A ligand is an ion or molecule, which donates a pair of electrons to the central metal atom or ion to form a coordination complex. The word ligand is from Latin, which means “tie or bind”. Ligands can be anions, cations, and neutral molecules. Ligands act as Lewis bases (donate electron pairs) and central metal atoms viewed as Lewis acid (electron pair acceptor). The nature of bonding between metal to ligand varies from covalent bond to ionic bond.
Occasionally ligands can be cations (NO+, N2H5+) and electron-pair acceptors. Examples for anionic ligands are F–, Cl–, Br–, I–, S2–, CN–, NCS–, OH–, NH2– and neutral ligands are NH3, H2O, NO, CO.
A ligand is an ion or molecule, which binds to the central metal atom to form a coordination entity or complex compounds. Classification of ligands is on the basis of the number of binding sites with the central metal atom, charge and size.
