CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF 2 2-DIMENSIONAL SHEET-LIKE POLYNUCLEAR COPPER-COMPLEXES WITH BRIDGING TRANS-OXAMIDATE AND 4,4'-BIPYRIDINE OR PYRIMIDINE

Two two-dimensional complex polymers [Cu2L(4,4'-bipy)2]n[ClO4]2n 1 and [Cu2L'(pym)2]n[ClO4]2n 2, where H-2L = N,N'-bis(2-aminoethyl)oxamide, H-2L' = N,N'-bis(2-aminopropyl)oxamide, 4,4'-bipy = 4,4'-bipyridine and pym = pyrimidine, have been synthesised, and characterized by crystallographic, spectroscopic and magnetic methods. Both compounds crystallize in the monoclinic system, space group P2(1)/c and Z = 4, with a = 6.859(1), b = 20.085(4), c = 11.860(4) angstrom and beta = 93.56(2)degrees for 1, and a = 8.721 (2), b =8.679(2), c = 16.741 (2) angstrom and beta = 98.59(1)degrees for 2. The structures of the two compounds consist of layers of two-dimensional networks along the a-axis. Within each layer, transoxamidato-bridged copper(II) dimers asymmetrically connected by 4,4'-bipyridine or pyrimidine extend along bc plane to form an infinite network. The copper(II) has a square-pyramidal coordination geometry with N3O atoms forming the basal plane and a nitrogen atom from 4,4'-bipyridine or pyrimidine occupying the apical position. Both compounds exhibit strong antiferromagnetic coupling with J = -335 for 1 and -560 cm-1 for 2, owing to the efficiency of the oxamidato bridges in facilitating such coupling between copper(II) ions which are separated by more than 5.2 angstrom.