In coordination chemistry, a ligand (/lɪɡənd/) is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex.The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs.he arrangement of the d-orbitals on the central atom (as determined by the 'strength' of the ligand), has a strong effect on virtually all the properties of the resulting complexes. E.g., the energy differences in the d-orbitals has a strong effect in the optical absorption spectra of metal complexes.