Optical Isomerism occurs in chiral complexes that lack a plane of symmetry.

• $[Co(en{)}_3{]}^{3+}$: This octahedral complex contains three bidentate ligands. The three rings wrap around the metal in a way that creates non-superimposable mirror images (called $\Lambda$ and $\Delta$ enantiomers).
• $[Co(N{H}_3{)}_6{]}^{3+}$ has three planes of symmetry (achiral).
• $[PtC{l}_4{]}^{2-}$ and $[Ni(CN{)}_4{]}^{2-}$ are square planar; they have the molecular plane as a plane of symmetry.