The interconversion of aqueous boron species and the interaction of borate with diols: a 11B n.m.r. study

11B n.m.r. spectroscopic studies have shown that the interconversion of boric acid and tetrahydroxyborate (borate) anions in aqueous solution is pH dependent. Evidence has also been obtained for the condensation of monomeric species in the pH range 5–11 to give polyborates. The interaction of 1,2-diols with borate anions at pH 12 to form 1:1 and 2:1 anionic complexes has been demonstrated by the existence of discrete 11B resonances for these three anions in the equilibrating systems. The effect of substituents of 1,2-diols on complex formation has been investigated. The difference in chemical shift between borate complexes of 1,2- and 1,3-diols can be used to distinguish 5- and 6-membered ring complexes. Evidence for a 7-membered ring complex in aqueous solution is reported.