Coordination Chemistry : Coordination
numbers, chelate effect, coordination
complexes and application. Bioinorganic
chemistry : Metal ions in biological
systems, environmental aspects of
metals, NOx, CO, CO2.
Bonding Models in Inorganic Chemistry :
Molecular orbital theory, Valence bond
theory, Crystal field theory.
Classes : September 01 to October 07,
1
2004
2
3
Coordination Chemistry
Coordination Equilibria
[Fe(H2O)6]3+ + NCS- → [Fe(H2O)5(NCS)]2+ + H2O
Kf = [Fe(H2O)5(NCS)]2+/ [Fe(H2O)6]3+[NCS-]
Equilibrium constant Kf ⇒ formation constant
M + L → ML K1 = [ML]/[M][L]
ML + L → ML2 K2 = [ML2]/[ML][L]
ML2 + L → ML3 K3 = [ML3]/[ML2][L]
MLn-1 + L → MLn Kn = [MLn]/[MLn-1][L]
4
Coordination Equilibria and Chelate effect
• K1, K2…. ⇒ Stepwise formation constant.
• To calculate
concentration of the final
product, use overall formation constant βn:
• βn = [MLn]/[M][L]n
• = K1 x K2 x K3 x …. x Kn
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What are the implications of these results?
NiCl2 + 6H2O
→ [Ni(H2O)6]+2
[Ni(H2O)6]+2 + 6NH3
→ [Ni(NH3)6]2+ + 6H2O
[Ni(NH3)6]2+ + 3 NH2CH2CH2NH2 (en)
→ [Ni(en)3]2+ + 6NH3
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Complex Formation: Major Factors
[Ni(H2O)6] + 6NH3
→[Ni(NH3)6]2+ + 6H2O
¾ NH3 is a stronger (better) ligand than H2O
¾ ΔO NH3 > ΔO H2O
¾ [Ni(NH3)6]2+ is more stable
¾ ΔG = ΔH - TΔS
(ΔH -ve, ΔS ≈ 0)
¾ ΔG for the reaction is negative
7
Complex Formation: Chelate Effect
• [Ni(NH3)6]2+ + 3 NH2CH2CH2NH2 (en)
→ [Ni(en)3]2+ + 6NH3
• en is bidentate ligand
• forms a 5 member ring known as chelate ring
• the complex is known as a chelate
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Complex Formation: Chelate Effect
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Complex Formation: Chelate Effect
[Ni(NH3)6]2+ + 3 (en) → [Ni(en)3]2+ + 6NH3
• Formation of chelate ring ⇒ reaction proceeds
in forward direction & the product is stable.
This stability is purely kinetic in nature. This
is known as chelate effect.
• ΔG = ΔH - TΔS
(ΔH -ve, ΔS ++ve)
• This extra kinetic stability is due to high
positivity of ΔS
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Crystal Field Theory
• Transition metals Complexes.
• Alfred Werner
• VBT
• Crystal Field Theory (CFT)
• Modified CFT, known as
Ligand Field Theory
• MOT
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Linkage isomerism – the same ligand may link
through different atoms
Ambidentate ligand – different potential donor
Atoms
NCS-
by nitrogen – isothiocyanato
sulfur - thiocyanato
[Co(NO2)(NH3)5]2+
Red
Yellow
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[Cr(edta)] –
(edta = ethylenediaminetetraacetic acid)
Not superimposable on its mirror image --- chiral
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15
• In the CFT, ligands are considered as point
charges.
• Interaction between ligand & metal ion is
considered to be purely electrostatic or
coulombic in nature.
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17
18
.[Ni(PR3)4]
Ni(PR3)4
[Ni2Cp3]+
Triple decker compound
Cp = cyclopentadienyl
Back to Chapter Index
19
.[Ce(NO3)6]2-
[Ce(NO3)6]2C.N. 12
Fe(Cp)2
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Pentadentate ligand
Hexadentate Ligand
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.[Pt(PPh3)2(C60)]
Pt(PPh3)2(C60)
[Zr(ox)4]4C.N. 8
Bhap d
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23
24
25
26
27
In Octahedral Field
dyz
dz2
dxz
dx2-y2
dxy
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29
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In Tetrahedral Field
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Crystal Field Splitting Energy (CFSE)
• In Octahedral field, configuration is: t2gxegy
• Net energy of the configuration relative to the
average energy of the orbitals is:
= (-0.4x + 0.6y)ΔO
BEYOND d3
• In weak field: ΔO < P, => t2g3eg1
• In strong field ΔO > P, => t2g4
• P - paring energy
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Ground-state Electronic Configuration,
Magnetic Properties and Colour
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Ground-state Electronic Configuration,
Magnetic Properties and Colour
[Mn(H2O)6]3+
Weak Field Complex
the total spin is 4 × ½ = 2
High Spin Complex
[Mn(CN)6]3Strong field Complex
total spin is 2 × ½ = 1
Low Spin Complex,
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Ligand-field theory
MO energy levels of a
typical Oh complex
CFT doesn’t take into
account the overlap of
ligand and metal orbitals
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Symmetry-adapted combinations of ligand σ orbitals37
LFT – application of MO theory
The valence orbitals on the metal and ligand are
used to form SALCs
Using empirical energy and overlap
considerations – the relative energies of the
MOs are estimated
σ Bonding – ligand has a single valence orbital
directed toward the central metal atom
π Bonding – the ligand has filled orbital of π
symmetry around the M-L axis
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n = no. of unpaired electrons
μ = {n(n+1)}1/2 μB
Ion
n
S
Ti3+
3+
V
Cr3+
Mn3+
3+
Fe
1
2
3
4
5
1/2
1
3/2
2
5/2
Experimental
μ/μB
Calculated
1.73
1.7 – 1.8
2.83
2.7 – 2.9
3.87
3.8
4.90
4.8 – 4.9
5.92
5.3
Similar Calculation can be done
for Low-spin Complex
39
Attraction/repulsion --Magnetic field --- change in
apparent weight of the sample
when the magnetic field is
turned on
Gouy balance to measure the magnetic susceptibilities
SQUID ‘superconducting quantum interference
device’
--- very sensitive magnetometer
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.[Cu(CH3CO2)4(OH2)2]
[Cu2(OAc)4(H2O)2]
Low magnetic moment
41
The origin of the color of the
transition metal compounds
E2
ΔE
hν
E1
Δ E = E 2 – E 1 = hν
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43
44
The optical absorption spectrum of [Ti(H2O)6]3+
Assigned transition:
eg
t2g
This corresponds to
the energy gap
ΔO = 243 kJ mol-1
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Promotion of electrons from
the porphyrin π HOMO to
the π* LUMO
The absorption spectrum of chlorophyll a1
Chlorophyll absorbs light and the absorbed energy is
Transferred to a reaction center
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Ligands influence ΔO, therefore the colour
• Spectrochemical Series: An order of ligand
field strength based on experiment:
Weak Field
I- < Br-< S2-< SCN-< Cl-<
NO3-< F- < C2O42-< H2O< NCS-<
CH3CN< NH3< en < bipy< phen<
NO2-< PPh3< CN-< CO Strong Field
H 2N
NH2
N
N
N
N
Ethylenediamine (en)
2,2'-bipyridine (bipy)
1.10 - penanthroline (phen)
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Stabilizing low oxidation state: CO can do the job
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Stabilizing low oxidation state: CO can do the job
Ni(CO)4], [Fe(CO)5], [Cr(CO)6], [Mn2(CO)10],
[Co2(CO)8], Na2[Fe(CO)4], Na[Mn(CO)5]
49
Metal complexes containing metals in
unusual formal oxidation states
Metals in High Oxidation States
• High oxidation states ⇒ highly electron
deficient or hard acids.
• To stabilize high oxidation states we require
ligands which can form very strong σ bond as
well as π bond, i. e. strong σ as well as π
donor.
• Ligands must be hard base.
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Stabilizing HIGH Oxidation State: Who Can Do the Job?
Such ligands are O2-, CN-, amide (-CO-NR2), or
ligands containing negatively charged nitrogen.
KMnO4, K2Cr2O7, FeO44 -, FeO43 ⇓
Mn(VII), Cr(VI), Fe(IV), Fe(V)
K2[MnF5], K2[MnF6]
⇓
Mn(III), Mn(IV)
⇒ stabilized
by O2-
⇒ stabilized
by F51
Coordination compounds - Catalysis - Nobel
2001
1973
1963
1918
1909
KNOWLES, NOYORI, SHARPLESS
WILKINSON
ZIEGLER, NATTA
HABER
OSTWALD
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Hydrogenation of Unsaturated Hydrocarbons
H
H
-CH=CH- + H2 → -CH-CHNOBEL : 2001
The most common catalyst
⇓
Wilkinson’s Catalyst, [RhCl(PPh3)3]
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WC
IN
A
C
T
I
O
N
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Conversion of MeOH to Acetic Acid
Methanol (MeOH) is converted to Acetic acid
industrially by using [RhI2(CO)2]- as catalyst.
This process is known as Monsanto Process
CO + MeOH
⇓
CH3COOH + CH3COOCH3
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MONSANTO
PROCESS
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Adipic Ester Synthesis
• Butadiene can be carbonylated to give adipic
acid esters, then hydrolyzed to the acid.
• This acid is used in synthesis of Nylon 6.
• The catalyst used is Co2(CO)8
CH2 = CH – CH = CH2 + MeOH + 2CO
⇓
MeO2C(CH2)4CO2Me
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Polymerization of Alkenes
• Propylene is commercially polymerized by a
heterogeneous catalyst developed by Ziegler
and Natta, and is known as Ziegler-Natta
catalyst.
• The catalyst is produced by a reaction of
TiCl4 and AlEt3.
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Ziegler-Natta
Polymerization
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Coordination Compounds in Biology
• Main group elements: K, Na, Ca, Mg
• Transition metals:
Fe, Cu, Mn, V, Cr,
Ni, Zn, Mo etc.
:Roles:
• Electron transfer
• Bind small molecules like O2, and thus take
part in the transport of O2.
• Templates for syntheses of biomolecules.
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The transition metals are usually bound to
proteins ⇒ Metalo-proteins.
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Transition metals bound to enzymes ⇒
Metalo-enzymes
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Metal Binding Groups
functional groups like
-COOH, -OH, -SH, NH2
CONH2 in peptide bond
63
PORPHYRIN:
A STRONG METAL BINDING Macrocylic Ligand
N
N
H
N
H
N
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Porphyrin bound iron:
Heme Proteins:
Heme Group
Hemoglobin
Hemoglobin
N
N
⇓
Transport O2
Fe
N
N
from lung
to muscles
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Hemoglobin: Before Oxygen Binds
O
HISTIDINE
H
N
HO
H2N
N
PORPHYRIN
N
N
Fe
N
N
Fe(II)
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OXYGEN BINDING: COOPERATIVITY
HEMOGLOBIN
MYOGLOBIN
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M
E
T
A
L
S
IN
M
E
D
I
C
I
N
E
• Li
Maniac depressive illness
• Cu
Anti inflammatory Drugs
• Bi
Peptic Ulcers
• Sn & Zn
Neonatal Jaundice
• V
Diabetics
• Ge(IV), Sb(III)
Hypertension
• As(III)
African Sleeping sickness
• Sb
Anti Parasitic
• Ag
Anti Fungal
• Au
Aurinofin- Arthritis
• Pt
Cisplain & Carboplatin- Cancer
Chemical Review Vol. 99, Issue 9, 1999
69
Anticancer Pt-Drugs in Chemotherapy
O
Cl
H3N
Pt
H3N
H3N
DNA-Binding
Cl
CISPLATIN
O
Pt
H3N
O
O
CARBOPLATIN
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Inorganic Chemistry & Environment
•
Acid Rain: Tajmahal is in danger
combustion of high sulfur fuels, roasting of
sulfur ores like Cu2S
⇒ Sulfur oxides ⇒ sulfuric acid
• Auto Exhaust ⇒ N2+O2 ⇒ Oxides of Nitrogen
NOx ⇒ nitric acid
•
Dissolved acids in Environment ⇒ “acid rain”
•
Some times, the pH is as low as 1.5
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Inorganic Chemistry & Environment
Depletion of Ozone Layer:
•
Nature ⇒ Photochemical process
⇓
Formation and Destruction of ozone
O2 + hν (below 242 nm) → O . + O .
O3
•
O . + O2 → O 3
+ hν (220 - 320 nm) → O . + O2
CULPRIT: NO & CFC (F3CCl)
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Inorganic Chemistry & Environment
Depletion of Ozone Layer:
Supersonic Concorde
⇓
NO
Refrigerant
⇓
CFC
NO + O3 → NO2 + 2O.
NO2 + O. → NO + O2
F3CCl
→ F3C. + Cl.
Cl. + O3
→ ClO. + O2
ClO. + O.
→ Cl. + O2
The net reaction is
O + O3 → 2O2
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CHEMISTRY:
INDEPENDENCE VS. INTERDEPENDENCE
Genomics
Proteomics
Biomimetics
Reagent
Catalyst
Green
Economy
GDP, WTO
Atom-economy
Supramolecular
Dendrimer
Nano
Patent
Turmeric, Basmati
Herbal, Ayurveda
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Thank You! I think I have tried to give
an overview in general chemistry
Can’t he explain
in Modern Terms
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