Synthesis and Crystal Structure of MCu(edta).cntdot.4H2O: Molecular Precursors for MCuO2 (M = Ca, Sr, Ba)

Abstract

The compounds MCu(edta){center_dot}4H{sub 2}O (edta = ethylenediaminetetraacetic acid; M = Ca, Sr, Ba) have been synthesized and characterized by analytical and spectroscopic techniques. The structures of the strontium and barium complexes have been determined by X-ray diffraction methods. Both compounds are isostructural and crystallize in the monoclinic system, space group P2{sub 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){degrees} for [SrCu(edta)(H{sub 2}O){sub 3}]{center_dot}H{sub 2}O and a = 8.818(1), b = 10.200(2), c = 19.737(2) {angstrom}, {beta} = 102.40(1){degrees} for [BaCu(edta)(H{sub 2}O){sub 3}]{center_dot}H{sub 2}O. The structures were refined to R = 0.046 (R{sub w}=0.051) and R = 0.034 (R{sub w}=0.037) for strontium and barium compounds, respectively. The geometry of the complexes consists of an intricate network of ligand-bridged coordination polyhedra, where the arrangement of the copper(II) ion exhibits a distorted octahedral topology. The geometry of the alkaline-earth metal cations is near to the bicapped trigonal prism, being bound to three water molecules and five oxygen atoms from different edta molecules. In comparison with the structural results of the [CaCu(edta)(H{sub 2}O){sub 2}]{center_dot}2H{sub 2}O, a change in the coordination polyhedron of calcium ion has been established. Thermal treatment ofmore » the complexes using TGA 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 MCuO{sub 2} phases (M = Ba, Sr, Ca). 33 refs., 6 figs., 4 tabs.« less