title: Synthesis and Characterization of Two New Copper Tellurites, Ba(2)Cu(4)Te(4)O(11)Cl(4) and BaCu(2)Te(2)O(6)Cl(2), in Supercritical H(2)O.
abstract: Two new compounds containing tellurite building blocks coordinated to copper and barium atoms have been isolated from hydrothermal solvents. A new layered compound, Ba(2)Cu(4)Te(4)O(11)Cl(4) (I), has been obtained by reacting BaCl(2).2H(2)O, CuO, and Te(OH)(6) in NH(4)Cl solution at 375 degrees C for 4 days. Green, platelike crystals of I crystallize in the centrosymmetric space group, P&onemacr;, with a = 9.275(2) Å, b = 12.135(2) Å, c = 9.263(2) Å, alpha = 98.23(3) degrees, beta = 108.35(3) degrees, gamma = 110.90(3) degrees, and Z = 2. The compound contains two types of layers, one based on copper oxides linked by Te(4)O(11) groups, and the other based on Cu(2)Cl(4) units. The tellurium atoms adopt the common TeO(3+1) units or TeO(3) pyramids, and the oxygen-coordinated copper atoms adopt a square planar CuO(4) arrangement. Dark green, prismatic crystals of BaCu(2)Te(2)O(6)Cl(2) (II) were obtained by reacting BaCl(2).2H(2)O, Cu(2)O, and Te(OH)(6) in NH(4)Cl solution at 375 degrees C for 18 h. Compound II was refined in the acentric monoclinic space group, P2(1) (a = 7.434(2) Å, b = 7.448(2) Å, c = 8.271(2) Å, beta = 97.42(3) degrees, Z = 2), and is based on Te(2)O(6) units connected by copper atoms or copper chloride groups. As in I, tellurium atoms are contained within TeO(3+1) or TeO(3) units and the connecting copper atoms are nearly square planar. The chloride-coordinated copper atoms group adopt a square pyramidal CuO(3)Cl(2) geometry with a chlorine atom occupying the apical position. The formal oxidation states of the copper atoms in compound I are distributed such that the connecting atoms in an oxide environment are 2+ and atoms within a chloride environment are 1+, whereas in compound II, all copper atoms are 2+. Bond valence sums for both compounds and magnetic susceptibility data for I support these assignments. The optical band gap for I was determined by diffuse reflectance spectroscopy and indicate that it is a wide band gap material (E(g)() = 3.00 eV).
authors.affiliation: Department of Chemistry, Clemson University, Clemson, South Carolina 29634-1905.
authors.forename: Christopher R.
authors.initials: CR
authors.lastname: Feger
authors.forename: Joseph W.
authors.initials: JW
authors.lastname: Kolis