Tricarboxylates

Tricarboxylates are chemical species that contain three carboxylate groups (−COO−) or three carboxyl functional sites within a single molecule. In practice, the term is commonly used for deprotonated triprotic carboxylic acids and for ligands that present three carboxylate binding sites. These compounds often act as multidentate ligands in coordination chemistry, capable of linking multiple metal centers.

Common examples include citrate, the tricarboxylate form of citric acid, and benzene-1,3,5-tricarboxylate (trimesate), derived from trimesic acid. Citric acid has three carboxyl groups and one hydroxyl group; when deprotonated to citrate, it forms a trianionic species with three carboxylate sites that can coordinate metals and complex with cations such as calcium or magnesium. Trimesate ligands feature three carboxylate groups arranged on an aryl core and are widely used to construct metal–organic frameworks (MOFs) and other coordination polymers due to their ability to bridge several metal centers.

Occurrence and uses vary by example. Citric acid and its citrate salts occur naturally in citrus fruits and are used industrially as buffering agents, sequestrants, and food additives. Trimesate and related tricarboxylate ligands are extensively employed in materials chemistry to build porous frameworks, catalysis platforms, and supramolecular assemblies.

Properties of tricarboxylates depend on structure and environment. They are typically triprotic or possess multiple deprotonation steps, with pKa values reflecting the three acidity stages. In coordination complexes, the carboxylate groups adopt various binding modes, including monodentate, bidentate, and bridging, enabling diverse geometries and network architectures.