A MnII6MnIII6 Single-Strand Molecular Wheel with a Reuleaux Triangular Topology: Synthesis, Structure, Magnetism, and DFT Studies

The use of the anion of 3-methyl-1,3,5-pentanetriol (mpt3–) in manganese carboxylate chemistry has afforded the new MnII/III12 cluster [MnII6MnIII6(mpt)6(CH3CO2)12(py)6]·3CH3CN (1·3CH3CN). Complex 1 was isolated in moderate yield by the reaction of Mn­(CH3CO2)2·4H2O and H3mpt in a 2.6:1 molar ratio in a solvent mixture of acetonitrile and pyridine. The structure of 1 consists of alternating [MnII2(CH3CO2)3(py)]+ and [MnIII2(μ-OR)2(CH3CO2)­(py)]3+ dimeric units (three of each dimer), linked at each end by two alkoxo and one acetate bridges; the mpt3– ligands adopt the η2:η2:η2:μ4 coordination mode. The overall metal topology of this new Mn12 wheel resembles a guitar plectrum, or a Reuleaux triangle. Complex 1 displays an unprecedented structural topology, being the first example of a MnII6MnIII6 wheel constructed from alternating homovalent dimers and the only known Mn12 loop with the trigonal symmetry of a Reuleaux triangle (all other reported loops were ellipsoids). Variable-temperature, solid-state direct- and alternating-current magnetization studies were carried out on complex 1, revealing the presence of antiferromagnetic exchange interactions between the metal ions in the molecule, which lead to a spin ground-state value S = 0; the exchange coupling parameters J were calculated using density functional theory employing a hybrid B3LYP functional.