Question

Define and explain ionisation isomerism.

Answer 1

Ionisation isomerism : The phenomenon of isomerism in the metal complexes in which there is an exchange of ions between coordination (or inner) sphere and outer sphere is known as ionisation isomerism.

Explanation :

• Ionisation isomers have same molecular formula but different arrangement of ions in the inner sphere and outer sphere in the complex,
• Hence on ionisation, these ionisation isomers produce different ions in the solution. This ionisation isomerism is also called ion-ion exchange isomerism.

Examples :

(A) [CO(NH₃)₄CI₂]Br and 

(B) [Co(NH₃)₄ CIBr] Cl 

Ionisation :

(A) [CO(NH₃)₄CI₂] Br ⇌ [CO(NH₃)₄CI₂]⁺ Br^-

(B) [Co(NH₃)₄CIBr]Cl ⇌ [CO(NH₃)₄ClBr]⁺ + CP

In the isomers (A) and (B),

There is an exchange of ions namely Br^- and CI^-.