Ionisation isomerism occurs when the counter ion in a complex salt becomes a ligand. In [Co(NH₃)₅(SO₄)]Br, SO₄ displaces a ligand, while in [Co(NH₃)₅Br]SO₄, Br⁻ becomes the ligand. This is similar to ‘hydrate isomerism’ when water is involved as a solvent.
Describe the phenomenon of ionisation isomerism with an example involving [Co(NH₃)₅(SO₄)]Br and [Co(NH₃)₅Br]SO₄.
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Ionization isomerism occurs when there is a difference in the positions of ions between two coordination isomers. In the complex [Co(NH₃)₅(SO₄)]Br, the sulfate ion (SO₄²⁻) is coordinated, while in [Co(NH₃)₅Br]SO₄, the bromide ion (Br⁻) is coordinated. The exchange of anionic ligands between the coordination sphere and the counterion leads to the formation of isomeric complexes with distinct properties. This phenomenon demonstrates that the arrangement of ligands and ions within a coordination compound can vary, affecting its chemical and physical characteristics. The given example highlights ionisation isomerism in cobalt coordination complexes.