Structural, electrochemical and magnetic analyses of a new octanuclear Mn III 2 Mn II 6 cluster with linked-defect cubane topology

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 III 2 Mn II 6 O 2 (PhCOO) 10 (dmhmp) 4 (H 2 O) 2 ]·4CH 3 CN ( 1 ). Complex 1 was isolated by the reaction of Mn(ClO 4 ) 2 ·6H 2 O, Hdmhmp and benzoic acid in a mixed solvent of acetonitrile and methanol. The structure of 1 can be described as a μ 4 -O 2− -linked pair of [Mn 4 O 3 ] defect cubanes protected by ten PhCO 2 − and four μ 3 -dmhmp − ligands. Complex 1 is slightly soluble in acetonitrile, and high-resolution electrospray mass spectrometry (HRESI-MS) indicated that it could keep the [Mn III 2 Mn II 6 O 2 ] 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.