Octaborate

Octaborate is a term used in inorganic chemistry to describe compounds that contain eight boron atoms organized in a boron-oxygen cluster. In this class, the eight boron atoms are connected through shared oxygen atoms to form polyborate units that can exist as discrete anions or as neutral solid salts when coordinated to metal cations. A widely known example is disodium octaborate tetrahydrate, Na2B8O13·4H2O, which has practical use and is a benchmark compound for this family.

Structure and bonding: Octaborate clusters are built from boron-oxygen polyhedra, typically involving BO3 triangles and BO4 tetrahedra linked by oxygen bridges. The exact connectivity varies among compounds, yielding a range of geometries from compact clusters to extended three-dimensional networks. Many octaborates incorporate water of hydration in solid forms.

Synthesis and occurrence: Octaborates are formed by condensation reactions of boric acid or borate esters in the presence of bases such as alkali metals or ammonium, often in aqueous or hydrothermal conditions. They also appear as components in polyborate mixtures arising from boron-containing minerals or during processing of borate-containing materials.

Applications and research: Octaborates find use in wood preservation and as additives in glass and ceramic formulations. They have been studied for properties relevant to materials science, including ion exchange behavior and potential nonlinear optical activity in certain crystallizations, though practical applications depend on specific structural motifs and cation choices.

See also: borate, polyborate, sodium octaborate tetrahydrate. Safety considerations: borates present moderate toxicity in some contexts; standard chemical-handling precautions apply.