chelate

n. (Chem.) a compound formed by combination of a metal ion in solution with a compound containing heteroatoms (such as oxygen or nitrogen), in which at least two heteroatoms are bound to the metal. The bonds may be covalent or non-covalent. Chelates in some cases have very low dissociation constants, and organic compounds (chelating agents) which form such chelates are therefore used to reduce the concentration of free metal ions in solution. [ PJC ]