Geometrical isomerism in complexes with didentate ligands occurs when the ligands can arrange in different orientations around the central metal atom. One example of a didentate ligand is ethylenediamine (en), which can coordinate through both nitrogen atoms. In a complex like [Co(en)₂Cl₂], geometric isomerism is observed as cis and trans isomers, where the two en ligands can be arranged either adjacent (cis) or opposite (trans) to each other. The ability of didentate ligands to adopt different spatial arrangements contributes to the occurrence of geometrical isomerism in coordination complexes.