A ligand may contain one or more unshared pairs of electrons which are called the donor sites of ligands. Now, depending on the number of these donor sites, ligands can be classified as follows:
(a) Unidentate ligands: Ligands with only one donor sites are called unidentate
ligands. For e.g., , NH3 ,Cl− etc.
(b) Didentate ligands: Ligands that have two donor sites are called didentate ligands. For e.g.,
