Question

List various types of isomerism possible for coordination compounds, giving an example of each

Answer 1

(a) Geometric isomerism:
This type of isomerism is common in heteroleptic complexes. It arises due to the different possible geometric arrangements of the ligands. For example:

(b) Optical isomerism:
This type of isomerism arises in chiral molecules. Isomers are mirror images of each other and are Non superimposable.

(c) Linkage isomerism:
This type of isomerism is found in complexes that contain ambidentate ligands. For example: $[Co(NH_3)_5 (NO_2)]Cl_2$ and $[Co(NH_3)_5 (ONO)Cl_2$ Yellow form Red form
(d) Coordination isomerism:
This type of isomerism arises when the ligands are interchanged between cationic and anionic entities of differnet metal ions present in the complex. $[Co(NH_3)_6] [Cr(CN)_6]$ and $[Cr(NH_3)_6] [Co(CN)_6]$
(e) Ionization isomerism:
This type of isomerism arises when a counter ion replaces a ligand within the coordination sphere. Thus, complexes that have the same composition, but furnish different ions when dissolved in water are called ionization isomers.
For e.g.,$Co(NH_3)_5SO_4)Br$ and $Co(NH_3)_5Br]SO_4.$
(f) Solvate isomerism:
Solvate isomers differ by whether or not the solvent molecule is directly bonded to the metal ion or merely present as a free solvent molecule in the crystal lattice. $[Cr[H_2O)_6]Cl_3 [Cr(H_2O)_5Cl]Cl_2┹”¦H_2O [Cr(H_2O)_5Cl_2]Cl┹”¦2H_2O$ Violet Blue-green Dark green