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 characteri zed by X-ray crystallography, and magnetic and spectroscopic measureme nts. 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 con sists 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 su sceptibility 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 t he efficiency of the trans-oxamidato and symmetric end-on azido bridge s 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 obtaine d 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.