Syntheses and Characterization of Dinuclear Manganese(II,II) and Manganese(II,III) Complexes with Phenolate and Two Carboxylate Bridges

Dinuclear manganese(II,II) and (II,III) complexes, [Mn2(L-py)(RCOO)2]ClO4·nH2O and [Mn2(L-py)(RCOO)2](ClO4)2·nH2O, were prepared, where L-py is 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenolate(1–) and RCOO denotes CH3COO or C6H5COO. X-Ray structure analysis of the mixed valence complex [Mn2(L-py)(C6H5COO)2](ClO4)2·H2O revealed that the complex cation involves octahedral manganese(II) and manganese(III) centers with N3O3 donor sets and that the two metal ions are linked by phenolato and two benzoato groups. Magnetic susceptibility measurements over temperature range 80–300 K indicated that both manganese(II,II) and (II,III) complexes exhibit weak antiferromagnetic interaction with spinexchange coupling constant, J=−5–−7 cm−1. Cyclic voltammograms of the mixed valence complexes showed two quasi-reversible redox couples at ca. 0.5 and ca. 1.0 V (vs. SCE), assignable to the redox reactions of MnII–MnIII/MnII–MnII and MnIII–MnIII/MnII–MnIII, respectively. The comproportionation constants for the reaction (MnIII–MnIII)+(MnII–MnII)2(MnII–MnIII at 20°C were estimated as 2–3×109.