X-ray characterization and magnetic properties of dioxygen-bridged CuII and MnIII Schiff base complexes

Abstract

The coordination chemistry of multinuclear metal compounds is important because of their relevance to the multi-metal active sites of various metalloproteins 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(mu-4-bromo-2-{[(3-oxidopropyl)imino]methyl}phenolato)dicopper(II), [Cu-2(C10H10BrNO2)(2)], (1), and bis(diaqua{4,4 '-dichloro2,2'-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}manganese(III)) bis{mu-4,4'-dichloro-2,2'-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}bis[aquamanganese(III)] tetrakis(perchlorate) ethanol disolvate, [Mn(C18H16Cl2N2O2)(H2O)(2)](2)[Mn-2(C18H16Cl2N2O2)(2)(H2O)(2)](ClO4)(4)center dot 2C(2)H(5)OH, (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 center dot center dot center dot O interactions of 2.8631 (13) angstrom linking the dinuclear halves of the centrosymmetric tetranucelar molecules, while each Mn-III atom is sixcoordinated. The shortest intra- and intermolecular nonbonding Mn center dot center dot center dot Mn separations are 3.3277 (16) and 5.1763 (19) angstrom for (2), while the Cu center dot center dot center dot Cu separations are 3.0237 (3) and 3.4846 (3) angstrom 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.