Isomerism in Co-ordination compound
ISOMERISM
The phenomena by which compounds having same molecular formula but having different physical and chemical properties it is due to different arrangement of atoms and molecules.
It is of two types :-
(A) Structural Isomerism
(B) Sterio Isomerism
(A) Structural Isomerism :- In such isomerism different arrangement of ligand in inside and outside the co-ordination sphere. It is of following types : –
(a) Ionisation isomerism
(b) Hydrated isomerism I
((c) Linkage Isomerism
(d) Co-ordination Isomerism
(a) Ionisation isomerism :- In such isomerism compounds having same molecular formula but having different ionisable group.
Eg – [CO(NH3)5Cl]SO4 → [CO(NH3)5Cl]2++S042-
[CO(NH3)5SO4Cl → [CO(NH3)5SO4]+ + Cl–
(b) Hydrated Isomerism :- Those isomerism in which compounds having different number of water molecules inside and outside the co-ordination sphere. Example
| [CO(H2O)6Cl3 ](Violet) | |||
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(C.) Linkage isomerism :-
In such isomerism same ligand has different atoms to donate lone pair electron to the central metal is called linkage Isomer. Generally such isomerism shown by ambidenate ligand.
( i.) [Co(NH3)5NO₂]Cl2 [CO(NH3)5.ONO]Cl2
(ii.) [Cr NH3)5CN].Cl2 [Cr(NH3)5NC]Cl2
(d.) Co-ordination Isomerism :- Such isomerism arises due to exchange of ligand in cationic and anionic sphere. It is possible in those co-ordination compound in which both cation and anion are complex.
[Cu(NH3)4] [PtCl4]
[CiCl4] [P(NH3)4]
(B) Sterio Isomerism :-
In such isomerism central metal and ligand are same. These differ only in the arrangement of ligand in three dimensional space or in spacial arrangement around central metal.
It is of two types :-
(a) Geometrical Isomerism.
(b) Optical Isomerism.
(a.) Geometrical Isomerism :-
Such isomerism shown by those co-ordination compound which has four and six ligand and their shape is square planar and octahedral respectively.In such isomerism compounds are differ by the arrangement of ligand. Similar ligands are present on same side Cis-isomer and similar ligand are present on opposite side is called Trans-isomer.
Condition for Geometrical Isomerism in Square planar.
Case-I. Ma2b2
Case-II. Ma2bc
Case-III. Mabcd
Condition for Geometrical Isomerism in Octahedral complex
Case-I Ma4b2
Eg- CO(NH3)4Cl₂]
(b.) Optical isomerism :-
The phenomena by which compound rotates the plane polarised light either towards right or left is called optically active isomer and phenomena is called Optical isomerism.
Those compound shows optical isomerism which has no plane of symmetry or which is asymmetrical.
Such compound rotates the plane polarised light due to irregular arrangement of atom. The direction rotation of light either in right direction or in left direction.In these way two optically active isomer i.e called dextro and laevo. Both are Enantiomers and they have different physical properties.
Condition for Optical Isomerism :-
Those co-ordination compound shows optical isomerism which has six ligand and has octahedral shape.
.Case – I. [Ma2b2C₂] → [CO(NH3)4Cl2]
Case – II. [M(AA)3] → [CO(en)3]