1. Geometrical isomerism exists in heteroleptic complexes due to different possible three diamensional spatial arrangements of the ligands around the central metal atom. This type of isomerism exist in square planar tetrahedral complexes.
2. In square planar complexes of the form [MA2B2]n± and [MA2BC]N+ where A, B and C are monodentate ligands and M is the central metal ion / atom.
3. Similar groups (A or B) present either on same side or on the opposite side of the central metal atom (M) give rise to two different geometrial isomers and they are called cis and trans isomers respectively.
4. The square planar complex of the type [M (XY)2]n± where XY is a bidentate ligand with two different coordinating atom also shows cis-trans isomerism.
5. Square planar complex of the form [MABCD]n± also shows cis – trans isomerism. In this case, by considering any one of the ligands [A,B,C,D] as a reference, the rest of the ligands can be arranged in three different ways leading to three geometrical isomers.
