Complex ions exhibit geometric isomerism and optical isomerism. Cis-Trans isomerism occurs if there are two different types of ligand e.g. [Pt(NH3)2Cl2] is a square planar molecule that has both cis- and trans- forms. Geometric isomerism also occurs in octahedral complexes if there are two types of ligands or 2 bidentate ligands with 2 monodentate ligands.Optical isomerism occurs in octahedral complexes with three bidentate ligands, or two bidentate ligands and two monodentate ligands in cis positions, as two enantiomers that are non-superimposable mirror images of each other will be formed.