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New single-molecule magnet based on Mn12 oxocarboxylate clusters with mixed carboxylate ligands, [Mn12O12(CN-o-C6H4CO2)12(CH3CO2)4(H2O)4]*8CH2Cl2: synthesis, crystal and electronic structure, magnetic properties

A new high symmetry Mn12 oxocarboxylate cluster [Mn12O12(CN-o-C6H4CO2)12(CH3CO2)4(H2O)4]*8CH2Cl2 (1) with mixed carboxylate ligands is reported. It was synthesized by the standard carboxylate substitution method. 1 crystallizes in the tetragonal space group I41/a. Complex 1 contains a [Mn12O12] core with eight CN-o-C6H4CO2 ligands in the axial positions, four CH3CO2 and four CN-o-C6H4CO2 those in equatorial positions. Four H2O molecules are bonded to four Mn atoms in an alternating up, down, up, down arrangement indicating 1:1:1:1 isomer. The Mn12 molecules in 1 are self-assembled by complementary hydrogen C-H...N bonds formed with participation of the axial o-cyanobenzoate ligands of the adjacent Mn12 clusters. The lattice solvent molecules (CH2Cl2) are weakly interacted with Mn12 units that results in solvent loss immediately after removal of the crystals from the mother liquor. The electronic structure and the intramolecular exchange parameters have been calculated. Mn 3d bands of 1 are rather broad and center of gravity of the bands shifts down from Fermi level. The overlap between Mn 3d bands and 2p ones of the oxygen atoms from carboxylate bridges is higher than in the parent Mn12-acetate cluster. These changes in electronic structure provide significant difference in the exchange interactions in comparison to Mn12-acetate. The magnetic properties have been studied on a dried (solvent-free) polycrystalline sample of 1. The dc magnetic susceptibility measurements in the 2-300 K temperature range support a high-spin ground state (S = 10).