A ligand is an ion or molecule that binds to a central metal atom or ion to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligands electrons to the metal. Ligands can be anions, cations, and neutral molecules, and they act as Lewis bases (donate electron pairs) . The central metal atoms are viewed as Lewis acids (electron pair acceptors) . The nature of bonding from metal to ligand varies from covalent bond to ionic bond. The term "ligand" comes from the Latin word "ligare," which means "to bind"/Coordination_Chemistry/Structure_and_Nomenclature_of_Coordination_Compounds/Ligands).
Ligands can be classified based on the number of binding sites with the central metal atom, charge, and the number of donor atoms. Examples of ligands include F–, Cl–, Br–, I–, S2–, CN–, NCS–, OH–, NH2–, NH3, H2O, NO, CO, NO+, and N2H5+ . A monodentate ligand has only one donor atom used to bond to the central metal atom or ion/Coordination_Chemistry/Structure_and_Nomenclature_of_Coordination_Compounds/Ligands). Bidentate ligands have two donor atoms, tridentate ligands have three donor atoms, and so on/Coordination_Chemistry/Structure_and_Nomenclature_of_Coordination_Compounds/Ligands).
In biochemistry, a ligand is defined as any molecule or atom that irreversibly binds to a receiving protein molecule, otherwise known as a receptor.
