Isomerism in Co-ordination complexes

1. Presented by
Dr. Neelam
Department of chemistry

2. Compound having same molecular formula but different physical &
chemical properties
difference properties because of
different structure
difference properties because of
different orientation

3. STRUCTURAL ISOMERISM :
Compound having same mol. formula difference in physical properties because of
different structure.
(A) Ionisation isomerism :
This type of isomerism occurs when the counter ion in a coordination compound
is itself a potential ligand and can displace a ligand which can then become the
counter ion.
For example:
(B) Solvate / hydrate isomerism :
It occurs when water forms a part of the coordination entity or is outside it. This is
similar to ionisation isomerism.
For examples:

4. (C) Linkage isomerism :
In some ligands, like ambidentate ligands, there are two possible coordination
sites. In such cases, linkage isomerism exist.
NO2 group can be bonded to metal ions through (-NO2) or (-ONO),
SCN : (-SCN) or (-NCS).
(D) Coordination isomerism :
Coordination compounds made up of cationic and anionic coordination entities
show this type of isomerism due to the interchange of ligands between the cation
and anion entities.
For examples:

5. (E) Ligand isomerism :
Since many ligands are organic compounds which have possibilities for
isomerism, the resulting complexes can show isomerism from this source.
For example :
ligands 1,2-diaminopropane(propylenediamine or pn) and
1,3-diaminopropane(trimethylenediamine or tn)
(F) Polymerisation isomerism :
Considered to be a special case of coordination isomerism, in this the various
isomers differ in formula weight from one another
For example :
These all have the empirical formula [Pt(NH3)2Cl2] 1: 2 :2
[Pt(NH3)2Cl2] Pt:NH3:Cl 1: 2 :2
[Pt(NH3)4] [PtCl4] Pt:NH3:Cl 2: 4 :4

6. Stereoisomers : Compound having same mol. formula difference in physical
properties because of different orientation.
Geometrical Isomerism
Cis isomer
 When ligands are present on
same side
 When ligands are present at 90
to each other
trans isomer
 When ligands are present on
opposite side
 When ligands are present at 180
to each other

7. Coordination Number Four :
Tetrahedral Complex :
The tetrahedral compounds can not show geometrical isomerism as we all know
that all four positions are equivalent in tetrahedral geometry.
[MA4], [MA3B] not show G. I.
Square Planar Complex :
In a square planar complex of formula [MA2B2] [A and B are unidentate], the two
ligands .A. may be arranged adjacent to each other in a cis isomer, or opposite to
each other in a trans isomer as depicted.
[MA2B2], [M(AB)2], [MA2BC], [MABCD] show G. I.

8. Coordination Number 6 :
Geometrical isomerism is also possible in octahedral complexes.
[MA6], [MA5B], [M(AA)3] not show G. I.
[MA2B2C2], [MA2B2CD], [MA2BCE], [MABCDEF], [M(AB)3], [MA4B2], [MA3B3]
show G. I.
Optical Isomerism :
 Plane of symmetry
 Center of symmetry
 Axis of symmetry
Should not be present

9. • Tetrahedral complexes with formula [MABCD] show optical isomers and
octahedral complexes (cis form) exhibit optical isomerism.
• Optical isomerism is common in octahedral complexes involving didentate
ligands. Cis-isomer of [PtCl2(en)2]2+ show optical isomerism as shown below
because of the absence of plane of symmetry as well as centre of symmetry.

10. 10