## Chemistry: Molecular Approach (4th Edition)

Cis-trans isomerism is one type of geometrical isomerism that occurs in the square planar complexes of the type $MA2{{B}_{2}}$ and octahedral complexes of the type $MA4{{B}_{2}}.$
For example: Square planar complex Pt ${{\left( N{{H}_{3}} \right)}_{2}}C{{l}_{2}}$ exhibits cis-trans isomerism. Octahedral complex ion ${{\left( Co{{\left( N{{H}_{3}} \right)}_{4}}C{{l}_{2}} \right)}^{+}}$ exhibits cis-trans isomerism. Cis-trans isomerism does not occur in tetrahedral complexes because all the bond angles around the central metal are $109.5,$ and each comer of a tetrahedron can be considered to be adjacent to all other corners. Similarly, a linear complex cannot exhibit cis-trans isomerism.