Question

Which type of isomerism exists between the complexes [CoBr(NH₃)₅]SO₄ and [CoSO₄(NH₃)₅]Br?

• A. Linkage isomerism
• B. Solvate isomerism
• C. Ionisation isomerism
• D. Coordination isomerism

Hint:

The anion inside the coordination sphere and the counter ion outside have been swapped; such isomers give different ions in solution.

Answer 1

The Correct Option is C

Step 1: Compare what each complex sets free in water. A quick test tells them apart: one solution gives a precipitate with BaCl₂ (free sulphate), the other gives a precipitate with AgNO₃ (free bromide).
Step 2: [CoBr(NH₃)₅]SO₄ keeps Br^- firmly bound to Co and lets SO₄^2- ionise, so it responds to BaCl₂. [CoSO₄(NH₃)₅]Br does the opposite, releasing Br^- and responding to AgNO₃.
Step 3: Because the only change is which anion sits inside the metal sphere and which sits outside as the ionising counter ion, the pair are ionisation isomers.
Result: The answer is ionisation isomerism, alternative (iii).