Zinktellurit: Kristallstruktur und Beziehungen zu einigen Seleniten

Order-disorder (OD) structures of Rb2Zn(TeO3)(CO3)·H2O and Na2Zn2Te4O11

Single crystals of the two alkali metal zinc oxidotellurates(IV), Rb2Zn(TeO3)(CO3)·H2O and Na2Zn2Te4O11, were obtained by reactions of mixtures of ZnO, TeO2, Rb2CO3 (molar ratios 2:3:6) and ZnO, TeO2, Na2CO3 (molar ratios 2:3:10), respectively, with small amounts of water as a mineralizer. Both compounds crystallize as order-disorder (OD) structures of layers and feature a high stacking fault probability. The crystal structure of Rb2Zn(TeO3)(CO3)·H2O is composed of layers extending parallel to (100). The structure is composed of two kinds of non-polar OD layers consisting of trigonal-pyramidal [TeO3]2−, tetrahedral [ZnO4]6−, Rb1+, and CO3 2−, H2O, Rb2+, respectively. Different centrings of the layer groups lead to an ambiguity in the stacking arrangement. The crystal structure of Na2Zn2Te4O11 is built from layers extending parallel to (001). Trigonal-pyramidal [TeO3]2− and bisphenoidal [TeO4]4− polyhedra form [Te4O11]6− groups, which are connected by longer Te–O-contacts to form 1 ∞[Te8O22]12− double chains oriented along either [100] or [010]. These chains form non-polar layers, which appear alternatingly in two orientations related by a fourfold rotoinversion. The Zn2+ and Na+ cations are located at the layer interface. The stacking ambiguity is due to different lattices of adjacent layers.

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

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).