Borate

[2] The main borate anions are: In 1905, Burgess and Holt observed that fusing mixtures of boric oxide B2O3 and sodium carbonate Na2CO3 yielded on cooling two crystalline compounds with definite compositions, consistent with anhydrous borax Na2B4O7 (which can be written Na2O·2B2O3) and sodium octaborate Na2B8O13 (which can be written Na2O·4B2O3).

The planar BO3 units may be stacked in the crystal lattice so as to have π-conjugated molecular orbitals, which often results in useful optical properties such as strong harmonics generation, birefringence, and UV transmission.

However, it more often acts as a Lewis acid, accepting an electron pair from a hydroxide ion produced by the water autoprotolysis:[11] This reaction is very fast, with characteristic time less than 10 μs.

The best known of these is the tetraborate ion [B4O7]2−, found in the mineral borax: Other anions observed in solution are triborate(1−) and pentaborate(1−), in equilibrium with boric acid and tetrahydroxyborate according to the following overall reactions:[13] In the pH range 6.8 to 8.0, any alkali salts of "boric oxide" anions with general formula [BxOy(OH)z]((q−) where 3x+q = 2y + z will eventually equilibrate in solution to a mixture of B(OH)3, [B(OH)4]−, [B3O3(OH)4]−, and [B5O6(OH)4]−.

More complex anions can be formed by condensing borate triangles or tetrahedra with other oxyanions to yield materials such as borosulfates, boroselenates, borotellurates, boroantimonates, borophosphates, or boroselenites.

Borosilicate glass, also known as pyrex, can be viewed as a silicate in which some [SiO4]4− units are replaced by [BO4]5− centers, together with additional cations to compensate for the difference in valence states of Si(IV) and B(III).

Lithium metaborate, lithium tetraborate, or a mixture of both, can be used in borate fusion sample preparation of various samples for analysis by XRF, AAS, ICP-OES and ICP-MS. Borate fusion and energy dispersive X-ray fluorescence spectrometry with polarized excitation have been used in the analysis of contaminated soils.

[8] Borate esters are organic compounds, which are conveniently prepared by the stoichiometric condensation reaction of boric acid with alcohols (or their chalcogen analogs[15]).

Growth by ALD was achieved using precursors composed of the tris(pyrazolyl)borate ligand and either ozone or water as the oxidant to deposit CaB2O4,[22] SrB2O4,[23] BaB2O4,[24] Mn3(BO3)2,[25] and CoB2O4[25] films.