Structural, electrochemical and magnetic analyses of a new octanuclear MnIII2MnII6 cluster with linked-defect cubane topology

Abstract

The employment of the 3,5-dimethyl-1-(hydroxymethyl)-pyrazole (Hdmhmp) ligand in a manganese carboxylate cluster afforded the new mixed-valent octanuclear manganese cluster [Mn^III₂Mn^II₆O₂(PhCOO)₁₀(dmhmp)₄(H₂O)₂]·4CH₃CN (1). Complex 1 was isolated by the reaction of Mn(ClO₄)₂·6H₂O, Hdmhmp and benzoic acid in a mixed solvent of acetonitrile and methanol. The structure of 1 can be described as a μ₄-O²⁻-linked pair of [Mn₄O₃] defect cubanes protected by ten PhCO₂⁻ and four μ₃-dmhmp⁻ ligands. Complex 1 is slightly soluble in acetonitrile, and high-resolution electrospray mass spectrometry (HRESI-MS) indicated that it could keep the [Mn^III₂Mn^II₆O₂] core integrity in solution but with detectable ligand exchange between PhCOO⁻ and dmhmp⁻. The electrochemical studies show that 1 possesses a characteristic Mn^II → Mn^III oxidation peak at +0.82 V and Mn^III → Mn^II reduction peaks at −0.79 and −1.51 V (versus Fc/Fc⁺), respectively. A detailed magnetic properties investigation has revealed only a weak intramolecular antiferromagnetic interaction between the Mn^II and Mn^III ions and no characteristic single-molecule magnetic properties.