Download Chapter 21. Transition Metals and Coordination Chemistry

Chapter 21. Transition Metals and
Coordination Chemistry
The Transition Metals: A Survey
General Properties
Main Group Elements
Main Group Elements
similar
properties
changing
properties
d-block transtion elecments
similar
properties
f-block transtion elecments
Transition Metals
Key reason: Last electrons added are inner electrons (d’s, f’s). These electrons d and f electrons
cannot participate as easily in bonding as can the valence s and p electrons.
But despite their many similarities, the transition metals do vary considerably in many ways.
Ex) mp of W = 3422 oC , mp of Hg = -38.83 oC
The Transition Metals: A Survey
General Properties (Transition Metal Ions)
• More than one oxidation state is often found.
• Forming complex ions, species where the transition metal ion is surrounded by a certain number of ligands (Lewis
bases).
L4
L3
L1
L2
• Several coordination numbers, number of ligands attached to a metal ion, and geometries exist.
Sc
V
Cr
Mn
Fe
Co
Ni
Cu
≤0
o
o
o
o
o
o
o
+1
o
o
o
o
o
o
O
o
O
o
O
O
O
O
O
o
o
O
o
O
O
o
o
O
o
o
O
o
o
o
+2
+3
+4
+5
+6
+7
O
Ti
O
o
o
△
O
o
o
O
Zn
+2
+3
Ex) Ionic compounds : FeCl2, FeCl3
+2
Complex ions: Co(H2O)62+
+3
Co(NH3)63+
O
+2
H2O
OH2
Cu
o
H2O
O : most common
NH3
OH2
OH2
OH2
H3N
Cu NH3
NH3
+2
The Transition Metals: A Survey
General Properties (Transition Metal Ions)
• Most compounds containing transition metal ions are colored because the ions can absorb visible light of
specific wavelength is often found.
Wulfenite (PbMoO4)
Rhodochrosite (MnCO3)
Ruby
Pure (Al2O3 : colorless)
Impurity (Cr3+, < 1%)
absorption : violet and green
emission : red
Co(H2O)62+
Cr(H2O)63+
Mn(H2O)62+
Ni(H2O)62+
Fe(H2O)63+
• Many compounds containing transition metal ions are paramagnetic (they contain unpaired electrons)
EPR
Cu2+
Mn2+
The Transition Metals: A Survey
Electron Configuration
[Ar] = 1s22s22p63s23p6
4s
3d
4s
3d
4s
3d
4s
3d
Ti3+ => [Ar]3d1
Mn2+ => [Ar]3d5
Fe3+ => [Ar]3d5
Cu2+ => [Ar]3d9
Zn2+ => [Ar]3d10
The Transition Metals: A Survey
Oxidation States, Ionization Energies
Sc
V
Cr
Mn
Fe
Co
Ni
Cu
≤0
o
o
o
o
o
o
o
+1
o
o
o
o
o
o
O
o
O
o
O
O
O
O
O
o
o
O
o
O
O
o
o
O
o
o
O
o
o
o
O
o
o
△
o
O
o
o
Oxidation States
+2
+3
+4
+5
+6
+7
Ionization Energy
O
Ti
Zn
O
O : most common
O
Removing of d-electron
M2+(g) → M3+(g) + eMore rapid decrease of energy level of 3d
Removing of s or d-electron
M(g) → M+(g) + eIncrease of nuclear charge
→ Decrease of energy level of 3d
The Transition Metals: A Survey
Reduction Potentials
E0 (Mn+ + ne- → M)
-2.08
-1.63
-1.2
-1.18
-0.91
-0.76
-0.44
-0.28
-0.23
0.34
E0 (2H+ + 2e- → H2) = 0
In acidic solution,
M(s) + 2H+(aq) → H2(g) + M2+(aq)
except for Cu
The Transition Metals: A Survey
The 4d and 5d Transition Series
3d
4d
5d
Atomic radii
Lanthanide contraction:
4f shielding effect is not big.
=> 5d contracts.
Nuclear charge ↑
The First-Row Transition Metals
Scandium (Sc): Ion => only +3
Titanium (Ti):
The First-Row Transition Metals
Coordination Compounds
Coordination coumpounds typically consists of a complex ion and counter ions (anions or cations
as needed to produce a neutral compound).
Complex ions: species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases).
L4
L3
L1
L2
H2O
[Co(NH3)5Cl]Cl2(s) → Co(NH3)5Cl2+(aq) + 2Cl-(aq)
complex ion counter ion (Cl-)
Co3+, Cl- => []2+
Two characteristics of coordination compounds (complex ions):
oxidation number of the transition metal and coordination number (and geometry)
Coordination Compounds
Coordination Number: number of ligands attached to a metal (typically 2 ~8)
Coordination Compounds
Ligand: A neutral molecule or ion having a lone electron pair that can be used to form a bond to a
metal ion (Lewis base).
coordinate covalent bond: metal-ligand bond
• monodentate ligand: one bond to metal ion
• bidentate ligand: two bonds to metal ion
• polydentate ligand: can form more than two
bonds to a metal ion
• chelate ligand: bidentate, polydentate ligands
• ambidentate ligand: bonding through different
atoms of a same ligand
Coordination Compounds
Nomenclatures
1.
2.
3.
4.
5.
6.
7.
[Co(NH3)5Cl]Cl2
As with any ionic compound, the cation is named before the anion. 국어이름에서는 반대 [“Chloride” goes
last.]
In naming a complex ion, the ligands are named before the metal ion. ["NH3, Cl-" named before cobalt]
For ligand, an “o” is added to the root name of an anion (Table 21.14). For neutral ligands the name of the
molecule is used, with exceptions of Table 21.14. ["Cl- = chloro", "NH3 = ammine"]
The prefixes di-, tri-, tetra-, penta-, and hexa- are used to denote the number of simple ligands.The prefix bis-,
tris-, tetrakis-, and so on are used for the ligands that already contain di-, tri-, etc. [pentaammine]
The oxidation state of the central metal ion is designated by a Roman numeral in parenthesis. [cobalt(III)]
When more than one type of ligand is present, they are named alphabetically. [pentaamminechloro]
If the complex ion has a negative charge, the suffix “-ate (산)” is added to the name of the metal with
exceptions of Table 21.15 [pentaamminechlorocobalt (III) chloride]
Ex) K3Fe(CN)6
potassium hexacyanoferrate(III)
[Fe(en)2(NO2)2]2SO4
철산
구리산
납산
은산
금산
주석산
bis(ethylenediamine)dinitroiron(III) sulfate
triamminebromoplatinum(II) chloride
[Pt(NH3)3Br]Cl
potassium hexafluorocobaltate(III)
K3[CoF6]
Isomerism
When two or more species have the same formula but different properties, they are said to be isomers.
Coordination isomerism:
The composition of the complex ion varies.
[Cr(NH3)5SO4]Br and [Cr(NH3)5Br]SO4
Linkage isomerism:
Same complex ion structure but point of attachment
of at least one of the ligands differs.
[Co(NH3)4(NO2)Cl]Cl
tetraamminechloronitrocobalt(III) chloride
[Co(NH3)4(ONO)Cl]Cl
tetraamminechloronitritocobalt(III) chloride
Geometrical isomerism (cis-trans): Atoms or groups of
atoms can assume different positions around a rigid ring.
cis-Pt(NH3)2Cl2
trans-Pt(NH3)2Cl2
trans-Co(NH3)4Cl2+
cis-Co(NH3)4Cl2+
Isomerism
Optical isomerism: the isomers have opposite effects on plane-polarized light.
early 19C
At his age of 26, he first realized that optical activity is exhibited by
molecules that have non-superimposable mirro images.
said to be chiral, called enantiomers
Louis Pateur (1822-95)
one of the isomers
dextrorotatory (d)
the other
levorotatory (l)
mixture of the two : racemic mixture , when mixed ratio is 1:1, no optical activity
Isomerism
Optical isomerism: the isomers have opposite effects on plane-polarized light.
Co(NH3)Br(en)22+
geometrical
NH3
N
N
N
N
N
N
N
Br
N
N
N
NH3
Br
Co(en)2Cl2+
cis
N
Co
Co
N
cis
N
N
3+
trans
NH3
Br
trans
optical
Co(en)3
N
Co
Co
H3N
N
Br
Bonding In Complex Ions: The Localized Electron Model
Bonding Theories of Complex Ions :
Valence bond theory (Localized electron bonding model)
Crystal field theory
Ligand field theory (Delocalized electron bonding model)
Review of Chapters 8 amd 9
Covalent Bond
Localized electron bonding models
•Lewis dot structure
•VSEPR (Valence shell electron pair repulsion)
•Valence bond theory (hybridization)
Delocalized electron bonding model
•Molecular orbital (MO) theory
Central idea: Formation of hybride atomic orbitals
that are used to share electron pairs to form s
bond between atoms
Bonding In Complex Ions: The Localized Electron Model
For complex ions
Covalent Bond
1. VSEPR model sometimes works. But it
generally does not work
Localized electron bonding models
•Lewis dot structure
•VSEPR (Valence shell electron pair repulsion)
•Valence bond theory (hybridization)
2. The interaction between a metal ion and a ligand
can be viewed as a Lewis acid-base reaction with
the ligand donating a lone pair of electrons to an
empty orbital of the metal ion to form a coordinate
covalent bond.
M
empty metal ion
hybrid orbital
sp3
Co(NH3)6+
d2sp3
L
lone pair on the ligand in a
hybrid atomic orbital
dsp2
M
L
coordinate covalent
bond
sp
Though the localized electron bonding model improved our understanding of metal-ligand
bondings, it does not explain well many important properties of metal ions, such as
magnetism and colors. So usually thesedays we do not use it for the complex ions.
The Crystal Field Model
Crystal field model focuses on the energies of the d orbitals to explain the magnetic properties and
color of complex ions.
Assumption
1. Ligands are negative point charge.
2. Metal-ligand bonding is entirely ionic.
To derive the energy splittings of the d-orbital
in complex ions.
Octahedral Complexes
eg (dz2, dx2-y2)
E
t2g (dxy, dyz, dxz)
d
Free metal ion
3d orbital energies
3d orbital energy splittings
in octahedral field
3d orbitals
3d orbitals in octahedral field
The Crystal Field Model
Octahedral Complexes (magnetic properties)
Co3+ (3d6)
= ligand
field
splitting
parameter
(low-spin, S = 0, diamagnetic)
(high-spin, S = 2, paramagnetic)
Spectrochemical Series for Ligands
CO > CN- > PPh3 > NO2- > phen > bipy > en > NH3 > py > CH3CN > NCS- > H2O > C2O42- >
OH- > RCO2- > F- > N3- > NO3- > Cl- > SCN- > S2- > Br- > Iπ acceptor
(strong field ligand)
π donor
(weak field ligand)
Spectrochemical Series for Metal Ions
(ox # ↑,ᇫ↑), (down a group in periodic table, ᇫ↑)
Pt4+ > Ir3+ > Pd4+ > Ru3+ > Rh3+ > Mo3+ > Mn4+> Co3+ > Fe3+ > V2+ > Fe2+ > Co2+ > Ni2+ > Mn2+
The Crystal Field Model
Octahedral Complexes (magnetic properties)
Ex) Fe(CN)63- has one unpaired electron. CN- is strong-field or weak-field ligand ?
Fe3+ (3d5)
eg
eg
t2g
t2g
weak-field
(high-spin, S=5/2, paramagnetic)
strong-field
(low-spin, S=1/2, paramagnetic)
Ex) How many unpaired electrons in Cr(CN)64- ?
Cr2+ (3d4)
eg
eg
CN- : strong-field ligand
t2g
Ex) S of Cu(H2O)62+ ?
Cu2+
(3d9)
S = 1/2
weak-field
(high-spin, S=2, paramagnetic)
t2g
strong-field
(low-spin, S=1, paramagnetic)
The Crystal Field Model
Octahedral Complexes (colors)
The Crystal Field Model
Octahedral Complexes (colors)
E
E = hn = hc/l
The Crystal Field Model
Other Coordination Geometries
Tetrahedral complexes
eg (dz2, dx2-y2)
t2 (dxy, dyz, dxz)
E
tet ≈ (4/9)oct
t2ge(d(dxyz2, ,ddyzx2-y2
, dxz))
d
Free metal ion
3d orbital energies
3d orbital energy splittings
in tetrahedral
octahedral field
All tetrahedral complexes are
weak-field cases (high-spin).
The Crystal Field Model
Other Coordination Geometries
Square-planar complexes
Linear complexes
dx2-y2 b1g
eg
dz2, dx2-y2
t2 dxy, dyz, dzx
d
dz2
b1g
a1g
o
t
dxy
e dz2, dx2-y2
Uniform Field
Tetrahedral (Td)
dx2-y2
dxy
2
dz2
b2g
a1g
b2g
3
dxy, dyz, dzx
t2g
1
eg
dyz, dzx
Octahedral (Oh)
Tetragonal elongation (D4h)
eg
dyz, dzx
Square-planar (D4h)
Bonding In Complex Ions: The Localized Electron Model
Bonding Theories of Complex Ions :
Valence bond theory (Localized electron bonding model)
Crystal field theory
Ligand field theory (Delocalized electron bonding model)
has not talked
about bonding
frontier orbitals
•electrons from d-orbitals
•same splitting pattern and d-orbital
configuration as in CFT
Higher Class
electrons from ligands
M
ML6
L6
The Biological Importance of Coordination Complexes
Roles of metals in biology – electron transport, oxygen storage, oxygen transport,
oxidation-reduction catalysis, metal ion storage and transport .......
The Biological Importance of Coordination Complexes
How to get energy in our body ?
O2 : source of energy - combustion (burning gasoline in automobiles)
- oxidation of carbohydrates, proteins, fats through respiratory chain (mammal)
heme = Fe + porphyrin
Air
O2 transport
protein
O2 storage and transport
O2 + nutrients
Hemoglobin
Hb(aq) + 4O2(g) ←
→ Hb(O2)4 (aq)
Oxyhemoglobin
Hemoglobin
e- transfer
(oxidation of nutrients)
cytochromes
(Heme proteins)
Myoglobin
The Biological Importance of Coordination Complexes
Others
Chlorophyll
Nitrogenase
Cisplatin
Metallurgy and Iron and Steel Production
Metallalurgy
1. Mining
2. Pretreatment of the ore
3. Reduction to the free metal
4. Purification of the metal (refining)
5. Alloying
removing CO2
FeCO3(s)heat
→ FeO(s) +CO2(g)
4FeO(s) + O2(g) →2F2O3(s)
3Fe2O3(s) + C(s) →Fe3O4(s)+CO(g)