SYNTHESIS, CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF CU(TZQ)(2)(HCO2))(2)(MU-HCO2)(2)]CENTER-DOT-4H(2)O (TZQ=[1,2,3]TRIAZOLO[1,5-A]QUINOLINE), A BINUCLEAR COPPER(II) COMPLEX WITH UNUSUAL MONOATOMIC FORMATE BRIDGES

The compound [{Cu(tzq)(2)(HCO2)}(2)(mu-HCO2)(2)]. 4H(2)O (tzq = [1,2,3 ]triazolo[1,5-a]quinoline) was obtained under mild conditions by react ion between the hydrazone of quinoline-2-carbaldehyde and copper(II) f ormate in ethanolic aqueous solution and its crystal and molecular str ucture have been determined by X-ray diffraction. methods: triclinic, space group <P(1)over bar>, Z = 1, a = 8.209(4), b = 12.156(4), c = 12 .649(4) Angstrom, alpha = 63.21(3), beta = 81.42(3), gamma = 89.12(3)d egrees. The compound is built of centrosymmetric neutral dimeric [{Cu( tzq)(2)(HCO2)}(2)(mu-HCO2)(2)] entities linked through hydrogen bonds involving water molecules and carboxylate groups. The. copper atom is involved in a CuN2O2O' chromophore and lies in a tetrahedrally distort ed square-pyramidal environment;The four equatorial donors are two Ira ns nitrogen atoms from two tzq molecules and two oxygen atoms from two formate. groups. One of the oxygens acts as a bridging ligand occupyi ng the apical position of the symmetry-related copper atom in the: dim er structure, which is viewed as two:edge-sharing distorted square pyr amids. This co-ordination behaviour (monoatomic bridging) is very unus ual for the HCO2- anion. The EPR spectrum is characteristic of a tripl et state with nbn-negligible zero-field splitting. Magnetic susceptibi lity measurements in the range 1.8-200 K showed weak antiferromagnetic exchange between the copper(II) ions (2J = -1.05 cm(-1)). The observe d behaviour is discussed on the basis of the crystal structure and com pared with those reported for related mu-oxo carboxylate-bridged [CuO2 Cu] dimers with parallel-planar geometry.