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

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 D_2d (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.

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