EDTA is classified as what type of ligand?

EDTA (ethylenediaminetetraacetic acid) is classified as a hexadentate ligand because it has six donor atoms that can coordinate to a metal center. In its typical form, EDTA has four carboxylate groups (–COO⁻) and two amine groups (–NH₂), which can participate in bonding with a metal ion. Each of these atoms can form a coordinate bond with a metal ion, allowing EDTA to effectively 'wrap around' the metal and create a stable chelate complex.

This multi-point attachment is what characterizes EDTA as hexadentate, distinguishing it from other types of ligands that bind through fewer donor atoms. For instance, a bidentate ligand would only use two donor atoms, a tetradentate would use four, and a monodentate would bind through just one donor atom. The ability of EDTA to form these stable complexes through multiple interactions is fundamental in applications such as metal ion sequestration, and it is widely used in analytical chemistry, biochemistry, and environmental science.