SiO44

SiO44 is not a standard neutral chemical formula, but in silicate chemistry it is commonly used to refer to the orthosilicate unit SiO4^4-. The orthosilicate ion is formed by deprotonation of orthosilicic acid H4SiO4 and carries a tetrahedral silicon center bonded to four oxide ions.

In the tetrahedron, typical Si–O bond lengths are around 1.6 Å, with O–Si–O angles close to the ideal tetrahedral angle of 109.5 degrees, though distortions occur in minerals. In solid materials, SiO4 tetrahedra link by sharing corners, edges, or faces to generate a wide range of silicate structures. Isolated tetrahedra (nesosilicates) include minerals such as forsterite, which balance charge with metal cations. More complex frameworks include inosilicates (chains), cyclosilicates (rings), and tectosilicates (three-dimensional frameworks like quartz and feldspars).

In aqueous solution, orthosilicic acid H4SiO4 can lose protons to form H3SiO4-, H2SiO4^2-, HSiO4^3-, and ultimately SiO4^4- at high pH. Silicate speciation influences processes such as precipitation, dissolution, and transport in geochemical and environmental contexts.

Preparation of orthosilicate salts, such as Na4SiO4, typically involves reaction of silica with strong bases (or fusion with alkali hydroxides) and subsequent dissolution. These salts serve as precursors to silica materials and find applications in ceramics, detergents, and industrial silicate chemistry. The neutral SiO4 unit is not typically isolated outside such salts or mineral structures.

See also Silicate, Orthosilicate, Silicate minerals.