Salts of the Bis(catecholato)borate Anion with Organic Cations

Abstract

In a series of six salts with organic nitrogen and phosphorus cations [2-methylpyridinium bis(pyrocatecholato-O,O′)borate, C6H8N+.C12H8BO4−, (1); 4-methylpyridinium bis(pyrocatecholato-O,O′)borate, C6H8N+.C12H8BO4−, (2) and (3) (two polymorphs); 1,10-phenanthrolinium bis(pyrocatecholato-O,O′)borate, C12H9N2+.C12H8BO4−, (4), and its dichloromethane solvate, C12H9N2+.C12H8BO4−.CH2Cl2, (5); and trimethylphosphonium bis(pyrocatecholato-O,O′)borate, C3H10P+.C12H8BO4−, (6)], the bis(catecholato)borate anion has approximate D2d (\overline{4}2m) symmetry, with the central spiro-B atom distorted from regular tetrahedral coordination geometry by reduction of the two intraring O—B—O bond angles. The two chelate rings show small deviations from planarity by folding about the O⋯O axis. Ion pairs are formed by N—H⋯O hydrogen bonding in all five salts with nitrogen-based cations, but there is no hydrogen bonding in the phosphonium salt; the hydrogen bonding leads to slight elongation of the B—O bond involved.