JEE Main 2025 — Coordination Compounds Question with Solution

In this octahedral complex with the molecular composition $\mathrm{Co}\cdot 5{\mathrm{NH}}_3\cdot {\mathrm{Cl}}^2\cdot {\mathrm{SO}}_4$, two isomers, A and B, are present.

Isomer A is represented as $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\left({\mathrm{SO}}_4\right)\right]\mathrm{Cl}$. When this isomer is dissolved in solution, it reacts with ${\mathrm{AgNO}}_3$, forming a white precipitate of silver chloride ($\mathrm{AgCl}$).

Isomer B is written as $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]{\mathrm{SO}}_4$. In solution, it reacts with ${\mathrm{BaCl}}_2$, forming a white precipitate of barium sulfate (${\mathrm{BaSO}}_4$).

These two isomers demonstrate ionisation isomerism. This type of isomerism occurs when the exchange of ions inside and outside the coordination sphere of a complex leads to the formation of isomers with different chemical behaviors in solution.