Explain hydrate isomerism with the help of an example.

Explanation

Solvate or hydrate isomerism : This type of isomerism arises due to the replacement of solvent (or water) molecules from the co-ordination sphere by the ions present outside. Compounds which have the same composition but differ in the number of solvent molecules present as ligands (i.e., in the co-ordination sphere) and as molecules of solvate (present outside the co-ordination sphere) are called solvate isomers e.g., there are three different hydrate isomers for the compound having formula `CrCl_3.6H_2O`. These are :
(a) `[Cr(H_2O)_6Cl_3]` (violet)
(b) `[Cr(H_2O)_5Cl]Cl_2.H_2O` (blue green)
(c) `[Cr(H_2O)_4Cl_2]Cl.2H_2O` (green)