CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF A 2-DIMENSIONAL SHEET-LIKE COPPER(II) COMPLEX WITH BRIDGING TRANS-OXAMIDATE AND AZIDE

A novel sheet-like complex polymer [Cu4L2(N3)3]n[ClO4]n.2nH2O, where H-2L is N,N'-bis(2-aminoethyl)oxamide, has been prepared and characterized by X-ray crystallography, and magnetic and spectroscopic measurements. It crystallizes in the triclinic system, space group P1BAR, with a = 11.486(2), b = 11.706(3), c = 12.291(3) angstrom, alpha = 77.42(2), beta = 67.59(2), gamma= 77.96(2)degrees and Z = 2. The structure consists of a two-dimensional network of copper(II) ions bridged by L in a trans conformation, and by azido ligands in three different bonding modes, i.e. asymmetric end-to-end, asymmetric end-on and symmetric end-on. The repeating asymmetric unit comprises a tetranuclear copper(II) fragment with two of the copper atoms in approximately square-planar environments, and two with distorted-pyramidal geometries. Magnetic susceptibility data have been measured in the temperature range 4-300 K indicating an antiferromagnetic exchange interaction between copper(II) ions bridged alternately by L and azido ligands. This results from the efficiency of the trans-oxamidato and symmetric end-on azido bridges in facilitating an antiferromagnetic exchange interaction (J= -516.8 cm-1) between copper(II) ions which are separated by about 5.2 and 3.3 angstrom, respectively. The best fit of the magnetic data is obtained by considering the system to comprise CuLCu dimers linked by end-on azido bridges which create a molecular field, with negligible exchange through the asymmetric end-to-end azido groups.