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Electronic Theses, Treatises and Dissertations
The Graduate School
2010
Multiferroic Metal Organic Frameworks
with Perovskite Architecture
Prashant Jain
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THE FLORIDA STATE UNIVERSITY
COLLEGE OF ARTS AND SCIENCES
MULTIFERROIC METAL ORGANIC FRAMEWORKS WITH PEROVSKITE
ARCHITECTURE
By
PRASHANT JAIN
A Dissertation submitted to the
Department of Chemistry and Biochemistry
in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy
Degree Awarded:
Summer Semester, 2010
The members of the committee approve the dissertation of Prashant
Jain defended on April 15, 2010.
__________________________________
Harold W. Kroto
Professor Directing Dissertation
__________________________________
James Brooks
University Representative
__________________________________
Naresh Dalal
Committee Member
__________________________________
Lei Zhu
Committee Member
Approved:
_____________________________________
Joseph B. Schlenoff, Chair, Department of Chemistry and Biochemistry
The Graduate School has verified and approved the above-named committee members.
ii
ACKNOWLEDGEMENTS
I would like to thank my supervisors Prof. Harry Kroto and Prof. Tony
Cheetham who have supported me throughout this dissertation process.
I am also thankful to Prof. Naresh Dalal who has advised me throughout
this PhD. I would also like to thank Cheetham, Kroto, and Dalal group
members, present and past, with whom I was fortunate to work. In particular, I would like to mention Vasanth Ramachandran, Dr. Steve Acquah, Dr. Crystal Merrill, Dr. Russel K. Feller, Dr. Gautam Gundiah, Dr.
Katherine Page, Dr. Kinson Kam, and Dr. Thirumurugan Alagarsamy. I
am also grateful to various interns who worked with me. I would like to
especially thank Rose who supported me and brought laughter and stability to my life. Finally, I would like to thank my family for all of their
support all these years.
iii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................................................................................ iii
TABLE OF CONTENTS.................................................................................................... iv
LIST OF TABLES ............................................................................................................... ix
LIST OF FIGURES ...............................................................................................................x
ABSTRACT ........................................................................................................................ xiv
CHAPTER 1 .......................................................................................................................... 1
INTRODUCTION ................................................................................................................ 1
1.1 Metal organic frameworks .................................................................................... 1
1.1.1 General introduction ............................................................................................ 1
1.1.2 Open and dense frameworks............................................................................ 3
1.2 Ferroelectrics and multiferroics ......................................................................... 7
1.2.1 Ferroelectric ............................................................................................................ 7
1.2.1.1 Crystallography and ferroelectrics ............................................................ 9
1.2.2 Multiferroic materials....................................................................................... 11
1.2.3 Glossary of terms ................................................................................................ 12
1.3 Ferroelectric metal organic frameworks ..................................................... 14
iv
1.3.1 Rochelle salt, KDP, and triglycine sulfate (TGS). ................................... 14
1.3.2 Ferroelectric MOFs ............................................................................................ 17
1.4 Summary .................................................................................................................... 26
CHAPTER 2 ....................................................................................................................... 28
EXPERIMENTAL TECHNIQUES AND SYNTHESIS ............................................ 28
2.1 Experimental techniques .................................................................................... 28
2.1.1 Single crystal and powder X-ray diffraction ........................................... 28
2.1.1.1 Single crystal X-ray diffraction.................................................................. 28
2.1.1.2 Synchrotron versus laboratory sources for X-ray diffraction ..... 29
2.1.2 Neutron diffraction ............................................................................................ 31
2.1.2
Magnetic
susceptibility
measurements
using
a
SQUID
magnetometer................................................................................................................. 34
2.1.3 Heat capacity measurements ........................................................................ 36
2.1.4 Dielectric properties (capacitance measurements) ............................ 38
2.2 Solvothermal synthesis ....................................................................................... 39
CHAPTER 3 ....................................................................................................................... 42
ORDER – DISORDER PHASE TRANSITION IN [(CH3)2NH2]Zn(HCOO)3 .. 42
3.1 Background............................................................................................................... 42
v
3.2 Synthesis .................................................................................................................... 43
3.3 Structure .................................................................................................................... 45
3.4 Structural phase transition ................................................................................ 46
3.5 Dielectric and heat capacity measurements ............................................... 48
3.6 Summary and conclusions ................................................................................. 51
3.7 Resulting publication and comments ............................................................ 52
CHAPTER 4 ....................................................................................................................... 53
MULTIFERROIC
METAL
ORGANIC
FRAMEWORKS:
[(CH3)2NH2]M(HCOO)3(M=Mn, Ni, Co, & Fe) ...................................................... 53
4.1 Background............................................................................................................... 53
4.2 Synthesis .................................................................................................................... 54
4.3 Crystal growth mechanism ................................................................................ 55
4.4 Structure .................................................................................................................... 57
4.4.1 Crystallographic data for DMAFeF .............................................................. 58
4.5 Magnetic properties of DMAMF ....................................................................... 61
4.5.1 Magnetic susceptibility .................................................................................... 61
4.6 Structural phase transition ................................................................................ 63
4.6.1 Temperature dependent X-ray diffraction data .................................... 63
vi
4.7 Low temperature structure ............................................................................... 64
4.8 Dielectric measurements .................................................................................... 70
4.9 Heat capacity measurements ............................................................................ 74
4.10 Summary and conclusions ............................................................................... 77
4.11 Resulting publications and comments ....................................................... 78
CHAPTER 5 ....................................................................................................................... 79
GLASSY BEHAVIOR OF (CH3)2NH2Zn(HCOO)3 .................................................. 79
5.1 Background............................................................................................................... 79
5.2 Debye law and remnant specific heat............................................................ 80
5.3 NMR measurements.............................................................................................. 82
5.4 Results and discussion ......................................................................................... 84
5.5 Summary and conclusions ................................................................................. 90
5.6 Resulting publications and comments .......................................................... 91
CHAPTER 6 ....................................................................................................................... 92
SUMMARY AND CONCLUSIONS............................................................................... 92
APPENDIX ......................................................................................................................... 95
CRYSTALLOGRAPHIC INFORMATION FILES ..................................................... 95
vii
Dimethylammonium iron formate: ........................................................................ 95
Dimethylammonium zinc formate ....................................................................... 106
Dimethylammonium manganese formate ........................................................ 113
Dimethylammonium nickel formate ................................................................... 123
Low temperature dimethylammonium manganese formate ................... 134
LIST OF REFERENCES .............................................................................................. 144
BIOGRAPHICAL SKETCH .......................................................................................... 160
viii
LIST OF TABLES
Table 1: 32 point groups. Polar point groups have been highlighted in
blue. ..................................................................................................................................... 10
Table 2: Comparison of single crystal and powder diffraction .................. 31
Table 3: Structure parameters for 1 from single crystal X-ray diffraction
at room temperature.................................................................................................... 46
Table 4: Structure parameters for DMAFeF ....................................................... 58
Table 5: Atomic parameters of DMAFeF.............................................................. 59
Table 6: Anisotropic displacement parameters for DMAFeF, in Å2 ......... 59
Table 7: Selected geometric information for DMAFeF .................................. 59
Table 8: Structural parameters for the low temperature polar phase of
DMAMnF ............................................................................................................................ 66
Table 9: Arrhenius parameters for the CH3 protons in DMAZnF in the PE
and FE phases.................................................................................................................. 89
ix
LIST OF FIGURES
Figure 1: MOF-5, a porous cubic zinc terephthalate which is
topologically analogous to ReO3. Gray spheres denote carbon, red
oxygen, and white hydrogen, with ZnO4 tetrahedra in blue. ......................... 4
Figure 2: Schematic representation of coordination polymers and
extended inorganic hybrids; (a) and (b) show 1-D and 2-D coordination
polymers, respectively, while (c) shows a system that has inorganic
connectivity in two dimensions and is connected in the third ..................... 6
Figure 3: Cubic perovskite structure. The small B cation (in black) is at
the center of an octahedron of oxygen anions (in gray). The large A
cations (white) occupy the unit cell corners......................................................... 9
Figure 4: Ferromagnets (ferroelectrics) form a subset of magnetically
(electrically) polarizable materials such as paramagnets and
antiferromagnets (paraelectrics and antiferroelectrics). The intersection
(red hatching) represents materials that are multiferroic. (Adopted from
ref. 17) ................................................................................................................................ 11
Figure 5: Views of the unit cell content of Rochelle salt (paraelectric
phase) (left), KDP (paraelectric phase) (middle) and TGS (ferroelectric
phase) (right) .................................................................................................................. 16
Figure 6: Molecular structure of crystal state of [CoCl3(H-MPPA)] and its
3D packing view along the b axis and electric hysteresis loop recorded
at room temperature (adopted from ref. 116). ................................................... 18
Figure 7: Molecular structure of [Ni3(TBPLA)2( 3-O)](ClO4)4(H2O)5
where water and ClO4− are omitted for clarity117 ........................................... 20
Figure
: Dielectric permittivity εr) of a single crystal of
[Ni3(TBPLA)2( 3-O)](ClO4)4(H2O)5 as a function of temperature upon
application of an electric field approximately parallel to the a (E//a),
b(E//b), and c(E//c) crystal axes directions. The measurements were
made at a high frequency of 1 MHz (adopted from ref. 117)...................... 21
x
Figure 9: A schematic illustration of the molecular structure of
RbI0.82MnII0.20MnIII0.80[FeII(CN)6]0.80 [FeIII(CN)6]0.14·H2O ................................. 22
Figure 10: (a) Crystal structure of [Mn3(HCOO)6](C2H5OH) viewed along
the b-axis: Mn, pink; C, gray; O, blue; H, pale sky blue. The C and O atoms
of guest C2H5OH molecules are shown by open circles. (b) The
arrangement of guest ethanol molecules along the channel ...................... 23
Figure 11: (a) Temperature dependence of the magnetization of
[Mn(HCOO)6](C2H5O( ( =
Oe . b Dielectric constants εr) of
[Mn(HCOO)6](C2H5OH) for the field E//a (blue), b (green), and c (pink).
The red line represents εr (E//a) of the crystal with deuterated ethanol,
[Mn(HCOO)6](C2H5OD).
(c)
The
hysteresis
loop
of
[Mn(HCOO)6](C2H5O(
E//a .
d
The
/εr vs T curve of
[Mn(HCOO)6](C2H5OH). In the dielectric measurements, the relatively
high speed of the temperature change − °/min was adopted to avoid
the escaping of guest molecules .............................................................................. 25
Figure 12: Difference between the relative sizes of the cross-sections
between X-ray and neutron for some elements. .............................................. 33
Figure 13: Scheme of a SQUID magnetometer. ................................................. 35
Figure 14: Cutaway view showing the PPMS -16T magnet and probe.
Inset shows a heat capacity puck............................................................................ 38
Figure 15: Cutaway of a general purpose (high temperature) 23 mL Parr
acid digestion bomb, used in the solvothermal synthesis of all the
compounds described in this dissertation.......................................................... 40
Figure 16: Crystal structure of [(CH3)2NH2]Zn(HCOO)3 , 1. It has the
same architecture as an ABX3 perovskite, with A=(CH3)2NH2+, B=Zn2+
and X=HCOO-. .................................................................................................................. 45
Figure 17: Synchrotron powder patterns collected with a wavelength of
0.608Å at APS: red data obtained at room temperature, black data at
100K. ................................................................................................................................... 48
Figure 18: Dielectric constant of 1 measured as a function of
temperature. .................................................................................................................... 50
xi
Figure 19: Heat capacity of 1 as function of temperature............................ 51
Figure 20: Optical images of [(CH3)2NH2]Mn(HCOO)3. .................................. 55
Figure 21: AFM image of a multiferroic MOF dimethylammonium
manganese formate. Crystals grow layer by layer during the room
temperature crystallization. Growth is perpendicular to the <012>
plane. ................................................................................................................................... 56
Figure 22: Building block of [(CH3)2NH2]Mn(HCOO)3, DMMnF. The DMA
cation (A) is at the center of an ReO3 type cavity, formed by manganese
(B) and formate (X) ions. Nitrogen is disordered over three positions. 57
Figure 23: Temperature dependence of χM of DMAMnF at H = 1000 Oe
from 2 to 300 K. 142........................................................................................................ 62
Figure 24: Magnetic susceptibility of DMAFeF ................................................. 63
Figure 25: PXRD pattern for DMAMnF, collected at the Advanced Photon
Source, ANL = .
Ǻ, BM-11) .......................................................................... 64
Figure 26: Rietveld refinement of PXRD data of DMANiF collected at 10
K with monoclinic unit cell of a=14.451(8) Å b=8.376(3) Å c=8.952(4) Å
and β=
.
°. Pattern is in red color, simulated pattern is in blue
and difference plot is in orange. .............................................................................. 66
Figure 27: Reietveld refinement of powder neutron data collected at
NIST with the low temperature Cc phase of DMAMnF. Black is the
experimental data, Red is simulated pattern, Blue is the Bragg positions
and Green is the difference between experimental and simulated. ........ 70
Figure 28: Dielectric constant of DMAMnF as a function of temperature
with no magnetic field and with that of 5 Tesla. The measurements were
done at 1 kHz, using amplitude of 1V. .................................................................. 71
Figure 29: Dielectric constant of DMAMnF measured as a function of
temperature and magnetic field. Bottom two plots reveal a magnetodielectic coupling. .......................................................................................................... 73
xii
Figure 30: Heat capacity of DMAMnF as a function of temperature. The
anomalies relating to electrical ordering and magnetic ordering are
clearly visible................................................................................................................... 75
Figure 31: Effect of magnetic field on the magnetic phase transition in
DMAMnF on cooling. .................................................................................................... 76
Figure 32: Temperature dependence of Q-Band EPR spectra of
DMAMnF. ........................................................................................................................... 77
Figure 33: Temperature dependent of low-temperature specific heat
(plotted as C/T3 versus T). ......................................................................................... 81
Figure 34: Crystal structure of [(CH3)2NH2]Zn(HCOO)3 at room
temperature. The purple spheres represent the three dynamically
disordered sites for the N atom of the dimethylammonium formate
moiety. The freezing of these positions is proposed to be the mechanism
underlying the ferroelectric transition at 156 K. ............................................. 83
Figure 35: Temperature dependence of the CH3 proton spin-lattice
relaxation rate, T1-1, of DMAZnF. A, B and, C refer to the glass,
ferroelectric (FE) and, paraelectric (PE) phases, respectively. Solid lines
are the theoretical fits to the BPP equation. Arrows indicate the
direction of the temperature scan. The inset shows the Arrhenius plot
for this path. ..................................................................................................................... 85
Figure 36: Thermal cycles for paths II and III, wherein the spin-lattice
relaxation rate jumps back to the main path (path I), are highlighted by
arrows. The dashed lines are the projected paths had no jumps
occurred. Solid (thick) lines are the theoretical fits to the BPP equation.
............................................................................................................................................... 86
xiii
ABSTRACT
Multiferroic materials are rare compounds featuring at least two ferroic
properties with a majority of them displaying (anti)ferro – electricity or
magnetism. Currently, the most famous compounds displaying such behavior are oxide perovskites. One of the most common mechanisms for
ferroelectric behavior in perovskites, requires an empty d-orbital which
usually means that the material is diamagnetic. Hence there is a need for
multiferroic materials in which two independent mechanisms can determine the electric and magnetic ordering. I was able to achieve this using hybrid perovskites.
Hybrid perovskites of general formula (CH3)2NH2M(HCOO)3 have a ReO3
type cage made up of formate and metal ions. The metal ions sit at the
corners of the cubes and are connected to each other via coordination
bonding with oxygen of the formate ion. The dimethylammonium cation
is located at the center of this cavity. The amine hydrogen atoms make
hydrogen bonds with the oxygen atoms of the metal formate framework. Because of this hydrogen bonding, the nitrogen of the ammonium
cation is disordered over three equal positions at room temperature.
Cooling down these materials below 180 K leads to a lowering in symmetry, a result of the ordering of nitrogen atoms.
This phase transition is associated with a dielectric anomaly. Carefully
done dielectric measurements show that the anomaly is a -type peak
xiv
usually associated with paraelectric to ferroelectric phase transition.
Low temperature single crystal measurements aided by powder X-ray
diffraction and neutron diffraction experiments show that low temperature phase crystallizes in monoclinic symmetry and Cc space group. Cc
belongs to one of the 10 polar point groups which are requirements for
ferroelectricity. Furthermore, magnetic fields seem to affect this dielectric anomaly, suggesting that these hybrid perovskites have a magnetodielectric effect. This phase transition was studied in detail by electron
paramagnetic resonance, heat capacity, and 1H NMR relaxation time
measurements.
Close to 0 K, specific heat data suggest that there is a remnant specific
heat, a classic signature of amorphous or glassy materials. NMR data
shows that these hybrid materials are indeed glassy below 40 K with
many confirmations with close underlying energies. This effect is related to the rotation of methyl motors. NMR results also show an anomaly at the same temperature where dielectric anomaly is present. Methyl protons slow down by a factor to suggest that dielectic anomaly is
indeed due to the ordering of nitrogen atoms.
xv
CHAPTER 1
INTRODUCTION
Hybrid inorganic-organic or metal-organic frameworks (MOFs) are a recently-identified class of crystalline material, consisting of metal ions
linked together by organic bridging ligands, and are a new development
on the interface between molecular coordination chemistry and materials science.1-10 A range of novel structures has been prepared which
feature amongst the largest pores known for crystalline compounds,
very high absorption capacities and complex sorption behavior not seen
in aluminosilicate zeolites.3,
11-14
Most of the efforts in this field have
been focused on discovering porous MOFs for gas storage applications,
and not much attention has been given to other physical properties for
which oxides are usually known for.15-16 In this dissertation, I focus on
the research that I have conducted in one such field called multiferroics.17-18 I have demonstrated that it is possible to achieve multiferroic
behavior in this upcoming class of MOF compounds.19-21 In this opening
chapter, I will give an introduction to metal organic frameworks, multiferroics, and, briefly talk about ferroelectric metal organic frameworks.
1.1 Metal organic frameworks
1.1.1 General introduction
Metal organic frameworks are crystalline materials built from inorganic
and organic building blocks with infinite inorganic−organic connectivity
in at least one dimension.1, 4, 6, 10, 22-27 Sometimes they are referred to as
1
hybrid inorganic-organic frameworks and a subset of which are inorganic−coordination polymers.28 These framework materials have recently developed into an important new class of solid-state materials
with approximately 2800 ISI web of science papers published in the
year 2009. This is, mainly, due to the infinite possibilities of new frameworks materials that can be created by varying the inorganic/organic
ratio.16 These materials can also offer wide range of physics and chemistries. Furthermore, it is possible to tailor their properties by changing
metal ions and/or organic ligands despite maintaining the structure topology.
Hybrid frameworks exist for a wide range of metals and involve a diverse range of organic ligands. Most of the published work involves
transition metals, including zinc, but there is a growing body of literature around rare-earth based systems, which are of interest for their
optical properties.29-31 In addition, there has been a certain amount of
effort with p-block elements, especially aluminium, gallium and tin, plus
a recent growth of interest in magnesium, driven by the search for
lightweight materials for hydrogen storage.32-34
In terms of organic ligands, much of the recent focus has been on connectivity through oxygen atoms of carboxylic acid groups.4, 35-36 Rigid dicarboxylic acids, such as benzene-1,4-dicarboxylic acid, have proved
very versatile, as have the simple but more flexible aliphatic systems,
such as succinic and glutaric acids.37-39 The simplest member of this family, oxalic acid, has been used extensively.40-42 As will be discussed later,
2
monocarboxylic acids can also form hybrids, and there has been some
recent effort with formic and acetic acids.43-50 Nor is the field limited to
carboxylic acids, since phosphonic acids and phenolic acids can also
form hybrid frameworks.51-54 Beyond network formation involving M–O
linkages, there has been a reasonable amount of work with other types
of ligands, such as pyridyls and imidazoles, as well as mixed ligands that
offer the possibility of more than one type of connection, e.g. M–O plus
M–N or M–S.7-8, 22, 26, 55 Much remains to be explored in the area of these
more complex linkages.
1.1.2 Open and dense frameworks
Hybrid frameworks could be divided into two broad categories: open
and dense frameworks. A majority of the publications in the field are
based upon the open frameworks with potential applications in gas storage, gas separation, catalysis, and sensors. A vast range of coordination
polymers or supramolecular architectures with different dimensionalities
– 1-D, 2-D and 3-D – have been discovered in recent years.15 3-D open
frameworks display some of the highest surface areas known and are
widely regarded as the potential hydrogen storage materials for various
energy related applications including the transportation industry. Some
of the most striking examples of porous 3-D coordination polymers can be
found in the work of Yaghi, O'Keeffe and co-workers, in which they have
exploited bridging of simple Zn4O groups via rigid aromatic dicarboxylates
such as benzene-1,4-dicarboxylic acid to build networks with remarkably
low densities and high porosity, such as MOF-5.9 They have shown that
3
large families based upon the same architecture can be created by altering
the length or other chemical details of the organic linker.56 In addition to
architectures based upon the topologies of simple inorganic structures;
there has also been success in building porous hybrids based upon known
zeolite structures. These include zinc, cadmium and indium coordination
polymers that adopt the ABW, BCT, MTN, RHO and SOD topologies.7 Imidazoles-based ligands are particularly effective for this purpose since they
can mimic the Si–O–Si angles that are found in typical zeolites.
Figure 1: MOF-5, a porous cubic zinc terephthalate which is topologically analogous to ReO3. Gray spheres denote carbon, red oxygen, and white hydrogen,
with ZnO4 tetrahedra in blue.
Focusing on dense hybrid frameworks, only recently has some attention
been paid to these materials. They are frameworks with extended inor4
ganic, for example M-O-M, connectivity in at least one dimension (Figure
2) or with limited porosity, for example, cation templated hybrid
frameworks. These materials show interesting magnetic, optical, electronic and dielectric properties. They exhibit rich diversity of behavior
in these areas and present some exciting opportunities for the physics
community. Cation-templated hybrid MOFs, described in this text at a
later stage, are an important subclass of dense frameworks. They do not
have extended inorganic connectivity; however, due to the template,
amajority do not have any accessible pores.
5
Figure 2: Schematic representation of coordination polymers and extended
inorganic hybrids; (a) and (b) show 1-D and 2-D coordination polymers, respectively, while (c) shows a system that has inorganic connectivity in two
dimensions and is connected in the third
Such extended inorganic hybrid materials not only open up a vast area
of new chemical and structural permutations, but they also provide a
basis for creating materials with properties that are traditionally found
6
in metal oxides. Thus it might be possible to make hybrid materials that
are metallic, superconducting, or high temperature ferromagnets.
1.2 Ferroelectrics and multiferroics
1.2.1 Ferroelectric
A ferroelectric material is one that undergoes a phase transition from a
high-temperature phase that behaves as an ordinary dielectric (so that
an applied electric field induces an electric polarization, which goes to
zero when the field is removed) to a low-temperature phase that has a
spontaneous polarization whose direction can be switched by an applied field57. Many properties of ferroelectric materials are analogous to
those of ferromagnets, but with the electric polarization, P, corresponding to the magnetization, M; the electric field, E; corresponding to the
magnetic field, H; and the electric displacement, D, corresponding to the
magnetic flux density, B.58 For example, ferroelectric materials also have
domains and show a hysteretic response of both polarization and electric displacement to an applied electric field. As a result, they also find
applications
in
data
storage.
The
onset
of
spontane-
ous electric polarization coincides with a divergence in the static dielectric permeability, ε, because at Tc, an infinitesimally small exter-
nal electric field will cause a large polarization. They find application as
capacitors because their concentration of electric flux density results in
high dielectric permeabilities. They are also used in electromechanical
7
transducers and actuators (because the change in electric polarization is
accompanied by a change in shape).
Early work on ferroelectric materials focused primarily on Rochelle
salt,59 KNa(C4H4O6)·4H2O. Although studies of Rochelle salt were pivotal
in establishing many of the basic properties of ferroelectric materials,
the complex structure and large number of ions per unit cell made it difficult to elucidate a coherent theory of ferroelectricity from the results
of experiments on this material.60-66 The most widely studied and widely
used ferroelectrics today are perovskite-structure oxides, ABO3, which
have the prototypical cubic structure shown in Figure 3. The cubic perovskite structure is characterized by a small cation, B, at the center of
an octahedron of oxygen anions, with large cations, A, at the unit cell
corners. Below the Curie temperature, there is a structural distortion to
a lower-symmetry phase accompanied by the shift off-center of the
small cation. The spontaneous polarization derives largely from the
electric dipole moment created by this shift. The comparatively simple
perovskite structure and the small number of atoms per unit cell have
made detailed theoretical studies of perovskite ferroelectrics possible
and resulted in a good understanding of the fundamentals of ferroelectricity.
8
Figure 3: Cubic perovskite structure. The small B cation (in black) is at the
center of an octahedron of oxygen anions (in gray). The large A cations
(white) occupy the unit cell corners.
1.2.1.1 Crystallography and ferroelectrics
The crystal classification of a material has immediate implications for
ferroelectric effects.
 There are 32 crystal classes
9
 11 of them have a centre of symmetry (centrosymmetric) and
cannot support ferroelectricity
 Of the remaining 21, the O-point group (432) also excludes ferroe
lectricity.
 The remaining 20 classes all exhibit the piezoelectric effect
 Of these, 10 (Table 1) have a unique polar direction.
Table 1: 32 point groups. Polar point groups have been highlighted in blue.
10
1.2.2 Multiferroic materials
Figure 4: Ferromagnets (ferroelectrics) form a subset of magnetically (electrically) polarizable materials such as paramagnets and antiferromagnets (paraelectrics and antiferroelectrics). The intersection (red hatching) represents
materials that are multiferroic. (Adopted from ref. 17)
Multiferroics are rare materials that exhibit more than one primary ferroic order parameter simultaneously within a single phase.17, 67-76 These
ferroic order parameters are ferroelasticity, ferroelectricity and ferromagnetism (See glossary of terms at the end of the section).77-78 However, the current trend is to exclude the requirement for ferroelasticity79-83
in practice, but to include the possibility of ferrotoroidic order84-85 (glossary of terms) in principle. Moreover, the classification of a multiferroic
has been broadened to include antiferroic order (glossary of terms).
11
Magnetoelectric coupling73, 75, 86-89, on the other hand, may exist whatever the nature of magnetic and electrical order parameters, and can for
example occur in paramagnetic ferroelectrics90-93 (Figure 4). Magnetoelectric coupling may arise directly between the two order parameters,
or indirectly via strain.72, 94-97 Currently there is a high level of interest in
magnetoelectrics and multiferroics. Given that there are indeed few
multiferroic materials, whatever the microscopic reasons, the relentless
drive towards ever better technology is aided by the study of novel materials. Aspirations here include transducers and magnetic field sensors,
but tend to centre on the information storage industry. It was initially
suggested that both magnetization and polarization could independently encode information in a single multiferroic bit. Four-state memory
has recently been demonstrated98, but in practice it is likely that the two
order parameters are coupled. 99 Coupling could in principle permit data
to be written electrically and read magnetically. This is attractive, given
that it would exploit the best aspects of 100-104 (FeRAM) and magnetic data storage, while avoiding the problems associated with reading FeRAM
and generating the large local magnetic fields needed to write.
1.2.3 Glossary of terms
Ferroics
Ferroelectric materials possess a spontaneous polarization that is stable and can be switched hysteretically by an applied electric field.
12
Antiferroelectric materials possess ordered dipole moments that cancel each other completely within each crystallographic unit cell.
Ferromagnetic materials possess a spontaneous magnetization that is
stable and can be switched hysteretically by an applied magnetic field.
Antiferromagnetic materials possess ordered magnetic moments that
cancel each other completely within each magnetic unit cell.
Ferroelastic materials display a spontaneous deformation that is stable
and can be switched hysteretically by an applied stress.
Ferrotoroidic materials possess a stable and spontaneous order parameter that is taken to be the curl of a magnetization or polarization. By
analogy with the above examples, it is anticipated that this order parameter may be switchable. Ferrotoroidic materials have evaded unambiguous observation.
Ferrimagnetic materials differ from antiferromagnets because the
magnetic moment cancellation is incomplete in such a way that there is
a net magnetization that can be switched by an applied magnetic field.
Order parameter coupling
Magnetoelectric coupling describes the influence of a magnetic (electric) field on the polarization (magnetization) of a material.
13
Piezoelectricity describes a change in strain as a linear function of applied electric field, or a change in polarization as a linear function of applied stress.
Piezomagnetism105-107 describes a change in strain as a linear function
of applied magnetic field, or a change in magnetization as a linear function of applied stress.
Electrostriction108-109 describes a change in strain as a quadratic function of applied electric field.
Magnetostriction110-112 describes a change in strain as a quadratic
function of applied magnetic field.
1.3 Ferroelectric metal organic frameworks
A summary of recent work is presented in this section describing noncentrosymmetric or homochiral metal-organic frameworks which belongs to 10 polar point groups with potential ferroelectric properties. It
is necessary to give a brief introduction of three typical well-known ferroelectrics: Rochelle salt, KDP and triglycine sulfate (TGS).57
1.3.1 Rochelle salt, KDP, and triglycine sulfate (TGS).
The well-known oldest ferroelectric crystal is Rochelle salt59(see Figure
5). The most outstanding property of Rochelle salt is that it exhibits two
14
curie points. The space group below 255 K and above 297 K is orthorhombic P21212, corresponding to the paraelectric phase while between
the temperature range the space group is monoclinic P21, corresponding
to the ferroelectric phase.113 The paraelectric–ferroelectric transition is
of the order–disorder type.
In the crystal structure, there are rows of tartrate ions parallel to
the a axis, linked along the b axis by rows of alternating K and Na ions.
Every tartrate ion is surrounded by six tartrate ions. K and Na ions act
as a bridge among tartrate ions.114 The K ions adopt a bicapped trigonal
prism geometry and the Na ions display a distorted octahedral geometry
via the coordination with the O atoms from acetate, OH and water. The
crystal structure of Rochelle salt is a combination of two kinds of different chains along the a axis. The main difference among the ferroelectric
structure and the two paraelectric structures is in the orientation of
each tartrate ion with respect to the crystallographic axes. It is assumed
that the ferroelectricity is produced by two nonequivalent chains along
the a axis, each with a different polarization vector parallel to the a axis.
As well-known hydrogen-bonded ferroelectrics, the pure inorganic
compound KDP has been the most intensively studied over the second
half of the last century57. There are extensive hydrogen bonds in its
structure that gives rise to a diamondoid network (see Figure 5).
15
Figure 5: Views of the unit cell content of Rochelle salt (paraelectric phase)
(left), KDP (paraelectric phase) (middle) and TGS (ferroelectric phase) (right)
KDP undergoes paraelectric–ferroelectric phase transition at 123 K. The
paraelectric phase adopts the tetragonal space group I−42d (point
group D2d) where the ferroelectric phase adopts the orthorhombic space
group Fdd2 (polar point group C2v). The spontaneous polarization of
KDP arises from the collective site-to-site transfer of protons in the O–
H O bonds, along with the displacive deformation of PO4 − ions. Upon
deuteration, KDP shows a huge isotopic effect of Curie temperature with
an increase of about 90 K.
TGS is another typical ferroelectric discovered by Matthias et al. in
1956115. It is synthesized from amino acid glycine and sulfuric acid. In
the crystal structure, there are three types of glycine molecules, i.e., I, II
and III (see Figure 5). The structural formula of TGS can be best written
as [(H3N+CH2COOH)2(H3N+CH2COO−)·SO4 −], among which the glycinium
ion H3N+CH2COOH corresponds to glycines I and II while the zwitterion
H3N+CH2COO− to glycine III. The C, N and O atoms in glycine II and III lo16
cate almost in-plane while the N atom in glycine I deviates of ca. 0.27 Å
from the OCO plane. The sulfate exhibits a distorted tetrahedral geometry. The glycines and sulfate ions are connected through hydrogen
bonds. The direction of spontaneous polarization Ps is due to the orientation of the polar group NH3+ of glycine I molecule along the b axis.
TGS displays a perfect hysteresis loop along the b axis and its Ps reaches
3.5 C cm− at room temperature. It shows a typical second order fer-
roelectric phase transition at Curie temperature of 322 K. The paraelectric phase is monoclinic P21/m belonging to the centrosymmetrical class
2/m while the ferroelectric phase below the transition temperature is
monoclinic P21 belonging to the polar point group 2. TGS crystal is one
of the best materials for use as a sensitive element in room temperature
infrared detectors and imaging systems due to its excellent ferroelectric
and pyroelectric properties115.
1.3.2 Ferroelectric MOFs
[Co(II)Cl3(H-MPPA)] is one of the successful ferroelectric examples,
where its electric hysteresis loop reaches perfect spontaneous polarization status, since the exploration of potential ferroelectrics based on
MOFs 116. It was prepared through the reaction of dichloride (R)-2methylpiperazine (MPPA) bi-cation with CoCl2. X-ray crystal structural
determination clearly shows that the local coordination environment
around Co center is a distorted tetrahedron composed of three terminal
Cl atoms and one N atom from unprotonated N atom of MPPA (see Figure 6). One of the N atoms from the MPPA ligand is protonated and loses
17
its coordination ability. Thus, three H atoms (H1, H2A and H2B) form
hydrogen bonds between three Cl atoms (Cl1, Cl2 and Cl3) to lead to the
formation of 3D framework created through hydrogen bonds as shown
in Figure 6. A careful investigation shows that three bond distances of
Co–Cl are not equal to each other and display some differences (Co–
Cl1 = 2.225 Å; Co–Cl1 = 2.283 Å; Co–Cl1 = 2.260 Å). As expected, the
bond distance of Co1–N1 is in the normal range of Co–N bond lengths.
The piperazine ring adopts a stable chair-type conformation.
Figure 6: Molecular structure of crystal state of [CoCl3(H-MPPA)] and its 3D
packing view along the b axis and electric hysteresis loop recorded at room
temperature (adopted from ref. 116).
[Co(II)Cl3(H-MPPA)] crystallizes in a chiral space group P21 which belongs to one of the ten polar point groups (C2), its ferroelectric property
would occur in principle. Figure 6 shows that an electric hysteresis loop
was indeed observed when the applied electric field was set at about
28 kV cm− . A spontaneous polarization (Ps ≈ 6.8 C cm− ) occurred in
the measuring conditions and remanent polarization (Pr ≈ 6.2 C cm− )
was almost equal to that of Ps. Ps of 1 is twice that of TGS
18
(Ps = 3.5 C cm− ) and significantly larger than that of KDP. The direction
of the spontaneous polarization in the ferroelectric phase might be perpendicular to the chains and to the Cl HN hydrogen bonds, analogous
to KDP and other KDP-type ferroelectrics.116
[Ni3(TBPLA)2(μ3-O)](ClO4)4(H2O)5: Another H-bonded discrete homochiral ferroelectric MOF is Ni3(TBPLA)2( 3-O)(ClO4)4(H2O)5 (3)
(TBPLA = (S)- , , -2,4,6-trimethylbenzene-1,3,5-triyl-
tris(methylene)-tris-pyrrolidine-2-carboxylic acid), which is obtained
by the hydrothermal reaction of Ni(ClO4)2·6H2O with TBPLA117. Frame-
work crystallizes in a chiral space group P21 belonging to one of the ten
polar point groups (C2). The TBPLA ligand is a zwitterionic neutral molecule similar to the amino acid in TGS, and acts as a hexadentate chelator with each of the ligand's bidentate carboxylate moieties coordinated
to the Ni atoms (see Figure 7). The molecular charge is balanced by four
free ClO4− anions and one
3-O
atom. The TBPLA ligand takes an all-
cis coordination mode resembling the shape of a parachute. Each Ni center displays a slightly distorted octahedron geometry which is composed of six O atoms, i.e., four of the O atoms from four different carboxylate groups and two from the oxo group and H2O. Similarly, 3D framework occurs in this framework through strong H-bond (see Figure 7).
19
Figure 7: Molecular structure of [Ni3(TBPLA)2( 3-O)](ClO4)4(H2O)5 where water and ClO4− are omitted for clarity117
Fu et. al reported that this framework displays large permittivity anisotropy along three crystallographic axes (See Figure 8). The dielectric
anisotropy ratios of
r//c/ r//b
and
r//c/ r//a
are ca. 3.47 and 2.22, re-
spectively, showing temperature-independence. Polarization − electric
field hysteresis curve was of typical ferroelectrics; the spontaneous polarization, Ps, reaches a value of ca. 3.4 nC/cm2 at room temperature
while the coercive field is relatively low, reaching ca. 0.8 kV/cm which is
smaller than those typically found in ferroelectric polymers.
20
Figure 8: Dielectric permittivity εr) of a single crystal of [Ni3(TBPLA)2( 3O)](ClO4)4(H2O)5 as a function of temperature upon application of an electric
field approximately parallel to the a (E//a), b(E//b), and c(E//c) crystal axes
directions. The measurements were made at a high frequency of 1 MHz
(adopted from ref. 117).
RbI0.82MnII0.20MnIII0.80[FeII(CN)6]0.80 [FeIII(CN)6]0.14·H2O was reported
by Ohkoshi et al. at low temperature118. It is arguable whether a cyano
bridged compound could be considered a metal organic framework. The
crystal structure resembles that of Prussian blue (see Figure 9). They
used variable-temperature powder x-ray diffraction (PXRD) measurements reveal that the title compound displays phase transition at high
temperature (276 K, a centrosymmetric space group F43m) and low
temperature (184 K, an acentric space group F222 belonging to nonpolar point group D2). The magnetization vs. temperature plots of the
low-temperature phase show ferromagnetism with a Curie temperature
of 11 K. The P–E plot for the low-temperature phase at 77 K, when ap21
plying a field up to 100 kV cm− , shows an electric hysteresis loop with
a Pr of 0.041 C cm− and an Ec of 17.5 kV cm− . The ferroelectricity may
be related to mixing of FeII, FeIII, Fe vacancy, MnII, and Jahn–Tellerdistorted MnIII. One of the possible mechanisms of the ferroelectricity
could be the creation of a local electric dipole moment because of an
iron vacancy. In addition, the difference in ionic radii among four metal
ions and MnIII Jahn–Teller distortion enhance the local structural distortion, for example, the deviation of M–CN–M linkages from a
° confi-
guration. Probably, in such a deviated structure, polarization will be induced by the applied electric field, and the polarization can be held by
the structural flexibility of the cyano-bridged 3D network.
Figure 9:
A schematic illustration of the molecular structure of
I
II
Rb 0.82Mn 0.20MnIII0.80[FeII(CN)6]0.80 [FeIII(CN)6]0.14·H2O
22
[Mn3(HCOO)6](C2H5OH)
119-120:
Research from Kobayashi group
showed, for the first time, a guest induced ferroelectric phase transition
in porous metal organic frameworks. More than often, depending on the
size of the solvent, when porous MOFs are synthesized, their pores contain solvent molecules. Depending on the size and the interaction of the
solvent molecules with the framework body, these solvent molecules
are usually disordered at room temperature.
Figure 10: (a) Crystal structure of [Mn3(HCOO)6](C2H5OH) viewed along the
b-axis: Mn, pink; C, gray; O, blue; H, pale sky blue. The C and O atoms of guest
C2H5OH molecules are shown by open circles. (b) The arrangement of guest
ethanol molecules along the channel
23
Kobayashi et al. showed that porous Mn3(HCOO)3 is a ferrimangnet below 8.5 K. 119-120. The guest molecules are easily removed under vacuum
and/or by heating. Framework shows a dielectric anomaly below 150 K
when the framework was loaded with polar solvents, for example, H2O,
CH3OH, or C2H5OH. This is due to the ordering of these polar guest molecules which are otherwise randomly disordered at room temperature.
Figure 10 shows the structure of [Mn3(HCOO)6](C2H5OH) viewed along
the b-axis and the arrangement of guest molecules along the channel.
Figure 11 shows the magnetic and structural phase transition leading to
the dielectric anomaly. As expected, dielectric anomaly is highly anisotropic.
24
Figure 11: (a) Temperature dependence of the magnetization of
[Mn(HCOO)6](C2H5O(
( =
Oe . b Dielectric constants εr) of
[Mn(HCOO)6](C2H5OH) for the field E//a (blue), b (green), and c (pink). The
red line represents εr (E//a) of the crystal with deuterated ethanol,
[Mn(HCOO)6](C2H5OD). (c) The hysteresis loop of [Mn(HCOO)6](C2H5OH)
E//a . d The /εr vs T curve of [Mn(HCOO)6](C2H5OH). In the dielectric
measurements, the relatively high speed of the temperature change
− °/min was adopted to avoid the escaping of guest molecules
25
1.4 Summary
Multiferroics are rare compounds with more than one ferroic properties. Traditionally, metal oxides are known to show this rare but very interesting behavior. Recent years have seen the resurgence of the field
mainly due to the long term technological applications. Metal organic
frameworks, especially the dense MOFs, are capable of showing this behavior as they are structurally similar to oxides. Also, it is possible to
make homochiral MOFs by starting with a chiral template or organic
linker. Most of the known MOF ferroelectric materials fall into this category of homochiral MOFs. However, homochiral frameworks cannot be
used for many typical multiferroic applications because they do not exhibit a paraelectric to ferroelectric phase transition. As discussed in section 1.3.2, some MOFs can also exhibit ferroelectric behavior by creating
a local electric dipole moment because of a vacancy. But these are very
uncommon. Guest induced ferroelectricity is an interesting concept via
which almost all the porous frameworks could potentially be turned into ferroelectrics or into multiferroics if they are made up of paramagnetic ions. Low molecular weight polar guest molecules interact weakly
with the framework lattice and are disordered at room temperature.
Upon lowering the temperature, these molecules order giving rise to net
polarization. However, as the authors pointed out the dielectric and polarization values are not reproducible. Volatile guest molecules tend to
evaporate when approaching room temperature or on storing for long
26
time. Hence, there is a need for new class of multiferroic MOFs which
are stable and can give reproducible results.
27
CHAPTER 2
EXPERIMENTAL TECHNIQUES AND SYNTHESIS
2.1 Experimental techniques
2.1.1 Single crystal and powder X-ray diffraction
2.1.1.1 Single crystal X-ray diffraction
For sample preparation, a suitable single crystal is usually selected under a polarizing microscope and glued to a thin glass fiber with cyanoacrylate (Superglue) adhesive. Crystal structure determinations by single
crystal X-ray diffraction were performed on a Bruker SMART-CCD diffractometer equipped with a normal focus, 2.4kW sealed tube X-ray
source (Mo Kα radiation,
= 0.71073Å) operating at 50kV and 40mA. A
hemisphere of intensity data was collected at various temperatures. An
empirical correction on the basis of symmetry equivalent reflections
was applied using the SADABS program121. The structure was solved by
direct methods using SHELXTL and difference Fourier syntheses122. The
relevant details of structure determination are presented in different
chapters. Full matrix least-squares refinement against |F2| was carried
out using the SHELXTL package of programs122. The hydrogen atoms
were found in the Fourier difference map; the proton remaining on the
acid was restrained. The last cycles of refinement included atomic positions and anisotropic thermal parameters for all atoms except hydrogen,
which used isotropic thermal parameters. At the end of the chapter are
supplementary tables containing atom coordinates, bond lengths and
28
angles, anisotropic displacement parameters, hydrogen atom coordinates, and hydrogen bonding specifics.
2.1.1.2 Synchrotron versus laboratory sources for X-ray diffraction
All the standard laboratory sources used for X-ray diffraction experiments generate radiation using the same physical principles but can
vary in their technical details. In our case, we have been using a BraggBrentano geometry using a sealed tube generator. The tube of X-rays is
made from a source of electrons and a metallic cathode put in the chamber under high vacuum. The source of electrons is a filament of tungsten
heated by an electric current, which expels electrons by the thermic effect. A high voltage from 40kV to 60kV is applied between the source of
electrons (cathode) and the metallic anode and accelerates the electrons. Due to the way in which radiation is produced, only a discrete
number of wavelengths and a broad background are available. For conventional X-ray diffraction, we have been using Kα of copper.
The generation of X-rays in a synchrotron radiation source involves a
different technology. From mechanics and the Maxwell equations, it is
well known that charged particles moving under the influence of an accelerating field emit electromagnetic radiation. This radiation can be
used for diffraction purpose if the charged particles have a high acceleration corresponding to a speed close to the speed of light. This is realized in a synchrotron radiation facility where the charged particles
(electrons or positrons) are kept circulating within an evacuated cavity
29
on a closed path (the ring) by a number of curved magnets (the bending
magnets). The different beamlines used for the different experiments
are tangential to the particle trajectory. The advantage of such facility is
the very bright source which is available and the possibility to tune the
wavelength to the value required for a particular experiment.
Most of the powder X-ray work for this dissertation was done on PANalytical or Brucker machines at University of California, Santa Barbara
and University of Cambridge respectively. Synchrotron data used in this
work were collected at 11BM beamline (advanced photon source) at the
Argonne national laboratory.
Materials were characterized by both single and powder X-ray diffraction. Paraelectric and ferroelectric phases were solved using single Xray technique. Powder X-ray diffraction (PXRD) was usually used to
check the purity of the sample. Synthesis conditions were optimized using PXRD. In case of low temperature phase, both powder and single
crystal X-ray data were used along with neutron data to solve the structure. Rietveld refinements were performed wherever required to get
unit cell parameters or to check the purity of a given sample. X’pert
Highscore was used for preliminary Rietveld refinements for phase
identification. Fullprof and GSAS were used for more advanced and difficult refinements.
30
Table 2: Comparison of single crystal and powder diffraction
Single crystal diffraction
Powder diffraction
Determination of the
crystal structure with
high precision and
accuracy
Identification of compounds or mixtures of different compounds
Information on ordering in crystals
Investigations on homogeneity
Information on
thermal motion and
dynamics in crystals
Information on stress, strain and
crystal size
Very precise bond
lengths
Quantitative phase analysis
Imprecise for cell parameters. Precise in
fractional coordinates
Determination of the crystal structure (Usually not as precise as from
single crystal structure analysis)
2.1.2 Neutron diffraction
Neutron beams are produced by nuclear reactions, such as nuclear fission or fusion, or by spallation of nuclei by accelerated particles. Since
for the moment nuclear fusion cannot be controlled sufficiently to produce stable neutron sources, all neutron centers use nuclear reactors
(fission) and spallation sources. Spallation is the process in which a
31
heavy nucleus emits a large number of nucleons as a result of being hit
by a high-energy proton.
A number of properties of the neutron make it very useful for the study
of solids. Since, neutrons are uncharged particles and of small dimensions (about 10− the size of an atom), they have a very penetrating
power. While the atomic scattering factors for X-rays increase through-
out the periodic table due to increasing numbers of electrons, this is not
the case for neutrons. For neutrons, although there is a small increase of
nuclear scattering factor with the mass number of the element, it is
largely hidden by resonance effects which vary in a seemingly arbitrary
fashion from atom to atom. As a result, the neutron scattering factors for
different nuclei are in general all of the same order within a factor 4. The
difference between the relative size of cross-sections (scattering factor)
for X-ray and neutron is illustrated in Figure 12.
32
Figure 12: Difference between the relative sizes of the cross-sections between
X-ray and neutron for some elements.
As a consequence, neutron diffraction is more sensitive to the light
atoms like oxygen or hydrogen than X-ray diffraction. In this respect,
these two techniques are complementary. Another main difference between X-ray and neutron diffraction is related to the size of the electron
cloud/nucleus ratio. While the electron cloud has dimensions of about
1ºA, which is comparable with the X-ray wavelength, the radius of a
nucleus is about 4 orders of magnitude smaller. As a result, the nucleus
may be considered as a point scatterer and there will be no decrease
with Θ of the neutron scattering factor. An additional property of the
neutron is that it carries a spin and, consequently, once it interacts with
the nuclei of the sample studied, it gives information about the magnetic
properties.
33
Neutron data used in this thesis was collected on high resolution powder diffractometer BT-1 of NIST laboratory.
2.1.2 Magnetic susceptibility measurements using a SQUID magnetometer
SQUIDs ("Superconducting Quantum Interferometer Device") are very
sensitive sensors for magnetic fluxes, with the ability to measure very
small magnetic fields. SQUIDs are used in several fields from electronics
to biomagnetism. In addition to magnetic fluxes, other physical values
can be measured if they can be adapted to the magnetic flux. Attainable
sensitivities of flux densities (10− T), of electrical current (10− A) and
of electrical resistance (10−12 Ω reflect the high accuracy of a SQUID.
The working principle of a SQUID is based on the quantum interference
of wave functions that describe the state of the superconducting charge
carriers, the so-called Cooper pairs. Each Cooper pair can be treated as a
single particle with a mass and charge twice that of a single electron,
whose velocity is that of the center of mass of the pair. A SQUID is based
on an interferometer loop in which two weak links (Josephson contacts)
are established. A weak link is realized by interrupting a superconductor by a very thin insulating barrier. The function of the SQUID is to link
the quantum mechanical phase difference of the Cooper pairs wave
functions over a weak link with the magnetic flux penetrating the interferometer loop.
34
Figure 13: Scheme of a SQUID magnetometer.
The components of a SQUID magnetometer (Figure 13) typically consist
of the following: a detection coil, which senses changes in the external
magnetic field and transforms them into an electrical current; an input
coil which transforms the resulting current into a magnetic flux in the
SQUID sensor; electronics which transform the applied flux into a room
temperature voltage output; and acquisition hardware and software for
acquiring, storing and analyzing data. Both the SQUID amplifier and the
detection coils are superconducting devices. Thus some type of refrigerant (liquid helium or liquid nitrogen) or refrigeration device (cryocooler) is needed to maintain the SQUID and detection coil in the superconducting state. Additional signal conditioning electronics may be needed
to improve signal-to-noise. The current work used a MPMS (Magnetic
Property Measurement System based on SQUID) from Quantum Design
having the following characteristics: Hmax=8T and ∆T=1.8 K-400 K.
35
2.1.3 Heat capacity measurements
Heat capacities of different samples were measured on a Quantum Design PPMS (physical property measurement system) both with and
without magnetic field using a specialized heat capacity puck. Magnetic
fields of up to 9T were used.
The heat capacity puck utilizes the standard PPMS 12-pin format for
electrical connections, and it provides a small microcalorimeter platform for mounting the sample. Samples are mounted to this platform by
a standard cryogenic grease or adhesive such as Apiezon N or H Grease.
The sample platform is suspended by eight thin wires that serve as the
electrical leads for an embedded heater and thermometer. The wires also provide a well-defined thermal connection between the sample platform and the puck. An additional thermometer embedded in the puck
provides a highly accurate determination of the puck temperature, and a
thermal shield aids in maintaining stable sample temperature and uniformity. To ensure that heat is not lost via exchange gas, the Heat Capacity option includes the PPMS High-Vacuum system, which maintains
the sample chamber pressure near 0.01 mbar and is automatically controlled by the software.
The heat capacity mounting station helps protect the sample platform
and its suspending leads when mounting and removing a sample. A
built-in vacuum line securely holds the platform in place so that samples
may be mounted or removed without generating stress on the support36
ing wires. A single heat capacity measurement consists of several distinct stages. First, the sample platform and puck temperatures are stabilized at some initial temperature. Power is then applied to the sample
platform heater for a predetermined length of time, causing the sample
platform temperature to rise. When the power is terminated, the temperature of the sample platform relaxes toward the puck temperature.
The sample platform temperature is monitored throughout both heating
and cooling, providing (with the heater power data) the raw data of the
heat capacity calculation.
37
Figure 14: Cutaway view showing the PPMS -16T magnet and probe. Inset
shows a heat capacity puck.
2.1.4 Dielectric properties (capacitance measurements)
Capacitance is a measure of the amount of electric charge (Q) stored (or
separated) for a given electric potential (V).
C = Q/V
38
In a capacitor, there are two conducting electrodes which are insulated
from one to another. The charge on the electrodes is +Q and -Q, and V
represents the potential difference between the electrodes. Capacitance
is measured in the SI unit of the Farad, 1F=1C/V. The capacitance can be
calculated if the geometry of the conductors and the dielectric properties of the insulator between the conductors are known. For example,
the capacitance of a parallel plate capacitor constructed of two parallel
plane electrodes of area A separated by a distance d is approximately
equal to the following:
C = (A/d)
Where C is the capacitance in farads, is the permittivity of the insulator
used, A is the area of each plane electrode, measured in m2 and d is the
separation between the electrodes, measured in m. This equation is a
good approximation if d is small compared to the other dimensions of
the electrodes. This is this geometry that we have used to measure the
capacitance and thus the dielectric constant of our different samples
(see chapter 3 and 4).
2.2 Solvothermal synthesis
All the metal organic frameworks described in this text were prepared
by solvothermal route at temperatures ranging from 100 °C to 200 °C or
at room temperature. In some cases a mixed approach was used: heating followed by room temperature crystallization.
39
Solvothermal synthesis is a batch method of synthesis where-in all reactants are placed in an autoclave and heated under autogenous (selfinduced) pressure at temperatures ranging from 100 °C to 200 °C. Steel
autoclaves lined with a Teflon cup obtained from Parr Instrument Company (Figure 15) were used for solvothermal synthesis in the present
work. All reagents were used as received.
Figure 15: Cutaway of a general purpose (high temperature) 23 mL Parr acid
digestion bomb, used in the solvothermal synthesis of all the compounds described in this dissertation.
40
There are many parameters which can be modified in a hydrothermal
synthesis reaction in order to synthesize new or different phases. Often
the first variable to modify is temperature. Broadly speaking, within the
same metal/ligand family, low dimensional structures are formed at
lower temperatures and more condensed phases are formed at higher
temperatures, and the degree of hydration per metal center decreases
with increasing reaction temperature. The effect of reaction time is also
easily investigated. Kinetically accessible structures can be trapped if
the reaction timescale is short (but long enough for a reaction to occur).
Thermodynamically stable phases can be achieved if longer times are
used. Metal:ligand ratios can be adjusted. The concentration of the reaction mixture is often used to control whether the sample is a powder or
single crystals. The head space in the cup (directly related to the pressure) can also be varied. The pH of the reaction solution can be varied,
generally in the acidic to weakly basic range, because if the solution is
too basic then metal hydroxides are the majority phase formed. Templating molecules or structure directing agents (SDAs) also can be added.
41
CHAPTER 3
ORDER – DISORDER PHASE TRANSITION IN
[(CH3)2NH2]Zn(HCOO)3
3.1 Background
The
discovery
of
Order
–
disorder
phase
transition
in
[(CH3)2NH2]Zn(HCOO)3 is described in this chapter. Materials that exhibit electrical ordering are of great interest because of their technological
importance. The high permittivity123 dielectric constant, ε) properties
of some of these electrically ordered materials have also made them important in development of dielectric resonators and filters for microwave communication systems. Many of these materials are oxides with
the perovskite structure, such as lead zirconate titanate (PZT)124-128 and
BaTiO367, 129-130 which have found applications in an entire set of technologies (actuators, sensors, transducers, memory elements, filtering
devices, high performance insulators).126, 131-132 In the case of PZT, the
remarkable electromechanical and electrical properties are associated
with the morphotropic phase boundary, which is formed by doping antiferroelectric PbZrO3 with ferroelectric PbTiO3 and which occurs for the
coexistence of tetragonal (P4mm symmetry FT), monoclinic (Cm symmetry FM), and rhombohedral (R3c symmetry FR) polar distortions of
the perovskite structure.133 These properties are technically important,
but concern about the environmental impact of Pb-based systems has
42
spurred considerable interest in the discovery of lead free ferro/antiferro-electric materials.
Much of the recent attention in this field has been focused on developing
devices based upon well-established inorganic compounds such as
KH2PO4 (KDP), BaTiO3, PZT and LiNbO3;3 consequently reports of new
electrically ordered systems have remained sparse.
3.2 Synthesis
[(CH3)2NH2]Zn(HCOO)3, 1 (Figure 16), was synthesized in a reaction between zinc chloride and water in dimethylformamide (DMF). In a typical
synthesis, 5 ml of DMF, 0.5 ml of water and 1 mmol of zinc chloride were
heated overnight in a Teflon lined autoclave at 125oC. In-situ hydrolysis
of DMF produces formic acid and dimethylammonium cation, which are
the building blocks for 1. The autoclave was taken out after three days
and was air−cooled on a metal rack. After, approximately
hours the
autoclave was opened and the reaction medium was transferred into
two centrifuge tubes equally. After centrifugation supernatant was
transferred into a clean glass beaker for room temperature crystallization. The beaker was covered with parafilm and few holes were created.
It is important to make these holes in order for 1 to crystallize . After
two to three days cubic crystals of 1 were recovered from the bottom of
the glass beaker.
43
1 could also be synthesized in Teflon lines glass vials at 125 °C. Vials
were taken out of the oven after approximately six hours, and supernatant was carefully transferred into another glass vial which was kept
open. Overnight room temperature crystallization usually leads to the
formation of flakes. Powder X-ray diffraction showed that these flakes
are of compound 1. Keeping the vial closed leads to the formation of
regular cubic morphology crystals of 1 after few months.
44
3.3 Structure
Figure 16: Crystal structure of [(CH3)2NH2]Zn(HCOO)3 , 1. It has the same architecture as an ABX3 perovskite, with A=(CH3)2NH2+, B=Zn2+ and X=HCOO-.
An analog of 1 was first prepared in 1973,134 but its relationship to the
perovskite structure was not recognized until 2005.135 The structure of
1 at room temperature, as shown in Figure 16, was confirmed by single
crystal X-ray diffraction. Important room temperature unit cell parameters for 1 are displayed in Table 3. 1 has the same architecture as that of
ABX3 perovskite. Zinc (Zn2+) and formate (HCOO−) ions make a ReO3
45
type net. Dimethylammonium cation (CH3)2NH2+ lies at the center of this
anionic net.
Table 3: Structure parameters for 1 from single crystal X-ray diffraction at
room temperature
Formula sum
C5 H11 N O6 Zn
Formula weight
246.52 g/mol
Crystal system
trigonal
Space-group
R -3 c (167)
Cell parameters
a=8.1924(8) Å c=22.277(2) Å
Cell ratio
a/b=1.0000 b/c=0.3677
c/a=2.7192
Cell volume
1294.76(17) Å3
Z
6
Calc. density
1.89687 g/cm3
3.4 Structural phase transition
We were struck by the observation that the dimethylammonium cation
at the center of the ReO3-type cavity in 1 is disordered with nitrogen
apparently existing in three different possible positions. This is a consequence of disordered hydrogen bonding between the hydrogen atoms of
the NH2 group and oxygen atoms from the formate framework N….O ~
46
2.9 Å). The knowledge that hydrogen bonding of this type can lead to
ferroelectric (e.g. in KDP) or antiferroelectric (as in NH4H2PO4, ADP)
transitions when ordering takes place on cooling led us to examine the
dielectric and phase transition behavior in this system.
The first evidence of a phase transition was noted when we saw splitting of spots while attempting to collect single crystal X-ray data at liquid nitrogen temperatures. Unfortunately, it was not possible to index
the low temperature data set due to complex twinning. However, synchrotron X-ray powder data collected on beamline 11-BM at the Advanced Photon Source (ANL) gave clear indications of a phase transition. As shown in Figure 17, peaks at 100K were shifted to higher angles
compared with the room temperature data as a consequence of lattice
contraction on cooling. More importantly, at 100K the main peaks also
had weak satellites due to the formation of a superlattice (features indicated by arrows, see inset in Figure 17).
Although the features are weak, our conclusion is supported by the observation of analogous features on all the other peaks in PXRD data. This
observation is consistent with ordering of the NH2 hydrogen atoms. It
was not possible to solve the structure of low temperature phase because of complex twinning. Efforts were made to prepare deuterated
sample to do neutron diffraction experiment as neutron would be much
more sensitive to the ordering of deuterium. Because the deuterium of
the DMA cation can easily exchange with hydrogen, this reaction was
47
carried out with the vial closed. Unfortunately, it was not possible to
getpure compound from this reaction for a neutron experiment.
Figure 17: Synchrotron powder patterns collected with a wavelength of
0.608Å at APS: red data obtained at room temperature, black data at 100K.
3.5 Dielectric and heat capacity measurements
In order to determine if this phase transition is accompanied by a dielectric anomaly, as expected for a perovskite, the dielectric constant ε
of 1 was measured as function of temperature. We used a pellet as sin48
gle crystals were too small to make silver paste contacts. ε showed a
clear anomaly around 160K (Figure 18), in agreement with the synchrotron data. The maximum value of εr real part of ε was found to be ra-
ther sample dependent, ranging from about 15 to 120, but the transition
temperature was essentially reproducible.
There was a clear hysteresis of about 10K, as is usual for pellet samples.
The shape of the dielectric plot around 160 K suggests that 1 becomes
antiferroelectric below 160K on cooling.136 The shape also resembles
the antiferroelectric transition for ADP (at 148K).57 However a close
look in the vicinity of phase transition suggests that the peak could also
be a
peak, characteristic of a ferroelectric phase transition (This point
will be further discussed in chapter 4.). As seen in Figure 18, εr starts increasing as we approach room temperature, which is usual for pellet
samples,120 but could also arise from ferroelectric domains.
49
Figure 18: Dielectric constant of 1 measured as a function of temperature.
In order to probe the transition mechanism, specific heat of 1 over the
temperature range 1.8 K – 300K was measured. A clear anomaly is seen
around 156K, in both the increasing and decreasing temperature scans
(Figure 19). The shape of the curve points to a second-order transition.
It is worth reminding that while this shape points to a second order
transition, the dielectric anomaly resembles a first order phase transition. The area under the Cp/T curve yielded a value of ΔS for the phase
transition of 1.1 J/mol-K. For an order-disorder transition, ΔS = R ln(N),
where N is the number of sites for the disordered system. However, for
N= , the value of ΔS should be . J/mol-K, i.e. almost an order of magni-
tude larger than the observed value. Clearly the transition is much more
50
complex than a simple 3-fold disorder model. This transition was further studied by 1H NMR and the results are presented in chapter 5.
Figure 19: Heat capacity of 1 as function of temperature.
3.6 Summary and conclusions
In conclusion, an order-disorder type ferroelectric phase transitions
was discovered in [(CH3)2NH2]Zn(HCOO)3(1) at 156K. 1 also falls into
the category of high-dielectric constant material with an εr value of ap-
proximately 15. 1 was characterized by single crystal and powder X-ray
51
diffraction methods. Phase transitions were studied with synchrotron
radiation, dielectric measurements, and heat capacity measurements.
This type of ferroelectric ordering associated with order-disorder phase
transition was unprecedented in hybrid frameworks and opened up an
exciting new direction in rational synthetic strategies to create extended
hybrid networks for applications in ferroic-related fields.
3.7 Resulting publication and comments
Work resulted into a publication in the Journal of the American Chemical
Society21. This chapter was adopted from the same publication. This
work was also highlighted in Journal Nature’s news and views section19
and was also highlighted in Angew. Chem. Int. Ed.137
52
CHAPTER 4
MULTIFERROIC METAL ORGANIC FRAMEWORKS:
[(CH3)2NH2]M(HCOO)3(M=Mn, Ni, Co, & Fe)
4.1 Background
In this chapter we demonstrate that multiferroic behavior can be
achieved in metal organic frameworks by using a combination of transition metal ions with hydrogen-bond ordering. Single-phase multiferroic
materials in which magnetic and electrical ordering co-exist are very
rare.58 This is because the two cooperative phenomena require very different molecular interactions that are difficult to incorporate in the
same compound. In the case of ABX3 perovskites, for example, the conventional mechanism for ferroelectricity in classical systems such as
BaTiO3 involves an off-centering of d0 cations on the B-site. This is incompatible with magnetic ordering which requires unpaired spins.58
The d0 requirement can be circumvented if the electrical ordering can
be achieved in a different way. In the classical cases of BiMnO3 and BiFeO3, the electrical ordering is driven by off-centre displacements of the
lone pair Bi3+ ions.58, 138-139 Similarly, in the case of nickel iodine boracite,
Ni3B7O13I, the first ferromagnetic ferroelectric material to be discovered,
the distorted iodine−oxygen octahedron provides the origin for the ferroelectricity.140 There are, of course, other ways in which ferroelectric
ordering can be generated. In non-magnetic ferroelectrics such as NaCaF3, the driving force involves Coulomb interactions, rather than cova53
lency. On the other hand, in potassium hydrogen phosphate, KDP, hydrogen-bond ordering leads to ferroelectricity.141 In CHAPTER 3, we
showed an order disorder structural phase transition at 160K in a cation-templated
MOF
with
the
ABX3
perovskite
topology,
[(CH3)2NH2]Zn(HCOO)3 (DMAZnF).21 In this chapter we show that this
same class of materials can become multiferroic when the zinc is replaced by a transition metal ion. We also give crystallographic evidence
of phase transitions mechanism and low temperature structure.
4.2 Synthesis
Samples of [(CH3)2NH2]M(HCOO)3 (DMAMF = dimethylammonium metal
formate), where M=Mn (Figure 22), Fe, Co, and Ni, were synthesized under solvothermal conditions at 140°C. Typically 5 mmol of metal chloride salts were dissolved in a 60 ml solution of 50 volume% DMF in water and transferred into a Teflon-lined autoclave. This was heated for 3
days at 140 0C. The autoclaves were air cooled and the supernatants
were transferred into a glass beaker for room temperature crystallization. Within a further three days, cubic colorless crystals for Mn and Fe,
red crystals for Co, and green crystals for Ni were obtained. DMAFeF has
not previously been reported in the literature (Structure information is
listed in Table 4, Table 5, Table 6, and Table 7). It was not possible to
make phase pure sample of DMAFeF, but it was possible to separate big
crystals manually under an optical microscope. The manganese analogue was easiest to make and also produced the biggest crystals. It was
also easy to scale up the process to make gram quantities of the frame54
work. Hence, throughout this work DMAMnF has been considered as the
representative of this family and full set of experiments were carried
out on it
4.3 Crystal growth mechanism
Shown in Figure 20 are the optical images of DMAMnF. The growth mechanism of these crystals is hypothesized to be layer by layer growth. In
some cases, as seen in the top left optical image in Figure 20, if the crystals are growing on a flat surface, the bottom most surface would be flat.
Figure 20: Optical images of [(CH3)2NH2]Mn(HCOO)3.
55
Further single crystals of DMAMnF were studied using atomic force microscopy (AFM) to understand the crystal growth mechanism. It was
found to be layer by layer growth. Shown in Figure 21 is a cross-section
of these layers in which steps of a few microns are clearly visible. Face
indexing using the X-rays followed by the AFM results show that the
growth is perpendicular to the <012> plane.
Figure 21: AFM image of a multiferroic MOF dimethylammonium manganese
formate. Crystals grow layer by layer during the room temperature crystallization. Growth is perpendicular to the <012> plane.
56
4.4 Structure
In DMAMF, the DMA cation at the center of the ReO3-type cavity is disordered at room temperature with nitrogen distributed over three
equivalent positions (Figure 22), as in the analogous zinc system (Figure
16). This is a consequence of disordered hydrogen bonding between the
hydrogen atoms of the NH2 group and the oxygen atoms of the formate
framework N…..O ~ . Ǻ .
Figure 22: Building block of [(CH3)2NH2]Mn(HCOO)3, DMMnF. The DMA cation
(A) is at the center of an ReO3 type cavity, formed by manganese (B) and formate (X) ions. Nitrogen is disordered over three positions.
57
4.4.1 Crystallographic data for DMAFeF
Crystallographic data for a multiferroic MOF, DMAFeF, has been presented in the tables below. This as well as other datasets have been
submitted to Cambridge strutural database and can be requested from
there.
Table 4: Structure parameters for DMAFeF
Formula sum
C2.5 H4.5 Fe0.5 N0.5 O3
Formula weight
117.49 g/mol
Crystal system
trigonal
Space-group
R -3 c (167)
Cell parameters
a=8.241(2) Å c=22.545(6) Å
Cell ratio
a/b=1.0000 b/c=0.3655 c/a=2.7357
Cell volume
1325.99(48) Å3
Z
12
Calc. density
1.76549 g/cm3
58
Table 5: Atomic parameters of DMAFeF
Atom Wy Site S.O.F.
ck.
Fe
6b -3.
O
36f 1
C1
18e .2
C2
12c 3.
N
18e .2 0.33
H1 18e .2
H2
36f 1
x/a
y/b
z/c
U [Å2]
0
-0.0084
0.1217
2/3
0.5804
0.231
0.788
1.00000
0.7830
0.7884
1/3
0.2471
0.898
0.358
0
0.0542
0.0833
0.0297
0.0833
0.0833
0.0120
0.059
0.29
Table 6: Anisotropic displacement parameters for DMAFeF, in Å2
Atom
Fe
O
C1
C2
N
U11
0.0195
0.0314
0.0249
0.066
0.032
U22
0.0195
0.0324
0.0249
0.066
0.032
U33
0.0299
0.0439
0.040
0.046
0.047
U12
0.0097
0.0168
0.012
0.0330
0.021
U13
0.0000
0.0062
0.0010
0.0000
-0.004
U23
0.0000
0.0049
0.0010
0.0000
0.004
Table 7: Selected geometric information for DMAFeF
Atoms 1,2
Fe—Oi
Fe—Oii
Fe—Oiii
Fe—Oiv
Fe—O
Fe—Ov
O—C1
C1—Ovi
d 1,2 [Å]
2.139(2)
2.139(2)
2.139(2)
2.139(2)
2.139(2)
2.139(2)
1.239(3)
1.239(3)
Atoms 1,2
C1—H1
C2—Nvii
C2—N
C2—Nviii
C2—H2
N—Nviii
N—Nvii
N—C2ix
59
d 1,2 [Å]
0.90(8)
1.403(7)
1.403(7)
1.403(7)
1.002(10)
1.23(2)
1.23(2)
1.403(7)
Table 7 continued.....
Atoms 1,2,3
Angle 1,2,3
Atoms 1,2,3
Angle 1,2,3 [°]
[°]
Oi—Fe—Oii
180.000
O—C1—Ovi
126.4(5)
i
iii
O —Fe—O
90.53(10)
O—C1—H1
116.8(2)
ii
iii
vi
O —Fe—O
89.47(10)
O —C1—H1
116.8(2)
i
iv
vii
O —Fe—O
89.47(10)
N —C2—N
52.1(8)
Oii—Fe—Oiv
90.53(10)
Nvii—C2—Nviii
52.1(8)
iii
iv
viii
O —Fe—O
89.47(10)
N—C2—N
52.1(8)
i
vii
O —Fe—O
90.53(10)
N —C2—H2
84.(4)
Oii—Fe—O
89.47(10)
N—C2—H2
130.8(18)
Oiii—Fe—O
90.53(10)
Nviii—C2—H2
120.(8)
iv
viii
vii
O —Fe—O
180.00(11)
N —N—N
60.000(2)
Oi—Fe—Ov
89.47(10)
Nviii—N—C2ix
64.0(4)
ii
v
vii
ix
O —Fe—O
90.53(10)
N —N—C2
64.0(4)
iii
v
viii
O —Fe—O
180.00(11)
N —N—C2
64.0(4)
Oiv—Fe—Ov
90.53(10)
Nvii—N—C2
64.0(4)
v
ix
O—Fe—O
89.47(10)
C2 —N—C2
119.1(9)
C1—O—Fe
127.4(3)
Atoms 1,2,3,4
Tors. an.
Atoms 1,2,3,4
Tors. an. 1,2,3,4 [°]
1,2,3,4 [°]
O—Fe—O—C1
-28.6(2)
Fe—O—C1—Ovi
-176.5(2)
viii
O—Fe—O—C1
151.4(2)
N—C2—N—N
67.6(3)
O—Fe—O—C1 -119.08(15) N—C2—N—Nvii
-67.6(3)
O—Fe—O—C1
118.5(5)
N—C2—N—C2ix
33.81(13)
ix
O—Fe—O—C1
60.92(15) N—C2—N—C2
-33.81(13)
(i) 1-y, 2+x-y, z; (ii) -1+y, -x+y, -z; (iii) -1-x+y, 1-x, z; (iv) -x, 2-y, -z;
(v) 1+x-y, 1+x, -z; (vi) 0, 0, 0; (vii) 1-y, x-y, z; (viii) 1-x+y, 1-x, z;
(ix) 0, 0, 0.
60
4.5 Magnetic properties of DMAMF
4.5.1 Magnetic susceptibility
Wang et. al. have shown that DMAMnF, DMACoF, and DMANiF are
canted weak ferromagnets with Tc values of 8.5 K (Figure 23), 14.9 K,
35.6 K, respectively.142 They have also shown that for DMACoF and
DMANiF, spin reorientation takes place at 13.1 K and 14.3 K, respectively. All of the samples show hysteresis loops below their critical temperatures. Using the model developed by Rushbrook and Wood for a Heisenberg antiferromagnet on a simple cubic lattice and/or the molecular
field theory for antiferromagnetism, the magnetic coupling parameters J
were estimated to be -0.23/-0.32 cm-1, -2.3 cm-1, and -4.85 cm-1 for Mn,
Co, and Ni, analogues respectively. Their J values indicate that the dominant superexchange mechanism is antiferromagnetic.
61
Figure 23: Temperature dependence of χM of DMAMnF at H = 1000 Oe from 2
to 300 K. 142
Wang et al. also suggested that the spin canting in these compounds
may originate from the noncentrosymmetric character of the threeatom formate bridge, CHOO-.142-143 In the present work, we have confirmed the findings of Wang et al. and also found that DMFeF is ferromagnetic below 20 K. It is important to note that it is possible to synthesize other weak ferromagnets simply by changing the central amine
cation.144
62
Figure 24: Magnetic susceptibility of DMAFeF
4.6 Structural phase transition
4.6.1 Temperature dependent X-ray diffraction data
Temperature dependent laboratory and synchrotron powder X-ray diffraction (PXRD) data for all samples gave clear indications of a phase
change between room temperature and 100 K (Figure 25). The PXRD
peaks for the DMAMFs at 100 K are shifted to higher angles compared
with those at room temperature as a consequence of lattice contraction
on cooling, and the main peaks in the PXRD pattern showed splitting as63
sociated with a lowering of symmetry. Attempts were made to solve the
structure using synchrotron data but due to the complex twinning nature of the low temperature phase these attempts were unsuccessful.
Figure 25: PXRD pattern for DMAMnF, collected at the Advanced Photon
Source, ANL = .
Ǻ, BM-11)
4.7 Low temperature structure
Single crystal x-ray data were collected for DMAMnF at 110 K, well below the transition temperature, but because of twinning it was not possible to solve and refine the structure to a satisfactory standard. The low
temperature data can be indexed in a monoclinic system and in principle in two possible space groups: C2/c (centrosymmetric) and Cc (non64
centrosymmetric). The monoclinic unit cell has been confirmed for all
the samples by low temperature powder X-ray diffraction.
When trying to refine the structure in the C2/c space group, a number
of drawbacks were encountered: the agreement factors were worst than
in the case of using the space group Cc; the results suggested disordered
DMA cations with the nitrogen atom apparently in two different positions and with two very different N−C bond lengths
.
Å and .
Å
that make no chemical sense for such cation. Because of all these incongruities, the space group (C2/c) was ruled out.
Meanwhile, the low temperature structure could be satisfactorily solved
in the Cc space group with cell parameters of a=14.451(8) Å,
b=8.376(3) Å, c=8.952(4) Å, β=
.
°. The most relevant structural
information is summarized in Table 8 that also includes bond lengths
and bond angles. In addition, we have to note that the crystal is twinned
and that a racemic twin is observed at low temperature, with a Flack parameter of 0.43(7).
65
Figure 26: Rietveld refinement of PXRD data of DMANiF collected at 10 K with
monoclinic unit cell of a=14.451(8) Å b=8.376(3) Å c=8.952(4) Å and
β=
.
°. Pattern is in red color, simulated pattern is in blue and difference plot is in orange.
Table 8: Structural parameters for the low temperature polar phase of
DMAMnF
Phase data
Formula sum
C5 H11 Mn N O6
Formula weight
236.09 g/mol
Crystal system
monoclinic
Space-group
C 1 c 1 (9)
Cell parameters a=14.451(8) Å b=8.376(3) Å c=8.952(4) Å β=
.
Cell ratio
a/b=1.7253 b/c=0.9357 c/a=0.6195
Cell volume
929.97(396) Å3
Z
4
Calc. density
1.68613 g/cm3
RAll
0.0649
66
°
Table 8 continued...
Atom Wyck. Site x/a
y/b
Mn1
4a
1 0.69954 0.25162
O1
4a
1 0.75670 0.02930
O2
4a
1 0.75270 0.16110
O3
4a
1 0.54010 0.14140
O4
4a
1 0.65010 0.33650
O5
4a
1 0.36080 0.14010
O6
4a
1 0.65350 0.51940
C1
4a
1 0.44990 0.21050
H1
4a
1 0.45700 0.33900
C2
4a
1 0.72430 -0.02990
H2
4a
1 0.67400 -0.00200
C3
4a
1 0.66410 0.47790
H3
4a
1 0.69200 0.55500
N11
4a
1 0.89750 0.30860
H11A 4a
1 0.88750 0.41730
H11B 4a
1 0.84180 0.26590
C12
4a
1 0.89510 0.23970
H12A 4a
1 0.95670 0.28020
H12B 4a
1 0.82790 0.27120
H12C 4a
1 0.89890 0.12300
C11
4a
1 1.00270 0.27350
H11C 4a
1 1.00770 0.15890
H11D 4a
1 1.00660 0.33340
H11E 4a
1 1.06250 0.30540
z/c
0.78210
0.93350
0.60700
0.61640
0.96160
0.44830
1.14780
0.53100
0.52800
1.02810
1.05600
1.02220
0.97500
0.52080
0.50780
0.52970
0.36260
0.35670
0.25730
0.37130
0.68460
0.70970
0.78170
0.66910
U [Å2]
0.0210
0.0180
0.0200
0.0230
0.0230
0.0410
0.0410
0.0410
0.0350
0.0350
0.0350
Atom
U11
U22
U33
U12
U13
U23
Mn1
0.0140
0.0121
0.0073
0.0004
0.0039
0.00053
O1
0.0211
0.0172
0.0049
0.0027
0.0057
0.00580
O2
0.0230
0.0210
0.0140
-0.0009
0.0130
0.00190
O3
0.0180
0.0200
0.0220
-0.0015
0.0090
0.00310
O4
0.0240
0.0150
0.0340
-0.0068
0.0160
-0.00900
O5
0.0130
0.0210
0.0210
-0.0010
0.0033
0.00590
O6
0.0320
0.0160
0.0450
-0.0059
0.0270
-0.01040
C1
0.0170
0.0182
0.0180
-0.0100
0.0080
0.00300
67
Table 8 continued...
Atom
U11
U22
U33
U12
U13
U23
C2
0.0211
0.0172
0.0049
0.0027
0.0057
0.0058
C3
0.0120
0.0190
0.0160
0.0040
0.0050
0.0033
N11
0.0160
0.0180
0.0240
-0.0006
0.0109
0.0028
C12
0.0330
0.0290
0.0220
-0.0030
0.0160
-0.0010
C11
0.0170
0.0200
0.0250
-0.0030
0.0050
0.0020
Selected geometric informations
Atoms 1,2
d 1,2 [Å]
Atoms 1,2
d 1,2 [Å]
Mn1—O6i
2.178(5)
O4—C3
1.275(8)
Mn1—O4
2.186(6)
O5—C1
1.255(10)
iv
Mn1—O1
2.200(5)
O5—Mn1
2.216(5)
Mn1—O3
2.203(5)
O6—C3
1.259(9)
Mn1—O2
2.203(5)
O6—Mn1v
2.178(5)
ii
vi
Mn1—O5
2.216(5)
C2—O2
1.256(8)
O1—C2
1.260(8)
N11—C11
1.503(12)
O2—C2iii
1.256(8)
N11—C12
1.513(14)
O3—C1
1.263(10)
Atoms 1,2,3
Angle 1,2,3 [°]
Atoms 1,2,3
Angle 1,2,3 [°]
O6i—Mn1—O4
89.8(2)
O3—Mn1—O5ii
179.3(2)
i
ii
O6 —Mn1—O1
175.7(3)
O2—Mn1—O5
89.30(19)
O4—Mn1—O1
89.0(2)
C2—O1—Mn1
126.6(4)
O6i—Mn1—O3
94.6(2)
C2iii—O2—Mn1
124.7(4)
O4—Mn1—O3
90.4(2)
C1—O3—Mn1
127.8(4)
O1—Mn1—O3
89.56(18)
C3—O4—Mn1
125.1(5)
i
iv
O6 —Mn1—O2
91.7(2)
C1—O5—Mn1
127.7(4)
O4—Mn1—O2
178.3(2)
C3—O6—Mn1v
126.4(5)
O1—Mn1—O2
89.40(18)
O5—C1—O3
124.7(4)
vi
O3—Mn1—O2
90.2(2)
O2 —C2—O1
126.6(7)
O6i—Mn1—O5ii
85.9(2)
O6—C3—O4
124.8(7)
ii
O4—Mn1—O5
90.1(2)
C11—N11—C12
111.3(7)
ii
O1—Mn1—O5
89.99(19)
(i) x, 1-y, -0.5+z; (ii) 0.5+x, 0.5-y, 0.5+z; (iii) x, -y, -0.5+z; (iv) -0.5+x, 0.5-y, 0.5+z;
(v) x, 1-y, 0.5+z; (vi) x, -y, 0.5+z.
68
Furthermore, Rietveld refinement of powder neutron data confirms the
low temperature space group. Despite several attempts it was not possible to synthesize deuterated analogue of DMAMnF. High intensity data
was collected at the NIST national laboratory. Despite the high background because of the hydrogenated sample, the fit to the low temperature Cc phase is remarkably good.
69
Figure 27: Reietveld refinement of powder neutron data collected at NIST
with the low temperature Cc phase of DMAMnF. Black is the experimental
data, Red is simulated pattern, Blue is the Bragg positions and Green is the
difference between experimental and simulated.
4.8 Dielectric measurements
As expected, this phase change is associated with a dielectric εr) ano-
maly. Dielectric constant measurements were carried out on single crystals of DMAMnF, DMAFeF, and DMACoF as well as on a powder sample
of the nickel phase. The dielectric constant of DMAMnF shows a clear
anomaly close to 185 K on cooling (Figure 28). A clear hysteresis of
about 10 K was seen when compared with the transition on heating. The
70
shape of the dielectric plot suggests that DMMnF is undergoing a paraelectric to antiferroelectric phase transition with εr values of around 25
and 9 respectively. This is a result of the structural phase transition due
to the ordering of the nitrogen atoms. No other dielectric anomaly was
observed while cooling the sample down to 1.8 K. The transition is of an
Figure 28: Dielectric constant of DMAMnF as a function of temperature with
no magnetic field and with that of 5 Tesla. The measurements were done at 1
kHz, using amplitude of 1V.
order-disorder nature, rather than displacive, and the shape resembles
the antiferroelectric transition for NH4H2PO4 (ADP).136 However the low
temperature structure is a polar structure. Careful experiment does indeed show a −type peak as shown in Figure 29. Figure 29 also reveals a
magneto-dielectric coupling in DMAMnF. Notice that rate of change sign
71
has changed from positive to negative for the dielectric constants of
DMAMnF measured below the phase transition temperatures as a function of magnetic field.
Similar hydrogen bond ordering is responsible for the ADP phase transition, which is at around 148 K. The dielectric constants for the paraelectric phases of DMFeF, DMCoF, and DMNiF were found to be approximately 45, 50, and 30, respectively; their transition temperatures on
cooling were found to be 160 K, 165 K, and 180 K, respectively. As expected from their similar structures and the origin of the disorder, the
shapes of the anomalies are essentially the same for the other three analogues.
72
Figure 29: Dielectric constant of DMAMnF measured as a function of temperature and magnetic field. Bottom two plots reveal a magneto-dielectic coupling.
73
4.9 Heat capacity measurements
Dielectric constant findings were corroborated by specific heat measurements. The measurements were carried out on 20-30 single crystals
by immersing them inside N-grease on a Quantum Design PPMS sample
holder. Measurements were performed several times to ensure reproducibility and appropriate backgrounds were measured before each experiment. The specific heat of DMAMnF, which was measured as a function of temperature from 1.8 K to 300 K, shows clear anomalies at 183 K
and 8.4 K corresponding to the transitions leading to electrical and
magnetic ordering, respectively (Figure 30). Both the transition temperatures are in agreement with dielectric and magnetic susceptibility
measurements. The area under the Cp/T curve around 183 K yielded a
value for ΔS of 0.9 J/mol-K. For a complete order-disorder transition ΔS
is expected to be given by Rln(N) where N is the number of sites in the
disordered system. For N=3, ΔS would therefore be 9.1 J/mol-K, which is
almost an order of magnitude larger than the observed value. This suggests that the transition is more complex than a simple 3-fold orderdisorder model. It appears, that as the sample is cooled through the
transition, the compound becomes only partly ordered and the long
range ordering takes place over a broad range of temperatures.
74
Figure 30: Heat capacity of DMAMnF as a function of temperature. The anomalies relating to electrical ordering and magnetic ordering are clearly visible.
Detailed studies of the specific heat changes for DMAMF (M=Mn, Co, Ni)
through the magnetic phase transition show that Tc decreases from 8.4
K to 6.7 K on increasing the magnetic field from 0 to 9 Tesla, (Figure 31).
This is consistent for the predominantly antiferromagnetic behavior of
these systems. Low temperature Q-Band EPR spectra for DMMnF
(Figure 32) have shed further light on the magnetic phase transition.
Measurements were made on single crystals of DMMnF to find if this
magnetic transition was accompanied by a structural phase transition,
since our PXRD facility did not enable us to reach these temperatures.
As seen in Figure 32 the single EPR peak clearly splits into two, implying
75
two differently oriented domains below about 6 K. Thus the magnetic
transition is accompanied by a structural change as well.
Figure 31: Effect of magnetic field on the magnetic phase transition in
DMAMnF on cooling.
76
Figure 32: Temperature dependence of Q-Band EPR spectra of DMAMnF.
4.10 Summary and conclusions
In conclusion, we report four multiferroic metal organic frameworks,
((CH3)2NH2)M(HCOO)3, with M= Mn, Fe, Co, and Ni, which belong to the
ABX3 type perovskite family with A = [(CH3)2NH2]+, B= M2+ and X= HCOO. The dimethylammonium cation is dynamically disordered in the rhombohedral paraelectric phase and the transition to the monoclinic ferroelectric phase involves hydrogen bond ordering of the DMA cations at
temperatures in the range 160 K - 185 K. On further cooling, these materials become magnetically ordered (8 K-36 K), and below these temperatures the antiferroelectric order co-exists with weakly ferromagnetic order. Our findings illustrate a new approach to the creation of sys77
tems exhibiting multiferroic behavior whereby electrical order involves
hydrogen bonding. These results suggest a highly promising new mechanism for this important behavior and opens up fresh opportunities
for production of lead-free multiferroic structures tailored for specific
technological applications.
4.11 Resulting publications and comments
Work resulted into a publication in the Journal of the American Chemical Society.20 This chapter was adopted from the same publication. This
work was highlighted in Journal Nature19, 145, and in Angew. Chem. Int.
Ed.137
78
CHAPTER 5
GLASSY BEHAVIOR OF (CH3)2NH2Zn(HCOO)3
5.1 Background
Glassy behavior related to orientational ordering is observed in fullerides and their rotor-stator complexes, as well as in many polymeric
systems and plastic crystals.146-150 A knowledge of the orientational ordering is important because it influences the properties and phase diagrams of such systems. For example, the superconducting properties of
A3C60 and Na2AC60 compounds are strongly influenced by the orientational state of the fulleride anions.151 In the case of C60, following a first
order phase transition around 260 K, a more subtle phase transition is
observed around 90 K.152 The later transition is attributed to the kinetics of molecular reorientation leading to glassy behavior. This glassy
state is obtained when the thermal energy is not sufficient to overcome
the potential energy barrier that separates the orientational configurations. Two energetically distinct orientations exist with the majority of
the molecules being in the lower energy orientation below 90 K. Above
90 K, the population of the dominant orientation decreases with increasing temperature until, at the 260 K transition, there is a discontinuous change of the fractional occupancy from 0.63 to 0.5.
In this chapter, we describe a comparable glassy behavior in a metal organic
framework
(MOF)
with
79
the
perovskite
architecture,
[(CH3)2NH2]Zn(HCOO)3 (DMAZnF). We also report a memory effect related to the temperature dependent relaxation in the same compound.
5.2 Debye law and remnant specific heat
In previous chapters we reported a series of multifunctional metal organic frameworks exhibiting ferromagnetic and ferroelectric order, simultaneously.20-21 During the thermodynamic characterization, we observed an unusually large specific heat at lower temperatures for these
materials. It is well known that at relatively low temperatures, in the
range of 2 - 30 K, glasses also have a phonon heat capacity that is larger
than the simple prediction of the Debye T3 law. This excess specific heat
gives rise to a peak in C/T3 vs T and is generally ascribed to localized vibrations, domain wall motions of the glassy mosaic structure, or transverse phonon modes.153-155 These modes are usually seen in Raman scattering as low-frequency peaks. Because these low-frequency states are
observed in glasses of all bonding types (metallic, ionic, covalent, etc.),
they are thought to be a fundamental feature of glass dynamics.156 A
number of crystalline materials also exhibit a low temperature peak in
C/T3. This has been used to study the nature of vibrations and disorder
in materials like quartz SiO2 and the pyrochlore Bi2Ti2O7.153 In the
present case, plotting C/T3 for the DMAZnF also revealed a clearly defined broad peak at 25 K (Figure 33), well below its ferroelectric phase
transition. This observation suggests that the ferroelectric ordering was
not the only cooperative process below the 156 K transition temperature (Tc), and that there is also another kind of ordering process, such as
80
glass formation, taking place at a shorter length scale. This prompted us
to study the kinetic behavior of the DMA cation in DMAZnF which is involved in the ferroelectric ordering in this compound.
Figure 33: Temperature dependent of low-temperature specific heat (plotted
as C/T3 versus T).
81
5.3 NMR measurements
For recollection, DMAZnF has the same architecture as that of oxide perovskites. Metal atoms sit at the corners of a cube and are connected by
formate ligands. The cavity of the cube is occupied by a dimethylammonium cation, the nitrogen of which is disordered over three distinct positions as a result of hydrogen bonding between the amine hydrogens
and oxygens of the framework (Figure 34). Upon cooling, the compound
goes under a phase transition, due to the ordering of nitrogen, leading to
ferroelectric ordering.
To study the kinetics we measured the NMR spin-lattice relaxation time
(T1) of DMAZnF over a wide temperature range (4-250 K). The sample
consisted of 20-30 sub-millimeter sized single crystals, synthesized as
described in section.21, 142 The nuclear spin-lattice relaxation time, T1, of
the CH3 protons was used as a probe of the local order and molecular
dynamics time scale ≈
-10 s)
of the (CH3)2NH2+ (DMA) unit.
82
Figure 34: Crystal structure of [(CH3)2NH2]Zn(HCOO)3 at room temperature.
The purple spheres represent the three dynamically disordered sites for the N
atom of the dimethylammonium formate moiety. The freezing of these positions is proposed to be the mechanism underlying the ferroelectric transition
at 156 K.
The CH3 proton resonance was chosen because it has a strong, sharp
peak, due to the motional narrowing caused by the CH3 group
rotation.157 The NH2 protons were undetectable, very likely because of
broadening due to the 14N quadrupolar interaction. T1 was measured using a Tecmag Aries/Libra spectrometer with a home-built NMR probe at
a field of .
T
. M(z for protons , using the standard π/ -τ-π/
saturation recovery procedure.158 Small temperature steps of 0.1 K were
utilized around Tc (156 K).
83
5.4 Results and discussion
Figure 35 summarizes the temperature dependence of the CH3 proton
T1-1 (the spin-lattice relaxation rate). The graph has been divided into
three regions (A, B and C) guided by natural breaks in the slope. In region C, DMAZnF is in the high-temperature, paraelectric (PE) phase. On
lowering the temperature, T1-1 increases steadily to a maximum around
Tc, whereafter it starts to decrease as DMAZnF enters the ferroelectrically ordered phase, regions A and B. In region A, T1-1 follows a different
curve, implying a change in the spin-lattice relaxation pathway. This is
because the motion is dominated by slowing of the methyl-group rotations below ~40 K. A similar observation has been reported by Clough
et. al.157 in methyl malonic acid and related compounds.
84
Figure 35: Temperature dependence of the CH3 proton spin-lattice relaxation
rate, T1-1, of DMAZnF. A, B and, C refer to the glass, ferroelectric (FE) and, paraelectric (PE) phases, respectively. Solid lines are the theoretical fits to the
BPP equation. Arrows indicate the direction of the temperature scan. The inset shows the Arrhenius plot for this path.
In the temperature range 65 K - 250 K, the spin-lattice relaxation time is
completely reversible along the main path (Path I, Figure 35). This reversibility holds as long as the sample is not cooled below 40 K. When
cooled below 40 K, T1 follows a different curve on warming. This important observation is discussed later.
85
Figure 36: Thermal cycles for paths II and III, wherein the spin-lattice relaxation rate jumps back to the main path (path I), are highlighted by arrows. The
dashed lines are the projected paths had no jumps occurred. Solid (thick)
lines are the theoretical fits to the BPP equation.
Temperature dependence of T1 for the paraelectric phase (region C) and
for path I in region B was analyzed using the Bloembergen-PurcellPound (BPP) formalism159, in which the relaxation rate is related to the
correlation time τc. Correlation time is the characteristic time between
significant fluctuations in the local magnetic field experienced by a spin
due to molecular motions or reorientations of a molecule. Relaxation is
caused by the molecular motion of the entity to which the proton is attached and so, we consider the homonuclear dipole-dipole interaction
86
between the protons in the methyl group in this case. The BPP
equation159 for rigid rotor motion of a methyl group in a rigid solid is
2
1
9   0   

T1 20  4r 3 
2
 c
4 c


 1   2 2 1  4 2 2
c
c





where γ is the gyromagnetic ratio of 1H, r = 1.67 Å is the distance between CH3 hydrogens11, and ω is the 1H resonance frequency.
It was assumed that the temperature dependence of τc follows an Arrhenius-like behavior with τc = τ0exp(Ea/RT), where τ0 is the single particle correlation time, Ea the activation energy for the dynamic process,
and R the gas constant. τc was extracted by fitting the experimental T1
data to the BPP and Arrhenius equations in the C and B regions, treating
Ea and τ0 as variables. T1 data within a few degrees of Tc were not included in the fitting procedure because of the cooperative phenomena
that occur close to Tc. The resulting values of Ea and τ0 enabled us to calculate the correlation times for the protons in the CH3 group; these values are presented in the inset of Figure 35 as an Arrhenius plot of ln τc
versus 1/T. It is clear that T1 follows Arrhenius-like behavior both above
and below Tc. Table 9 summarizes the Arrhenius parameters obtained in
the PE and FE phases over the reversible range, 65 - 250 K. As can be
seen in Table 9, Ea remains essentially unchanged (8 ± 0.3 kJ/mol) for
this path while τ0 increases by an order of magnitude as the material enters the ferroelectric phase. Consequently, τc shows an anomalous in87
crease below Tc, e.g. it increases from 3.0·10-10 s at 160 K to 1.7·10-9 s at
150 K. Such large anomalous slowing down of the motional fluctuations
(hopping) of the DMA unit coincident with Tc implies that the FE transition results from a freezing of the DMA hopping motion between its
three possible sites (shown in Fig. 2).
In region B, T1 becomes multi-valued over the range 65 K - Tc, and the
behavior depends on the cooling history. Figure 36 shows two sets of
our T1 measurements (labeled paths II and III), made on raising the
temperature after the sample was cooled down to about 4 K. In general,
T1 shows sudden jumps at unpredictable temperatures depending on
the thermal cycling range and cooling rate. The jumps from a given metastable path (such as II and III) occur at unpredictable temperatures,
implying that the structures attained are very close in energy. This existence of several different local structures is also consistent with glassy
behavior.
88
Table 9: Arrhenius parameters for the CH3 protons in DMAZnF in the PE and
FE phases
Phase
τ0 (s)
Ea
(kJ/mol)
PE
8.0 ± 0.1
(7.4 ± 0.5)·10-13
FE, Path I
7.9 ± 0.2
(2.8 ± 0.4)·10-12
FE, Path II (jump)
6±1
~ 1·10-10
FE, Path III (jump)
9±1
~ 4·10-12
FE, Path IV (no jump)
9.7 ± 0.3
(1.8 ± 0.4)·10-12
Paths for which the T1 curve remains smooth without any jumps, but
different from the main path, occurred only when the sample was
cooled rather quickly (>5 K/min). An Arrhenius analysis of one such a
path, following the above BPP procedure, yielded Arrhenius parameters
Ea=9.7±0.3
kJ/mol
and
τ0=(1.8±0.4)·10-12
89
s
(Path
IV
in
Table 9, not shown in Figure 36). For this case both τc and Ea increase
significantly as compared to the slow cooling case (path I). Since T1 depends on the local geometry, these data show that the DMA moiety finds
distinctly different local environments depending on the sample cooling
history, a clear signature of a glassy phase.
The relaxation rate, which decreases rapidly between 156 and 65 K,
starts to decrease more slowly at about 40 K, implying that a new relaxation pathway begins to operate at this temperature and below. The T1-1
data can be decomposed into three component curves: one following
that of pathway I, the second showing a maximum around 40 K, and a
third essentially constant below about 10 K. The latter two pathways
are analogous to the relaxation processes found in many methylcontaining solids. The second relaxation curve can be ascribed to thermally activated rotation and the third to a methyl group tunneling
process.
5.5 Summary and conclusions
In summary, we used the specific heat and 1H NMR T1 measurements to
study the motional dynamics of the central amine moiety that is responsible for ferroelectric ordering of DMAZnF at 156 K. In particular, we
were able to study the long-range and short-range ordering behavior
using spin lattice relaxation rates. Both behaviors appear to be related
to the motional dynamics of the DMA moiety. Below 156 K, the moiety
starts becoming more ordered with decreasing temperature. Initially,
90
this involves ordering of the amine NH2 group. Further, below 40 K, rotations of the associated methyl groups start freezing, leading to multiple states with close underlying energies showing a glass-like effect.
Local coordination environments in the framework remain unchanged
as no other anomalies were observed in the specific heat. Warming up
from 4 K, results in a memory effect, leading to different random paths
in the temperature range of 65 -140 K due to the glass-like behavior of
the framework below 40 K. To the best of our knowledge, this is the first
report of a MOF showing glassy behavior and memory effect related to
dynamics. These effects could potentially be used for manipulating other properties, such as gas absorption, catalysis, and electronic behavior,
for which the MOFs are well known.15, 160
5.6 Resulting publications and comments
This work has been adopted from a manuscript which will be submitted
shortly. Work has been presented in American physical society and
American chemical society meetings.
91
CHAPTER 6
SUMMARY AND CONCLUSIONS
During the course of this dissertation, I worked on several projects related to the field of metal organic frameworks. I was able to synthesize a
new family of nickel-1,4-cyclohexanedicarboxylate. This family was studied in detail and I found that, akin to zeolite synthesis, kinetic control
could also be applied to the synthesis of metal organic frameworks. I also proposed a new method to make nanoparticles of MOFs by using nano-channels of anodized alumina template. This method was viable and
30-60 nm size nanorods of a nickel-1,4cyclohexanedicarboxylate
framework.were synthesized I also spent considerable time of my PhD
towards depositing a single monolayer of a two dimensional metal organic framework. This project was challenging as metal organic framework are usually synthesized at higher temperatures. However, I was
able to make some beautiful nanostructures during my attempts to deposit a single monolayer of a MOF.
During this PhD, I discovered approximately 15 new structures or phases of metal organic frameworks. These materials were thoroughly characterized and relevant properties were measured. Some of this work is
still in progress and will likely result into further publications.
For this dissertation, I have focused on frameworks with perovskite architecture. Perovskites are arguably the most important inorganic class
92
of materials with applications ranging from surfactants to superconductivity. I was able to synthesize six different metal organic frameworks
with this famous topology, though four of them are previously know. I
have deliberately left one of them out of this dissertation as it did not
fall into the overall theme of multiferroic/multifunctional metal organic
frameworks.
Multiferroic materials are rare compounds featuring at least two ferroic
properties with a majority of them displaying (anti)ferro – electricity or
magnetism. Currently, the most famous compounds displaying such behavior are oxide perovskites. One of the most common mechanism for
ferroelectric behavior requires an empty d-orbital which usually means
that the material is diamagnetic. Hence there is a need for multiferroic
materials in which two independent mechanisms can determinethe
electric and magnetic ordering. I was able to achieve this using the hybrid perovskites.
Hybrid perovskites of general formula (CH3)2NH2M(HCOO)3 have a ReO3
type cage made up of formate and metal ions. The metal ions sit at the
corners of the cubes and they are connected to each other via coordination bonding with oxygen of the formate ion. The dimethylammonium
cation is located at the center of this cavity. The amine hydrogen atoms
make hydrogen bonds with the oxygen atoms of the metal formate
framework. Because of this hydrogen bonding, the nitrogen of the ammonium cation is disordered over three equal positions at room tem93
perature. Cooling down these materials below 180 K, leads to a lowering
in symmetry, a result of the ordering of nitrogen atoms.
This phase transition is associated with a dielectric anomaly. Carefully
done dielectric measurements show that the anomaly is a -type peak
usually associated with paraelectric to ferroelectric phase transition.
Low temperature single crystal measurements aided by powder X-ray
diffraction and neutron diffraction experiments show that low temperature phase crystallizes in monoclinic symmetry and Cc space group. Cc
belongs to one of the 10 polar point groups which are requirements for
ferroelectricity. Furthermore, magnetic fields seem to affect this dielectric anomaly, suggesting that these hybrid perovskites have a magnetodielectric effect. This phase transition was studied in detail by electron
paramagnetic resonance, heat capacity, and 1H NMR relaxation time
measurements.
Close to 0 K, specific heat data suggest that there is a remnant specific
heat, a classic signature of amorphous or glassy materials. NMR data
shows that these hybrid materials are indeed glassy below 40 K with
many confirmations with close underlying energies. This effect is related to the rotation of methyl motors. NMR results also show an anomaly at the same temperature where dielectric anomaly is present. Methyl protons slow down by a factor to suggest that dielectic anomaly is
indeed due to the ordering of nitrogen atoms.
94
APPENDIX
CRYSTALLOGRAPHIC INFORMATION FILES
Dimethylammonium iron formate:
# Methyl Moiety X-C-H Angles are unusual because of the disorder
data_Dimethylammoniumironformate
_audit_creation_method
SHELXL-97
_chemical_name_systematic
_chemical_name_common
Dimethylammoniumironformate
_chemical_formula_moiety
'C9 H9 Fe3 O18, 3(C2 H6 N)'
_chemical_formula_sum
'C15 H27 Fe3 N2.97 O18'
_chemical_formula_weight
704.53
loop_
_atom_type_symbol
_atom_type_description
_atom_type_scat_dispersion_real
_atom_type_scat_dispersion_imag
_atom_type_scat_source
'C' 'C' 0.0033 0.0016
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'H' 'H' 0.0000 0.0000
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'N' 'N' 0.0061 0.0033
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'O' 'O' 0.0106 0.0060
95
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'Fe' 'Fe' 0.3463 0.8444
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
_symmetry_cell_setting
Hexagonal
_symmetry_space_group_name_H-M R-3c
loop_
_symmetry_equiv_pos_as_xyz
'x, y, z'
'-y, x-y, z'
'-x+y, -x, z'
'y, x, -z+1/2'
'x-y, -y, -z+1/2'
'-x, -x+y, -z+1/2'
'x+2/3, y+1/3, z+1/3'
'-y+2/3, x-y+1/3, z+1/3'
'-x+y+2/3, -x+1/3, z+1/3'
'y+2/3, x+1/3, -z+5/6'
'x-y+2/3, -y+1/3, -z+5/6'
'-x+2/3, -x+y+1/3, -z+5/6'
'x+1/3, y+2/3, z+2/3'
'-y+1/3, x-y+2/3, z+2/3'
'-x+y+1/3, -x+2/3, z+2/3'
'y+1/3, x+2/3, -z+7/6'
'x-y+1/3, -y+2/3, -z+7/6'
'-x+1/3, -x+y+2/3, -z+7/6'
'-x, -y, -z'
96
'y, -x+y, -z'
'x-y, x, -z'
'-y, -x, z-1/2'
'-x+y, y, z-1/2'
'x, x-y, z-1/2'
'-x+2/3, -y+1/3, -z+1/3'
'y+2/3, -x+y+1/3, -z+1/3'
'x-y+2/3, x+1/3, -z+1/3'
'-y+2/3, -x+1/3, z-1/6'
'-x+y+2/3, y+1/3, z-1/6'
'x+2/3, x-y+1/3, z-1/6'
'-x+1/3, -y+2/3, -z+2/3'
'y+1/3, -x+y+2/3, -z+2/3'
'x-y+1/3, x+2/3, -z+2/3'
'-y+1/3, -x+2/3, z+1/6'
'-x+y+1/3, y+2/3, z+1/6'
'x+1/3, x-y+2/3, z+1/6'
_cell_length_a
8.241(2)
_cell_length_b
8.241
_cell_length_c
22.545(6)
_cell_angle_alpha
90.00
_cell_angle_beta
90.00
_cell_angle_gamma
_cell_volume
_cell_formula_units_Z
120.00
1326.2(5)
2
_cell_measurement_temperature
273(2)
97
_cell_measurement_reflns_used
?
_cell_measurement_theta_min
?
_cell_measurement_theta_max
?
_exptl_crystal_description
_exptl_crystal_colour
Cube
colorless
_exptl_crystal_size_max
0.2
_exptl_crystal_size_mid
0.1
_exptl_crystal_size_min
0.1
_exptl_crystal_density_meas
?
_exptl_crystal_density_diffrn
1.765
_exptl_crystal_density_method
_exptl_crystal_F_000
'not measured'
720
_exptl_absorpt_coefficient_mu
1.705
_exptl_absorpt_correction_type 'multi scan'
_exptl_absorpt_correction_T_min ?
_exptl_absorpt_correction_T_max ?
_exptl_absorpt_process_details 'SADABS'
_exptl_special_details
_diffrn_ambient_temperature
273(2)
_diffrn_radiation_wavelength
0.71073
_diffrn_radiation_type
_diffrn_radiation_source
MoK\a
'fine-focus sealed tube'
_diffrn_radiation_monochromator graphite
_diffrn_measurement_device_type 'CCD area Detector'
_diffrn_measurement_method
'Omega scan'
_diffrn_detector_area_resol_mean ?
98
_diffrn_standards_number
?
_diffrn_standards_interval_count ?
_diffrn_standards_interval_time ?
_diffrn_standards_decay_%
?
_diffrn_reflns_number
1107
_diffrn_reflns_av_R_equivalents 0.0560
_diffrn_reflns_av_sigmaI/netI
0.0493
_diffrn_reflns_limit_h_min
-10
_diffrn_reflns_limit_h_max
10
_diffrn_reflns_limit_k_min
-10
_diffrn_reflns_limit_k_max
7
_diffrn_reflns_limit_l_min
-26
_diffrn_reflns_limit_l_max
22
_diffrn_reflns_theta_min
3.38
_diffrn_reflns_theta_max
26.71
_reflns_number_total
_reflns_number_gt
301
228
_reflns_threshold_expression
>2sigma(I)
_computing_data_collection
?
_computing_cell_refinement
?
_computing_data_reduction
?
_computing_structure_solution
'SHELXS-97 (Sheldrick, 1990)'
_computing_structure_refinement 'SHELXL-97 (Sheldrick, 1997)'
_computing_molecular_graphics
?
_computing_publication_material ?
_refine_special_details
99
;
Refinement of F^2^ against ALL reflections. The weighted R-factor wR
and goodness of fit S are based on F^2^, conventional R-factors R are
based on F, with F set to zero for negative F^2^. The threshold expression of F^2^ > 2sigma(F^2^) is used only for calculating R-factors(gt)
etc. and is not relevant to the choice of reflections for refinement. Rfactors based on F^2^ are statistically about twice as large as those
based on F, and R-factors based on ALL data will be even larger.
;
_refine_ls_structure_factor_coef Fsqd
_refine_ls_matrix_type
full
_refine_ls_weighting_scheme
calc
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.0503P)^2^+0.0000P]
where P=(Fo^2^+2Fc^2^)/3'
_atom_sites_solution_primary
direct
_atom_sites_solution_secondary difmap
_atom_sites_solution_hydrogens geom
_refine_ls_hydrogen_treatment
_refine_ls_extinction_method
mixed
none
_refine_ls_extinction_coef
?
_refine_ls_number_reflns
301
_refine_ls_number_parameters
_refine_ls_number_restraints
31
3
_refine_ls_R_factor_all
0.0561
_refine_ls_R_factor_gt
0.0403
100
_refine_ls_wR_factor_ref
0.0930
_refine_ls_wR_factor_gt
0.0883
_refine_ls_goodness_of_fit_ref 1.074
_refine_ls_restrained_S_all
_refine_ls_shift/su_max
_refine_ls_shift/su_mean
1.069
0.002
0.000
loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_U_iso_or_equiv
_atom_site_adp_type
_atom_site_occupancy
_atom_site_symmetry_multiplicity
_atom_site_calc_flag
_atom_site_refinement_flags
_atom_site_disorder_assembly
_atom_site_disorder_group
Fe Fe 0.0000 1.0000 0.0000 0.0229(4) Uani 1 6 d S . .
O O -0.0084(3) 0.7830(3) 0.05427(11) 0.0355(7) Uani 1 1 d . . .
C1 C 0.1217(6) 0.7884(6) 0.0833 0.0298(12) Uani 1 2 d S . .
C2 C 0.6667 0.3333 0.0297(3) 0.059(2) Uani 1 3 d SD . .
N N 0.5804(14) 0.2471(14) 0.0833 0.035(3) Uani 0.33 2 d SPD . .
H1 H 0.231(10) 0.898(10) 0.0833 0.059(19) Uiso 1 2 d S . .
101
H2 H 0.788(10) 0.358(19) 0.012(3) 0.29(6) Uiso 1 1 d D . .
loop_
_atom_site_aniso_label
_atom_site_aniso_U_11
_atom_site_aniso_U_22
_atom_site_aniso_U_33
_atom_site_aniso_U_23
_atom_site_aniso_U_13
_atom_site_aniso_U_12
Fe 0.0195(4) 0.0195(4) 0.0299(7) 0.000 0.000 0.0097(2)
O
0.0314(14)
0.0324(15)
0.0439(15)
0.0049(12)
-0.0062(12)
0.0168(12)
C1 0.0249(19) 0.0249(19) 0.040(3) -0.0010(12) 0.0010(12) 0.012(2)
C2 0.066(3) 0.066(3) 0.046(4) 0.000 0.000 0.0330(16)
N 0.032(5) 0.032(5) 0.047(8) 0.004(3) -0.004(3) 0.021(5)
_geom_special_details
;
All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are
only used when they are defined by crystal symmetry. An approximate
(isotropic) treatment of cell esds is used for estimating esds involving
l.s. planes.
;
loop_
102
_geom_bond_atom_site_label_1
_geom_bond_atom_site_label_2
_geom_bond_distance
_geom_bond_site_symmetry_2
_geom_bond_publ_flag
Fe O 2.139(2) 2_675 ?
Fe O 2.139(2) 20_455 ?
Fe O 2.139(2) 3_465 ?
Fe O 2.139(2) 19_575 ?
Fe O 2.139(2) . ?
Fe O 2.139(2) 21_665 ?
O C1 1.239(3) . ?
C1 O 1.239(3) 16_454 ?
C1 H1 0.90(8) . ?
C2 N 1.403(7) 2_655 ?
C2 N 1.403(7) . ?
C2 N 1.403(7) 3_665 ?
C2 H2 1.002(10) . ?
N N 1.23(2) 3_665 ?
N N 1.23(2) 2_655 ?
N C2 1.403(7) 16_544 ?
loop_
_geom_angle_atom_site_label_1
_geom_angle_atom_site_label_2
_geom_angle_atom_site_label_3
_geom_angle
103
_geom_angle_site_symmetry_1
_geom_angle_site_symmetry_3
_geom_angle_publ_flag
O Fe O 180.0 2_675 20_455 ?
O Fe O 90.53(10) 2_675 3_465 ?
O Fe O 89.47(10) 20_455 3_465 ?
O Fe O 89.47(10) 2_675 19_575 ?
O Fe O 90.53(10) 20_455 19_575 ?
O Fe O 89.47(10) 3_465 19_575 ?
O Fe O 90.53(10) 2_675 . ?
O Fe O 89.47(10) 20_455 . ?
O Fe O 90.53(10) 3_465 . ?
O Fe O 180.00(11) 19_575 . ?
O Fe O 89.47(10) 2_675 21_665 ?
O Fe O 90.53(10) 20_455 21_665 ?
O Fe O 180.00(11) 3_465 21_665 ?
O Fe O 90.53(10) 19_575 21_665 ?
O Fe O 89.47(10) . 21_665 ?
C1 O Fe 127.4(3) . . ?
O C1 O 126.4(5) . 16_454 ?
O C1 H1 116.8(2) . . ?
O C1 H1 116.8(2) 16_454 . ?
N C2 N 52.1(8) 2_655 . ?
N C2 N 52.1(8) 2_655 3_665 ?
N C2 N 52.1(8) . 3_665 ?
N C2 H2 84(4) 2_655 . ?
104
N C2 H2 130.8(18) . . ?
N C2 H2 120(8) 3_665 . ?
N N N 60.000(2) 3_665 2_655 ?
N N C2 64.0(4) 3_665 16_544 ?
N N C2 64.0(4) 2_655 16_544 ?
N N C2 64.0(4) 3_665 . ?
N N C2 64.0(4) 2_655 . ?
C2 N C2 119.1(9) 16_544 . ?
loop_
_geom_torsion_atom_site_label_1
_geom_torsion_atom_site_label_2
_geom_torsion_atom_site_label_3
_geom_torsion_atom_site_label_4
_geom_torsion
_geom_torsion_site_symmetry_1
_geom_torsion_site_symmetry_2
_geom_torsion_site_symmetry_3
_geom_torsion_site_symmetry_4
_geom_torsion_publ_flag
O Fe O C1 -28.6(2) 2_675 . . . ?
O Fe O C1 151.4(2) 20_455 . . . ?
O Fe O C1 -119.08(15) 3_465 . . . ?
O Fe O C1 118.5(5) 19_575 . . . ?
O Fe O C1 60.92(15) 21_665 . . . ?
Fe O C1 O -176.5(2) . . . 16_454 ?
N C2 N N 67.6(3) 2_655 . . 3_665 ?
105
N C2 N N -67.6(3) 3_665 . . 2_655 ?
N C2 N C2 33.81(13) 2_655 . . 16_544 ?
N C2 N C2 -33.81(13) 3_665 . . 16_544 ?
_diffrn_measured_fraction_theta_max 0.941
_diffrn_reflns_theta_full
26.71
_diffrn_measured_fraction_theta_full 0.941
_refine_diff_density_max 0.401
_refine_diff_density_min -0.487
_refine_diff_density_rms 0.092
Dimethylammonium zinc formate
Crystal data and structure refinement for dimethylammonium zinc
formate.
Empirical formula
C5 H11 N O6 Zn
Formula weight
246.52
Temperature
273(2) K
Wavelength
0.71073 A
Crystal system, space group
Hexagonal, R-3c
Unit cell dimensions
a = 8.1924(8) A alpha = 90 deg.
b = 8.192 A beta = 90 deg.
c = 22.277(2) A gamma = 120 deg.
Volume
1294.81(18) A^3
Z, Calculated density
6, 1.897 Mg/m^3
106
Absorption coefficient
2.845 mm^-1
F(000)
756
Crystal size
0.25 x 0.1 x 0.05 mm
Θ range for data collection
3.40 to 27.32 deg.
Limiting indices
10<=h<=10, -8<=k<=10, -27<=l<=28
Reflections collected / unique 2979 / 318 [R(int) = 0.0230]
Completeness to theta =
27.32
96.4 %
Absorption correction
Multi scan
Refinement method
Full-matrix least-squares on F^2
Data/restraints/parameters 318 / 2 / 31
Goodness-of-fit on F^2
1.145
Final R indices [I>2sigma(I)] R1 = 0.0236, wR2 = 0.0581
R indices (all data)
R1 = 0.0277, wR2 = 0.0602
Largest diff. peak and hole
0.378 and -0.247 e.A^-3
107
Atomic coordinates ( x 10^4) and equivalent isotropic
displacement parameters (A^2 x 10^3) for dimethylammonium zinc
formate.
U(eq) is defined as one third of the trace of the orthogonalized
Uij tensor.
________________________________________________________________
x
y
z
U(eq)
________________________________________________________________
Zn
0
O(1)
-79(2)
2086(2)
C(1)
1236(4)
3333
C(2)
6667
N
6667
0
0
3333
2462(11)
23(1)
538(1)
833
1376(2)
833
34(1)
30(1)
57(1)
43(2)
________________________________________________________________
108
Bond lengths [Å] and angles [°] for dimethylammonium zinc formate
_____________________________________________________________
Zn-O(1)#1
2.1149
Zn-O(1)#2
2.1149
Zn-O(1)#3
2.1149
Zn-O(1)
2.1149
Zn-O(1)#4
2.1149
Zn-O(1)#5
2.1149
O(1)-C(1)
1.2390
C(1)-O(1)#6
1.2390
C(1)-H(1)
0.8400
C(2)-N
1.4040
C(2)-N#7
1.4040
C(2)-N#8
1.4040
C(2)-H(2)
0.9980
N-N#7
1.2370
N-N#8
1.2370
N-C(2)#9
1.4040
O(1)#1-Zn-O(1)#2
91.02
O(1)#1-Zn-O(1)#3
180.00
O(1)#2-Zn-O(1)#3
88.98
O(1)#1-Zn-O(1)
88.98
O(1)#2-Zn-O(1)
180.00
109
O(1)#3-Zn-O(1)
91.02
O(1)#1-Zn-O(1)#4
88.98
O(1)#2-Zn-O(1)#4
88.98
O(1)#3-Zn-O(1)#4
91.02
O(1)-Zn-O(1)#4
91.02
O(1)#1-Zn-O(1)#5
91.02
O(1)#2-Zn-O(1)#5
91.02
O(1)#3-Zn-O(1)#5
88.98
O(1)-Zn-O(1)#5
88.98
O(1)#4-Zn-O(1)#5
180.00
C(1)-O(1)-Zn
127.02
O(1)#6-C(1)-O(1)
125.7
O(1)#6-C(1)-H(1)
117.17
O(1)-C(1)-H(1)
117.17
N-C(2)-N#7
52.3
N-C(2)-N#8
52.3
N#7-C(2)-N#8
52.3
N-C(2)-H(2)
87.9
N#7-C(2)-H(2)
117
N#8-C(2)-H(2)
138
N#7-N-N#8
60.0
N#7-N-C(2)
63.9
N#8-N-C(2)
63.9
N#7-N-C(2)#9
63.9
N#8-N-C(2)#9
63.9
C(2)-N-C(2)#9
118.9
110
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 x-y,x,-z #2 -x,-y,-z #3 -x+y,-x,z
#4 -y,x-y,z #5 y,-x+y,-z #6 x-y+1/3,-y+2/3,-z+1/6
#7 -y+1,x-y,z #8 -x+y+1,-x+1,z #9 y+1/3,x-1/3,-z+1/6
Anisotropic displacement parameters (A^2 x 10^3) for dimethylammonium zinc formate
The anisotropic displacement factor exponent takes the form:
-2 pi^2 [ h^2 a*^2 U11 + ... + 2 h k a* b* U12 ]
_____________________________________________________________________
U11
U22
U33
U23
U13
U12
____________________________________________________________________
Zn
23
23
23
0
0
12
O(1)
32
33
37
-11
-5
16
C(1)
28
27
34
1
1
14
C(2)
68
68
35
0
0
34
N
38
31
62
3
6
19
_____________________________________________________________________
Hydrogen coordinates ( x 10^4) and isotropic displacement parameters (A^2 x 10^3) for dimethylammonium zinc formate
111
________________________________________________________________
x
y
z
U(eq)
________________________________________________________________
H(2)
7100(200)
H(1)
2260(40)
2550(160)
3333
1577(13)
833
350(50)
12(7)
________________________________________________________________
Torsion angles [°] for dimethylammonium zinc formate
________________________________________________________________
O(1)#1-Zn-O(1)-C(1)
-152.22(15)
O(1)#2-Zn-O(1)-C(1)
-148(58)
O(1)#3-Zn-O(1)-C(1)
27.78(15)
O(1)#4-Zn-O(1)-C(1)
118.81(9)
O(1)#5-Zn-O(1)-C(1)
-61.19(9)
Zn-O(1)-C(1)-O(1)#6
177.27(14)
N#8-C(2)-N-N#7
67.68(19)
N#7-C(2)-N-N#8
-67.68(19)
N#7-C(2)-N-C(2)#9
-33.84(9)
N#8-C(2)-N-C(2)#9
33.84(9)
________________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 x-y,x,-z #2 -x,-y,-z #3 -x+y,-x,z
112
#4 -y,x-y,z #5 y,-x+y,-z #6 x-y+1/3,-y+2/3,-z+1/6
#7 -y+1,x-y,z #8 -x+y+1,-x+1,z #9 y+1/3,x-1/3,-z+1/6
Dimethylammonium manganese formate
_audit_creation_method
SHELXL-97
_chemical_formula_sum
'C3 H9 Mn N O2'
_chemical_formula_weight
146.05
loop_
_atom_type_symbol
_atom_type_description
_atom_type_scat_dispersion_real
_atom_type_scat_dispersion_imag
_atom_type_scat_source
'C' 'C' 0.0033 0.0016
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'H' 'H' 0.0000 0.0000
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'N' 'N' 0.0061 0.0033
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'O' 'O' 0.0106 0.0060
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'Mn' 'Mn' 0.3368 0.7283
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
_symmetry_cell_setting
?
_symmetry_space_group_name_H-M "R -3 c"
113
loop_
_symmetry_equiv_pos_as_xyz
'x, y, z'
'-y, x-y, z'
'-x+y, -x, z'
'y, x, -z+1/2'
'x-y, -y, -z+1/2'
'-x, -x+y, -z+1/2'
'x+2/3, y+1/3, z+1/3'
'-y+2/3, x-y+1/3, z+1/3'
'-x+y+2/3, -x+1/3, z+1/3'
'y+2/3, x+1/3, -z+5/6'
'x-y+2/3, -y+1/3, -z+5/6'
'-x+2/3, -x+y+1/3, -z+5/6'
'x+1/3, y+2/3, z+2/3'
'-y+1/3, x-y+2/3, z+2/3'
'-x+y+1/3, -x+2/3, z+2/3'
'y+1/3, x+2/3, -z+7/6'
'x-y+1/3, -y+2/3, -z+7/6'
'-x+1/3, -x+y+2/3, -z+7/6'
'-x, -y, -z'
'y, -x+y, -z'
'x-y, x, -z'
'-y, -x, z-1/2'
'-x+y, y, z-1/2'
'x, x-y, z-1/2'
114
'-x+2/3, -y+1/3, -z+1/3'
'y+2/3, -x+y+1/3, -z+1/3'
'x-y+2/3, x+1/3, -z+1/3'
'-y+2/3, -x+1/3, z-1/6'
'-x+y+2/3, y+1/3, z-1/6'
'x+2/3, x-y+1/3, z-1/6'
'-x+1/3, -y+2/3, -z+2/3'
'y+1/3, -x+y+2/3, -z+2/3'
'x-y+1/3, x+2/3, -z+2/3'
'-y+1/3, -x+2/3, z+1/6'
'-x+y+1/3, y+2/3, z+1/6'
'x+1/3, x-y+2/3, z+1/6'
_cell_length_a
8.3279(8)
_cell_length_b
8.3279(8)
_cell_length_c
22.881(5)
_cell_angle_alpha
90.00
_cell_angle_beta
90.00
_cell_angle_gamma
120.00
_cell_volume
1374.3(3)
_cell_formula_units_Z
9
_cell_measurement_temperature
273(2)
_exptl_crystal_description
Cubic
_exptl_crystal_colour
light pink
_exptl_crystal_density_diffrn
1.588
_exptl_crystal_density_method
'not measured'
_exptl_crystal_F_000
675
115
_exptl_absorpt_coefficient_mu
2.059
_diffrn_ambient_temperature
273(2)
_diffrn_radiation_wavelength
0.71073
_diffrn_radiation_type
MoK\a
_diffrn_radiation_source
'fine-focus sealed tube'
_diffrn_radiation_monochromator
graphite
_diffrn_reflns_number
2288
_diffrn_reflns_av_R_equivalents
0.0294
_diffrn_reflns_av_sigmaI/netI
0.0178
_diffrn_reflns_limit_h_min
-10
_diffrn_reflns_limit_h_max
8
_diffrn_reflns_limit_k_min
-10
_diffrn_reflns_limit_k_max
10
_diffrn_reflns_limit_l_min
-27
_diffrn_reflns_limit_l_max
28
_diffrn_reflns_theta_min
3.34
_diffrn_reflns_theta_max
26.41
_reflns_number_total
321
_reflns_number_gt
277
_reflns_threshold_expression
>2sigma(I)
_computing_structure_solution
'SHELXS-97 (Sheldrick, 1990)'
_computing_structure_refinement
'SHELXL-97 (Sheldrick, 1997)'
;
Refinement of F^2^ against ALL reflections. The weighted R-factor wR
and goodness of fit S are based on F^2^, conventional R-factors R are
116
based on F, with F set to zero for negative F^2^. The threshold expression of
F^2^ > 2sigma(F^2^) is used only for calculating R-factors(gt) etc. and
is not relevant to the choice of reflections for refinement. R-factors
based on F^2^ are statistically about twice as large as those based on F,
and R- factors based on ALL data will be even larger.
;
refine_ls_structure_factor_coef
Fsqd
_refine_ls_matrix_type
full
_refine_ls_weighting_scheme
calc
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.0716P)^2^+21.3666P]
where P=(Fo^2^+2Fc^2^)/3'
_atom_sites_solution_primary
direct
_atom_sites_solution_secondary
difmap
_atom_sites_solution_hydrogens
geom
_refine_ls_hydrogen_treatment
mixed
_refine_ls_extinction_method
SHELXL
_refine_ls_extinction_coef
0.0028(11)
_refine_ls_extinction_expression
'Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^'
_refine_ls_number_reflns
321
_refine_ls_number_parameters
32
_refine_ls_number_restraints
3
_refine_ls_R_factor_all
0.0405
117
_refine_ls_R_factor_gt
0.0334
_refine_ls_wR_factor_ref
0.0865
_refine_ls_wR_factor_gt
0.0781
_refine_ls_goodness_of_fit_ref
0.609
_refine_ls_restrained_S_all
0.608
_refine_ls_shift/su_max
0.000
_refine_ls_shift/su_mean
0.000
loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_U_iso_or_equiv
_atom_site_adp_type
_atom_site_occupancy
_atom_site_symmetry_multiplicity
_atom_site_calc_flag
_atom_site_refinement_flags
_atom_site_disorder_assembly
_atom_site_disorder_group
Mn Mn 0.0000 1.0000 0.0000 0.0263(4) Uani 1 6 d S . .
O1 O -0.0103(3) 0.7792(3) 0.05449(8) 0.0417(6) Uani 1 1 d . . .
C1 C 0.1174(5) 0.7840(5) 0.0833 0.0346(9) Uani 1 2 d S . .
118
C2 C 0.6667 0.3333 0.1362(3) 0.0626(17) Uani 1 3 d SD . .
H1 H 0.223(5) 0.889(5) 0.0833 0.015(8) Uiso 1 2 d S . .
H2 H 0.68(3) 0.445(12) 0.1571(7) 0.33(6) Uiso 1 1 d D . .
N N 0.6667 0.4211(12) 0.0833 0.044(2) Uani 0.33 2 d SPD . .
loop_
_atom_site_aniso_label
_atom_site_aniso_U_11
_atom_site_aniso_U_22
_atom_site_aniso_U_33
_atom_site_aniso_U_23
_atom_site_aniso_U_13
_atom_site_aniso_U_12
Mn 0.0258(4) 0.0258(4) 0.0272(6) 0.000 0.000 0.0129(2)
O1 0.0396(11) 0.0392(12) 0.0463(11) 0.0086(8) -0.0076(9) 0.0197(9)
C1 0.0316(15) 0.0316(15) 0.040(2) 0.0008(8) -0.0008(8) 0.0157(17)
C2 0.072(3) 0.072(3) 0.043(3) 0.000 0.000 0.0361(14)
N 0.034(5) 0.031(4) 0.067(7) 0.003(2) 0.006(5) 0.017(3)
_geom_special_details
;
All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are
only used when they are defined by crystal symmetry. An approximate
119
(isotropic) treatment of cell esds is used for estimating esds involving
l.s. planes.
;
loop_
_geom_bond_atom_site_label_1
_geom_bond_atom_site_label_2
_geom_bond_distance
_geom_bond_site_symmetry_2
_geom_bond_publ_flag
Mn O1 2.1878(18) 20_455 ?
Mn O1 2.1878(18) 2_675 ?
Mn O1 2.1878(18) . ?
Mn O1 2.1878(18) 21_665 ?
Mn O1 2.1878(18) 3_465 ?
Mn O1 2.1878(18) 19_575 ?
O1 C1 1.234(3) . ?
C1 O1 1.234(3) 16_454 ?
C1 H1 0.88(4) . ?
C2 N 1.412(6) 3_665 ?
C2 N 1.412(6) 2_655 ?
C2 N 1.412(6) . ?
C2 H2 0.998(10) . ?
N N 1.265(17) 2_655 ?
N N 1.265(17) 3_665 ?
N C2 1.412(6) 16_544 ?
loop_
120
_geom_angle_atom_site_label_1
_geom_angle_atom_site_label_2
_geom_angle_atom_site_label_3
_geom_angle
_geom_angle_site_symmetry_1
_geom_angle_site_symmetry_3
_geom_angle_publ_flag
O1 Mn O1 180.00(8) 20_455 2_675 ?
O1 Mn O1 89.26(8) 20_455 . ?
O1 Mn O1 90.74(8) 2_675 . ?
O1 Mn O1 90.74(8) 20_455 21_665 ?
O1 Mn O1 89.26(8) 2_675 21_665 ?
O1 Mn O1 89.26(8) . 21_665 ?
O1 Mn O1 89.26(8) 20_455 3_465 ?
O1 Mn O1 90.74(8) 2_675 3_465 ?
O1 Mn O1 90.74(8) . 3_465 ?
O1 Mn O1 180.0 21_665 3_465 ?
O1 Mn O1 90.74(8) 20_455 19_575 ?
O1 Mn O1 89.26(8) 2_675 19_575 ?
O1 Mn O1 180.00(10) . 19_575 ?
O1 Mn O1 90.74(8) 21_665 19_575 ?
O1 Mn O1 89.26(8) 3_465 19_575 ?
C1 O1 Mn 127.3(2) . . ?
O1 C1 O1 126.9(4) 16_454 . ?
O1 C1 H1 116.54(19) 16_454 . ?
O1 C1 H1 116.54(19) . . ?
121
N C2 N 53.2(6) 3_665 2_655 ?
N C2 N 53.2(6) 3_665 . ?
N C2 N 53.2(6) 2_655 . ?
N C2 H2 126(8) 3_665 . ?
N C2 H2 133(6) 2_655 . ?
N C2 H2 87.8(9) . . ?
N N N 60.0 2_655 3_665 ?
N N C2 63.4(3) 2_655 . ?
N N C2 63.4(3) 3_665 . ?
N N C2 63.4(3) 2_655 16_544 ?
N N C2 63.4(3) 3_665 16_544 ?
C2 N C2 117.7(8) . 16_544 ?
loop_
_geom_torsion_atom_site_label_1
_geom_torsion_atom_site_label_2
_geom_torsion_atom_site_label_3
_geom_torsion_atom_site_label_4
_geom_torsion
_geom_torsion_site_symmetry_1
_geom_torsion_site_symmetry_2
_geom_torsion_site_symmetry_3
_geom_torsion_site_symmetry_4
_geom_torsion_publ_flag
O1 Mn O1 C1 152.20(19) 20_455 . . . ?
O1 Mn O1 C1 -27.80(19) 2_675 . . . ?
O1 Mn O1 C1 61.46(12) 21_665 . . . ?
122
O1 Mn O1 C1 -118.54(12) 3_465 . . . ?
O1 Mn O1 C1 131(100) 19_575 . . . ?
Mn O1 C1 O1 -176.96(19) . . . 16_454 ?
N C2 N N 68.0(2) 3_665 . . 2_655 ?
N C2 N N -68.0(2) 2_655 . . 3_665 ?
N C2 N C2 34.00(11) 3_665 . . 16_544 ?
N C2 N C2 -34.00(11) 2_655 . . 16_544 ?
_diffrn_measured_fraction_theta_max 1.000
_diffrn_reflns_theta_full
26.41
_diffrn_measured_fraction_theta_full 1.000
_refine_diff_density_max 0.397
_refine_diff_density_min -0.230
_refine_diff_density_rms 0.067
Dimethylammonium nickel formate
_audit_creation_method
SHELXL-97
_chemical_formula_sum
'C5 H11 N Ni O6'
_chemical_formula_weight
239.86
loop_
_atom_type_symbol
_atom_type_description
_atom_type_scat_dispersion_real
_atom_type_scat_dispersion_imag
_atom_type_scat_source
'C' 'C' 0.0033 0.0016
123
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'H' 'H' 0.0000 0.0000
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'N' 'N' 0.0061 0.0033
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'O' 'O' 0.0106 0.0060
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'Ni' 'Ni' 0.3393 1.1124
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
_symmetry_cell_setting
Hexagonal
_symmetry_space_group_name_H-M
'R -3 c'
loop_
_symmetry_equiv_pos_as_xyz
'x, y, z'
'-y, x-y, z'
'-x+y, -x, z'
'y, x, -z+1/2'
'x-y, -y, -z+1/2'
'-x, -x+y, -z+1/2'
'x+2/3, y+1/3, z+1/3'
'-y+2/3, x-y+1/3, z+1/3'
'-x+y+2/3, -x+1/3, z+1/3'
'y+2/3, x+1/3, -z+5/6'
'x-y+2/3, -y+1/3, -z+5/6'
'-x+2/3, -x+y+1/3, -z+5/6'
'x+1/3, y+2/3, z+2/3'
124
'-y+1/3, x-y+2/3, z+2/3'
'-x+y+1/3, -x+2/3, z+2/3'
'y+1/3, x+2/3, -z+7/6'
'x-y+1/3, -y+2/3, -z+7/6'
'-x+1/3, -x+y+2/3, -z+7/6'
'-x, -y, -z'
'y, -x+y, -z'
'x-y, x, -z'
'-y, -x, z-1/2'
'-x+y, y, z-1/2'
'x, x-y, z-1/2'
'-x+2/3, -y+1/3, -z+1/3'
'y+2/3, -x+y+1/3, -z+1/3'
'x-y+2/3, x+1/3, -z+1/3'
'-y+2/3, -x+1/3, z-1/6'
'-x+y+2/3, y+1/3, z-1/6'
'x+2/3, x-y+1/3, z-1/6'
'-x+1/3, -y+2/3, -z+2/3'
'y+1/3, -x+y+2/3, -z+2/3'
'x-y+1/3, x+2/3, -z+2/3'
'-y+1/3, -x+2/3, z+1/6'
'-x+y+1/3, y+2/3, z+1/6'
'x+1/3, x-y+2/3, z+1/6'
_cell_length_a
_cell_length_b
8.1101(14)
8.110
125
_cell_length_c
21.986(4)
_cell_angle_alpha
90.00
_cell_angle_beta
90.00
_cell_angle_gamma
120.00
_cell_volume
1252.4(3)
_cell_formula_units_Z
6
_cell_measurement_temperature
273(2)
_exptl_crystal_description
cube
_exptl_crystal_colour
green
_exptl_crystal_size_max
0.1
_exptl_crystal_size_mid
0.1
_exptl_crystal_size_min
0.08
_exptl_crystal_density_diffrn
1.908
_exptl_crystal_density_method
'not measured'
_exptl_crystal_F_000
744
_exptl_absorpt_coefficient_mu
2.323
_exptl_absorpt_correction_type
'emperical'
_exptl_absorpt_correction_T_min
0.329
_exptl_absorpt_correction_T_max
0.432
_exptl_absorpt_process_details
'Psi scan'
_exptl_special_details
_diffrn_ambient_temperature
273(2)
_diffrn_radiation_wavelength
0.71073
_diffrn_radiation_type
MoK\a
_diffrn_radiation_source
'fine-focus sealed tube'
_diffrn_radiation_monochromator
graphite
126
_diffrn_measurement_device_type
'CCD area detector'
_diffrn_measurement_method
'Omega scan'
_diffrn_reflns_number
1930
_diffrn_reflns_av_R_equivalents
0.0491
_diffrn_reflns_av_sigmaI/netI
0.0361
_diffrn_reflns_limit_h_min
-9
_diffrn_reflns_limit_h_max
9
_diffrn_reflns_limit_k_min
-7
_diffrn_reflns_limit_k_max
10
_diffrn_reflns_limit_l_min
-27
_diffrn_reflns_limit_l_max
21
_diffrn_reflns_theta_min
3.44
_diffrn_reflns_theta_max
26.51
_reflns_number_total
291
_reflns_number_gt
227
_reflns_threshold_expression
>2sigma(I)
_computing_structure_solution
'SHELXS-97 (Sheldrick, 1990)'
_computing_structure_refinement
'SHELXL-97 (Sheldrick, 1997)'
;
Refinement of F^2^ against ALL reflections. The weighted R-factor wR
and goodness of fit S are based on F^2^, conventional R-factors R are
based on F, with F set to zero for negative F^2^. The threshold expression of F^2^ > 2sigma(F^2^) is used only for calculating R-factors(gt)
etc. and is not relevant to the choice of reflections for refinement. R127
factors based on F^2^ are statistically about twice as large as those
based on F, and R-factors based on ALL data will be even larger.
;
_refine_ls_structure_factor_coef
Fsqd
_refine_ls_matrix_type
full
_refine_ls_weighting_scheme
calc
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.0680P)^2^+0.0000P]
where P=(Fo^2^+2Fc^2^)/3'
_atom_sites_solution_primary
direct
_atom_sites_solution_secondary
difmap
_atom_sites_solution_hydrogens
geom
_refine_ls_hydrogen_treatment
mixed
_refine_ls_extinction_method
none
_refine_ls_number_reflns
291
_refine_ls_number_parameters
29
_refine_ls_number_restraints
2
_refine_ls_R_factor_all
0.0532
_refine_ls_R_factor_gt
0.0405
_refine_ls_wR_factor_ref
0.1056
_refine_ls_wR_factor_gt
0.0994
_refine_ls_goodness_of_fit_ref
1.081
_refine_ls_restrained_S_all
1.078
_refine_ls_shift/su_max
0.000
_refine_ls_shift/su_mean
0.000
loop_
128
_atom_site_label
_atom_site_type_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_U_iso_or_equiv
_atom_site_adp_type
_atom_site_occupancy
_atom_site_symmetry_multiplicity
_atom_site_calc_flag
_atom_site_refinement_flags
_atom_site_disorder_assembly
_atom_site_disorder_group
Ni Ni 1.0000 1.0000 0.0000 0.0228(4) Uani 1 6 d S . .
O O 0.7925(4) 0.7865(4) 0.05342(12) 0.0324(7) Uani 1 1 d . . .
C1 C 0.6667 0.7939(7) 0.0833 0.0298(13) Uani 1 2 d S . .
C2 C 0.6667 0.3333 0.0288(4) 0.052(2) Uani 1 3 d SD . .
N N 0.7536(17) 0.4203(17) 0.0833 0.041(4) Uani 0.33 2 d SPD . .
H1 H 0.6667 0.896(10) 0.0833 0.050 Uiso 1 2 d S . .
H2 H 0.614(6) 0.201(3) 0.0132(13) 0.050 Uiso 1 1 d D . .
loop_
_atom_site_aniso_label
_atom_site_aniso_U_11
_atom_site_aniso_U_22
_atom_site_aniso_U_33
129
_atom_site_aniso_U_23
_atom_site_aniso_U_13
_atom_site_aniso_U_12
Ni 0.0227(5) 0.0227(5) 0.0231(6) 0.000 0.000 0.0113(2)
O
0.0322(16)
0.0323(16)
0.0340(14)
0.0051(12)
0.0083(12)
0.0170(12)
C1 0.023(3) 0.034(2) 0.029(3) -0.0007(11) -0.001(2) 0.0116(14)
C2 0.059(3) 0.059(3) 0.037(4) 0.000 0.000 0.0293(16)
N 0.036(6) 0.036(6) 0.045(8) 0.003(3) -0.003(3) 0.014(6)
_geom_special_details
;
All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are
only used when they are defined by crystal symmetry. An approximate
(isotropic) treatment of cell esds is used for estimating esds involving
l.s. planes.
;
loop_
_geom_bond_atom_site_label_1
_geom_bond_atom_site_label_2
_geom_bond_distance
_geom_bond_site_symmetry_2
130
_geom_bond_publ_flag
Ni O 2.073(2) 20_565 ?
Ni O 2.073(2) 2_765 ?
Ni O 2.073(2) 21_655 ?
Ni O 2.073(2) 3_675 ?
Ni O 2.073(2) 19_775 ?
Ni O 2.073(2) . ?
O C1 1.241(4) . ?
C1 O 1.241(4) 18_654 ?
C1 H1 0.83(8) . ?
C2 N 1.392(10) 3_665 ?
C2 N 1.392(10) . ?
C2 N 1.392(10) 2_655 ?
C2 H2 0.998(10) . ?
N N 1.22(2) 2_655 ?
N N 1.22(2) 3_665 ?
N C2 1.392(10) 16_544 ?
loop_
_geom_angle_atom_site_label_1
_geom_angle_atom_site_label_2
_geom_angle_atom_site_label_3
_geom_angle
_geom_angle_site_symmetry_1
_geom_angle_site_symmetry_3
_geom_angle_publ_flag
131
O Ni O 180.00(12) 20_565 2_765 ?
O Ni O 91.05(10) 20_565 21_655 ?
O Ni O 88.95(10) 2_765 21_655 ?
O Ni O 88.95(10) 20_565 3_675 ?
O Ni O 91.05(10) 2_765 3_675 ?
O Ni O 180.00(12) 21_655 3_675 ?
O Ni O 91.05(10) 20_565 19_775 ?
O Ni O 88.95(10) 2_765 19_775 ?
O Ni O 91.05(10) 21_655 19_775 ?
O Ni O 88.95(10) 3_675 19_775 ?
O Ni O 88.95(10) 20_565 . ?
O Ni O 91.05(10) 2_765 . ?
O Ni O 88.95(10) 21_655 . ?
O Ni O 91.05(10) 3_675 . ?
O Ni O 180.0 19_775 . ?
C1 O Ni 127.1(3) . . ?
O C1 O 125.2(5) 18_654 . ?
O C1 H1 117.4(3) 18_654 . ?
O C1 H1 117.4(3) . . ?
N C2 N 52.1(9) 3_665 . ?
N C2 N 52.1(9) 3_665 2_655 ?
N C2 N 52.1(9) . 2_655 ?
N C2 H2 82(2) 3_665 . ?
N C2 H2 132.6(17) . . ?
N C2 H2 111(2) 2_655 . ?
N N N 60.000(1) 2_655 3_665 ?
132
N N C2 64.0(4) 2_655 16_544 ?
N N C2 64.0(4) 3_665 16_544 ?
N N C2 64.0(4) 2_655 . ?
N N C2 64.0(4) 3_665 . ?
C2 N C2 119.1(10) 16_544 . ?
loop_
_geom_torsion_atom_site_label_1
_geom_torsion_atom_site_label_2
_geom_torsion_atom_site_label_3
_geom_torsion_atom_site_label_4
_geom_torsion
_geom_torsion_site_symmetry_1
_geom_torsion_site_symmetry_2
_geom_torsion_site_symmetry_3
_geom_torsion_site_symmetry_4
_geom_torsion_publ_flag
O Ni O C1 -61.10(15) 20_565 . . . ?
O Ni O C1 118.90(15) 2_765 . . . ?
O Ni O C1 -152.2(3) 21_655 . . . ?
O Ni O C1 27.8(3) 3_675 . . . ?
O Ni O C1 -131(58) 19_775 . . . ?
Ni O C1 O 177.5(2) . . . 18_654 ?
N C2 N N -67.6(3) 3_665 . . 2_655 ?
N C2 N N 67.6(3) 2_655 . . 3_665 ?
N C2 N C2 -33.81(14) 3_665 . . 16_544 ?
133
N C2 N C2 33.81(14) 2_655 . . 16_544 ?
_diffrn_measured_fraction_theta_max
0.990
_diffrn_reflns_theta_full
26.51
_diffrn_measured_fraction_theta_full
0.990
_refine_diff_density_max
0.899
_refine_diff_density_min
-0.541
_refine_diff_density_rms
0.123
Low temperature dimethylammonium manganese formate
_audit_creation_method
SHELXL-97
_chemical_formula_sum
'C5 H11 Mn N O6'
_chemical_formula_weight
236.09
loop_
_atom_type_symbol
_atom_type_description
_atom_type_scat_dispersion_real
_atom_type_scat_dispersion_imag
_atom_type_scat_source
'C' 'C' 0.0033 0.0016
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'H' 'H' 0.0000 0.0000
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'N' 'N' 0.0061 0.0033
134
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'O' 'O' 0.0106 0.0060
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
'Mn' 'Mn' 0.3368 0.7283
'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
_symmetry_cell_setting
'monoclinic'
_symmetry_space_group_name_H-M
'Cc'
loop_
_symmetry_equiv_pos_as_xyz
'x, y, z'
'x, -y, z+1/2'
'x+1/2, y+1/2, z'
'x+1/2, -y+1/2, z+1/2'
_cell_length_a
14.451(8)
_cell_length_b
8.376(3)
_cell_length_c
8.952(4)
_cell_angle_alpha
90.00
_cell_angle_beta
120.879(7)
_cell_angle_gamma
90.00
_cell_volume
930.0(7)
_cell_formula_units_Z
4
_cell_measurement_temperature
103(2)
_exptl_crystal_size_max
0.18
_exptl_crystal_size_mid
0.14
_exptl_crystal_size_min
0.08
135
_exptl_crystal_density_diffrn
1.686
_exptl_crystal_density_method
'not measured'
_exptl_crystal_F_000
484
_exptl_absorpt_coefficient_mu
1.419
_exptl_absorpt_correction_T_min
0.7843
_exptl_absorpt_correction_T_max
0.8974
_diffrn_ambient_temperature
103(2)
_diffrn_radiation_wavelength
0.71073
_diffrn_radiation_type
MoK\a
_diffrn_radiation_source
'fine-focus sealed tube'
_diffrn_radiation_monochromator
graphite
_diffrn_reflns_number
3697
_diffrn_reflns_av_R_equivalents
0.0506
_diffrn_reflns_av_sigmaI/netI
0.0671
_diffrn_reflns_limit_h_min
-18
_diffrn_reflns_limit_h_max
18
_diffrn_reflns_limit_k_min
-11
_diffrn_reflns_limit_k_max
11
_diffrn_reflns_limit_l_min
-11
_diffrn_reflns_limit_l_max
11
_diffrn_reflns_theta_min
2.93
_diffrn_reflns_theta_max
28.76
_reflns_number_total
2035
_reflns_number_gt
1841
_reflns_threshold_expression
>2sigma(I)
_computing_structure_solution
'SHELXS-97(Sheldrick, 2008)'
136
_computing_structure_refinement
'SHELXL-97(Sheldrick, 2008)'
;
Refinement of F^2^ against ALL reflections. The weighted R-factor wR
and goodness of fit S are based on F^2^, conventional R-factors R are
based on F, with F set to zero for negative F^2^. The threshold expression of F^2^ > 2sigma(F^2^) is used only for calculating R-factors(gt)
etc. and is not relevant to the choice of reflections for refinement. Rfactors based on F^2^ are statistically about twice as large as those
based on F, and R-factors based on ALL data will be even larger.
;
_refine_ls_structure_factor_coef
Fsqd
_refine_ls_matrix_type
full
_refine_ls_weighting_scheme
calc
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.1010P)^2^+3.5096P]
where P=(Fo^2^+2Fc^2^)/3'
_atom_sites_solution_primary
direct
_atom_sites_solution_secondary
difmap
_atom_sites_solution_hydrogens
geom
_refine_ls_hydrogen_treatment
mixed
_refine_ls_extinction_method
SHELXL
_refine_ls_extinction_coef
0.002(2)
_refine_ls_extinction_expression
'Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^'
137
_refine_ls_abs_structure_details
'Flack H D (1983), Acta Cryst. A39, 876-881'
_refine_ls_abs_structure_Flack
0.43(7)
_refine_ls_number_reflns
2035
_refine_ls_number_parameters
125
_refine_ls_number_restraints
2
_refine_ls_R_factor_all
0.0649
_refine_ls_R_factor_gt
0.0614
_refine_ls_wR_factor_ref
0.1723
_refine_ls_wR_factor_gt
0.1693
_refine_ls_goodness_of_fit_ref
1.086
_refine_ls_restrained_S_all
1.086
_refine_ls_shift/su_max
0.001
_refine_ls_shift/su_mean
0.000
loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_U_iso_or_equiv
_atom_site_adp_type
_atom_site_occupancy
_atom_site_symmetry_multiplicity
_atom_site_calc_flag
_atom_site_refinement_flags
138
_atom_site_disorder_assembly
_atom_site_disorder_group
Mn1 Mn 0.69954(17) 0.25162(10) 0.7821(3) 0.0119(3) Uani 1 1 d . . .
O1 O 0.7567(4) 0.0293(5) 0.9335(5) 0.0148(7) Uani 1 1 d . . .
O2 O 0.7527(3) 0.1611(5) 0.6070(5) 0.0178(10) Uani 1 1 d . . .
O3 O 0.5401(4) 0.1414(6) 0.6164(7) 0.0207(10) Uani 1 1 d . . .
O4 O 0.6501(4) 0.3365(5) 0.9616(7) 0.0238(12) Uani 1 1 d . . .
O5 O 0.3608(4) 0.1401(5) 0.4483(7) 0.0209(11) Uani 1 1 d . . .
O6 O 0.6535(4) 0.5194(6) 1.1478(8) 0.0278(12) Uani 1 1 d . . .
C1 C 0.4499(7) 0.2105(6) 0.5310(13) 0.0178(9) Uani 1 1 d . . .
H1 H 0.457(9) 0.339(7) 0.528(16) 0.021 Uiso 1 1 d . . .
C2 C 0.7243(6) -0.0299(7) 1.0281(8) 0.0148(7) Uani 1 1 d . . .
H2 H 0.674(7) -0.002(9) 1.056(11) 0.018 Uiso 1 1 d . . .
C3 C 0.6641(5) 0.4779(8) 1.0222(8) 0.0168(12) Uani 1 1 d . . .
H3 H 0.692(6) 0.555(10) 0.975(10) 0.020 Uiso 1 1 d . . .
N11 N 0.8975(4) 0.3086(6) 0.5208(7) 0.0191(9) Uani 1 1 d . . .
H11A H 0.8875 0.4173 0.5078 0.023 Uiso 1 1 calc R . .
H11B H 0.8418 0.2659 0.5297 0.023 Uiso 1 1 calc R . .
C12 C 0.8951(11) 0.2397(8) 0.3626(18) 0.027(3) Uani 1 1 d . . .
H12A H 0.9567 0.2802 0.3567 0.041 Uiso 1 1 calc R . .
H12B H 0.8279 0.2712 0.2573 0.041 Uiso 1 1 calc R . .
H12C H 0.8989 0.1230 0.3713 0.041 Uiso 1 1 calc R . .
C11 C 1.0027(8) 0.2735(11) 0.6846(15) 0.023(2) Uani 1 1 d . . .
H11C H 1.0077 0.1589 0.7097 0.035 Uiso 1 1 calc R . .
H11D H 1.0066 0.3334 0.7817 0.035 Uiso 1 1 calc R . .
H11E H 1.0625 0.3054 0.6691 0.035 Uiso 1 1 calc R . .
139
loop_
_atom_site_aniso_label
_atom_site_aniso_U_11
_atom_site_aniso_U_22
_atom_site_aniso_U_33
_atom_site_aniso_U_23
_atom_site_aniso_U_13
_atom_site_aniso_U_12
Mn1 0.0140(4) 0.0121(4) 0.0073(4) 0.00053(19) 0.0039(3) 0.0004(2)
O1
0.0211(17)
0.0172(17)
0.0049(13)
0.0058(11)
0.0057(12)
0.0027(13)
O2 0.023(2) 0.021(2) 0.014(2) -0.0019(17) 0.013(2) -0.0009(18)
O3 0.018(2) 0.020(2) 0.022(3) 0.0031(18) 0.009(2) -0.0015(17)
O4 0.024(2) 0.015(2) 0.034(3) -0.009(2) 0.016(2) -0.0068(19)
O5 0.013(2) 0.021(3) 0.021(2) 0.0059(18) 0.0033(19) -0.0010(16)
O6 0.032(3) 0.016(2) 0.045(3) -0.0104(19) 0.027(2) -0.0059(19)
C1 0.017(2) 0.0182(19) 0.018(2) 0.003(5) 0.0080(17) -0.010(5)
C2
0.0211(17)
0.0172(17)
0.0049(13)
0.0058(11)
0.0057(12)
0.0027(13)
C3 0.012(3) 0.019(3) 0.016(3) 0.0033(19) 0.005(2) 0.0040(19)
N11 0.016(2) 0.018(2) 0.024(2) 0.0028(19) 0.0109(19) -0.0006(17)
C12 0.033(5) 0.029(4) 0.022(5) -0.001(3) 0.016(4) -0.003(3)
C11 0.017(4) 0.020(3) 0.025(5) 0.002(3) 0.005(3) -0.003(3)
_geom_special_details
140
;
All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are
only used when they are defined by crystal symmetry. An approximate
(isotropic) treatment of cell esds is used for estimating esds involving
l.s. planes.
;
loop_
_geom_bond_atom_site_label_1
_geom_bond_atom_site_label_2
_geom_bond_distance
_geom_bond_site_symmetry_2
_geom_bond_publ_flag
Mn1 O6 2.178(5) 2_564 ?
Mn1 O4 2.186(6) . ?
Mn1 O1 2.200(5) . ?
Mn1 O3 2.203(5) . ?
Mn1 O2 2.203(5) . ?
Mn1 O5 2.216(5) 4 ?
O1 C2 1.260(8) . ?
O2 C2 1.256(8) 2_554 ?
O3 C1 1.263(10) . ?
O4 C3 1.275(8) . ?
141
O5 C1 1.255(10) . ?
O5 Mn1 2.216(5) 4_454 ?
O6 C3 1.259(9) . ?
O6 Mn1 2.178(5) 2_565 ?
C2 O2 1.256(8) 2 ?
N11 C11 1.503(12) . ?
N11 C12 1.513(14) . ?
loop_
_geom_angle_atom_site_label_1
_geom_angle_atom_site_label_2
_geom_angle_atom_site_label_3
_geom_angle
_geom_angle_site_symmetry_1
_geom_angle_site_symmetry_3
_geom_angle_publ_flag
O6 Mn1 O4 89.8(2) 2_564 . ?
O6 Mn1 O1 175.7(3) 2_564 . ?
O4 Mn1 O1 89.0(2) . . ?
O6 Mn1 O3 94.6(2) 2_564 . ?
O4 Mn1 O3 90.4(2) . . ?
O1 Mn1 O3 89.56(18) . . ?
O6 Mn1 O2 91.7(2) 2_564 . ?
O4 Mn1 O2 178.3(2) . . ?
O1 Mn1 O2 89.40(18) . . ?
O3 Mn1 O2 90.2(2) . . ?
142
O6 Mn1 O5 85.9(2) 2_564 4 ?
O4 Mn1 O5 90.1(2) . 4 ?
O1 Mn1 O5 89.99(19) . 4 ?
O3 Mn1 O5 179.3(2) . 4 ?
O2 Mn1 O5 89.30(19) . 4 ?
C2 O1 Mn1 126.6(4) . . ?
C2 O2 Mn1 124.7(4) 2_554 . ?
C1 O3 Mn1 127.8(4) . . ?
C3 O4 Mn1 125.1(5) . . ?
C1 O5 Mn1 127.7(4) . 4_454 ?
C3 O6 Mn1 126.4(5) . 2_565 ?
O5 C1 O3 124.7(4) . . ?
O2 C2 O1 126.6(7) 2 . ?
O6 C3 O4 124.8(7) . . ?
C11 N11 C12 111.3(7) . . ?
_diffrn_measured_fraction_theta_max 0.885
_diffrn_reflns_theta_full
28.76
_diffrn_measured_fraction_theta_full 0.885
_refine_diff_density_max 1.673
_refine_diff_density_min -0.761
_refine_diff_density_rms 0.164
143
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159
BIOGRAPHICAL SKETCH
Education
Florida State University, Fl, USA, Aug. 2005 – April 2010
Ph.D. in Chemistry and Biochemistry
Indian Institute of Technology, Madras (IIT-M), India , 2000 - 2004
B.Tech in Chemical Engineering (First class)
Thesis: Investigations on the Use of Nanoparticles for Environmental
remediation
Honors and awards
Best poster prize, Florida ACS meeting, Tampa, USA
2010
H.H.Sheikh Saqr Al Qasimi Fellowship, University of Cambridge, UK
2008 – 2009
Visiting fellowship, ICMR, Univ. of California, Santa Barbara, USA
2006 – 2007
Congress of Graduate Studies award, Florida State University, FL, USA
December 2007
International center for materials research bursary award, UCSB, USA
December 2006
Overseas Research Scholarship (ORS), University of Leeds, UK
De-
cember 2005 (Declined)
King’s Gold medal, Best student overall performance, Senior year, )ndia
May 1999
160
Merit certificate, Regional Mathematics Olympiad, India
1998
Merit certificate and Internship, Homi Bhabha Centre, TIFR, India
May 1997
Teaching experience
General Chemistry Laboratory, FSU, USA, Fall 2007
Taught the class and administered all grades
Teaching assistant, Intr. to Thermodynamics, FSU, USA, Fall 2005
Supervision, group problem sessions and administered all the grades
Research, supervision and entrepreneurial experiences
Director, Founder of PM9, 2007-2008
Technology and business development director at Nanotechnology
software Simulation Company which completed exclusive software licensed to our strategic partner.
Guest Editor, Special Issue on CNTs, Journal of Nanoengineering and
Nanosystems, 2009
Organizer and Committee member, 2008
International symposium organized by Cambridge students, Also the
member of the Cambridge CNT society
Research Assistant, 2006
161
Florida State University, FL, USA
Visiting Researcher, 2006 – 2007
Materials Research Laboratory, University of California, Santa Barbara,
CA, USA
Visiting Researcher, May 2008 –
Dept. of Materials Science, University of Cambridge, UK
Mentor, April 2007 – June 2007
California Nano System Institute, University of California, Santa Barbara,
CA, USA
Supervised 3rd year undergraduate student, taught various instruments
and lab skills, research resulted into a conference talk
Mentor
Dept. of Materials Science, University of Cambridge, UK, July 2009 – Dec
2009
Conceived the project idea and supervised a visiting postgraduate student from Chulalongkorn University, Thailand.
Journal publications and patents
1.
Jain P., et al. (2009) Multiferroic Behavior Associated with an Order-Disorder Hydrogen Bonding Transition in Metal-Organic
Frameworks (MOFs) with the Perovskite ABX3 Architecture. J. Am.
Chem. Soc. 131(38):13625-13627. (Highlighted in nature research
162
highlights: Marvelous metal-organics, doi: 10.1038/462961c; and Angew.
Chem. Int. Ed. Research highlights: Multiferroic Materials: The Attractive
Approach
of
Metal-Organic
Frameworks,
doi:
10.1002/anie.200906660)
2.
Jain P. and Spear R. (2009) Guest editorial. Special issue on carbon
nanotubes. Proc. IMechE Vol. 222 Part N: J. Nanoengineering and
Nanosystems.
3.
Jain P., Dalal NS, Toby BH, Kroto HW, & Cheetham AK (2008) Order-disorder antiferroelectric phase transition in a hybrid inorganic-organic framework with the perovskite architecture. J. Am.
Chem. Soc. 130(32):10450-10451. (Highlighted in nature news &
views article Emerging Routes to Multiferroics, doi: 10.1038/4611218A)
4.
Jain P., and Pradeep T. (2005) Potential of silver nanoparticlecoated polyurethane foam as an antibacterial water filter. Biotechnology and Bioengineering, 90 (2005) 59-63.
5.
Nair AS et. al. (2005) Nanoparticles-chemistry, new synthetic approaches, gas phase clustering and novel applications. Pramana,
Journal of Physics, (65), 4, 631-40.
6.
7.
)ndian Patent, no.
urethane foam
/che/
, Silver nanoparticle coated Poly-
SR measurements of the hybrid organic-inorganic multiferroics
[(CH3)2NH2]M(HCOO)3, M =Ni;Co;Mn. P. J. Baker, T. Lancaster, I.
Franke, W. Hayes, S. J. Blundell, and P. Jain. (Submitted to Phys Rev
B)
163
8.
Glassy behaviour in a metal organic framework. Prashant Jain, Tiglet Besara, Naresh Dalal, Philip Kuhns, Arneil Reyes, Harold W.
Kroto and Anthony K. Cheetham. (Submitted to PNAS)
9.
A porous magnet with three dimensional metal-oxygen-metal and
metal-ligand-metal connectivity. P. Jain, N. S. Dalal, H. W. Kroto, and
A. K. Cheetham (In preparation)
164