Post on 08-Apr-2018
8/7/2019 Ist yr-3-2006
1/30
Complex ion defined as electrically charged radical whichconsists of a central metal ion surrounded by a group of ions or
neutral moleculesEx. [ Ni(NH3)6]
++, [ Pt (NH3)4Cl2]++
Central ion and ligands The cation to which one or more neutralmolecules or anions are attached is called the central ion while
molecules or ions attached are called ligands
Ex. [ Ni(NH3)6]++, [ Fe (CN)6)]
- - -
Ligands Central metal atom coordinatebonds
Central ion ligand
Should have lone
pair of electrons
Should have vacant
orbitals
attached to
8/7/2019 Ist yr-3-2006
2/30
Donor atom atom of ligand which can donate the electron pair
is called donor or coordination atom
Coordination number Total number of ligands attached to a
central ion is called the coordination number of the ion
Charge of complex ion charge carried by a complex ion is the
algebraic sum of charges carried by central ion and ligandscoordinated to it
[Cu (NH3)6]++ , [Fe (CN)6]
4-
8/7/2019 Ist yr-3-2006
3/30
In coordination compound
Metal exhibits two types of
valency
Primary Secondary
ionizable non-ionizable
Corresponds to
Oxidation state coordination number Fixed for every metal
CO
NH3Cl
NH3
NH3
ClNH3
H3N
H3N
Cl
Example CoCl3
.6NH3
8/7/2019 Ist yr-3-2006
4/30
Effective atomic number (EAN)
In complex formation each ligand donates a electron pair to the
central metal ion. Total number of electrons possessed by the
central metal in complex including those gained by it in bonding iscalled its EAN
Atom At. No. Complex Electron lost
in ion
formation
Electron
gained by
coordination
EAN
Cr
Fe
Co
Cu
Pd
Pt
24
26
27
29
46
78
[Cr (CO)6]
[Fe(CN)6]4-
[CO(NH3)6]+++
[Cu(CN)4]---
[Pd(NH3)6
]4+
[PtCl6]--
? ? ?
8/7/2019 Ist yr-3-2006
5/30
Atom At. No. Complex Electron lost in
ion formation
Electron gained
by coordination
EAN
Cr
Fe
Co
Cu
Pd
Pt
24
26
27
29
46
78
[Cr (CO)6
]
[Fe(CN)6]4-
[CO(NH3)6]+++
[Cu(CN)4]---
[Pd(NH3)6]4+
[PtCl6]--
0
2
3
1
4
4
12
12
12
8
12
12
36
36
36
36
54
86
Valence Bond Theory Developed by Pauling
Coordination compounds contain complex ions in which ligands
from coordinate bonds to the metal.
So, ligand must have lone pair of electrons and metal must have
empty orbital of suitable energy available for bonding.
According to the atomic orbital of the metal used for bonding, shape
and stability of the complex is predicted.
8/7/2019 Ist yr-3-2006
6/30
8/7/2019 Ist yr-3-2006
7/30
8/7/2019 Ist yr-3-2006
8/30
8/7/2019 Ist yr-3-2006
9/30
8/7/2019 Ist yr-3-2006
10/30
8/7/2019 Ist yr-3-2006
11/30
8/7/2019 Ist yr-3-2006
12/30
8/7/2019 Ist yr-3-2006
13/30
8/7/2019 Ist yr-3-2006
14/30
8/7/2019 Ist yr-3-2006
15/30
8/7/2019 Ist yr-3-2006
16/30
Crystal field theory
In an isolated metal ion, all the five d orbitals degenerate
On approach of ligand, d orbital electrons will be repelled by
ligands lone pair
Repulsion raises the energy of d orbitals
If field produced by the ligands is spherically symmetrical (allthe ligands are an equal distance from each of the d orbitals),
energy of the d orbital will be raised but they still remain
degenerated hypothetical situation
But, field produced by the ligands is not spherically symmetricalbecause d orbitals differ in their orientations
Energy of the orbitals lying directly in ligands direction will be
raised more than the orbitals lying in between the ligands
8/7/2019 Ist yr-3-2006
17/30
Crystal field theory
So, d orbital splits into two sets of different energies
This crystal field splitting forms the basis of Crystal Field Theory
Relative energies of d orbital depends on the number of ligands
and their arrangement around central metal ion
So crystal field splitting will be different in different structureswith different coordination number
Electrons of the metal ion are repelled by negative field of
electrons, therefore, the metal electrons will occupy those d
orbitals which have their lobes farthest away from the directionof ligand
Complexes with coordination number 6 and 4 are more common
giving octahedral, tetrahedral and square-planar complexes
8/7/2019 Ist yr-3-2006
18/30
+0.6 (O
-0.4 (O
8/7/2019 Ist yr-3-2006
19/30
8/7/2019 Ist yr-3-2006
20/30
8/7/2019 Ist yr-3-2006
21/30
8/7/2019 Ist yr-3-2006
22/30
8/7/2019 Ist yr-3-2006
23/30
8/7/2019 Ist yr-3-2006
24/30
8/7/2019 Ist yr-3-2006
25/30
Crystal
8/7/2019 Ist yr-3-2006
26/30
8/7/2019 Ist yr-3-2006
27/30
The d-d transition is the single broad peak with a maximum at20,300 cm-1
1 kJmol-1 = 83.7 cm-1
(o
for [Ti(H2O)6]3+ is 20,300 / 83.7 = 243 kJmol-1
Most convenient way for measuring (o values
Single d electron occupies an energy level 2/5 (obelow the
average energy level
CFSE for this complex = 2/5 x 243 = 97 kJmol-1
8/7/2019 Ist yr-3-2006
28/30
Magnitude of CFS depends on 3 factors
Nature of ligand
Charge on the metal ion Whether the metal is in 1st, 2nd and 3rd row of transition
elements
Magnitude of increases as the charge on the metal ionincreases
M+++ complexes have greater than M++
(o
(o
Oxidation state V Cr Mn Fe Co
(+II) electronic configuration
in cm-1d3
12600
d4
13900
d5
7800
d6
10400
d7
9300
(+III) electronic configuration
in cm-1d2
18900
d3
17830
d4
21000
d5
13700
d6
18600
(o
(o
8/7/2019 Ist yr-3-2006
29/30
Value of CFS increases by about 30% between adjacentmembers down a group of transition elements
Crystal field splitting in one group
values range 7000 30000 cm-1
Nature of Ligand CFS by various ligands
Complex cm-1 kJmol-1
[Co(NH3)6]3+ 24800 296
[Rh(NH3)6]3+ 34000 406
[Ir(NH3)6]
3+
41000 490
Complex cm-1 kJmol-1
[CrCl6]3- 13640 163
[Cr(H2O)6]3+ 17830 213
[Cr(NH3)6]3+ 21680 259
[Cr(CN)6]3-
26280 314
(o
8/7/2019 Ist yr-3-2006
30/30