tetrahydroxyborate

Tetrahydroxyborate, also called tetrahydroxyborate(1−) or the borate ion, is the inorganic anion [B(OH)4]−. It is the conjugate base of boric acid and is the predominant borate species in aqueous solutions under modestly alkaline conditions. The boron atom is four-coordinate, with four hydroxyl groups arranged around a central boron in a roughly tetrahedral geometry.

In water boric acid acts as a Lewis acid, and the common aqueous equilibrium can be described as B(OH)3 + 2 H2O ⇌ B(OH)4− + H3O+. Thus, tetrahydroxyborate forms when boron is present with hydroxide. The relative proportions of B(OH)3 and B(OH)4− depend on pH, with B(OH)4− predominating at higher pH and boric acid prevailing in acidic solutions.

Occurrence and applications: The [B(OH)4]− ion arises in solutions derived from boron-containing compounds such as borax (sodium tetraborate) and other borates. It is a key component of borate buffers, providing stability in the pH range around 9–10. In addition to buffering roles, borate systems are used in various chemical and biological contexts, and tetrahydroxyborate can participate in coordination and complexation reactions with metal ions. In solid-state chemistry, borates and related species form minerals and glass networks that incorporate tetrahydroxyborate units.

Safety and notes: Tetrahydroxyborate is generally of low toxicity under typical laboratory use, but should be handled with standard chemical hygiene practices as with other boron-containing compounds.