$\left[Co{\left(N{H}_3\right)}_{5}S{O}_4\right]Br$ and $\left[Co{\left(N{H}_3\right)}_{5}Br\right] S{O}_4$ , are ionisation isomers. These compounds give different ions in the solution although they have same composition. It 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.