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.
(b) Didentate ligands:
Ligands that have two donor sites are called didentate ligands.
For e.g.:
(a) Ethane – 1, 2 - diamine.
(b) enolic acid
(c) Ambidentate ligand:
Ligands that can attach themselves to the central metal atom through two different atoms are called ambidentate ligands.
For Example:
(a)
(b)
