ligand

In chemistry, a group that bonds symmetrically to a central atom or ion of a metal; the result is called a coordination complex. An example of a neutral ligand is ammonia; the nitrosyl ion NO+ is a charged ligand. An example of a coordination complex is hexaminocobalt chloride, [Co(NH3)6]Cl3, in which the central cobalt ion (Co3+) is surrounded by covalent bonds with six ammonia molecules and ionic bonds with three chloride ions.

Ligands are used in medicine as an antidote to heavy metal poisoning, removing the metal ions by attaching themselves to form a harmless compound.