THE CRYSTAL AND MOLECULAR STRUCTURE OF DI-μ-(PYRIDINE-1-OXIDE)-BIS(DIBROMOCOPPER(II)), [(C₅H₅NO)CuBr₂]₂

Abstract

The crystal structure of di-μ-(pyridine-1-oxide)-bis(dibromocopper(II)), [(C₅H₅NO)CuBr₂]₂, has been determined by single crystal X-ray diffraction techniques. Counter methods were used to collect 759 non-zero reflections. The complex crystallizes in the monoclinic space group P2_1/c with 2 dimeric molecules per unit cell. The cell dimensions are a = 10.977(5), b = 10.007(5), c = 7.88(1) Å and β = 110° 30′ (10). The observed and calculated densities are 2.601 and 2.608, g. cm⁻³, respectively. The structure was refined by least-squares methods to a conventional R factor of 072. The oxygen-bridged dimer has a center of symmetry which requires the two Cu(II) ions and the two bridging oxygen atoms to lie in a plane. Each Cu(II) ion is five coordinate and the geometry is best described as a square-based pyramid. Two bridging oxygen atoms and two bromine atoms form the square base while the apical site is occupied by a bromine from an adjacent dimer. The Cu[sbnd]O distances are 1.965(9) and 1.994(6) Å, the basal Cu[sbnd]Br distances are both 2.332(2) Å and the intermolecular Cu[sbnd]Br distance is 3.130(3) Å. The complex is not isostructural with the chloride complex, and there is little distortion of the square-basal geometry due to steric interactions. The d _x2-y2 orbitals in the bromide complex are able to overlap to a greater extent than in the chloride complex, and the magnetic moment is reduced. The nephelauxetic effect need not be introduced to rationalize the differences in magnetic behavior.