Nickel (II) and Cobalt (II) transition metals formed bidentate and tetradentate ligands respectively. A Ni (II) ion forms a bidentate complex with a Schiff base ligand by coordinating to the lone pair electrons on the nitrogen atom of the azomethine group (imine bond) and the oxygen atom of a phenolic group within the ligand, creating a chelate ring where the metal ion is bound to two donor atoms on the same ligand molecule, thus exhibiting a bidentate coordination mode. This interaction is typically facilitated by the deprotonation of the phenolic oxygen (Figure ), allowing for a stronger electrostatic attraction to the metal center, often resulting in a square planar geometry for the Ni (II) complex.