Tetrahydroxo

Tetrahydroxo is a descriptor used in inorganic chemistry to denote the presence of four hydroxo ligands (OH−) coordinated to a central atom in a complex. It appears in systematic naming to indicate that four hydroxo groups accompany the central element, often forming an anionic species or a highly hydrolyzed complex.

In naming conventions, tetrahydroxo is attached to the central atom’s name to yield a specific compound name. A common example is tetrahydroxoaluminate(III), referring to the anion [Al(OH)4]−, in which aluminum(III) is coordinated by four hydroxido ligands. The four hydroxo ligands in such a complex typically arrange around the central atom in a four-coordinate geometry, such as tetrahedral for aluminum in [Al(OH)4]−.

Hydroxo ligands arise from deprotonated water and are prevalent in aqueous metal chemistry, formed during hydrolysis of metal salts or oxides. The presence of four hydroxo ligands affects the charge, basicity, and solubility of the species and can influence stability and reactivity of the complex. Depending on the metal and ligands, tetrahydroxo complexes may adopt different geometries or undergo condensation reactions to form oxo-bridged structures.

The term is mainly used within systematic nomenclature rather than as a standalone chemical species. It is related to other hydroxo counts such as dihydroxo-, trihydroxo-, and polyhydroxo descriptors, which likewise specify the number of hydroxo ligands in a complex.

See also: hydroxo ligand; aluminate; coordination chemistry; hydrolysis.