Write one example of each of ionisation, linkage and hydrated isomerism.

Answer:

(1) Ionisation isomerism (exchange of an ion between the coordination sphere and the ionisation sphere):

[Co(NH₃)₅Br]SO₄ (violet; gives white ppt with BaCl₂) and [Co(NH₃)₅SO₄]Br (red; gives pale yellow ppt with AgNO₃)

(2) Linkage isomerism (an ambidentate ligand bonds through different donor atoms):

[Co(NH₃)₅(NO₂)]Cl₂ (nitro, bonded through N, yellow) and [Co(NH₃)₅(ONO)]Cl₂ (nitrito, bonded through O, red)

(3) Hydrate (solvate) isomerism (water present as ligand or as water of hydration):

[Cr(H₂O)₆]Cl₃ (violet), [Cr(H₂O)₅Cl]Cl₂·H₂O (blue-green) and [Cr(H₂O)₄Cl₂]Cl·2H₂O (dark green)