Synthesis, crystal structure and magnetic properties of three unprecedented tri-nuclear and one very rare tetra-nuclear copper(ii) Schiff-base complexes supported by mixed azido/phenoxo/nitrato or acetato bridges

Abstract

Three novel mixed bridged trinuclear and one tetranuclear copper(II) complexes of tridentate NNO donor Schiff base ligands [Cu(3)(L(1))(2)(mu(1,1)-N(3))(2)(CH(3)OH)(2)(BF(4))(2)] (1), [Cu(3)(L(1))(2)(mu(1,1)-N(3))(2)(mu-NO(3)-1kappaO:2kappaO')(2)] (2), [Cu(3)(L(2))(2)(mu(1,1)-N(3))(2)(mu-NO(3)-1kappaO:2kappaO')(2)] (3) and [Cu(4)(L(3))(2)(mu(1,1)-N(3))(4)(mu-CH(3)COO-1kappaO:2kappaO')(2)] (4) have been synthesized by reaction of the respective tridentate ligands (L(1) = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol, L(2) = 2-[1-(2-diethylamino-ethylimino)-ethyl]-phenol, L(3) = 2-[1-(2-dimethylamino-ethylimino)-methyl]-phenol) with the corresponding copper(ii) salts in the presence of NaN(3). The complexes are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. Complex 1 is composed of two terminal [Cu(L(1))(mu(1,1)-N(3))] units connected by a central [Cu(BF(4))(2)] unit through nitrogen atoms of end-on azido ligands and a phenoxo oxygen atom of the tridentate ligand. The structures of 2 and 3 are very similar; the only difference is that the central unit is [Cu(NO(3))(2)] and the nitrate group forms an additional mu-NO(3)-1kappaO:2kappaO' bridge between the terminal and central copper atoms. In complex 4, the central unit is a di-mu(1,1)-N(3) bridged dicopper entity, [Cu(2)(mu(1,1)-N(3))(2)(CH(3)COO)(2)] that connects two terminal [Cu(L(3))(mu(1,1)-N(3))] units through end-on azido, phenoxo oxygen and mu-CH(3)COO-1kappaO:2kappaO' triple bridges to result in a tetranuclear unit. Analyses of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the copper(II) ions in complexes 1-3, with the exchange parameter J of -9.86, -11.6 and -19.98 cm(-1) for 1-3, respectively. In complex 4 theoretical calculations show the presence of an antiferromagnetic coupling in the triple bridging ligands (acetato, phenoxo and azido) while the interaction through the double end-on azido bridging ligand is strongly ferromagnetic.