Some ligands have more than one binding site. An example is the oxalate ion: C₂O₄^-2



which has two binding sites: one on each oxygen. Each of these binding sites can bind to the central metal atom. These types of ligands are known as chelating agents (after the Latin chela: claw)

Ligands with two binding sites are known as bidentate: there are also ligands that bind to three (tridentate) or four (tetradentate) sites

The coordination number of the central metal ion stays the same: if six things are bound to it, the coordination number is six, even if one ligand is bound in more than one place. For example, the ion Cu(C₂O₄)₂^-2 has two oxalate ions bound to it: each has two binding sites so the coordination number of Cu⁺² is four.

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