Ionisation isomerism: Different ions inside and outside coordination sphere. [Co(NH3)5Br]SO4 (gives BaSO4 precipitate) vs [Co(NH3)5SO4]Br (gives AgBr precipitate). Linkage isomerism: Ambidentate ligands bonding through different atoms. NO2- binds through N (nitro, more stable) or O (nitrito, less stable). Coordination isomerism: Ligand exchange between two coordination centres in a salt. [Cu(NH3)4][PtCl4] vs [Pt(NH3)4][CuCl4]. Hydrate/Solvate isomerism: H2O as ligand vs in crystal lattice. Three isomers of CrCl3.6H2O are distinguishable by colour and AgNO3 test.