Define ionisation isomerism and write one ionisation isomer of :`[CoSO_4 (NH_3)_5]Br`.

Explanation

Ionization isomerism : Complex compounds which have the same empirical formula, but give different ions in solution on ionization, are called ionization isomers. This type of isomerism is known as ionisation isomerism.
Examples. The following two isomers
`underset("sulphate (Red complex)")underset("bromopentaammine cobalt(III)")([Co(NH_3)_5Br]SO_4)` and `underset("bromide (Violet complex)")underset("sulphatopenaamine cobalt(III)")([Co(NH_3)_5SO_4]Br)`
Complex `[Co(NH_3)_5Br]SO_4` gives the test for sulphate ions (i.e., a white precipitate of `BaSO_4` with `BaCl_2` solution), while the complex `[Co(NH_3)_5SO_4]Br` gives test for bromide ions (ie, a yellow precipitate of AgBr with `AgNO_3` solution) and not for sulphate ions, when dissolved in water. The modes of ionization of these two isomers are as follows.
`[Co(NH_3)_5Br]SO_4 harr [Co(NH_3)_5Br]^(2+) + SO_4^(2-)`
`[Co(NH_3)_5SO_4]Br harr [Co(NH_3) SO_4]^(+)+Br^(-)`