1
Coordination Chemistry
Alfred Werner
(1866-1919)
NP in Chemistry
1913
[CoII(gly)3]-
1893 To central atom, more
ligands can be bound then is
its oxidation number
2
[Co(NH3)6]Cl3 [Co(NH3)5Cl]Cl2 [Co(NH3)4Cl2]Cl
3+ 2+ +
Coordination Compounds
Metal in oxidation state n+ (primary valence)
Complex has coordination number m (secondary valence)
Ligands bound to central atom by donor-acceptor bonds
3
n+/Central
metal cation / neutral atom surrounded by a set of
ligands. Each ligand provides 2 electrons to empty d-orbitals
at metal and forms donor-acceptor bond.
Number of ligands = Coordination number
Central cation / metal atom
Ligands
Complex
charge
X+/-
n
Anion/cation (opposite charge)
Coordination Compounds
4
Inner and Outer Coordination Sphere
Inner Coordination Sphere = ligands driectly bound to the central atom
Outer Coordination Sphere = ions asociated with a complex, not bound
H2O
H2O
OH2
H2O
H2O
OH2
Mn2+
SO4
2Inner
Coordination Sphere
Outer Coordination Sphere
H2O
H2O
OSO3
H2O
H2O
OH2
Mn2+
[Mn(OH2)6][SO4]: outer coordination of SO4
2[Mn(OH2)5(SO4)5]:
Inner Coordination of SO4
2-
counterion
ligand
5
Coordination Compounds
K2[PtCl6]
6
Energy Level Ordering
Ar [Ne] 3s2 3p6 (4s0)
K [Ar] 4s1 (3d0 4p0)
Ca [Ar] 4s2 (3d0 4p0)
Sc [Ar] 3d1 4s2 (4p0)
Ti [Ar] 3d2 4s2 (4p0)
7
Stability of Half- / Filled d-Orbitals
Cr [Ar] 3d5 4s1 (4p0)
Cu [Ar] 3d10 4s1 (4p0)
8
Oxidation States of TMs
21,21,2
3,4
1,2,3
,4
2,3,
4,5,6
1,2,
3,4,
5,6,7
1,2,
3,4,
5,6
1,2,3
4,5
2,3
4
3
ZnCuNiCoFeMnCrVTiSc
9
d-Electron Count
Number of electrons in valence
level
Cr [Ar] 3d5 4s1 (4p0)
Number of electrons removed
during cationt formation: electrons
of s-orbital are removed first
Cr3+
Number of electrons remaining in d-
orbitals
Cr3+ [Ar] 3d3 4s0 (4p0)
Cr3+ is a d3 cation
10
1 2
3 4 5 6 7 8 9 10 11 12
1 2
3 4 5 6 7 8 9 10 11 12
OO
-O Oox
=
OO
-O Oox
=
NH2
en =
H2N NH2
en =
H2N
Complex Ox.No. (Ligand) Ox.No. (M) No. d-electrons
[Cr2O7]2- -2 +6 d0
[MnO4]- -2 +7 d0
[Ag(NH3)2]+ 0 +1 d10
[Ti(H2O)6]3+ 0 +3 d1
[Co(en)3]3+ 0 +3 d6
[PtCl2(NH3)2] -1, 0 +2 d8
[V(CN)6]4- -1 +2 d3
[Fe(ox)3]3- -2 +3 d5
11
Donor-Acceptor Bond
Acceptor
Empty orbital
Donor
Free e pair
donor-acceptor bond is equivalent to a covalent bond
Covalent Bond
12
H
NH H
F
BF F+
H
NH H
F
BF F
H
NH H
F
BF F
Donor-Acceptor Bond
NH3 BF3 H3N
_> BF3
Donor-Acceptor Bond
+
VB theory
13
Donor-Acceptor Bond
F
F
F
H
H
H
H
H
H
F
F
F
H
H
H
F
F
F
NH3 BF3 H3N
_> BF3
+
B
N
VB theory
MO theory
14
[Co(NH3)6]3+
H
N
H
H
Co3+
+
H3N
NH3
NH3
NH3
H3N
NH3
3+
6
"Lewis Acid"
"Lewis Base"
Donor-Acceptor Bond
Each ligand provides 2
electrons
VB theory
15
Pt2+ [Xe] 4f14 5d8 4s0
PtCl4
2dsp2
hybrid orbitals
Electrons from Cl-, square planar
Ni2+ [Ar] 3d84s0
NiCl4
2sp3
hybrid orbitals
Electrons from Cl-, tetrahedral
d s p
d s p
16
Co3+ [Ar] 3d64s0
CoF6
3sp3d2
hybrid orbitals
Electrons from F-, octahedral
Co3+ [Ar] 3d64s0
Co(NH3)6
3+
d2sp3 hybrid orbitals
Electrons from NH3, octahedral
L
L
L
L
L
L
d
d
s p
s p
17
Monodentate Ligands
NH3
ammonia
H2O
water
SR2
thioether
PPh3
phosphane
P
CO
Carbon dioxide
C O
Cr
Ni(CO)4, Fe(CO)5, Mo(CO)6
18
HSAB = Hard and Soft Acids and Bases
R. Pearson 1963
High oxidation states of central atoms are stabilised by F−, O2−
Low oxidation states are stabilised by CO, CN−
Base
Acid
Hard
Soft
19
NH3, F-, H2O, OH-, CO3
2Small
donor atoms
High electronegativity
Difficult to polarize
Fe(III), Mg(II), Cr(III), Al(III)
Small atoms (1st trans. row)
Large charge
HARD donor atoms
CO, PPh3, I-, C2H4, SRH, CN-,
SCNLarge
donor atoms
Low electronegativity
Easily polarized
Ag(I), Cu(I), Hg(II), Au(I)
Large atoms (2nd and 3rd transition row)
Small charge
SOFT donor atoms
Hard metals Soft metals
Stabile complexes Stabile complexes
Weak
complexes
HSAB
20
H2N NH2
1,2-diaminoethane = ethylendiamine = en
[PtCl2(en)]
Five-membered chelate cycle
square planar complex
Ph2P PPh2
1,2-difenylphosphinoethane
dppe
2,2'-bipyridine
bipy
N N
N N
1,10-phenanthroline
phen
Neutral Bidentate Ligands
21
acetate = ac-
O
O
-
OO
H3C
O
O
oxalate = ox2complex
Pd(II)-oxim
π-donor bidentate ligand
Fe
C C
C
O O
O
[Fe(CO)3(h4-C4H6)]
R O
O
N
R1
RO
O
N
R1
H
H
Pd
Anionic Bidentate Ligands
22
H2N NH NH2
2,2':6',2"-terpyridine
tpy
diethylentriamine
dien
N
H
NHHN1,2,4-triazacyclononane
Macrocyclic ligand
N
N
N
Tridentate Ligands
23
N
HNN
NH
N
N
N
N
N
HNN
NH
porfyrine
ftalocyanine
NH2
NH2
N
NH2
tris(2-aminoethyl)amine
tren
Tetradentate Ligands
24
N N
O
-
O
--
O
-
O
O
OO
O
tetraanion of ethylendiamintetraacetic acid
EDTA
Hexadentate
O N
NO
O
O
M
O
O
O
O
Multidentate Ligands
25
Nomenclature of Coordination Complexes
H2O-Aqua
NH3-Ammine
CO-Carbonyl
NO-Nitrosyl
CH3NH2-Methylamine
C5H5N-Pyridine
F--Fluoro
Cl--Chloro
Br--Bromo
I--Iodo
O2--Oxo
OH--Hydroxo
CN--Cyano
SO4
2--Sulfato
S2O3
2--Thiosulfato
NO2
--Nitrito-N-
ONO--Nitrito-O-
SCN--Thiocyanato-S-
NCS--Thiocyanato-N-
26
Stability of Complexes
Stability constant of a complex
= equilibrium constant of its formation
High value of K =
stabile complex
27
Stability of Complexes
Stability constant of a complex MLn
28
Stability of Complexes
Total stability constant of a complex MLn
29
Chelate Effect
[Ni(H2O)6]2+ + 6 NH3 [Ni(NH3)6]2+ + 6 H2O
[Ni(H2O)6]2+ + 3 en [Ni(en)3]2+ + 6 H2O
logK = 8.61
logK = 18.28
ΔG = - RT lnK = ΔH - TΔS
ΔH same for both reactions (Ni-O → Ni-N)
ΔS high for chelate, more product particles
30
Chelates, Macrocycles, Cryptates
NP in Chemistry 1987
Donald J. Cram Jean-Marie Lehn Charles J. Pedersen
31
Chelates, Macrocycles, Cryptates
O
O
N N
HOOC
COOH
COOH
COOH
O
Co
N
ON
O
O
O
O
EDTA
tetraanion of ethylendiamintetraacetic acid
Chelatation therapy of Pb poisoning
Chelatometry
Dissolves CaCO3
32
Chelates, Macrocycles, Cryptates
N
N N
N
R7
R8 R1
R2
R3
R4R5
R6
M
R9
R10
R11
R12
Metalloporphyrins: M = Fe (hem, cytochrom c),
Mg (chlorophyl), Co (B12)
33
Hemoglobine
34
6CO2 + 6H2O → C6H12O6 + 6O2
Mg chlorophyl
35
Chelates, Macrocycles, Cryptates
Valinomycine
36
L
M
L
LL
L
L
L
M
L
L
L
Octahedral complexes Oh
Tetrahedral complexs Td
Geometry of Complexes
37
Tetrahedral 109o 28' C.N. 4
Square planar 90o C.N. 4
Trigonal bipyramidal 120o + 90o C.N. 5
Square pyramidal 90o C.N. 5
Octahedral 90o C.N. 6
Geometry of Complexes
38
Isomers of Complexes
Structural isomers
Bonding
Coordination
Ionization
Stereo isomers
Geometric
Optical
39
Bonding : SCN-, NO2
-, OCN-
NH3
Co
NH3
H3N
NH3
NH3N
O
O
2+
NH3
Co
NH3
H3N
NH3
OH3N
N
2+
O
nitro- nitritoStructural
Isomers
40
Structural Isomers
Coordination
[Pt(NH3)4][CuCl4] [Cu(NH3)4][PtCl4]
Ionization
[Co(NH3)5SO4]Br [Co(NH3)5Br]SO4
41
Stereo Isomers
Geometric: cis-trans, diastereomers
42
Stereo Isomers
cis trans
Pt
H3N
Cl
ClH3N Pt
H3N
NH3
ClCl
Geometric:
cis-trans
diastereomers
43
Antitumor Medicine
H3N
Pt
H3N
Cl
Cl
Cisplatin
H3N
Pt
H3N
O
O
O
O
Carboplatin
H3N
Pt
H3N
O
O
O
O
Nedaplatin
H2
N
Pt
N
H2
O
O
O
O
Oxaliplatin
Inactive H2
N
Pt
NH
Cl
NH2
H3N
Pt
Cl
Cl
NH3
44
Stereo Isomers
H
N
N
N
OH2N
N
O
H
HH
HH
O
PO
O-
O
O
NH
N
N
O
NH2
N
O
H
HH
HH
O
PO
O-
O
Pt
H3N
NH3
DNA
Cisplatin = cancerostatics
45
Geometric: mer-fac, diastereomers
Stereo Isomers
A
A BM
B
B
A
A
A BM
A
B
B
S
L
S
M
L
S
L
N
N
N
M
L
L
L
mer
fac mer
fac
46
Stereo Isomers
Optical: enantiomers
47
Stereo Isomers
Optical: enantiomers
No Sn
S1 = symmetry plane
S2 = inversion center
[Co(en)3]3+
48
Optical Rotation
49
Bonding in Complexes
1) VB
2) CFT = Crystal Field Theory 1929 Hans Bethe
Electrostatic interactions between ligands and metal
3) LFT = Ligand Field Theory
1935 modification J. H. Van Vleck covalence
4) MO
50
Ligand Field Theory
Octahedral complex
Central atom in the
center of octahedron
Ligands as negative
point charges
x
z
y
51
d-Orbitals in Octahedral Ligand Field
52
Splitting of d-Levels in Oh Field
eg
t2g
Stabilization 0.4 Δo
Destabilization 0.6 Δo
5 degenerate
d-orbitals
in isolated cation
53
CFSE = Crystal Field Stabilization Energy
Δo Δo
Weak field
Δo < P (pairing energy)
High spin complexes
Strong field
Δo > P (pairing energy)
Low spin complexes
54
Crystal Field Stabilization Energy
Weak field
Strong field
Δo increases
55
CFSEeCFSEe
1.2 Δo2t2g
6 eg
2
1.2 Δo2t2g
6 eg
2d8
1.8 Δo1t2g
6 eg
1
0.8 Δo3t2g
5 eg
2d7
2.4 Δo0t2g
6
0.4 Δo4t2g
4 eg
2d6
2.0 Δo1t2g
5
0.0 Δo5t2g
3 eg
2d5
1.6 Δo2t2g
4
0.6 Δo4t2g
3 eg
1d4
1.2 Δo3t2g
3
1.2 Δo3t2g
3d3
0.8 Δo2t2g
2
0.8 Δo2t2g
2d2
0.4 Δo1t2g
1
0.4 Δo1t2g
1d1
CFSE = (n t2g ) 0.4 Δo − (n eg) 0.6 Δo
e = number of unpaired electrons
Weak field Strong field
56
Splitting of d-Levels in Oh Field
t2g
eg
3/5Δo
2/5Δo
10Dq
[Ti(H2O)6]3+ d1
t2g
1eg
0 t2geg
1
pink
243 kJ mol−1 (Δo)
57
UV-vis Absorption Spectrum of [Ti(H2O)6]3+
58
Electronic Transitions
Energy increases
This energy is just sufficient to excite electron
Electronic
Transition
59
60
Splitting of d-Levels in Td Field
e
t2
2/5Δt
3/5Δt
Δt = 4/9 Δo
Td complexes are always high spin
No d-orbital points directly to ligands = weaker
interaction
61
d-Orbitals in Tetrahedral Ligand Field
62
Splitting of d-Levels in Square Planar Field (d8)
t2g
eg
xz, yz
xy
z2
x2- y2
x2- y2
z2
xy
xz, yz
eg
a1g
b2g
b1g
Removing ligands in z direction
Ni(CN)4
2,
PdCl4
2-
,
Pt(NH3)4
2+
, PtCl4
2-
,
AuCl4
-
d8
63
18-electron Rule
Cr(CO)6 Cr d6
6 × CO 6 × 2 = 12
Sum 18
[Co(NH3)3Cl3] Co d9
3 × NH3 3 × 2 = 6
3 × Cl 3 × 1 = 3
Sum 18
Number of d-electrons of neutral metal
+ 2 e neutral ligands
+ 1 e anionic ligands Sum 18 for stabile complexes
64
Properties of Complexes
Ligand field splitting
t2g
eg
65
Spectrochemical Series:
Central atom:
3d < 4d < 5d
2+ < 3+ < 4+
Ligand Field Splitting Factors
Bond length and strength M-L
Type of coordination 4/9 ΔO = Δt
Mn2+ < Ni2+ < Co2+ < Fe2+ < V2+ < Fe3+ < Co3+ < Mn3+ < Mo3+ < Rh3+ < Ru3+ < Pd4+ < Ir3+ < Pt4+
I- < Br- < S2- < SCN- < Cl- < N3
-, F-< OH- < ox, O2- < H2O < NCS- < py, NH3
< en < bpy, phen < NO2
- < CH3
-, C6H5
- < CN- < CO
66
67
Bonding in Complexes by MO
SALCAO
Orbitals
of ligands
5x (n−1) d
1x ns
3 x np
Orbitals of
metal
68
x
y
z
Metal Valence Orbitals
s px py pz
dxy dxz dyz
dx2-y2 dz2
69
a1g
t1u
eg
M-L Sigma bonds
3 x np
70
t2g
Nonbonding d-Orbitals
There is no suitable
combination of AOs of
ligands (for sigma
bonding)
71
72
t1u
a1g
eg, t2g
t1u
*
a1g
*
eg
*
t2g
eg
t1u
a1g
a1g, eg, t1u
(n+1)p
(n+1)s
nd
M ML6 6L
Δo
73
t2
a1
e, t2
t2
*
a1
*
e
t2
a1
a1, t2
(n+1)p
(n+1)s
nd
M ML4 4L(LGOs)
t2
*
Δt
74
a2u, eu
a1g
eg, a1g, b1g, b2g
eu
*
a2u
a1g
b2g, eg
eu
b1g
a1g
a1g, eg, t1u
(n+1)p
(n+1)s
nd
M ML4 (D4h) 4L(LGOs)
Δ
b1g
*
a1g
*
75
C O
H
H
pπ-dπ RO
,
RS
,
O
2,
F
,
Cl
,
Br
,
I
,
R2N
dπ-dπ
R3P, R3As, R3S
dπ-π* CO, RNC, pyridine, CN
,
N2,
NO2
,
ethylene
dπ-σ* H2, R3P, alkanes
MO in π-Bonding
76
Pi base Pi acid
77
Ligands with pi Orbitals
Pi base Pi acid
78
Back pi donation
M → CO
Sigma donation
M ← CO
79
Kinetics
10 10 10 10 10 10 10 10 10 10 10
-10 -8 -6 -4 -2 0 2 4 6 8 10
10 10 10 10 10 10 10 10 10 10 10
10 8 6 4 2 0 -2 -4 -6 -8 -10
Ir Rh
Pt
At Fe Ga
V
Be Mg
Pd
Ti
Ni
Fe
Mn
Zn Cd Hg
Cr
Cu
Gd
Tb
DyHoEr
Tm
Yb
In
Ca
Sr
Ba
Na
K Rb
Cs
Ru
Ru
3+ 3+ 3+ 3+ 3+
3+
3+
3+
3+3+
3+
3+3+
3+
3+
3+
2+
2+
2+2+
Li+
+
+
+
+
2+
2+
2+
2+
2+
2+
2+
2+2+
2+
2+
2+
3+
Cr
V2+ 2+
Co
Metalion
k (s )–1
H O2
τ (s)H O2
[M(H2O)n]x+ + H2O* [M(H2O*)(H2O)n-1]x+ + H2O
INERT
LABILE
80
Mechanisms of Complex Reactions
Mechanism
Dissociative (D)
W(CO)6 W(CO)5 + CO
W(CO)5 + PPh3 W(CO)5(PPh3)
Associative (A)
[Ni(CN)4]2- + 14CN- [Ni(CN)4(14CN) ]3[Ni(CN)4(14CN)
]3- [Ni(CN)3(14CN) ]2- + CN-
81