Tetrahydroxyborate, [H₄BO₄]⁻ or B(OH), is a boron

Boron

Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

 oxoanion

Oxyanion

An oxyanion or oxoanion is a chemical compound with the generic formula AxOyz− . Oxoanions are formed by a large majority of the chemical elements. The formulae of simple oxoanions are determined by the octet rule...

 with a tetrahedral

Tetrahedral molecular geometry

In a tetrahedral molecular geometry a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1 ≈ 109.5° when all four substituents are the same, as in CH4. This molecular geometry is common throughout the first...

 geometry

Molecular geometry

Molecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.- Molecular geometry determination...

. It is isoelectronic with the hypothetical compound orthocarbonic acid

Orthocarbonic acid

Orthocarbonic acid or methanetetraol is the name given to a hypothetical compound with the chemical formula H4CO4 or C4. Its molecular structure consists of a single carbon atom bonded to four hydroxyl groups. It would be therefore a fourfold alcohol...

.

B(OH) is formed by the addition of hydroxide, OH⁻, to boric acid

Boric acid

Boric acid, also called hydrogen borate or boracic acid or orthoboric acid or acidum boricum, is a weak acid of boron often used as an antiseptic, insecticide, flame retardant, as a neutron absorber, and as a precursor of other chemical compounds. It exists in the form of colorless crystals or a...

, B(OH)₃:

B(OH)₃ + OH⁻ B(OH)

Though it is still represented as simple hydrolysis, the formation of tetrahydroxyborate in aqueous solution is responsible for the acidity of boric acid:

B(OH)₃ + H₂O B(OH) + H⁺

pK = 9.25

The tetrahydroxyborate anion is found in Na[B(OH)₄], Na₂[B(OH)₄]Cl and Cu^II[B(OH)₄]Cl.

ball-and-stick model Ball-and-stick model In chemistry, the ball-and-stick model is a molecular model of a chemical substance which is to display both the three-dimensional position of the atoms and the bonds between them...  of the crystal structure of sodium tetrahydroxyborate	space-filling model Space-filling model In chemistry a space-filling model, also known as calotte model, is a type of three-dimensional molecular model where the atoms are represented by spheres whose radii are proportional to the radii of the atoms and whose center-to-center distances are proportional to the distances between the atomic... of the crystal structure of sodium tetrahydroxyborate