Chelation (/kiːˈleɪʃən/) is a type of bonding and sequestration of metal atoms. It involves two or more separate dative covalent bonds between a ligand and a single metal atom, thereby forming a ring structure. The ligand is called a chelant, chelator, chelating agent, or sequestering agent. It is usually an organic compound, but this is not a requirement.
The word chelation is derived from Greek χηλή, chēlē, meaning "claw", because the ligand molecule or molecules hold the metal atom like the claws of a crab. The term chelate (/ˈkiːleɪt/) was first applied in 1920 by Sir Gilbert T. Morgan and H. D. K. Drew, who stated: "The adjective chelate, derived from the great claw or chele (Greek) of the crab or other crustaceans, is suggested for the caliperlike groups which function as two associating units and fasten to the central atom so as to produce heterocyclic rings."
