Q. What is Hydrate Isomerism?

In a compound, water molecules may be present in either coordinated form or as water of crystallisation In the former case water  molecules are directly attached to the metal ion, or in the latter case they may occupy lattice sites in a crystal without getting attached to the metal ion. This type of isomerism is known as hydrate isomerism and the physical and chemical properties of hydrate isomers are quite different. As an example, we consider at least three well established isomers of a complex CrCl₃.6H₂O these are:

(i) [Cr (H₂0)4Cl₂] Cl₂H₂0, a dark green compound where four molecules of water are coordinated to Cr (III) ion and the other two molecules occupy the lattice position..

(ii) [Cr (H20)₅CI] Cl2.H20 is blue green in colour and has five coordinated and one lattice molecules of water.

iii) [Cr(H₂O) ₆[ Cl₃ is violent in colour and all the molecules of  water are coordinated.

A few other examples are:

[Co (NH₃)₄(H₂0)CI]Br₂, [Co(NH₃)₄Br₂]CI-H₂0  and

[Co(NH₃)₃(H₂0)₂CI]Br:. [Co(NH₃)₃Br₂ (H₂O)IBr.H₂0