Question

Which type of isomerism is exhibited by the following compounds? (a) [Co(NH₃)₄ Br₂]Cl and [Co(NH₃)₄ ClBr]Br
(b) [Co(NH₃)₅ NO₂]²⁺ and [Co(NH₃)₅ ONO]²⁺
(c) [Pt(NH₃)₄][PdCl₄] and [Pd(NH₃)₄][PtCl₄]

Hint:

To quickly identify these: - Ionisation: Look for different ions outside the brackets [ ]. - Linkage: Look for ambidentate ligands (NO₂, SCN, CN). - Coordination: Look for two sets of brackets [ ][ ] with swapped metals/ligands.

Answer 1

Concept: Isomerism in coordination compounds occurs when two or more compounds have the same molecular formula but different structural arrangements of atoms. These three cases represent different types of structural isomerism.
(a) Ionisation Isomerism
In these two compounds, the counter ion in the outer sphere and the ligand in the inner coordination sphere are interchanged. • [Co(NH₃)₄ Br₂]Cl gives a precipitate with AgNO₃ (due to Cl^-). • [Co(NH₃)₄ ClBr]Br gives a precipitate with AgNO₃ (due to Br^-). Type: Ionisation Isomerism
(b) Linkage Isomerism
This occurs when an ambidentate ligand (like NO₂^-) can bind to the central metal atom through two different atoms. • In [Co(NH₃)₅ NO₂]²⁺, Cobalt is linked through Nitrogen (Nitro ligand). • In [Co(NH₃)₅ ONO]²⁺, Cobalt is linked through Oxygen (Nitrito ligand). Type: Linkage Isomerism
(c) Coordination Isomerism
This type of isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex. • The ligands (NH₃ and Cl^-) are swapped between the Platinum (Pt) and Palladium (Pd) centers. Type: Coordination Isomerism