Tetrahydroxyborate

Tetrahydroxyborate is an inorganic anion with the formula [BH4O4]⁻ or [B(OH)4]⁻. It is colorless and found in the mineral hexahydroborite, Ca(B(OH)4)2 · 2 H2O. This anion acts as a weak base and can be considered the conjugate base of boric acid. Its structure is symmetric and tetrahedral, similar to orthocarbonic acid.

Tetrahydroxyborate exhibits both Brønsted-Lowry and Arrhenius basicity. It reacts with cis-vicinal diols, such as mannitol or glucose, forming stable anion esters. These reactions can be used to titrate borate content using a strong base like NaOH.

In chemical reactions, tetrahydroxyborate converts to boric acid when treated with strong acids. It oxidizes to perborate and decomposes upon heating into metaborates or boric acid. Production involves treating boric acid with alkali such as sodium hydroxide.

Tetrahydroxyborate is used as a cross-linker in polymers and occurs naturally in salts like Na[B(OH)4], Na2[B(OH)4]Cl, and CuII[B(OH)4]Cl.