The oxygen chemistry of boron

like silicon, occurs in nature exclusively as oxy-compounds, particularly hydroxyborates of calcium and sodium. In borates based exclusively on BO3 coordination groups there would be a simple relation between the 0 B ratio and the number of 0 atoms shared by each BO3 group, assuming these to be equivalent and each bonded to 2 B atoms  

3 Orthoborates discrete BO ions Pyroborates discrete B2OS ions 0 

OH bonded to B as part of a 3- or 4-coordination group this is in marked contrast to the rarity of hydroxysilicates. Examples are known of all 4-coordination groups from BO4 through B03(0H) and B02(0H)2, both of which occur in CaB304(0H)3.H20, and BO(OH)3 (in Mg[B20(0H)g]), to B(OH)4 in tetra-hydroxyborates such as NaB(OH)4- The recognition of this fact, as the result of structural studies, has led to the revision of many formulae as in the case of antimonates (p.719), for example  

Bandylite, CUCI2. CUB2O4.4 H2O, is CuClB(OH)4, and Teepleite, NaB02. NaCl. 2 H2O, is Na2ClB(OH)4. 

The chemistry of borates is complex both in solution and in the melt. It is concluded from B n.m.r. and other studies that Na3B30g dissociates in solution to B(0H)4 ions and that at low concentrations tetraborates dissociate completely into B(0H)3 and B(OH)4, but that in more concentrated solutions of borates various polyborate ions coexist in equilibrium with one another. From melts extensive series of borates are obtained, the product depending on the composition of the melt, for example  

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