SYNTHESIS AND CRYSTAL-STRUCTURE OF MCU(EDTA)CENTER-DOT-4H2O - MOLECULAR PRECURSORS FOR MCUO2 (M=CA, SR, BA)

The compounds MCu(edta).4H2O (edta = ethylenediaminetetraacetic acid; M = Ca, Sr, Ba) have been synthesized and characterized by analytical and spectroscopic techniques. The structures of the strontium and bari um complexes have been determined by X-ray diffraction methods. Both c ompounds are isostructural and crystallize in the monoclinic system, s pace group P2(1)/c, with four formula weights in a cell measuring a = 8.717(1), b = 10.568(3), c = 19.374(3) angstrom, beta = 100.39(1)degre es for [SrCu(edta)(H2O)3].H2O and a = 8.818(1), b = 10.200(2), c = 19. 737(2) angstrom, beta = 102.40(1)degrees for [BaCu(edta)(H2O)3].H2O. T he structures were refined to R = 0.046 (R(w) = 0.051) and R = 0.034 ( R(w) = 0.037) for strontium and barium compounds, respectively. The ge ometry of the complexes consists of an intricate network of ligand-bri dged coordination polyhedra, where the arrangement of the copper(II) i on exhibits a distorted octahedral topology. The geometry of the alkal ine-earth metal cations is near to the bicapped trigonal prism, being bound to three water molecules and to five oxygen atoms from different edta molecules. In comparison with the structural results of the [CaC u(edta)(H2O)2].2H2O, a change in the coordination polyhedron of calciu m ion has been established. Thermal treatment of the complexes using T GA involves three consecutive steps: dehydration, ligand pyrolysis and the formation of inorganic residue. Taking these results into account , further thermal treatments have been performed in order to obtain MC uO2 phases (M = Ba, Sr, Ca).