) AAS
were
10 g of
highly
crystallinity
and
found to exhibit strong
an
N2 atmosphere.
in
immediately
HN03
a
The
pH of the resulting
and 3 mL of
total Cu
a
10
concentration
M
sus-
Cu(N03)2
Cu^= 1.4-10"
after the addition of the copper solution
was
collected
on a
Buchner fil¬
liquid nitrogen
cylindrical shape.
measurements: The amount of copper in solution
function of time by atomic
after 24
and dried under
washed with double distilled water and stored in
blocks of
as
added to 220 mL of N2-saturated double dis¬
stirring, resulting
taken
study
and after 30 and 90 and 150 minutes. The solid carbonate
ter
experiment
washed with acetone
lowered from 9.8 to 8.5 with 1 M
pension
M.
In the third
for twelve hours. All other commercial calcites of lower
possibly higher specific
2+
were
immediately
well
as
in
above.
(D) Adsorption experiment CaC03(calc):
crystalline
C-
lowered to 8.5 with 1 M
after the addition of the copper solution and after 5,15 and 60 minutes
hours, according
13
double distilled
N2-saturated
was
g of
adsorption spectroscopy.
was
The measurements
determined
were
as a
performed
Experimental Section
6.2
on
filtrates obtained from
amount
the filter
on
C02:Ca COs(vat) adsorption experiment.
a
determined
was
by treating
HNOj(conc) solution to dissolve the calcium
imental
error
of these measurements
CW and
pulse EPR spectra
two-pulse ESEEM spectra
delay X was
section
K
pulses
on
the filter. The exper¬
were
recorded with
single
a
T
fixed to
a
recorded
on
the Bruker ESP 380E spectrome¬
value. Control
room
using
surements
a
liquid helium cryostat from
measured with
performed
introduced
the amount of
experiments
temperature the filter
into
a
APD
sample
cryogenics.
amplitude
of the
pulse
a
was
cut in
values
by
blind
stripes and
taken after 24 hours
sample
was
The 16 K spectrum of this
CaC03(calc) experiment
maximum of
truncated
x
of 0.03 mT. For the CW EPR
finger dewar and measured
EPR spectra
inter-pulse
with different
accidently
were not
that could be measured exceeded 1 g,
sample
For the
modulation
samples
on
directly
a
and the
respectively
C HYSCORE spectra shown in the result
quartz flat cell. The temperature series for the
was
signals.
13
that the lines
to assure
described in section 5.2.3, except for
8 and 16 ns,
The
ns.
as
recorded
were
spots. For the CW EPR measurement at
were
known amount of
a
10%.
were
incremented in steps of 8
however, performed
series
carbonate collected
recorded
were
which
of the 7C/2 and
length
ter. The
were,
was
the filters with
The copper
Equipment
6.2.2
the
105
leading to
was
cylinders
the frozen
at 77 K. With this
more
packed
mea¬
procedure
intense EPR
into
a
standard
EPR tube.
The XRD
analysis
The AAS data
were
was
performed
obtained with
a
on a
Scintag
graphite
XDS 2000 with
tube AAS 2100/HGA 700 from Perkin
Elmer. Merck Titrisol 9987 standard copper solutions
bration of the instrument.
factor 100 prior to
Data
6.2.3
Data
samples
from
Na
or
with
higher
(0
-
40
H-g/L)
were
copper concentrations
used for cali¬
were
diluted
by
a
measuring.
Manipulation
processing
were
Samples
CuKa irradiation.
was
prepared
done in
analogy to the procedures given
without the
glass forming agent NaN03,
T>J had to be eliminated. The AAS data
were
in section 5.2.4. As the
no
drawn
background signals
using
the program
6 Interactions of Cu2+ with Solid Calcium Carbonates
106
MICROCAL ORIGIN 3.5.
EPR and HYSCORE Simulations
6.2.4
The g- and A "- values obtained from the
refined
were
by simulations performed with
assumed to be
axially symmetric
HYSCORE spectra
of the program,
mula
in
published
dipole approach
of the program
the vector
MATLAB 4.2c routines, based
coinciding principal
simulated with
a
ESEEM time-domain
an
axial g matrix
T/ge
thus aiso,
connecting
The HF
were
and the
-states
were
6.3.1
AAS Measurements
angle 8j
signal,
was
couplings
were
(3100 (ig/L)
scale in
Figure
and is indicated
the addition to the vaterite,
this
rapid
initial
six hours the
more
by
computation
between the z-axis
by
AAS
the dashed line in
In
EPR
Figure
point-
Input parameters
(g(| direction)
and
contributions of
as
a
function of time
Figure
experimental
t
are
=
0
prep¬
6-1. Five minutes after
than 95% of the copper is removed from solution. After
is close to the blank
in solution decreases
signal (5 (Xg/L).
hours shows that 90% of the copper is found
6.3.2
for¬
of the nuclear fre¬
6-1. The initial copper concentration at time
uptake the copper concentration
signal
were
using the
treated in the
is in agreement with the theoretical concentration calculated from the
aration
matrices
calculated
Orientation-dependent
The solution copper concentrations measured
logarithmic
second
taken into account for the simulations.
Results
on a
on
axes.
taken into account [42].
electron and nuclear spin.
6.3
drawn
u
home-written C++ program. The output
discussed in section 2.2.2. For the
as
were
the different ml
with
[37,47] (Appendix B.3).
the effects of
quencies
were
four-pulse
a
CW EPR spectra at 130 K
formulae [120]. For the simulations the g and A
perturbation
order
experimental
on
The control
more
slowly. After
experiment
after 24
the filter, associated with the vaterite.
Spectra
6-2 the EPR spectra of vaterite
mental procedure
13
12
C02:Ca CO^vat)
are
samples prepared according
shown. These spectra
are
to the
experi-
very similar to
6.3 Results
107
A
O
1000
A
solution
0
filter
"a
100,
O
A
-
A
A
A
I
10
I
,
,
10
time
Fig. 6-1
Copper
A
I
I
15
20
.
.
25
(h)
concentrations in the filtrates and filter solutions
as
determined
by
AAS. The dashed
line indicates the calculated total copper concentration.
those obtained from
samples
from the Ca
shown. The time scale for the two
illustrated in
changes
ment,
Figure
approximately by
The
a
6-2 take
experiments is, however,
place
region
different: the
spectral
C03(vat) experi¬
in the Ca
rapidly
therefore not
indicate the presence of two copper
associated with the vaterite surface, marked
cate the
more
are
factor of five.
views of the g,,
enlarged
which
CO^vat) experiment
A|| hyperfine splitting.
No
by (A)
and
in
(B)
major spectral changes
are
Figure
species
6-2. The bars indi¬
observed
during
the first 30
minutes after the addition of the copper solution to vaterite. The initial spectrum is dom¬
inated
by
the
(A) species.
The
principal
from the simulations of the EPR spectra
are
typical
parallel
for
axially-distorted
direction
marginal effects
being
on
den by the intense
signal (A)
(see below)
octahedral
a
are
complexes
given
signal. After two hours
spectral
(C)
in
ligands [98],
of the filtrates has
the spectrum of a second
taken after six hours:
linewidth of ~5 mT, labeled
matrices obtained
with six oxygen
signal (A) in the initial spectrum shows up clearly.
sample
u
in Table 6-1. These values
by the distortion axis. Washing
has decreased. Two additional
obtained from the
2.247 and
this
defined
values of the axial g and A
an
features
are
only
species (B), hid¬
The intensity of the
marked in the spectrum
isotropic spectrum
Figure 6-2,
the
and weak
with
narrow
a
g-value
peaks
of
at the
108
6 Interactions of Cu2+ with Solid Calcium Carbonates
—i
260
1
1
1
280
300
320
Magnetic
Fig. 6-2
CW EPR spectra of vaterite filter
K. The
samples
enlarged
views of the
samples
obtained from
were
g^ region
four-line pattern in the low-field
continuously
taken at different time intervals and measured at 130
13
an
B0 (mT)
12
C02.Ca CO/vat) experiment.
to illustrate the presence of several
region and labeled by A, B,
lower end of the spectrum, tentatively
features grows
Field
1—
340
assigned
to a
The insets show
species, identified by the
and D.
species (D).
The
intensity
in the first 6 hours. After 24 hours, however, the
spectrum (C) is the only remaining spectral feature.
of both
isotropic
6.3 Results
109
100 K
27 K
300
280
260
Magnetic
Fig.
6-3
Temperature dependence
13
of the
sample
12
sample
observed for
an
signal
B0 (mT)
taken after 24 hours
C02:Ca CO^vat) experiment. The scaling of the spectra is arbitrary.
recorded with
If the
of the EPR
Field
340
320
a
modulation
as
illustrated in
Figure
copper spectrum. Further
a
was
of 0.3 G.
taken after 24 hours is cooled down below 100 K
signal (C),
anisotropic
amplitude
in
The 16 K spectrum
6-3. At 40 K the
a
drastic
change
is
isotropic line converts to
lowering of the temperature leads
to a
line
rowing of the anisotropic spectrum and the complete disappearance of the isotropic
nar¬
spec-
6 Interactions of Cu2+ with Solid Calcium Carbonates
110
Table 6-1
EPR parameters of the different copper species observed
and Figure 6-3 and refined by simulations (Figure 6-4)
\A1 1
Si
(±0 001)
(± 0 001)
(MHz ±10)
2 358
2 066
440
20
2 305
2 065
510
20
Species A
Species B
Species
C
(T>100 K)
Species
C
(T<20 K)
«,so=2
the
-2106
coupling
An
in
a
copper spectrum with very
the gx region
values given
mam
In
Figure
were
and
are
by
(A)
spectrum (C) has
narrow
Cu and
perpendicular
simulations
values
a
weighted addition of the
no
(B)
are
physical
given
lines
Cu
are
shown
is
observed, which allows for
the g,, region The additional
in
only
by
NQI
The g,, and
(C)
estimates, able to
are
taken
reproduce
which the g- and A-values
Figure 6-5
section) which
to the
the second
in
the
are
leading
in
(2 h)
corresponding
compares the
figure
The
peculiar
not accounted for
to
rrij
Table 6-1
EPR
between the spectra
line width of
-
is an
6
m
in
are
weighting factors
mechanisms
leading
the simulation
are
an
in
to this
procedure
neglected
In
The g«
estimates from the EPR spectrum
spectrum from Figure 6-2, recorded
additional feature
to
factor of the isotropic
-dependent line widths
spectrum observed
mT, marked by
experimental spectra
weighting
at room
taken after three hours The S/N ratio of the RT spectrum
a
(65Cu)
-
individual spectra The
meaning due to the
values for species (D)
compared
are
Figure 6-4b
drawn
are
the simulations strain effects
and
90
-240
due to second order effects of the copper
spectral
and
line (see discussion
In
(63Cu)
determined In Figure 6-4a the simulated spectra of the individual species
(C) (isotropic)
for the species
||"
(65Cu)
90
-
Table 6-1 for the low temperature spectrum of species
in
6-4 the
best fits, obtained
and A
230
-
features of the spectrum
Table 6-1
(A), (B)
(63Cu)
to the nuclear spin of copper is not resolved
from simulations whereas the
the
10)
±
-
215
-
the distinction of the two copper isotopes
splittings
(MHz
a
A
-
-251
At 16 K
trum
247
2 530
Species D
a
6-2
Figure
in
is
poor The
the RT spectrum with
astensk
in
Figure
at 130
temperature for
6-5
a
main
a
K,
is
sample
difference
g-value
of 2 16
6.3 Results
Simulation
(=
A
2B
+
+
xC)
300
280
260
Magnetic
Fig.
6-4
by
Field
So far
m
Table 6 1
B0 (mT)
(b) Simulations of the experimental spectra
combination of the individual spectra The
given
in
we
the
figure
have
The
weighting
only shown
C02:Ca C03(vat) experiments
In
340
320
(a) Simulations of the individual spectra of the three species (A), (B) and (C) with the
parameters given
ilar.
111
Figure
6-6 two
CaCO^calc) experiment
those found for the vatente
factor of spectrum
factors for the
(C) has
no
of spectra
obtained
Figure
6-2
(A) and (B) spectra
shown
are
samples
obtained from
C03(vat) spectra are
from
calcite
very sim¬
samples
drawn The features observed in these spectra
samples.
in
physical meaning (see text)
EPR spectra of vatente
and noted that the Ca
examples
are
weighting
are
of
a
similar to
The dominant species after 10 minutes labeled
by
6 Interactions of Cu2+ with Solid Calcium Carbonates
112
—]
260
1
1
1
280
300
320
Field
Magnetic
Fig.
6-5
Comparison of the
at room
A||
*
=
the two spectra due to the different MW
frequencies
marked
is
by
an
asterisk
the RT spectrum
in
430 MHz, gL
-
2.07).
260
corresponding
samples,
Temperature T
Field
77 K
in
B0-offset
between
this
The line
plot
the text
in
Figure
6-2
(glt=2.37,
isotropic spectrum (C) observed
vatente
after
spectrum since the spectra
320
are
340
B0 (mT)
obtained from
=
in
species (A)
300
280
CW EPR spectra of calcite
different time intervals.
of
ones
Magnetic
6-6
experiment, measured
has been corrected
discussed
The linewidth of the
90 minutes is broader than the
Fig.
C02'Ca C03(vat)
a
at 130 K and taken after similar time intervals. The
temperature and
exhibits EPR parameters close the
(A')
B0 (mT)
spectra of samples from
EPR
r—
340
a
CaCO/calc)
experiment and taken
at
6.3 Results
i
1
1
1
0
113
1
10
1
1
20
30
Frequency (MHz)
Fig.
6-7
ESEEM
Two-pulse
absolute-value
spectra
the
of
sample
taken
after
2
hours
in
a
I3C02:Ca'2COj(vat) experiment, measured at field positions 281 mT (a), 312 mT (b), and 336
mT (c), indicated
frequency vc
by
2vH are marked by
by asterisks,
recorded
the Ca
at lower
arrows
in the echo-detected EPR spectrum
of carbon and vH of protons
are
as
well
as
the
dashed lines for each spectrum. The
sum
peaks
spectrometer artifacts. MW frequency vmw
=
temperatures. The transformation shows
CO^yat) experiment.
The S/N ratio is poor
as
(inset). The nuclear Zeeman
combination
at 15.6 and
frequencies 2vc and
31.25 MHz, marked
9.709 GHz, temperature T
a
=
similar time evolution
compared
to the vaterite
16 K.
as
in
spectra
due to the lower copper concentration.
Two-Pulse ESEEM
6.3.3
The
and Ca
13
two-pulse
ESEEM spectra of the
C03(vat) experiments
samples
exhibit both intense
obtained from
13
13
12
C02:Ca C03(vat)
C and proton signals. This is illus-
114
6 Interactions of Cu2+ with Solid Calcium Carbonates
trated
Figure
in
6-7 for
hours The three spectra
sample
a
were
the echo-detected EPR spectrum
peaks approximately
and at the
at the
taken
in
in
the inset The
nuclear Zeeman
sity decreases
signal
Ca
C03(vat)
main
m
frequencies
peak
is
going from g^ to g± The carbon
close to
while the
2vc
The proton
signals
experiment after 2
of carbon
sum
broadened
sum
arrows in
combination
are
four
vc and hydrogen vH
indicated
by shoulders
combination line consists
arising from the
by
features of the spectra
corresponding sum-combination frequencies 2vc and 2vH,
lines for each spectrum The basic carbon
frequency
C02
a
recorded at different field positions, mdicated
peak is
mainly
by dashed
and its inten¬
narrow
with
a
of the matrix
strongly coupled equatorial protons shifted
Frequency (MHz)
Fig.
6-8
Two-pulse
ESEEM
spectra of the sample taken after 24 hours
experiment, measured
at field
arrows in
the echo detected EPR spectrum
and the
sum
vmw
=
combination
in
a
l3C02 Ca'2COJ[vat)
positions 267 mT (a), 307 mT (b) and 330 mT (c), indicated by
(inset) The nuclear Zeeman frequency vc of carbon
frequency 2vc
9 706 GHz, temperature T
=
16 K
are
marked
by dashed lines
MW
frequency
6.3 Results
away from
2vH
higher frequencies (cf Figure
to
humps.The peaks
at 15.6 and 31.25
trometer artifacts. The
cies
(A)
and/or
115
two-pulse
(B) since these
5-9
on
page
85) appear
MHz, marked by asterisks in Figure 6-7,
ESEEM spectra shown above
species give
can
as
small
are
spec¬
be attributed to spe¬
the main contribution to the
corresponding
EPR spectrum.
Figure
6-8 shows
obtained from
cated
by
13
a
arrows
ute to these
two-pulse
ESEEM spectra for the 24 hours
12
C02:Ca C03(vat)
in the echo-detected EPR spectrum in the inset.
spectra; proton signals
about the carbon nuclear Zeeman
MHz with shoulders
increasing
field
a
split by
increased to 2.1 MHz
going from gn
to
sum
Only
missing completely. At g||
frequency
are
observed
splittings
are
13
positions,
C
peaks
The
intensity
combination
peaks
of the
are
contrib¬
split by approximately
indicated in
narrow
shifted
indi-
two lines centered
Figure
of these lines is observed and at g± the
(Figure 6-8c).
gL. The
are
1.5 MHz. Both
broadening
sample (species (C))
recorded at three different field
1.2
6-8a. With
splitting
has
vc peak decreases when
by approximately
2
0.15 MHz
3
Time
(usee)
12
Frequency (MHz)
Fig. 6-9 (a) Two-pulse
ESEEM time trace of the
experiment, recorded
sample taken
at the lower end of the
after 2 hours in
a
,SC02:Ca12C03(vat)
EPR spectrum (observer field 270 mT /
species
(D)). (b) Corresponding ESEEM spectrum. The nuclear Zeeman frequency vc of carbon and the
sum
combination
temperature T
=
frequency 2vc are
16 K.
marked
by
dashed lines. MW
frequency vmw
=
9.712 GHz,
6 Interactions of Cu2+ with Solid Calcium Carbonates
116
from the
In
of the
2vc position.
6-9a and b
Figure
13
Figure 6-2.
signal.
C
the
two-pulse ESEEM
one
A
a
splitting
of
~
sample
were
important changes are
unaltered
C02:Ca C03(vat) experiment are
gu in
Figure
position
deep
shown. The
related to species (D)
modulations observed for the
frequency
6-8a is observed. Proton
observed in the gj|
At
B0
=
similar to
signals
In this section
no
Ca
The asterisks
region and
In the
g±
are
similar to the spectra observed for
the somewhat broader line widths,
arrows
again
in
mark
Figure
(b)
and 336 mT
affect the relative
(c).
intensity
are
observed for the spec¬
intensity
6-10b. The
of these
spectrometer artifacts.
shown because
they
are
12
very
C02:Ca CO^vat) experiment samples, except
leading
to a
lower resolution. This
'
relaxation processes,
samples
region the spectra remain prac¬
C03(vat) experiment spectra are
13
ESEEM spectra for
312 mT extra features
minutes, indicated by
rapidly.
two-pulse
280 mT (a), 312 mT
signals (Figure 6-10a).
(Figure 6- 10c).
features decreases
T2
corresponding spectrum
taken after 5 minutes, 30 minutes and 3 hours. The
recorded at the field
trum taken after 5
to
poor S/N ratio.
12
the time evolution of the
of the carbon and proton
tically
at
a
in this spectrum.
C02:Ca C03(vat) experiment
The most
time trace and the
1 MHz about the carbon nuclear Zeeman
12
time series
a
resulting in
at the low observer field 270 mT and can be
found for the 24 hours
Figure 6-10 shows
13
hours in
13
The time trace is drawn to illustrate the
again missing
of
a
sample taken after two
spectrum was recorded
in
C modulation is shallow
At g± the
indicating
a
higher density
2+
of Cu
broadening
for
is due
ions at the vaterite
sur¬
face.
6.3.4
HYSCOREof13C
In the HYSCORE
the
two-pulse
experiment
ESEEM spectra
the determination of the
(low temperature)
In
13
a
Figure
are
the broad
clearly
C lines observed
as
truncated features in
revealed. Simulations of the spectra allow for
coupling parameters,
summarized for
species (A), (B) and (C)
in Table 6-2.
6-11
experimental
HYSCORE spectra of the
12
C02:Ca C03(vat) experiment are
and g± field
13
positions,
indicated
sample
shown. The measurements
by (a)
and
(c)
taken after 2 hours in
were
recorded at the g„
in the echo-detected spectrum in
6.3 Results
117
CS
Fig. 6-10 Two pulse
ESEEM spectra of
after time intervals 5 mm, 30
samples
mm
obtained from
C02
a
Ca
CO/vat)
expenment taken
and 3 hours, and measured at the at the field positions 280 mT
(a), 312 mT(b), and 336 mT(c) The nuclear Zeeman frequency vc of carbon and vH of protons
as
well
Mw
as
the
sum
combination
frequency vmw
discussed
in
=
frequencies 2vc are marked by dashed lines
9 705 GHz, temperature T
=
for each time
16 K The features marked with
series
arrows are
the text The asterisks indicate spectrometer artifacts
Figure
6-7
mately
0 08 MHz from the
(inset). The spectrum
at
g± consists of
anti-diagonal (Vj
=
-v2 +
one
broad
2vc)
peak,
At gn the
shifted
by approxi¬
peak is narrower and
118
6 Interactions of Cu2+ with Solid Calcium Carbonates
Table 6-2
Hyperfine coupling parameters
species,
(MHz ±0.05)
(±5°)
0.2
0.5
75°
0
0.3
20°
0.7
0.45
80°
Species (C) (axial coord.)
Species (C) (equal coord.)
the shift has decreased to
=
13
1/2 nucleus of
hand side of
Figure
-
0.06 MHz. No
C is observed,
splitting
indicating
6-11 simulations of the spectra
0
2
4
side,
experimental
HYSCORE
with
side:
GHz, T
=
16
in
K)
Figure 6-7)
in
Table 6-2
4
as
On the
right
described in
6
>le
taken
after
the field positions 279 mT
x
values of 144
The dashed lines indicate the
corresponding simulations, performed
parameters given
performed
2
spectra of the
(field positions (a) and (c)
9 706
shown
for the
Frequency v, [MHz]
at
=
isotropic coupling.
0
6
13C02 Ca12COj(vatj experiment, recorded
(vmw
are
ridges expected
Simulation
Frequency Vj [MHz]
6-11 Left
of the two
small
a
Experiment
Fig.
C nuclei for the different
(MHz ±0.05)
Species (A)/(B)
/
of the
obtained from simulations of the HYSCORE spectra.
as
described
ns
2
hours
m
a
(a) and 336 mT (b)
and 160 ns,
respectively
proton Zeeman frequency. Right
in
the text with the
coupling
63 Results
the
experimental
section
by
using the parameters given
tion the contributions of three
absorption peak
Uons from the
are
at the
13
high-field
C matrix line
In
13
Figure
C02
6-12
Ca
12
experimental
in
(A)
(B)
and
side
4
experimental
shown and
described
in
6-11
mam
contributions to
were
taken after 24 hours
sample
to simulations
performed
measured at the g^ and gL posi-
2
4
6
Frequency v, [MHz]
spectra of the sample taken after 24 hours
at the field
Figure 6 8) with
The dashed hnes indicate the proton Zeeman
performed as
Figure
C spectra
compared
0
6
HYSCORE
in
in
Simulation
experiment, recorded
(field positions (a) and (c)
13
HYSCORE spectra of the
Frequency Vj [MHz]
l3C02 Ca'2COj(vat)
which give the
exhibit very similar
Experiment
Fig. 6-12 Left
the extra-
taken at earlier time mtervals From this
samples
Table 6-2 The spectra
2
including
account,
added The HYSCORE spectra shown
C03(vat) experiment are
with the parameters given
Table 6-2 For the g± simula¬
end of the EPR spectrum In both simulation contnbu-
are
samples
in
-states are taken into
conclude that species
we
the EPR spectra of these
in a
m,
identical to those obtained from
observation
119
the text with the
a t
in
a
positions 268 mT(a) and 330 mT (b)
value of 160
frequency Right
ns
(vmw
side
=
9 706
GHz, T
=
16
K)
corresponding simulations,
coupling parameters given
in
Table 6 2
6 Interactions of Cu2+ with Solid Calcium Carbonates
120
tions indicated by (a) and (c) in the echo-detected spectrum in Figure 6-8 (inset). Unlike
in the ESEEM
spectra strong signals
mental spectra consist of two
man
frequency by
isotropic coupling
the
right
values
dipolar coupling.
and is
larger at g±
estimated from
the matrix line
are not
The
shifted from the nuclear Zee-
ridges,
separation
of the
and axial
equatorial
by
discussion),
is
considered. Since
pulse
13
EPR spectra
clearly
obtained from the
sample
taken
in the
ligands
non-zero
C carbonate nuclei. The
measured
are
by
Gj-
constituting
at
of the
(arrows
in
16 K these
experiment,
Figure 6-10b,
the HYSCORE spectra shown in
immediately
on
species (C).
early stages
ESEEM spectra
two-pulse
demonstrated
indicates
ridges
models. Contributions from nuclei
geometrical
weak features in the
positions. The experi¬
than at gH. The simulations of the spectra shown
The presence of bidentate carbonate
13
curved
be attributed to the low temperature modification of
can
indicated
observed for both field
overlapping,
side include contributions of
were
spectra
the
are
see
Figure 6-13,
after the addition of the solution in
a
12
C02:Ca C03(vat) experiment. The three spectra were recorded at field positions close
gn (285 mT(a)) and close
to
features from die strong
frequencies
were
(Figure 6-13c)
an arrow.
anisotropy is
to
C
gx (327 mT (b) and 336 mT (c)). To emphasize the weak
coupling
suppressed by
the bidentate
ends of the central
by
13
an
At lower fields the
reflected in the
strong coupling
case
appropriate choice
coupling
straight ridges.
in measurements
ridges
separation
applies
(Figure 6-13c) where the ridges
the
are now
of the
peaks
C nuclei
of the
the
(bidentate coordination)
weakly coupled
are now
nuclei (monodentate
two-pulse ESEEM spectra in Figure
highest
values. At the
two curved
approximately
ridges
field
at the outer
6 MHz is indicated
5-8
peaks (Figure 6-13b). Close
are
in
observed
to
gH the
(-+) quadrant
diagonal. They
are
spectral
features of the
strongly coupled
completely separated
coordination)
on
the
to the
parallel
-5.8 MHz and centered around ~4 MHz. The
13
of
by
T
detached from the main lines and the strong
are
triangular shape
and
of the
manifests itself
The
(b) and (c) the nuclear Zeeman
in the
separated by
from the contributions
(++) quadrant, unlike
page 83, where the spectra
overlap.
in
6.3 Results
-8
-6
-4
-2
121
0
Frequency Vj [MHz]
8
b
2
6
4
Frequency v, [MHz]
Fig. 6-13HYSCORE spectra
of the
recorded at the field
and 288
are
ns
(b,c).
suppressed by
In
a
sample
positions
(b)
and
taken
in
13
a
12
C02:Ca CO^vat) experiment,
285 mT (a), 327 mT (b), 336 mT (c) with
(c) the
blind spot
immediately
(vn
C nuclear Zeeman
:
9.701 GHz, T
=
frequencies,
16
K).
T
values of 248
indicated
by
ns
(a)
dashed lines,
122
6 Interactions of Cu2+ with Solid Calcium Carbonates
2vk
H
eq
Cu(H20)6
2+
13C02:Ca12CO?(vat)
experiment
Ca13CO?(vat)
experiment
CaC03(calc)
experiment
26
25
27
28
29
30
Frequency [MHz]
Fig.
6-14
Comparison
four-pulse proton
of the
copper vatente
samples
the copper calcite
ESEEM spectra of the
obtained from
sample
from the
C02
(vn
=
9.71
GHz, T
=
frequency 2vH
equatorial
16
ns
The shaded
water or
were
K) and represent the
(16
ns
steps).
area
C03(vai)
experiment, taken
recorded
sum
copper-hexaaquo complex,
and Ca
at
the
experiments and
immediately after the
the magnetic field position 312 mT
of 30 signal traces, measured with
i
values
The dashed Ime indicates twice the proton Zeeman
marks the
hydroxyl molecules
'CO^vat)
CaCOs(calc)
addition of the copper solution The spectra
between 96 and 576
Ca
signals
which
can
be
assigned
to
protons of
6.4 Discussion
6.3.5
ID Four-Pulse ESEEM of Protons.
In
Figure
and calcite
6-14
four-pulse
samples
ments, taken
mixing
thus be
assigned
can
we
approximately
the axial water protons shifted
6.4
species (A)
and
(B)
at the mineral
surface.
spectrum of the copper-hexaaquo complex
peak
in the copper
shifted
Instead of this
is observed. The
-0.5 MHz from
peak
intensity
2vH
is
by
1.5 MHz from
hexaaquo spectrum
a
has
van¬
combination spec¬
sum
small
hump
shifted
by
of the contributions from
considerably
reduced. The S/N
is very poor due to the low copper concentration.
experimental results presented
in the
preceding
section indicate that copper ions
interact with solid calcium carbonates in different ways. In the
actions
on
by
CaC03(calc) experi¬
Discussion
The
can
sample
2vH
shown for vaterite
are
and
which exhibit very similar
adsorption experiments.
ratio for the calcite
to
frequency
complexes
1.8 MHz from
CO^vat),
Ca
refer to section 5.3.4. The
twice the proton nuclear Larmor
ished for all copper surface
frequency spectra
of the copper solutions and the solid calcium
to the sum combination
for the discussion of which
tra in the three
combination
after the
immediately
compared
are
sum
C02:Ca C03(vat),
from
carbonate. The spectra
They
123
are
discussed and conclusions
concerning
calcium carbonates and the influence
The results
6.4.1
are
further
compared
the
adsorption
reactivity
following
these inter¬
behavior of metal ions
of the minerals
speciation calculations presented
are
deduced.
in section 4.3.
AAS Measurements
The AAS results indicate
under
to
the
on
the
our
experimental
a
high affinity
conditions. The
five minutes and is followed
by
a
rapid
of Cu
initial
remaining
interactions between Cu
by
2+
copper ions from solu¬
number of transition metal ions. The
explained by coprecipitation reactions [8,78,81],
of the copper observed
surements.
a
for the calcium carbonate surface
adsorption reaction is complete after
slow removal of the
tion. This two-step behavior has been observed for
slow step is
2+
We
can
conclude that most
EPR is associated with the carbonate mineral.
and the filter material
are
excluded based
on
Significant
EPR control
mea¬
124
6 Interactions of Cu2+with Solid Calcium Carbonates
6.4.2
Structural
Assignment
The various copper
species
of the Observed
Copper Species
observed in the CW and
EPR spectra
pulse
related to different steps in the transformation of vaterite into calcite and/or the
[66,67]). For
lization of calcite in aqueous solution (cf.
dynamic effects
it is, however, necessary to discuss the
tures of the individual
adsorption experiment suggests that
cite surfaces. The
2+
meric Cu
species
formation of
amounts
excluded based
of the
son
bonate
the
these
species
over
are
complexes
are
carbonate
or
the RT EPR spectrum in
in solution
Figure
(Table 5-2
copper-carbonate complexes
are
at
pH
a
carbonate surface. Since
crystal
face
layer [16].
6-5
(see
eters have
at the surface
mono-
on
page
77)
allow
(A) species
are
two
been found for
adjacent
>SiOH
us to
or
or
cal¬
mono-
important
can
be
6.4.3). Compari¬
in
similar
a
and
on
on
to
on
square-planar
cluded that the binuclear coordination should
Kucherov et al. [123] and Dedecek et al. [124]
on
one or
same
(A')
several carbon¬
initial behavior. The
are not
to
unexpected
since
influence the geom¬
also the structure of a thin
species. Spectra
edges
or
sur¬
significantly
with similar param-
synthetic clay
complexes
respectively.
at
geometric
6-2 formed imme¬
the other hand deviate
surface
occur
first
is also observed in the
silica sols [121] and
>A10H surface sites,
a
page 77). We thus conclude
expected
to some extent
species (B)
adsorbed
Figure
species (A')
are
give
close to the values found for
monodentate fashion to
and bidentate solution
2+
Cu
[122]. They have been assigned
or
also section
both vaterite and calcite show the
The parameters of
from the values of the
of
bound to the mineral surface
structures of calcite and vaterite
etry of coordination sites
The presence of
species.
5.5. (cf. Table 5-2
coordinated in
CaCO^calc) experiment
adsorption
indicative for
small differences between the EPR parameters of (A) and
the different
(B) at the early stages of the
in Table 6-1 with the results obtained for the copper-car¬
The g- and A-values found for the
ate ions at the
and electronic struc¬
associated with the vaterite
after addition of the copper solution to vaterite
that this copper ions
of this
the calcium carbonate surface rather than for the
copper-carbonate species loosely
on
interpretation
geometric
and
species (A)
resolved EPR spectra
well distributed
spectral parameters
interpretation.
diately
clearly
polymeric hydroxyl
of free
recrystal-
species first.
and (B). The appearance of
Species (A)
reliable
a
be
can
with
minerals
binding
to
Clarke et al. [122]
four
con¬
'defects' in the structure.
the other hand
proposed
square-pyra-
6.4 Discussion
midal structures for copper
parameters. In analogy
square-pyramidal
bly
at kinks or
complexes
copper
steps of the vaterite crystals
obtained for the
Figure
13
compare the
we
5-8
on
C
assign
the
or
83)
page
frequency
striking
paramagnetic
are
newly
surrounded
2
The
.
13
by
are
missing
ligand
These
2+
electron
signals
are
revealed
by
be
assigned
to monodentate
can
equatorial plane (cf.
and proton
peaks
in
with its main axis
equatonal plane
the time
nuclei.
signals.
Along gf[
section
Figure
The
can
be
single
Numerical values for the
coupling
peak,
13
C
are
to
observed for the
species (A)
From the
(Figure
There
A
is
5-6
peaks
peak
at
page 80 and
on
observed at the
13
C
2+
vc indicates that the Cu
signal similar to
if
ion
13
the
weakly coupled
one
observed for
larger hyperfine couplings to
peak
C matrix
at lower
ligands
to the
are
13
(cf. Figure 5-14
page
assigned mainly
expected resulting
fields.
in the
Figure
matrix
94). In the
decays
to matrix
of
13
C
in small lines with intense
6-7.
obtained from the simulations of the
are
based
on
leads to broad lines with fast
observed in
couplings
dipolar coupling
we assume a
thus be
can
on
the
point-dipolar approximation the
C nuclei must be small. No
(B)
are
therefore described
is estimated,
=
0.5 MHz
assuming
a
a
by
a
single
set of
qualitative changes
simple geometrical model
evidence for bidentate coordination in the spectra of the
two-pulse ESEEM spectra (section 6 4.3)
coupling parameters.
Cu-C distance of 2.71
the addition of the copper solution This observation
of the
6-7 to the results
C spectra within the first three hours. The carbonate coordination
dipolar coupling T~lge
tance of 1.9
2
and
spin density
is
as
HYSCORE spectra. As the simulations
13
2+
couplings
observed at g±
small
contributions close to the matrix
delocalization of the
Figure
coordination of carbonate
explained
towards the Cu
peaks
possi¬
of the features attributed to the
the shoulders of the
the distribution of the
a
or
5.4.3). The changes of the relative intensities of the carbon
6-7
pointing
square-planar
to a
C-labeled carbonate ions
centers. This leads to a matrix
EPR
same
at these sites.
the
the protons of the solvent water molecules. Carbonates with
the Cu
the
formed calcite nuclei. An octa¬
in solution
differences
and the apparent
bidentate coordination of the carbonate
ions at the vaterite surface
species (B)
ESEEM spectra shown in
two-pulse
the most
the
geometrical constraints
copper-carbonate complexes
nuclear Zeeman
to the
we
exhibiting
with coordination to several carbonate groups,
complex
hedral coordination is difficult due to
If
in zeolite matrices,
findings
to these
125
is
discussed
A
with
a
and
a
Cu-O dis¬
C-0 distance of
samples taken immediately after
together
with the time evolution
6 Interactions of Cu2+ with Solid Calcium Carbonates
126
1.3
A
A
is
and
an
typical
angle (Cu-O-C)
for
=
equatorial
Cu-0
(sp2 hybridization of the O atom). The value of 1.9
120°
bondlengths [24].
The
much smaller than the value of 1.2 MHz found for monodentate
plexes
in solution
(chapter 5).
The proton spectra for
copper ion at the mineral surface is coordinated
rial
metal and
copper
plane, yielding
ligand orbitals.
derealization of
A tilt
spin density
for the small
explanation
mechanisms is
given
to the
sphere
Figure 6-7
2+
system leads
n
A
ions. The
ions at the vaterite surface is
and the
narrow
ligands
Figure
in the
of these protons
larger coupling
signal arising
signals
weaker
species
can
in solution at
equatorial plane
complexation of the
species (A) and (B).
coupling
obtained
based
on
is not
by
The
be
pH
changed.
As
a
compared
to
is however obtained in
experiments it
of the surface
to
predicted by
as a
Cu(OH)4
5-10
or
axial water
complexes [125].
on
page 86. The
elonga¬
result of the carbonate coordina¬
distorted
complexes.
This
points
small alsg value found for
considerably reduced
square-pyramidal
ligands,
to
is
unlikely
for
but the
structure,
species (A)
reduction of the axial proton line may be
hydroxyl ligands.
the
complexes
the results obtained for the copper-
Figure
species
intensity
can
the protons of the water mole-
found for
compared
square-planar
equatorial
hydroxyl
8 shown in
one or two
considerably
small number of coordinated
of the axial proton line is
axial coordination to
the mineral surface is
bonding
the weak,
ligands, reflected in the
carbonate
intensity
the removal of
an
plausible
assign
is not observed for the surface
the EPR parameters the
explained by
to a
as
tion of the axial bond found for the solution
tion in the
a
from the
6-14. From these
equatorial plane
high bonding covalency
The spectra of the surface
complexes
2vH
1.8 MHz from
cules is in line with the
carbonate
to a disturbed
detailed discussion of the
more
carbonate ions both for vaterite and calcite and for different cT We
by
between
bonding
Jt
reveal that the number of water molecules in
spectra in
combination peak
broad lines shifted
that the
in the equato¬
C nuclei of the carbonate ions and is
of the Cu
be concluded that the dominant
are
13
molecules is weak. A better resolution of the proton
four-pulse
ligands
out-of-plane
twist of the carbonate
isotropic coupling.
reduced. The proton matrix line is
the
(B) indicate
chapter 5.
in
the first coordination
and
in-plane
poor
or a
The proton lines observed in
water
and
com¬
We expect the steric hindrance to tilt the carbonate ions out of the
plane (see below).
equatorial
species (A)
copper-carbonate
four carbonate
to
of 0.2 MHz is
isotropic coupling
speciation
The presence of these
calculations (section
4.3.6).
ligands
at
6.4 Discussion
The well defined EPR parameters
in the
water/hydroxyl ligands
structured
layer
well
as
13
experiments.
2+
ligands
dominantly
monodentate. For this conclusion
experiment
are
important
13
a
beled.
Although
based
the
on
show the
C data
similarity
same
complexation
of
carbonate
complexation
HYSCORE
ridges.
spectrum into the
Figure
orthorhombicity
(-+) quadrant
MHz and centered at A 12
84). Experimentally
Species (C).
observed
trapped
paramagnetic species
Figure
6-3.
6-13
an
with
in
m
the surface
found
layer is
the results of the Ca
pre¬
C03(vat)
CaC03(calc) experiment we
estimate,
of the
the bidentate
largest
where the
peaks
of
a
program
are
the
~
copper-carbonate
coupling
5. Simulation of the
as
the
13
C
expected
two-pulse
coupling
to be
shape
of the
=
(Table 5-3
Q
a
strongly
separated by 2vc
A 12 value of
(C) found after 24 hours
EPR spectrum
is
matrix shifts the
ESEEM data
5.9 MHz and
from the
correspond-
coupling
is reflected in the
component of the
splitting
find
chapter
coupling
species
vaterite.
one on
our
on
we
as
where the carbonate lattice is unla-
showing
4.5 MHz, based
They
signal
concluded that this
-
6
on
4 MHz.
at 130 K was
arised either from small clusters
in the bulk of the solid with strong
or
from structure-bound Cu
have to be revised
Lowering
spectrum with
couplings
Nassrallah-Aboukais et al. in their studies of the vaterite-calcite
by
interpretations
~
isotropic
The
transformation [66,67].
of copper ions
possible
Close to g^ the
Q
Both
than the
two-pulse ESEEM spectra
orthorhombic. The
initial dissolu¬
EPR and proton spectra, that the calcite surface
me
a
be concluded that the coordination
especially
available for the
are
HYSCORE spectra is not
already
only
C
confirm the EPR parameters obtained for the bidentate
simulation of the
page
are
can
12
no
bound in
bidentate coordination to the vaterite surface cannot be
as a
The HYSCORE spectra in
ing
it
C02:Ca C03(vat) experiment
13
are
observed at the initial stage
ions both to the surface and to the other carbonates
excluded from
13
C02:Ca C03(vat) experiment. Large
intensity
coordinated
and/or the carbonate ions present in the
experiments
From their weak
ions
by rapid
12
for bidentate coordination of the carbonate
directly
indicate that the Cu
of carbonate ions at the mineral surface formed
copper solution in the
of the Cu
the absence of
as
2+
equatorial plane
tion of the vaterite in both types of
of the
127
as
can
2+
and
a
between the
g-values (gn < g±).
be inferred from the spectra shown in
the temperature leads to the
unusually high gB value
dipolar coupling
ions with inverted
development
small
AB
"
of
a
very neat copper
value, typical for copper com-
128
6 Interactions of Cu2+with Solid Calcium Carbonates
plexes
in an
octahedral environment with
observed
was
by
Rivaro et al
carbonate [127] The
lattice has
nearly
field of
crystal
Only coupling
field
crystal
can remove
axes
isotropic signal with glso
forwarded the
explanation
50 K At 1 2 K
It
is
=
is
in
removed
the small
by
leading
(Figure 4-1
(gn
on
2g±)/3
+
among
equivalent
to the value
the calcite lattice
of calcite,
Cu
The 20 K spectrum
incorporated
2+
a Ca
ion in
forming
a
trigonal
tetragonal
to
51)
page
for
an
Jahn-Teller
The glso
=
axis
at
or
distortion
[20])
the calcite
orbitals
e
along
the
c-
For
a
small
may jump between the three
higher temperatures yielding
distorted Jahn-Teller
an
Coffman
interconversion
configurations
isotropic spectrum for Cu
is
into the
rhombic distortions of
distortion
sufficiently rapid
equivalent
anisotropic behavior
by tunneling
equal
to
degeneracy (Jahn-Teller
for the appearance of
spectrum Species (C)
rated
the
tunneling
highly
between
tortion axis or
hire
a
[126]
substituted for
ion
2+
in
as
MgO above
observed for this system
obvious that the behavior of the spectra
conversion
100 K
is not
lattice vibrations
to
octahedral
equivalent
another
Cu
assigned
2+
deformation of the complex, the distortion
resulting
[128]
study
a
distortion
of the interaction between trace metals and
octahedral symmetry (cf section 4 2 1) which leaves the two
degenerate This degeneracy
axis
trigonal
carbonates (marine mussel shells) and
biogemc
the
their
in
in
Figure
configurations,
6-3
can
either
be
explained by
by hopping
inter¬
of the dis¬
2 247 value found for the isotropic species above
calculated from the g9 and g±_ parameters of the low temperacan
dunng
thus be
unambiguously assigned
the vatente calcite transformation
dilute solid solution,
the very
since
narrow
2+
to Cu
ions
incorpo¬
by recrystallization
or
lines exclude
significant
dipolar broadening
This assignment
further
is
spectra of species (C) which show only
the mineral lattice
can not interact
13
C
matnx
in
the
with the protons
(B) The intensity
newly
equatorial plane,
of the
formed calcite
for the copper
3 The
12
C
13
ions
C ratio
in
a correct
13
12
is
m
be
ESEEM and HYSCORE
The electron spins of
solution The
explained by
to the
analysis
13
a
2+
Cu
ions m
C spectra
are
we
we
given for species
expect
must, however,
13
C
better
mainly dipolar
couplings
keep
in
cou¬
(A) and
reduced due to the isotopic dilution
interpretation
the calcite lattice
the
can
analogy
C matnx line
For
in
in
two-pulse
signals
resolved than those of the surface species and
pling
the
supported by
in
the
mind that
both to carbonate
C02Ca CO/vat) experiment for the whole system is approximately
5 1
6.4 Discussion
ligands
equatorial plane
in the
bonate ions the
so
and at the axial coordination
largest splitting
expected along g]t in
is
that the shoulders observed at gB
equatorial
This
and axial
13
129
For the axial
contributions from
C carbonate nuclei.
of the
qualitative interpretation
13
C spectra of
species (C)
is confirmed
HYSCORE simulations. The HYSCORE spectra obtained for the copper ions
rated into the calcite lattice
both axial and
equatorial
assumed to be very small
dx2_ji orbital,
based
the Cu-0 distance
pared
carbonate
as
the
A,
(section 4.2.1).
(from rCu.c
we
by
the
incorpo¬
include the contributions of
isotropic coupling
electron is
of the axial
expected to be localized
dipolar coupling
slightly
In the
2.8
=
The
if
of 0.3 MHz
ligand
equatorial plane we
find
a
yields
axial
an
is
larger
than the
one
A
A for
value close to 2
A) which corresponds to a reduction of 15%
isotropic coupling
is
in the metal
smaller than the Ca-O distance of 2.38
but still smaller than the value obtained for the
complexes
as com¬
found for the
copper-carbonate
com¬
in solution.
low temperatures it
2+
stituted for Ca
can
single, clearly resolved
a
2+
from the
13
crystal
hopping
lattice in its
vicinity
of the distortion axis
EPR
mined in the low-field
probably
geometric
ion
region due
to the
are
thus
distorts
only
2+
the
ion.
be deter¬
strong overlapping EPR spectra from species (A)
are
one or two
explanations
are
incorporated
into defect lattice sites where
possible
ions
data obtained
high temperatures
can
at
ions sub-
considerably
very similar to those found for the low-
species (C). Species (D) shows, however,
coordination of
2+
leads to lattice vibrations close to the Cu
at 130 K which means that the
possibly due to the
foreign
parameters for the weak signals of species (D)
temperature spectrum of
already
2+
due to the Jahn-Teller effect. At
The parameters listed in Table 6-1
distortion
highly symmetric.
The
coordination octahedra. The
species (C)
of the Cu
sphere
C spectra at 16 K indicate further that the small Cu
Species (D).
(B).
EPR spectrum for
be concluded that the coordination
ions in the calcite lattice is
located at the centers of the Ca
and
reproduced
ligands.
which is
From the observations of
the
be
unpaired
to the Ca-0 distance. The
surface
plexes
only
can
the EPR data. The
on
Cu-O distance of ~2.3
observed in calcite
car¬
point-dipolar approximation
explained by overlapping
be
can
the
positions.
for this behavior.
a
distortion axis of the
weaker
ligands
static Jahn-Teller
complex
at the axial
is fixed,
positions.
Two
(1) Either the signal arises from copper ions
one or
two carbonate
ligands
are
missing. (2)
6 Interactions of Cu2+ with Solid Calcium Carbonates
130
Or the copper ion is
on
the
that it is located at
means
a
of
point
kink
being incorporated
growth site where three
into the calcite lattice which
four
or
ligands
are
lattice
car¬
bonate ions.
The
two-pulse
ESEEM results allow to
distinguish
The spectrum recorded at the observer field 270 mT for the
13
in the
12
C02:Ca CO^vat) experiment,
low-field ESEEM spectrum of the Cu
cies(C)).
site
shown in
2+
to the
in the calcite lattice
(spe-
complete missing of proton signals makes
The
improbable.
only
Furthermore
tively assign species (D)
13
one
complex
to a
sample
a
coordination at
hyperfine splitting
C
taken after two hours
Figure 6-9, is again very similar
incorporated
ions
possibilities.
between these two
a
surface kink
is observed at gh. We tenta¬
in the calcite lattice with
one or
missing axial
two
ligands.
6.4.3
Interpretation
Mechanistic
In the
preceding paragraphs
face and bulk Cu
2+
we
have related the CW and
pulse
EPR spectra to
sur-
associated with the solid calcium carbonate minerals. For the
species
discussion of the mechanism which lead to the formation of the different
back to the first step of the
adsorption experiment:
species
we
go
the transition of the copper ions from
solution to the mineral surface.
Species
plete
in solution. The AAS data showed that the
at the time the first
large cTthe speciation
cies in solution
the Ca
sample
is taken. For
prior to the
is
is
expected
to
predict
expected to
suspension.
give
rise to
In both
pling
The
are,
com-
a
large
predominantly monodentate.
2+
cases
13
C
whereas in
pH
8.5 upon
the bidentate coordination
coupling
in the cancellation
ions to the carbonate ions
Remnants of the bidentate
13
C
cou¬
however, observed in the initial stage of both vaterite adsorption experiments.
intensity
of these features decreases
explained by adsorption
remaining
13
Cu( C03)2
form in solution at
range. The EPR results show that the coordination of the Cu
the mineral surface is
practically
that the dominant copper spe-
2+
at
is
C02:Ca C03(vat) experiment with the
addition to the carbonate mineral is
C03(vat) experiment Cu( C03)
ligands
a
adsorption
12
calculations in section 4.3
addition of the copper to the vaterite
of carbonate
13
solution
of bidentate
species
in
rapidly.
The
large
13
C
coupling
copper-carbonate species
equilibrium
at the
with the adsorbed copper
can
either be
surface
complexes.
or
by
We favor
6.4 Discussion
explanation
the second
as
it is
supported by the
131
AAS measurement which show
decrease of the copper concentration in solution after the initial
Furthermore, the bidentate coupling
be related to the
can
observed in the room temperature EPR spectrum in
hyperfine coupling
is observed
(cf
and low temperature spectrum in
study freezing
Figure
effects which led to
copper-carbonate complexes
in the
possible
section
equilibrium
in solution
rapid adsorption process.
tumbling
pH
room
no
copper
temperature
demonstrates that in the present
shifts in the
not relevant
are
CaC03-water suspension.
clearly
and
complex
copper
Figure 6-5, although
5.4.2). The similarity of the
6-5 also
slow
a
as
investigation
aggregation
We estimate that the
of the
of solute is not
tumbling species
are
present in pores of the vaterite spherulites.
Species (A) and (B). Species (A)
is the first
complex
to be formed
the addition of the copper solution to the solid mineral and
ously
with the vaterite
in aqueous solution (
calcite surface.
or
During
C02:Ca C03(vat)
product
for calcite is exceeded
by
2+
the Ca
C03(vat) experiments)
crystals
and
C03
CaCOjfcalc) experiment calcite undergoes ripening,
tals grow at the expense of smaller
expense of
vaterite
experiments
face of the
be
unambiguous
place simultaneously
its calcite
(B)
can
by
growth
nucleate and grow
2-
a
the EPR spectra
explained
either
or
by
a
by
process
planar
or
in the
a
amount
during
the
more
the
solubility
as
sol¬
which
large
crys¬
of species (B) at the
the first few hours of the
species (B)
the
at
sur¬
transformation from (A) to (B) at the vaterite
distinction between the different processes which may also
possible
is not
and dissolution [80]. A
with
our
data. It is well known that Cu
probable explanation
2+
for the increase of
dissolving
dissolution is blocked due to the different structure of the
and/or
during
the formation of
is then the accumulation at steps and kinks of the
plexes
unambigu¬
concentrations in solution. In the
[2]. The increase in
ones
newly precipitated calcite
surface. An
take
species (A)
revealed
be associated
after
the transformation of vaterite to calcite
and Ca
uble vaterite dissolves and less soluble calcite
can
immediately
vaterite
species
crystals
square-planar
inhib¬
copper
where
com¬
formation at similar structures of the calcite surface where the square-
square-pyramidal complexes
inhibit
CaCOs(calc) experiment probably
found that also in
experiments
copper concentration
crystal growth. Species (B)
due to the small copper concentration. We
with vaterite the formation of
vs. amount
is not observed
(B) depends
on
of solid calcium carbonate. If the number of
dissolution sites at the mineral surface
largely
2+
exceeds the number of Cu
the ratio
growth and
ions
capable
132
6 Interactions of Cu2+ with Solid Calcium Carbonates
blocking
the
growth
copper ions
are
buried in the
of
The transformation
formation with
etal.
our
experimental
increasing
is then also
expected
observations. A
copper concentrations
was
to take
delay of the
observed
can
place
and the
accumulate.
more
rapidly
vaterite-calcite trans¬
by Nassrallah-Aboukais
[66,67].
Information about
Cu
crystal
precipitation proceeds rapidly
lattice before large amounts of (B)
recrystallization
or
which is in line with
sites die dissolution and
2+
the formation of
during
ions
obtained from the
and the free
opened
ligand exchange
13
C
two-pulse
equatorial
processes in the first coordination
species (A)
complexes is
from solution copper
ESEEM spectra. The bidentate carbonate
coordination sites
vaterite surface. Driving forces for this ring
several monodentate surface ions, the
are
occupied by
opening
nucleophilic
are
carbonate
possibly
nature of
of the
sphere
rings
ligands
are
at
the
the chelate effect of
the surface
hydroxyl
ions
and the cumbersome geometry of the bidentate coordination. In experiments with low cT
in solution
(Co C03(vat)
stitution of water
13
In the
the
ligands by
C02:Ca C03(vat) experiment
is weak
larger influence of
be
sphere
upon
of
adsorption from
substituted
exchange
by
13
13
C carbonate
ligands
observed in the
region
ligands
replaced
on
ligands
where
13
C-labeled
not
sub¬
the
adsorption
13
be answered
ligands
unexpected
from
as
a
exchange
surrounding
surface
can
in the first coordination
ligands
12
C02:Ca C03(vat) expericomplexes
are
completely
unambiguously
as a
expected
intensity
rapid
to take
of the
13
layer
out
or
experiment prior
amounts of the unlabeled vaterite. This
C-
of the unlabeled carbonate
of solution. Such
the carbonate ions at the surface and die solution
labeled species in tiiis initial stage of the
of
expect the
the spectra. This
reaction. The increase in
an
early stage
we
the bidentate carbonate
of the solution
can not
observed after 30 minutes indicates
important
signal
in the gh
solution. The question whether in the
C-labeled carbonate
unlabeled carbonate ions
exchange is
mainly
C
between labeled and unlabeled carbonates at the surface is
ligands by
an
coordinated
copper ions which have
place simultaneously with
peaks
13
the presence of unlabeled carbonate
species (A)
ment the initial
the
(cf. Figure 6-10), especially
directly
explained by
adsorption reaction also involves
the
surface carbonate groups.
12
experiment
only
CaC03(calc))
and
assumption
is
are
to the dissolution of
supported by
the
spectra in the g± region which arise mainly from matrix carbonates and which do
13
C
not
6.4 Discussion
change considerably
13
beginning
The
on as
only
following
reflected in the
13
within the first three hours. In the Ca
signals arising from monodentate
C
labeled carbonate
reaction
two-pulse
in
however,
seem
of species
expected
13
a
ligands
region, pointing
C02:Ca C03(vat) experiment.
mainly
and
the
on
excess
a
of
C03
is formed
13
C
C
ate
complexes
bulk
13
C
-
couplings
is
signal
intensity
C carbonate
for the two
ligand
species,
hint to the association
a
in solution.
2+
or
recry stallization of the calcite the Cu
species (C).
From the EPR spectra it
is related to structural disorder in the
disappears upon recry stallization
by
is not
of the
early stages of the experiment calcite is
2-
can
ions
calcite bulk
be inferred that
these defect centers may be
by species (B).
in addition to
The
13
C
when
(D)
pulse
responsible
to
the
phase.
cal¬
The strain intro¬
for the accumulation of
of
blocking
growth and
EPR spectra do not reveal other intermedi¬
from the surface
going
freshly precipitated
of the mineral
(D) during the first hours of the experiments in analogy
dissolution sites
species (B)
intermediate step in the vaterite-calcite transformation. The
as an
species (D)
duced into the lattice
12
continued
13
to
further increase in
a
The
in the
13
observed from the
are
dissolving carbonate mineral and incorporated into the
which leads to the formation of
cite nuclei which
as
(D). Upon formation
detached from the
appearance of
to
intense
present in the system.
step namely the shift from species (A)
(B) with newly formed calcite
species (D)
are
12
to grow
C03(vat) experiment
complexation
to be identical. The increase of the
Species (C)
are
carbonate
ESEEM spectra except for
C spectra observed in the
g||
exchange
133
species (A)
and (B) to the
species (C).
6.4.4
In this
paragraph
nistic model for the
complexes given
In the
13
Cu(C03)2
2-
C02:Ca
the results of the
adsorption
Results
preceding
process is
section
compared
are
to the
summarized. The mecha¬
predictions
for the surface
12
pH
CO ^ vat)
9
as
experiment
predicted by
the dominant
the
speciation
species
in solution and at the
calculations
2+
are
Ca
,
HC03,
-
,
>CaC03
Cu(C03)2
species (A)
Experimental
in section 4.3.6.
vaterite surface at
tion of
of the
Summary
with
2-
and
solution
>C03
.
This situation is illustrated in
complexes into
opening of the bidentate
the surface
layer leads
coordination and
Figure
to
6-15a.
Adsorp-
the formation of the
partial ligand exchange. The
134
6 Interactions of Cu2+ with Solid Calcium Carbonates
crcfcA-o
(solution)
hco,
3
o
o
HCO,"
3
2+
Ca2+
NcK
NC
cu2+
^C
ca2+
^ry
Cu2+
060606060
A, Ca+A> ca+cA Ca+oAca+cACa+
(vaterite lattice)
HCO3-
(solution)
HCO
'3
OO
^C
°
O
O
Cu2+
O
^cy
°
O
o
o
NC
°
O
o
C:
NC
>-0
O
o
A>CaV^CaVVaVVfcfT
Ca+A>Ca+oA
(vaterite lattice)
(solution)
HCO3"
2-
Cu(C03)2'
ua
O^
O
CI
\:'
O^O
O
^T
^C'
O
-
Ca2+
O
^c'
oo6o°o0o°o
i.
Y Cu2+
6
0
^
o
jt
Ca+
Ca+
jt
Cu2+ i.
°^^
A>Ca+oA Ca+co32cu-co32(calcite lattice)
Fig.
6-15 Illustration of the interactions between Cu
and carbonate
carbonate surface for the different stages of the
(A) by adsorption of Cu(C03)2
leads to the formation of
crystal growth
species (B)
adsorption
at
into the surface
square-planar species (B)
of calcite with
incorporation
ligand sphere
in solution and at the calcium
Formation of the surface
layer, (b)
kink and step sites,
into the
crystal
bonding of the surface carbonates
as
isotropic
compared
C
to
(c) Nucleation and
lattice. The formation of
drawing.
nearly complete
13
species
Dissolution of vaterite
removal of the copper from
of the isolated surface copper ions consists
odentate carbonate ions. The small
constraints in the
a
at
of Cu
the calcite surface is included in the
process is fast and leads to
solution. The
to sterical
complexes
ions
experiment, (a)
coupling
the
equatorial complex plane.
constants
bonding
mainly
mon-
suggest weaker
in solution,
The shift from
of
probably
species (A)
to
due
(B) is
6.4 Discussion
explained by
plexes
accumulation of the
an
precipitation
of calcite is blocked
mation goes
the copper ions
and
a
on
from the
C
good agreement
(Figure
are
locally.
6-15b and c). As the vaterite-calcite transfor¬
incorporated
with the
given in Appendix
predictions
an
8.5
we
are
more
expected
we
copper ions to be
are
based
and
be Ca
to
the
high
,
by
[78,81]
layers
face
occupied by
are
the strong
and where
[16,83].
con¬
constant
present situation.
constant for the
reproduces
the
experi¬
water or
one or
two
of
an
species
in solution at
At the surface there is
by
>CaC03"
equatorial
hydroxyl ligands
and
a excess
of
>C03Ca+. For
coordination sites of the
which is not the
speciation
case.
In this
calculations which
ordered, cystalline surface. The presence of protons in
spheres
of the surface copper ions is, however,
2vH peak in the four-pulse ESEEM spectra in Figure 6-14.
ions for the
they
thick surface
.
thus in bad agreement with the
assumption
The
to the
the dominant
counterbalanced however
Our results support thus the concept of
hydroxyl
apply
not
composite complexation
HC03~ and Cu(C03)
the second and third coordination
revealed
in
single monodentate carbonate coor¬
a
obviously
a
are
for the
complexation
coordination number and
would expect at least
the results
on
which does
12
C02:Ca C03(vat) experiment
CaC03(calc) experiments
>C03" species,
these conditions
experiment
distances calculated
accurately.
C03(vat)
and
>CaOH2
analogy
that reflects the
complex
13
C. This constant is derived from
have therefore derived
pH
geometric
calculated with the
complexes,
In section 4.3.6
In Ca
species into the calcite lattice
isolated
speciation calculations, except
of the
dination in solution,
13
as
The results for the
centration of the copper surface
mental data
com¬
copper
hyperfine parameters suggest that the Jahn-Teller elongated copper ions dis-
tort the calcite lattice
surface
square-pyramidal
or
solid solution is formed. The
CUjCa^CO^s)
13
square-planar
surface sites where the dissolution of vaterite and the simultaneous
exposed
at
135
CaC03
are
layer
surface into which the Cu
predominantly
is
expected
uniformity
parameters of the two surface
thin surface
a
bound
by
species
binding
ions
sphere to
a
sites
explains
(A) and (B). However,
surface
layer
strongly adsorbed
are
some extent
one
pulse EPR probes only the close environment of the copper ions.
the copper coordination
of carbonate and
layer
carbonate ions. A
to be structured to
of the metal
2+
is based
on
one or two mono¬
by
the mineral
sur¬
the well denned EPR
should not
The
forget
that
extrapolation from
chemical considerations.
136
6 Interactions of Cu2+ with Solid Calcium Caibonates
6.4.5
Application
In this
sition
metal
results
our
study
we
to other Metal Ions
have used Cu
we must estimate in
In section 4 2
probe
high reusability
COy
2
are
ions
+
for carbonate
and Ca
small [64]
integration
into
Ionic
are
radii,
a
by
and
lattices
the
summarized for
the
complexation
and
a
ions
,
carbonate
)b
logK
show
in
,
Ni
2+
for
and Zn
[81]
constants
and
ions
(C032 )b
AH
(kJ/mol)c
Ca2+
Mg2+
72
1 0
3
Mn2+
83
195
4 10
-1841
Fe2+
78
2 17
4 73
-1946
Co2+
74 5
22
441
1996
N,2+
69
2 22
4 83
2105
Cu2+
73
22
6 73
-2100
Zn2+
74
22
48
2046
Cd2+
95
2
4 35
1807
spin
configuration
from
[130]
to an
ions
complexation
and 6 fold octahedral coordination
-1577
1921
[21 129]
and
2+
ions
32
high
lesser
HC03
1 1
given for
radii
the affinities of the
constants
2+
on
misci
same is true to a
are
of
with
ionic
complete
energies of the
number of metal
selection of Me
logK (HC03
g
like Co
high hydration
a
e
similar The
our
metal radii
ionic
MexCa(1 x)C03(s)
general discussion
in a
in
are
CdC03
tran¬
specific properties
the
100
b taken from [5] and [60]
c
by
bicarbonate
Kprn)a
ion
influenced
the reluctance of
for
general
between
conclusions from
formed if the differences
CaC03
reflected
explained
h> dration enthalpies
Metal
are
crystal
the calcite lattice
Table 6 3 these values
Table 6-3
hgands,
are
interaction
carbonates Solid solutions
Other important factors
[6] Zachara et al
investigate the
To derive
noted the influence of the
already
MeC03(s)
the properties of the two
extent for Mn
metal
have
between Me
between the two cations
bility
to
how far the results
we
the structures of the solid
as
probe
as
and solid calcium carbonates
ions
In
6.4 Discussion
Our results show that the Cu
although
surface
The
equilibrium
complexation
hydration
the
2+
ions
rapidly dehydrated
are
form at the mineral
observed.
Although
the Cu
into the calcite lattice
2+
and Ni
2+
.
surface, is in line with the values of the other metal
ion is small
resulting
Zn
copper-carbonate coordination, the dominant
ions. Bidentate carbonate coordination for which Cu
2+
at the calcium carbonate
highest together with
energy is among the
constant for monodentate
137
as
or
Zn
shows the
2+
compared
in the formation of
observed for other ions like Co
2+
a
which
[83,85]. Differentiation between the cations based
to Ca
,
highest affinity
the metal is
is not
integrated
solid-solution. A similar behavior is
only slightly larger
are
on
than Cu
the properties in Table 6-3 is thus
difficult.
So far
we
configurations
have not included the electronic
erties of the metal ions in the discussion. For Cu
for the
integration
into the calcite lattice has
Teller distorted Cu
ing
in
badly
into the
2+
crystal growth
regular
mainly geometrical reasons.
larger
octahedral is
a
key
adsorption
ligands
properties
and
Complexation
geometries
high-spin configurations
2+
common.
assumes a
Zn
in
at
Cu
2+
result¬
square-pyramidal
evidence for
or
Zn
by
to some extent via
the coordinative bond¬
to be influenced
considerably by
to Cu
2+
the
are
perfect geometries in octahedral
observed and coordination numbers
2+
compounds
generally prefers
distortion of the
2+
Me06
octahedra
complexes
[131]
2+
2+
(see
6
2+
et al.
(C03)2 with Me
<
where Cd
tetrahedral
ligands, including OH" [130]. Rosenberg
trigonal
into the
kinks and step sites with well defined
of transition metal dolomites CaMe
to a
integration
of the cations.
coordination number of six and Co
instability
ion
proceed
often shows tetrahedral coordination in
with monodentate anionic
,
analogy
can
and is favored
For several metal ions in Table 6-3 distortions from
Ni
or
spectroscopic
foreign
layer
configurations [85] is, however, expected
coordination
lated the
planar
the
on
factor in the control of
into the thin surface
several surface carbonates.
structural
are
The small Jahn-
coordination octahedra of Ca
and dissolution. Based
structural rearrangement of the surface
to
have concluded that the reluctance
suggest that the formation of complexes with coordination geometries other
we
calcite lattice. The
ing
and the coordination prop-
and steps of the mineral surface. This leads to the inhibition of cal¬
at kinks
cium carbonate
than
ions fit
we
distortion of the lattice and the formation of square
a
complexes
Cu
2+
2+
=
Fe
also
corre-
,
[64]
Co
2+
for
,
a
6 Interactions of Cu2+ with Solid Calcium Carbonates
138
comparison of the Me06 octahedra dimensions).
octahedra, e.g., is the rule rather than the
In many minerals distortion of the
exception
Fe06
and is also attributed to the Jahn-
Teller effect [129].
We suggest that not the
tural distortions
incorporation
are
they
although strongly
e.g.),
,
responsible for the
into the calcite lattice
concluded that,
than Mn
adsorption
2+
of Co
,
2+
and Zn
in
a
to
high hydration energies,
In his
[132]
»
investigation
the
set up
Zn
2+
>
Co
>
strong inhibition
metal ions,
layer
on
Ni
2+
2+
.
we
impurities
as
on
the
Mn
2+
growth
which shows
explained by
(kinks) by
crystal faces
resulting
the different sizes and
2+
Reeder found, however, that for Zn
actions have to be considered, which
,
'poorly
Based
on
also bound
are
is not due
kinks and steps.
at
Meyer
who
explained
the cations. For
2+
with Ca
,
affinities
to an
These
The differences between Cu
are
quite large
2+
2+
and Ca
for the
step-specific
the surface sites.
specific
present' [85].
surface
properties
which makes it difficult to discuss the
copper-carbonate complexes
ions may also be bound in
species
as
a
ion-site inter¬
Our results sug¬
'precipitation agents'
account
listed in Table 6-3,
precipitation and
on our
highly
suggest however that Ca
layer supporting
high pH.
finally,
dissolution kinet¬
results. The observation of
at the calcite surface
carbonate surface
at
unequal
incorporation into calcite.
ics of solid calcium carbonate minerals, based
coordinated
the
number of
varying
leading
[77,85].
a
gest that specific coordination properties and geometries of the metal ions may
for these factors in the control of trace-metal
Meyer
2+
geometries of
known at
until
the strong
of the other metal ions: Fe
e.g., additional factors like
are
strongly
more
rate of calcite
have been observed,
solid solution
to an
Zachara et al.
desorbability
growth
high miscibility
a
and Zn
hydrated complexes
complexes
efficiency
struc-
2+
[81].
is absorbed
Our results support the conclusion of
sites
2+
propose that the cations
series for the inhibition
of the
Ni
,
recrystallization.
but the formation of distorted
distribution of the metal ions in the
were
calcite
on
for coordination sites at different
preferences
calcite (Zn
2+
2+
2+
Cd
at the mineral surface and that their
by blocking
including
on
and
to Mn
the calcite surface
of the influence of
following
2+
adsorbed
2+
into the calcite lattice upon
Ni
carbonate surface
compared
mainly
in Table 6-3 but
observed reluctance of Co
as
persist
these ions
incorporated
are
physico-chemical properties
the
theory
of
CaC03
6.5 Conclusions
139
Conclusions
6.5
In
detailed CW and
a
2+
metal ion Cu
gated. During
various
EPR
pulse
analysis
the interactions between the transition
and the solid calcium carbonates vaterite and calcite have been investi¬
the transformation of vaterite to calcite and the
copper-carbonate complexes
are
observed which
steps in the transformation process: a) strong adsorption
mation of
bonate surface
exposed
coordinated monodentate
in
layer; b) accumulation of square-planar
or
lattice sites of vaterite and the
newly
growth processes; c) incorporation
per ions exhibit
a
based
on
a
assigned
surface with for¬
pling
constant observed for the surface
carbonate solution
13
complexes
effect. These
13
incorporation
of Cu
2+
adsorption
into the
a
responsible
also
Fe
apply
,
Co
to
,
explain
Ni
as
compared
.
to
assignments
was
found for
isotropic
13
C
cou¬
monodentate copper-
sterical constraints. Simulations of the
complexes.
of copper ions at calcium carbonate surface sites and
crystal
leads to considerable distortions of the
foreign
crystal
lat¬
ion. We conclude that these distortions
for the inhibition of calcium carbonate
the presence of Cu
crystal
C (enriched) and
detailed structural characterization of the
tice in the immediate environment of the
are
surface. The smaller
complexes
explained by
are
C HYSCORE spectra allow for
Our results show that
at the
at
into the calcite lattice where the cop¬
proton nuclei from carbonate and water/hydroxyl ligands. No evidence
ligands
car¬
square-pyramidal complexes
hyperfine couplings to neighboring
bidentate coordination to carbonate
different
to
thin, structured calcium
temperature-dependent dynamic Jahn-Teller
EPR parameters and
be
of calcite
formed calcite due to inhibition of
dissolution and
are
can
to the mineral
complexes
highly
recrystallization
Similar mechanisms based
on
crystal growth and
geometrical
dissolution in
considerations should
the inhibition effects observed for other transition metal ions like
and Zn
.
140
6 Interactions of Cu2+ with Solid Calcium Carbonates
Basic Theoretical
appendix a
Concepts
chapter
In this
spin systems
background
in
mathematical concepts
some
pulse
EPR and NMR
5 and 6 is described.
A.l
Spin
itfbf a molecular system
nates of electrons and nuclei can be very
nian
H^p,
over
the
The
resonance
obtained
spin
is
by averaging
coordinates of the
spin Hamiltonian
B0)
spin angular
momentum
can
or
complex.
The
considerably simplified by
the static field
which
for CW and
description
of
and the theoretical
pulse
EPR spectra in
Hamiltonian
complete Hamiltonian
of magnetic
used for the
[32,133,134]
introduced
procedures
of the different simulation
chapters
The
are
commonly
is
space and
spin coordi¬
quantum-mechanical description
the introduction of the
of the full Hamiltonian
over
spin Hamilto¬
the lattice coordinates and
paired electrons.
interaction of the electron
expressed in linear (e.g.
bilinear terms
(e.g. coupling
properties
of the
finite dimension of the Hilbert space for
an
spin
between electron and nuclear
operators and contains
be related to the
including
a
few
phenomenological
spin system (e.g.
electron
spin
S
nuclear ga
coupled
to
n
with
spins)
of
constants
factors).
nuclear
The
spins Iv
I2,..., /„is given by
«
dHS
The
=
(25+l)f[(2/,+
spin quantum
(A.1)
l)
number S reflects either the true electron
spin
for systems where
142
the contributions of orbital
radicals)
earth
or an
with
ions
A.2
angular momentum
effective spin of
a
subsystem
large spin-orbit coupling,
ground
state are small
with 25 +1 states
(e
(e g organic
ground
g
state of rare
chapter 2)
Density Operator Formalism
In the
terized
density operator formalism the
by
The
density operator
a
description
of spin
dynamics
density operator
dimension
^hs^hs
tions of the
'n
in
a is a
me
pulse
EPR and NMR
an
ensemble of spins
density operator
can
be
of
^
can
whereas
facilitate the
represented by
eigenbasis of J^. the diagonal elements
corresponding eigenstate
charac¬
is
considerably [133]
hermitian operator and
(single-quantum coherence)
iM
actual state of
The properties of this
a
superpositions of eigenstates which
Mx±
cf
to the
off-diagonal
of a
matrix
the
are
elements
a
are
of
popula¬
coherent
be related to the transverse magnetization
The time evolution of the system
is
given
by
the
Liouville-von-Neumann equation
g
For
MW
a
=
-iWsp,0(t)]
time-independent
pulses),
(A 2)
Hamiltonian (e g undisturbed spin system
integration of the Liouville-von-Neumann equation
o(0
=
yields
in
the absence of
the solution
e~"*"c(0) e'H"
(A3)
With this equation the evolution of the spin system under different Hamiltonians and
for different time intervals
nient for the theoretical
t can
be calculated
descnption
The expectation value of
an
of
in
subsequent steps
which
is
very
complex pulse expenments
arbitrary
observable operator P
is
found
by evaluating
the trace of the product of the observable operator P with the density operator
<P>
The
=
descnption
Tr{Pa(t)}
of
pulse
conve¬
EPR experiments
a
(A 4)
can
be
highly formalized by
expressing
143
the
density operator
and the Hamiltonian
by products
and the unit operator. In this formalism
Sy, Sz
e.g., while the operators
Sx
spin operators 5X,
equilibrium magnetization
contribute to the observable
S
or
of the cartesian
is written
magnetization
as
Sz,
in the xy-
plane.
A.3
Calculation of CW and Pulse EPR
From the
obtained
by
cally
can
this
spin Hamiltonian
the energy level scheme and thus the EPR spectrum is
determination of the
be
iltonian matrix
eigenvalues
Mathemati¬
performed either by analytical or numerical diagonalization
of the Ham¬
by application
or
spin systems
above. Numerical
systems. In that
in the
spin
interactions
the
of perturbation
like the S
diagonalization
case
important
it is
separately
if
they
In this
these terms and treat the
The simulation of
four-pulse
derived
1/2
is
always possible
to
using
case or
by
spin
based
1/2, /
=
is determined
on
diagonalize
as
small
experiments, given
1/2 system discussed
energies
can
on
magnitude.
mainly by
large spin
of the terms involved
be obtained
the
by treating
In most
large
EZI
cases
or
the
the Hamiltonian with respect to
perturbations.
second order
in
=
only possible
but may be tedious for
simplifications
EPR spectra is based
density operator
be handled is
at least two orders of
it is useful to
are
the S
can
consider the relative
remaining interactions
pulse
ESEEM
the
differ
case
CW EPR spectra in this thesis
and
=
axis of the electron
splitting.
theory [18,19].
to results which
Hamiltonian since considerable
quantization
zero-field
and transition
probabilities.
Analytical diagonalization leading
for small
Spectra
All simulations of
perturbation formulae [95,120].
the
Appendix
analytical formulae
for two-,
B. These formulae have been
formalism outlined in the
preceding
section [30,36].
144
Analytical ESEEM
appendix b
Formulae
In this
appendix
formulae for the electron
are
given
for
S
an
=
analytical two-pulse, three-pulse
the
spin
1/2, /
=
echo
intensity
as a
2.
B.l
Two-Pulse ESEEM Formula
=
1-7
k
2
From these formulae it
T|
=
0° and thus
no
coupling).
values close to 0
cos(2jtv+x)
+
cos(2jcv_ t)],
(ViB \2
2
=
can
H—
be
seen
(B-2)
•
that the modulation
ESEEM effect is observed for
This leads to
or
exact cancellation.
found in
(B.l)
depth given by
isotropic coupling.
In
tems zero modulation is further obtained at the canonical orientations
axial
are
depth parameter
4sin r|cos T|
=
function of the different time intervals
[2-2cos(2jtvaT)-2cos(2jtvp-c)
+
with the modulation
four-pulse ESEEM
1/2 system. The definitions of the parameters
Chapter
E{x)
and
a
considerable distortion of the
90°. Maximum modulation
depth
with k
=
powder
k is
zero
anisotropic
(9
=
Une
sys¬
0/90° for
shapes
1 is obtained for r|
=
for
an
for 9
45° at
146
Three-Pulse ESEEM Formula
B.2
E(tx,z)
=
i-| [[l-ooB(2«vaT)] [l-cos(2jcvp[T
+
The modulation
fundamental
only
[1
n
=
frequencies
and [1
cos(2jtvai:)]
-
depth parameter
-
[1
k is defined
as
observed.
are
cos(2jtvoT)]
[1
cos(2;tvpT)]
-
cos(2jtva[t + fj])]
Eq. (B.2).
in
Due
blind spots
-
are
to
In
the
J.
three-pulse ESEEM
amplitude
observed for
x
factors
with
=
va/p
0, 1, 2,...
B.3
(B.3)
f1])]
+
Four-Pulse ESEEM Formula
£(T, tv t2)
=
1
-
k-
(E, + EIIa
+
Em
+
Ema
+
EllIb),
with the contributions from five different coherence transfer
E[
C0(T)
=
=
EUa
=
Em
=
EUla
=
pathways given by
3-cos(2ltvat)-cos(2jtvot)
-sin
2
2
t|cos(2jiv+t)-cos T|cos(2jtv.T),
Ca(T)cos[2jtva(f2
+
-c/2)]+
Cp(T)cos[2jtvp(/2 + -t/2)],
Ca(i)cos[2Jtva(/,+-c/2)]+ CpOtJcos^jcvp^+T/^)],
Cc(T)coS2Tl(C0S[2jt(var1+Vpf2
+cos[2jc(vp/j
+
V+t/2)]
+vat2
+
(B.4)
v+l/2)]),
147
Enib
-Cc(T)sin2Ti(cos[27t(vaf1-vpf2
=
v.T/2)]
+
+cos[2jt(vpf1-va/2-v+-u/2)]),
with the coefficients
Ca(x)
=
cos2ti
cos[2^vpT-^J
+sin T|cos
Cp(T)
COS2T]
=
The
general
important
to
sequence the
-2
=
tion
given
in
chapter
J
-
27t(vaT -2-j
+
simplified
for the
notice that in this formulae the
labelling
-2-
8in[2ii^| sin[27t(^J
formula is
the weak to the strong
+
cos|2jt[-|-J
-
cos|2jt[-£- j]
coupling
case
sum-peak experiment by setting t,
angle T)
is defined
as
allowed transition is
0°
<
r|
<
=
90°. As
t2. It is
a con¬
changes when going from
with exact cancellation at T|
intensity of the
,
.
of the allowed and forbidden transitions
2 the
,
C0s[~2jl(vaT--|-J
+sin rjcos
Cc(t)
2jt(vpt
(B.5)
=
45°. With the
always given by
conven-
2
cos
T|.
148
Equilibrium
appendix c
Calculations
C.l
Equilibrium
Constants
In Tables CI and C2 of this
calculations in aqueous solution
from Smith et al.
and /
umn.
=
[60]
appendix
the
presented
in
Davies formula
The
a
given
in solution are formulated
-
HC03
or
C03
2-
+
,
and H
ChemEQL [25]
in
.
The
K4
and
tabulated for ionic
strength
ionic
as
Appendix
C.2
K3
In Table C3
are
intrinsic
1.
complexation
of
H2C03
logK
the components
phase (vaterite) and
H2C03
=
constants for calcium
constants for surface
using
complexation
with
strengths /
=
0M
calculated using the
=
species using
written in bold. As
*(i)
the compo-
an
example
which is obtained
equilibria
CaC03(s),
C02(aq)
3.8. At 25 °C
+
only
complexes
are
given
>CaOH
the neutral surface
constants are taken from Van
K
=K
[HC03][H+] [C023][H+]
complexation
formulated
sent the solid
taken
are
used to set up the EXCEL matrices
[HCO\]
[H2CQ3]
[C02-][H+]2
are
speciation
the index in the last col¬
are
formation of
=
ria
given.
The values
by
we
com¬
K5:
[H2CQ3]
intrinsic
constants for the
according to
equations
write down the formation constant
bination of
are
[1].
for the program
explicitly
are
numbered
are
M, the activities for
equilibria
2+
nents Cu
,
chapter 4
and Palmer et al. [13] and
1 M and 25 °C. The AT-values
For / < 0.5
complexation
,
=
1016.68
in solution
as
for / = 0 M. The
and
>C03H
well
equilib¬
which repre¬
complexes, respectively.
Cappellen
et al.
H2C03, HjCOj being
the true carbonic acid with
C02 is present
as
H2C03.
The
[6].
0.3% of the dissolved
an
as
acidity
constant
150
logK(at25°C)
1
Table CI: The
=
C032"
H20
+
+
0M
1=1M
CO/H20 system.
H20
C02(g)
=
Index
2H+
=
=
HC03+H+
=
C032
=
+H+
OH'
+
H+
H2C03*
H2C03*
H2C03*
HC03
-14
-13.79
1
-1.47
-1.53
2
16.68
15.59
3
6.35
6
4
10.33
9.57
5
6
Cu*/COJH20 system.
Table C2: The
Cu2+ + H20
=CuOH+
Cu2+ + 2H20
=
Cu2+ + 3H20
=
Cu2+ + 4H20
2Cu2+ + 2H20
H+
-7.7
-8.2
Cu(OH)2°
+
2H+
-16.2
-15.2
7
Cu(OH)3'
+
3H+
(-27.5)
-27.5
8
-39.6
-40.4
9
-10.6
-11
10
12.13
10.57
11
1.8
1
12
+
=Cu(OH)42" 4H+
Cu2(OH)22+ + 2H+
+
=
Cu2+ + C032 + H+ =CuHC03+
Cu2+ + HC03"
CuHC03+
=
Cu2+ + C032"
=
CuC030
6.77
5.73
13
Cu2+ + 2C032"
=
Cu(C03)2'
10.2
9.32
14
Cu2+ + 2H+
2Cu2+ + C032 + 2H20
Table C3: The
CaC03(s)/Cu
=
CuO(s)
=
Cu2C03(OH)2(s)
+
2H+
5.8
-
-
15
16
/H20 system.
=
CaC03(s) + H20
=
CaC03(s) + H+
-7.65
2+,
CaC03(s)
Ca2+ + H20
0
=
=
Ca2+ + C032"
-7.9
17
-20.6
18
CaOH+ + H+
-12.7
19
CaHC03+
3.53
20
CaOH+ +
C032"+H+
151
logK(at25°C)
I
Table C3:
=
OM
Index
I=1M
(continued)
Ca2+ + HC03"
=
CaHC03+
1.1
21
CaC03(s)
=
CaC03°
-4.68
22
Ca2+ + C032"
=
CaCO30
3.22
23
=
>CaO'
-17
24
=
>CaOH2+
12.2
25
>CaOH° + C032" + 2H"h=>CaHCO30 + H2O
24
26
>CaOH0+CO32
16
27
>Ca0H°
>CaOH°+H+
+
H+
>C03H°
>CO3H0+CaCO3(s)
>CO3H0+Cu2+
=
=
=
=
For the calcite system the
replaced by A'jg
c= -21.2,
solubility product
H+
>CaC03"
+
H20
-4.9
>C03+H+
>C03Ca+ + C032+ H+ -1110.7
-2
>C03Cu+ + H+
complexation
Kc2l
of calcite
+
°= 3,
Kxl
=
Kc^
-8.48.
constants
of
equations 18, 20,
c- -5.26, and if
23
28
29
30
22 and 29
are
=-11-3, obtained with the
152
C.2
EXCEL
Input Matrices
In Tables C4 to C7 the EXCEL
The
corresponding
Table C4: The
calculations
are
for
input
ChemEQL
matrices for the program ChemEQL
shown in section 4.3.
CO^/H20 system.
C03-
H+
total
free
{logK}
H2C03
2
16 68
HC03-
1
10.33
C03-
0
0
-1
-14
1
0
OHH+
5.00E-02 1.00E-07
Table C5: The Cu
2+/
IH20 system.
Cu++
H+
total
free
{logK}
*
Cu++
1
0
0
CuOH+
1
-1
-7.7
Cu(OH)20
Cu(OH)3-
1
-2
-16.2
1
-3
-27.5
Cu(OH)4Cu2(OH)2-f
1
-4
-39.6
2
-2
-10.6
OH-
0
-1
-14
H+
0
1
0
5.00E-04
1.00E-07
Table C6: The
Cu*IC02m10 system (I
Cu++
CuOH+
Cu(OH)20
Cu(OH)3Cu(OH)4Cu2(OH)2++
CuHC03+
CuCO30
Cu(C03)2-
'
=
1M)
Cu++
C03-
H+
total
tota
free
logK}
1
0
0
0
1
0
-1
-8.2
-15.2
1
0
-2
1
0
-3
-27.5
1
0
-4
-40.4
2
0
-2
1
1
1
10 57
1
1
0
5.73
1
2
0
9.32
H2C03
0
1
2
15.59
HC03-
0
1
1
9.57
C03-
0
r
0
0
OH-
0
0
-1
-13.79
0
0
1
0
H+
5.00E-04 5.00E-02 1.00E-07
-11
are
given.
153
Tkble C7: The
CaCO^s)/Cu
2+,
/H20 system.
hNonsniiiiimqonaoiSNOsoNtiDf
?-i-IM<Oi-1c3'*C0
,-
'
'
,
O
CD
1-
1-
'
t-
*-
•
j
0*-CUCMi-OOOi-0'-0t-CM*-*-i-0'-0t-C\It-t-t-£.
,
.
,
.
.
,
,
'9
til
8
I
t-T-i-CMi-T-T-OOOOOOOOOi-OOOOOOOO
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5
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m
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m
m
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S
O
n
9
in
S
cm
o
o
co
154
References
[I]
Morgan, Aquatic Chemistry (Third Edition), Wiley Inter¬
W. Stumm, and J.J.
science: New York, 1996.
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1
unity
A
hyperfine interaction matrix
matrix
A
secular part of the
hyperfine coupling
axis element of the HFI matrix
\
principal
\
element of the HFI matrix in the
a,so
isotropic hyperfine coupling
Ai
hyperfine coupling
laboratory
frame
constant
constant
parallel
constant
perpendicular
to
the radius vector for
an
axial HFI matrix
A±
hyperfine coupling
for
an
to the radius vector
axial HFI matrix
of the
hyperfine coupling
B
pseudo-secular part
BQ
static
cT
total carbonate concentration
magnetic
field vector
C«T
total copper concentration
D
fine structure/zero-field
g
g interaction matrix
8e
free electron
8n
nuclear
8±
g-value in
Sll
g-value along
h
Planck constant,
H
Hamilton operator
I
nuclear
splitting
tensor
g-value, 2.0023
g-factor
the
xy-plane
for
an
the z-axis for
axial g matrix
an
axial g matrix
6.6260755xl0"34 Js
spin operator
nuclear spin quantum number
x,.y,z-component of the nuclear spin operator
intensity
of
intensity
of
modulation
an
a
allowed EPR transition
forbidden EPR transition
depth parameter
chemical reaction rate
chemical
equilibrium constant
solubility product
quadrupole interaction
radius vector,
tensor
connecting
electron and nucleus
magnetic quantum number of the nuclear spin
magnetic quantum
number of the electron
spin
macroscopic magnetization
magnetization in x.y.z-direction
electron
spin operator
electron
spin quantum
number
x,y,z-component of the electron
dipolar hyperfine coupling
longitudinal relaxation
spin operator
constant
time
transverse relaxation time
phase
memory time
pulse length
Bohr magneton, 9.2740154x10
nuclear magneton,
one
half of the
between the nuclear
spin
frequency
and the z-axis of the
axes
g/A
matrix.
frequency
of the transition
microwave
quantization
manifolds
polar angle between B0
nuclear Zeeman
-1
JT
5.0507866xl0"27 JT1
angle
the two electron
-94
(i'|
<->
<j\
frequency
density operator of a spin system
interpulse delays
resonance
offset of the electron
spins
in the
rotating frame
in
Abbreviations
ID
One-Dimensional
2D
Two-Dimensional
AAS
Atomic
AFM
Atomic Force
CF
Crystal-Field
CW
Continuous Wave
DEFENCE
Deadtime Free ESEEM
ENDOR
Electron Nuclear DOuble Resonance
Absorption Spectroscopy
Microscopy
by
Nuclear Coherence-transfer Echoes
EPR
Electron
Paramagnetic
ESEEM
Electron
Spin
EZI
Electron Zeeman Interaction
FID
Free Induction
FT
Fourier Transform
HFI
HyperFine Interaction
HYSCORE
HYperfine
IR
InfraRed
LEED
Low
MW
MicroWave
NMR
Nuclear
Magnetic
NQI
Nuclear
Quadrupole
NZI
Nuclear Zeeman Interaction
PAS
Principal
RF
Radio
Frequency
RT
Room
Temperature
S-band
2-4 GHz
SEM
Scanning
SOC
Spin-Orbit Coupling
Echo
Resonance
Envelope
Modulation
Decay
Sublevel Correlated ESEEM spectroscopy
Energy
Electron Diffraction
Axes
Resonance
Interaction
System
Electron
Microscopy
S/N
Signal-to-Noise
TEM
Transmission Electron
TM
Transition Metal
UV
Ultraviolet
Vis
Visible
ratio
Microscopy
X-band
8-12 GHz
XAS
X-ray Absorption Spectroscopy
XPS
X-ray Photoelectron Spectroscopy
XSW
X-ray Standing Wave
166
Acknowledgement
This thesis could not have been written without the support and encouragement of
many
-
people.
I would like to thank
Prof. Dr. Arthur
between
physical
conditions. The
me
-
-
to grow
both
Dr. Thomas
my
Schweiger and Prof.
and
friendly
on a
environmental
and
chemistry
Wehrli, who agreed to a joint project
and
open-minded atmosphere
scientific and
a
provided
excellent research
in their research groups allowed
human level.
Wacker, who supervised my first steps in the field of pulse EPR.
lab-mates, Dr. Gustavo Sierra and Dr. Michael Wilier, for the warm-hearted
working atmosphere
-
Dr. Bernhard
and the
numerous
discussions about life, EPR and
everything.
Josef Granwehr, Dr. Gustavo Sierra, Dr. Beat H. Meier, Dr. Tilo Levante, Dr. Tobias
Bremi, and Christoph Scheurer for their excellent computer system management.
-
Jorg Forrer,
keep
-
Joe
experience
whose vast
up memories of the
Eisenegger,
days
when
Willi Groth, Rene
allows him to solve any electronic
pulse
EPR
was
problem
and to
still young.
Gunzinger for the
skillful
design
and
building
of the
tiniest mechanical devices.
-
Walter Lammler, Christian Dinkel and Ruth Stierli for their advice and support in
practical laboratory
-
work.
Erwin Pleisch, Andreas Hunkeler and Roland Schmidli for
always providing
the
liquid
168
nitrogen
-
and helium to
keep
my
samples
cool.
Verena Baumann, Konrad Boss, Karl Burkhalter, Walter
Jaggi,
Doris Kaufmann, Bruno
Lambillote, Dr. Erich Meister, Irene Miiller, Marie-Therese Werder, Heinrich Willi for
ensuring
-
the excellent
functioning
of the LPC and
supporting
former and present members of the groups of Prof.
Rainer Bachmann, Josef Granwehr, Dr. Michael
me
in
Schweiger
Hubrich,
numerous
ways.
and Prof. Wehrli: Dr.
Dr. Eric
Hoffmann, Dr.
Gunnar Jeschke, Lorenz Liesum, Dr. Alessandro Ponti, Dr. Rafail Rakhmatoulline, Axel
Sammet, Dr. Jochen Sebbach, Dr. Matthias Schuler, Dr. Jaap Shane, Stefan Stoll, Dr.
Sabine Van Doorslaer and Markus Bott, Dr. Gabriela Friedl, Dr. Martin
Regula Miiller,
-
PD Dr. Andreas
reminded
-
-
-
-
-
Dr. Tobias
Schaller, for their
Gehring,
who
taught
me
friendship, help
Mengis,
Dr.
and advice in all situations.
the art of social
paper-writing
and
always
me
of the fact that science should be fun.
Dr. Peter Weidler for the XRD
analysis
and for
sharing
his vast
Dr. Beat Miiller, the father of
ChemEQl,
for his competent
Prof. Dr. R. Giovanoli for the
fascinating
REM and TEM
geological knowledge.
proof-reading
of
chapter 4.
images.
Erwin Grieder for the AAS measurements.
the Swiss National Science Foundation for their generous financial support.
Finally,
during
I would like to thank my parents for their selfless support and affection
all these years.
Curriculum Vitae
Personal data
Name
Paul Michel Schosseler
Birth
April 3,1969
Nationality
Luxembourg
in Ettelbriick,
Luxembourg
Studies
1993 -1998
applied EPR spectroscopy at ETH Zurich
supervision of Prof. Dr. A. Schweiger and Prof. Dr.
Wehrli (EAWAG)
Ph. D. studies in
under the
B.
Diploma
1992
1988 -1992
physical chemistry
Schweiger
thesis in
Prof. Dr. A.
Studies of
chemistry
in the research group of
at ETH Zurich
Education
1981 -1988
1975
-
1981
Lycee classique
Primary
de Diekirch,
school in
Luxembourg
Diekirch, Luxembourg
170