SiO4tetraeedride

SiO4tetraeedride is a term used in silicate chemistry to denote the tetrahedral oxoanion [SiO4]4−, commonly referred to as the orthosilicate unit. The name emphasizes the four-oxygen coordination around a central silicon atom in a tetrahedral arrangement.

Structure and properties: In its isolated form, the silicon atom is in a +4 oxidation state and bonded to four oxide ligands, producing a tetrahedral geometry with Td symmetry. The formal charge of the unit is −4. In solid compounds, [SiO4]4− exists as a counterion to various cations, giving salts such as Na4SiO4 or K4SiO4. In solution, high deprotonation of silicic acid leads to a family of silicate species whose overall charge depends on pH, with [SiO4]4− representing the fully deprotonated limit.

Relation to silicate minerals: The orthosilicate tetrahedron is a fundamental building block in silicate chemistry. In minerals, [SiO4]4− units often polymerize by corner sharing to form a wide spectrum of structures, including single tetrahedra (nesosilicates), pairs (sorosilicates), chains (inosilicates), sheets (phyllosilicates), and three-dimensional frameworks (tectosilicates). The specific connectivity governs the mineral’s physical properties and its classification.

Occurrence and synthesis: The discrete [SiO4]4− unit occurs predominantly in synthetic salts and in highly basic environments. In natural systems, orthosilicate motifs appear as part of broader silicate structures rather than as isolated anions. Sodium orthosilicate and related salts illustrate practical preparations, typically involving reaction of silica or silicic acid derivatives with strong bases.

See also: Silicate, Orthosilicate, Silicate minerals, Nesosilicate, Tectosilicate.