Polydentaatit

Polydentaatit (Finnish for polydentate ligands) are ligands in coordination chemistry that can bind a central metal ion through more than one donor atom. The number of donor atoms that participate in binding is called the denticity. Ligands with denticity greater than two are described as polydentate; common subcategories include bidentate (two donors), tridentate (three donors), tetradentate, hexadentate, and so on. Polydentate binding often occurs when a ligand has several donor atoms arranged to form ring structures with the metal, a phenomenon that stabilizes metal complexes.

Examples include ethylenediamine (bidentate via two amine nitrogens), terpyridine (tridentate via three nitrogens), and EDTA in its hexadentate form, which can wrap around a metal to form six coordinate bonds. Porphyrins are tetradentate in typical metal complexes; crown ethers and related polyethers can act as multidentate ligands through ether oxygens. The chelate effect refers to the generally higher stability of complexes formed with polydentate ligands compared with equivalent monodentate ligands, due to favorable entropy and enthalpy from ring closure.

Applications span catalysis, metal separation and purification, environmental remediation, and medicine (for example, chelation therapy to remove heavy metals). In biochemistry, polydentate ligands participate in the active sites of many metalloproteins and cofactors, contributing to specificity and reactivity. This article provides a concise overview of polydentaatit as multidentate ligands and their role in coordinating chemistry. See also denticity, chelate, and coordination compound.