Crystal structure and electrochemical properties of Cu^II complexes with 1,2-bis(2-hydroxybenzamido)benzene

The tetramethylammonium and potassium salts of [1,2-bis(2-oxybenzamidato)benzene]copper(II) abbreviated as [NMe₄]₂[Cu(hbab)] and K₂[Cu(hbab)] were prepared and characterized. The x-ray analysis of the potassium salt, K₂[Cu(hbab)]·5DMF, revealed a unique one-dimensional chain structure consisting of {[KO₃][K(Cu(hbab)O]}_n as the resulting unit, where each K⁺ ion is surrounded octahedrally by six oxygen atoms and all the oxygen atoms play the role of a bridging group to the K⁺ ion. The tetramethylammonium salt, [NMe₄]₂[Cu(hbab)]·H₂O, behaves as a 2 : 1 electrolyte in the 10^-3 mol dm^-3 solutions of methanol, acetonitrile and DMF, while the potassium salt behaves as a 2 : 1 electrolyte in methanol and as a 1 : 1 electrolyte in acetonitrile and DMF. The Cu^II/III redox potentials of the tetramethylammonium salt in DMF under the presence of 2 equivalent molar of K⁺, Na⁺, and Li⁺ shift to more positive values than those without alkali metal ions, where the magnitude of the positive shift increases with increasing of charge density of alkali metal ion, namely Li⁺ > Na⁺ > K^-. The charge effect due to ion pair formation between [Cu(hbab)]^2- and Na⁺ or K⁺ causes the potential shift, while the potential shift in the case of the Li⁺ ion is brought about by the decrease of donor ability of the phenolic oxygens, besides the charge effect.