X-ray characterization and magnetic properties of dioxygen-bridged Cu~II and Mn~III Schiff base complexes

摘要

The coordination chemistry of multinuclear metal compounds is important because of their relevance to the multi-metal active sites of various metallo-proteins and metalloenzymes. Multinuclear Cu~II and Mn~III compounds are of interest due to their various properties in the fields of coordination chemistry, inorganic biochemistry, catalysis, and optical and magnetic materials. Oxygen-bridged binuclear Mn~III complexes generally exhibit antiferromagnetic interactions and a few examples of ferromagnetic interactions have also been reported. Binuclear Cu~II complexes are important due to the fact that they provide examples of the simplest case of magnetic interaction involving only two unpaired electrons. Two novel dioxygen-bridged copper(II) and manganese(III) Schiff base complexes, namely bis(μ-4-bromo-2-{[(3-oxidopropyl)imino]methyl}-phenolato)dicopper(II), [Cu_2(C_10H_10BrNO_2)_2], (1), and bis(diaqua{4,4'-dichloro-2,2'-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}man-ganese(III)) bis{μ-4,4'-dichloro-2,2'-[(1,1-dimethylethane-1,2-diyl)bis(nitrilo-methanylylidene)]diphenolato}bis[aquamanganese(III)] tetrakis(perchlorate) ethanol disolvate, [Mn(C_18H_16Cl_2N_2O_2)(H_2O)_2]_2[Mn_2(C_18H_16Cl_2N_2O_2)_2(H_2O)_]-(ClO_4)4·2_2H_5OH, (2), have been synthesized and single-crystal X-ray diffraction has been used to analyze their crystal structures. The structure analyses of (1) and (2) show that each Cu~II atom is four-coordinated, with long weak Cu···O interactions of 2.8631 (13) A linking the dinuclear halves of the centrosymmetric tetranucelar molecules, while each Mn~III atom is six-coordinated. The shortest intra- and intermolecular nonbonding Mn···Mn separations are 3.3277 (16) and 5.1763 (19) A for (2), while the Cu···Cu separations are 3.0237 (3) and 3.4846 (3) A for (1). The magnetic susceptibilities of (1) and (2) in the solid state were measured in the temperature range 2-300 K and reveal the presence of antiferromagnetic spin-exchange interactions between the transition metal ions.