JEE Class main Answered

(1) Ionisation isomerism:

Compounds which gives different ions in solution although they have the same composition are called ionisation isomerism.

This form of isomerism arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which can then become the counter ion.

An example is provided by the ionisation isomers [Co(NH₃)₅SO₄]Br and [Co(NH₃)₅Br]SO₄.

Another example is, [Pt(NH₃)₄(OH)₂]SO₄ and [Pt(NH₃)₄SO₄](OH)₂.

(2) Hydrate Isomerism (Solvate Isomerism):

In a complex compound, water molecules behave in two ways:

(i) Water molecules which behave as ligands are coordinated with the metal atom and are part of the complex ion, e.g. [M (H₂O)x].

(ii) Water molecules act as the water of crystallization and these appear outside the coordination sphere,

e.g. [MLx].nH₂O.Isomerism which occurs due to a dissimilar number of water molecules as ligands (inside the sphere) and as the water of crystallization (outside the sphere), is known as hydrate isomerism.

This isomerism is analogous to ionization isomerism, in which water molecules inside and outside the sphere are exchanged.

For example,Cr (H₂O)₆Cl₃ has three possible structures:

(i) [Cr (H₂O)₆] Cl₃ (violet)

(ii) [Cr (H₂O)₅Cl] Cl₂H₂O (green)

(iii) [Cr (H₂O)₄Cl₂] Cl₂H₂O (dark green)