Ionization isomerism is exhibited by the complex [Co(NH3)5Cl]SO4. Compounds made of same element and having same composition but give different ions in solution are called ionization isomers. These isomers are formed by the interchange of the position of ligands inside and outside the coordination sphere. Such isomers can be detected by conductance measurements or by chemical tests.
Note:
In aqueous solution, [Co(NH3)5Cl]SO4 gives sulphate ions and [Co(NH3)5SO4Cl] gives chloride ions. Thus, [Co(NH3)5Cl]SO4 and [Co(NH3)5SO4]Cl represents ionization isomers.