Optical isomerism is not shown by square planar complexes. Octahedral complexes of general formulae, [Ma2b2c2]n±,[Mabcdef], [M(AA)3]n±,[M(AA)2a2]n± (where AA= symmetrical bidentate ligand), [M(AA)2ab]n± and [M(AB)3]n± (where AB= unsymmetrical ligands) show optical isomerism.
does not show optical isomerism (superimposable mirror image). But cis-form shows optical isomerism.