Phase Formation Studies of Lead(II) Copper(II) Oxotellurates: The Crystal Structures of Dimorphic PbCuTeO5, PbCuTe2O6, and [Pb2Cu2(Te4O11)](NO3)2

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.

Polytypism in mcalpineite: a study of natural and synthetic Cu3TeO6

Synthetic and naturally occurring forms of tricopper orthotellurate, Cu^II₃Te^VIO₆ (the mineral mcalpineite) have been investigated by 3D electron diffraction (3D ED), X-ray powder diffraction (XRPD), Raman and infrared (IR) spectroscopic measurements. As a result of the diffraction analyses, Cu^II₃Te^VIO₆ is shown to occur in two polytypes. The higher-symmetric Cu^II₃Te^VIO₆-1C polytype is cubic, space group Ia3, with a = 9.537 (1) Å and V = 867.4 (3) ų as reported in previous studies. The 1C polytype is a well characterized structure consisting of alternating layers of Cu^IIO₆ octahedra and both Cu^IIO₆ and Te^VIO₆ octahedra in a patchwork arrangement. The structure of the lower-symmetric orthorhombic Cu^II₃Te^VIO₆-2O polytype was determined for the first time in this study by 3D ED and verified by Rietveld refinement. The 2O polytype crystallizes in space group Pcca, with a = 9.745 (3) Å, b = 9.749 (2) Å, c = 9.771 (2) Å and V = 928.3 (4) ų. High-precision XRPD data were also collected on Cu^II₃Te^VIO₆-2O to verify the lower-symmetric structure by performing a Rietveld refinement. The resultant structure is identical to that determined by 3D ED, with unit-cell parameters a = 9.56157 (19) Å, b = 9.55853 (11) Å, c = 9.62891 (15) Å and V = 880.03 (2) ų. The lower symmetry of the 2O polytype is a consequence of a different cation ordering arrangement, which involves the movement of every second Cu^IIO₆ and Te^VIO₆ octahedral layer by (1/4, 1/4, 0), leading to an offset of Te^VIO₆ and Cu^IIO₆ octahedra in every second layer giving an ABAB* stacking arrangement. Syntheses of Cu^II₃Te^VIO₆ showed that low-temperature (473 K) hydrothermal conditions generally produce the 2O polytype. XRPD measurements in combination with Raman spectroscopic analysis showed that most natural mcalpineite is the orthorhombic 2O polytype. Both XRPD and Raman spectroscopy measurements may be used to differentiate between the two polytypes of Cu^II₃Te^VIO₆. In Raman spectroscopy, Cu^II₃Te^VIO₆-1C has a single strong band around 730 cm^-1, whereas Cu^II₃Te^VIO₆-2O shows a broad double maximum with bands centred around 692 and 742 cm^-1.

The crystal structure of the first synthetic copper(II) tellurite arsenate, CuII5(TeIVO3)2(AsVO4)2

Crystals of the first synthetic copper tellurite arsenate, Cu^II₅(Te^IVO₃)₂(As^VO₄)₂ [systematic name pentacopper(II) bis-oxotellurate(IV) bis-oxoarsenate(V)], were grown by the chemical vapour transport method and structurally determined using single-crystal X-ray diffraction. Cu^II₅(Te^IVO₃)₂(As^VO₄)₂ possesses a novel structure type including a new topological arrangement of Cu^II and O atoms. Cu^II₅(Te^IVO₃)₂(As^VO₄)₂ is formed from a framework of two types of Jahn-Teller distorted [Cu^IIO₆] octahedra (one of which is considerably elongated) and [Cu^IIO₅] square pyramids, which are linked by edge-sharing to form chains and dimers and by corner-sharing to complete a three-dimensional framework. [As^VO₄] tetrahedra and [Te^IVO₅] polyhedra bridge the edges of channels along the a-axis direction, with void space remaining for the Te^IV stereoactive 5s² lone pairs. A comparison is made between the crystal structure of Cu^II₅(Te^IVO₃)₂(As^VO₄)₂ and those of known compounds and minerals, in particular fumarolitic Cu minerals.