Incoordination chemistry, denticity (from Latin dentis 'tooth') refers to the number of donor groups in a given ligand that bind to the central metal atom in a coordination complex.[1][2] In many cases, only one atom in the ligand binds to the metal, so the denticity equals one, and the ligand is said to be monodentate (sometimes called unidentate). Ligands with more than one bonded atom are called polydentateormultidentate. The denticity of a ligand is described with the Greek letter κ ('kappa').[3] For example, κ6-EDTA describes an EDTA ligand that coordinates through 6 non-contiguous atoms.
Denticity is different from hapticity because hapticity refers exclusively to ligands where the coordinating atoms are contiguous. In these cases the η ('eta') notation is used.[4] Bridging ligands use the μ ('mu') notation.[5][6]
Polydentate ligands are chelating agents[7] and classified by their denticity. Some atoms cannot form the maximum possible number of bonds a ligand could make. In that case one or more binding sites of the ligand are unused. Such sites can be used to form a bond with another chemical species.
In general, the stability of a metal complex correlates with the denticity of the ligands, which can be attributed to the chelate effect. Polydentate ligands such as hexa- or octadentate ligands tend to bind metal ions more strongly than ligands of lower denticity, primarily due to entropic factors. Stability constants are a quantitative measure to assess the thermodynamic stability of coordination complexes.