Chelation

Chelation is the binding of a metal ion by a molecule through multiple coordinate bonds. The resulting ring-shaped assembly is called a chelate complex.

Chelate effect: The enhanced stability of complexes formed by multidentate ligands compared with similar complexes formed by monodentate ligands. It explains why several donor atoms in one ligand often bind more strongly than separate molecules do.
Coordination bond: A covalent bond in which both shared electrons are supplied by one bonding partner. Each donor atom in a chelator forms this kind of bond to the metal.
EDTA: A synthetic aminopolycarboxylate ligand that binds many metal ions through six donor atoms. EDTA is a widely used chelator in analysis, water treatment, and medicine.
Monodentate ligand: A ligand that binds a central atom or ion through a single donor atom. Unlike chelators, it forms only one coordinate bond to a given metal center.
Coordination chemistry: The study of compounds in which central atoms or ions bond to surrounding ligands. Chelation is a major pattern of ligand binding within this broader chemistry.
Coordination number: The number of donor atoms directly bonded to a central atom or ion in a coordination complex. Chelating ligands occupy multiple coordination sites on a metal center.
Dimercaprol: A sulfur-containing drug used as a chelating agent in treatment of poisoning by certain metals. Its metal-binding groups support treatment of selected heavy-metal poisonings.
Bidentate ligand: A ligand that binds a central atom or ion through two donor atoms. It is the simplest common case of chelation by one molecule.
Ligand: An atom, ion, or molecule that donates electron density to a central atom or ion in a coordination complex. Chelating molecules are ligands with multiple atoms able to coordinate the same metal.
Lewis acid: A chemical species that accepts an electron pair to form a bond. Metal ions accept electron pairs from the donor atoms of chelating molecules.

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