Formation of pentagonal tunnels bordered with P2O7 groups in diphosphate tungsten bronzes (P2O4)2(WO3)2m: A HREM investigation

During the investigation of the phosphate bronzes (PO₂)₄(WO₃)_2m [MPTB_P] and K_x(P₂O₄)₂WO₃)_2m [DPTB_H] crystals of a new type were observed. HREM images of these crystals showed twinned ReO₃-type slabs the junction of which was parallel to the (102)_ReO3 plane. The proposed model identified the twin boundary as built from P₂O₇ groups involving the formation of pentagonal tunnels. The structure of this new type of extended defects is quite original: it corresponds to a new structural type named “diphosphate tungsten bronzes with pentagonal tunnels” [DPTB_P], for which no regular member could be synthesized. Image calculations were performed to confirm the junction model. Apart from the disordered stacking of the ReO₃-type slabs, very few defects were observed and shear planes were only obtained in reduced samples. This new structural type takes its place in the large family of phosphate tungsten bronzes where all members (DPTB_H, MPTB_H, MPTB_P) are very closely related.     

HNbWO6 and HTaWO6: Novel oxides related to ReO3 formed by ion exchange of rutile-type LiNbWO6 and LiTaWO6

Both LiNbWO₆ and LiTaWO₆ undergo ion exchange in hot aqueous H₂SO₄ yielding the hydrates HMWO₆ · H₂O (M = Nb or Ta). The reaction is accompanied by a structural transformation from the rutile to the ReO₃ structure. The cell constants are a = 3.783(3)Å for HNbWO₆ · H₂O and a = 3.785(5)Å for HTaWO₆ · H₂O. The ReO₃ structure is retained by the dehydration products HMWO₆ and MWO_5.5 as well. HMWO₆ phases yield H_1+xMWO₆ hydrogen bronzes on exposure to hydrogen in the presence of platinum catalyst.     

Lithium and sodium insertion reactions of phosphate tungsten bronzes

Lithium insertion reactions of monophosphate tungsten bronzes, (PO₂)₄(WO₃)_2m and diphosphate tungsten bronzes K(P₂O₄)₂(WO₃)_2m indicate that a maximum of two Li/W and one Na/W may be inserted in these materials. The phosphate tungsten bronzes are three-dimensional network structures made up of slabs of ReO₃-type WO₆ octahedra connected by phosphate groups with large interconnected cavities. Ion-exchange reactions of selected members of K(P₂O₄)₂(WO₃)_2m show that potassium which occupies the large hexagonal tunnels in the lattice may be exchanged for various alkali metal cations. Upon lithium insertion, the metallic host materials become insulating. This is attributed to the filling of the π* conduction band formed by the overlap of Wt_2g − 5d and oxygenπ − 2p orbitals.     

Das Schwingungsspektrum von Ba5(ReO6)2

The infrared and laser-Raman spectra of crystalline Ba₅(ReO₆)₂ are reported and discussed. From the obtained spectroscopic data a calculation of force constants and mean amplitudes of vibration for the ReO₆ ^5– ion has been carried out.

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Mit 2 Abbildungen     

A Titanium and Tantalum Phosphate LiNaTiTa2P2O13 with An Open Framework hosting Li and Na Ions

Herein, we report a detailed structural, electric, thermal and optical analysis of a titanium and tantalum phosphate LiNaTiTa₂P₂O₁₃. The title compound is comprised of typical ReO₃-type layers constituted by corner-sharing TiO₆ and TaO₆ octahedra, bridged by PO₄ tetrahedra, and the structure is closely related to monophosphate niobium bronzes. The existence of pentagonal tunnels, hosting the Li⁺ and Na⁺ ions, endows LiNaTiTa₂P₂O₁₃ a moderate ion transportation behavior (4.67×10⁻⁴ S/cm at 823 K). In addition, the successful substitution of Nb for Ta in LiNaTiTa₂P₂O₁₃ results in the optical absorption red-shift towards visible range with a narrowing band gap, which may provide a route of isomorphic replacement to band engineering for photo-catalysis.     

Composition-dependent microhardness and its relationship to bonding in sodium tungsten bronzes

The technique of microhardness measurements using diamond indenters is outlined and assessed for its potential use in quantifying bonding changes and studying reactions in nonstoichiometric crystals. Results are presented for both Vickers and Knoop hardness values on {001} and {011} crystal planes of cubic sodium tungsten bronzes, Na_xWO₃, with x in the range 0.5 to 0.75. The Knoop data show that in only one direction, 〈110〉 on {001}, is the hardness sensitive to changes in composition. Hardness in the 〈110〉 directions and the degree of anisotropy increase as the sodium content of the bronze increases. All the crystal faces examined showed marked anisotropic behavior, with 〈110〉 being about 50% harder than 〈100〉 on {001} faces, while on {011} planes hardness increases in the sequence $\text{〈100〉:〈21}\text{1}\text{〉:〈11}\text{1}\text{〉 ≈ 〈01}\text{1}\text{〉}$. Hardness results from isomorphous and isoelectronic ReO₃ are considered with the Na_xWO₃ data to show the dominant role played by Na⁺WO₃ matrix interactions in determining the properties of these materials. The results are discussed in terms of current bonding theories for bronzes.     

The Pentagonal Column and the ReO3-Type Structure

The pentagonal column (PC), consisting of MX₇ bipyramids sharing their equatorial edges with five MX₆ octahedra, is a structural feature frequently occurring in association with frameworks of the ReO₃-type, where it enables accomodation of an anion deficiency. The present article discusses the geometry of the PC and its compatibility with the ReO₃-type structure, which naturally emerges from the finding that a PC may result from twinning of an ReO₃-type structure on the unit cell level. A new symbolism is presented which facilitates visualization of a large variety of crystal and defect structures of MX_3–x stoichiometry. This symbolism may also serve as a convenient aid in deriving models of possible new structures that may be of value in the interpretation of HREM images.     

Les differentes formes cristallines de Y3ReO8: Relations avec la structure fluorine

The monoclinic Y₃ReO₈β phase is synthetized at 40 kbar and 900°C. The crystal structure is solved to an R value of 0.058 for 1341 observed reflections, by conventional methods using automated four-circle diffractometer data. This structure can be visualized as a fluorite-related superstructure, the large difference between the ionic radii of Re⁷⁺ and Y³⁺ being favorable to cation ordering. The heating to 500°C of this phase under atmospheric pressure leads to a disordered fluorite structure of the form Y₃ReO₈α. An intermediary metastable phase Y₃ReO₈α′ is obtained by heating a Y₃ReO₈β single crystal to 350°C. The structural relations between these three crystalline forms of Y₃ReO₈ and the fluorite structure are discussed.     

Thermal,dielectric, and electrical transport properties of some bivalent metal perrhenates

Thermal, dielectric, and electron transport properties of dihydrated and anhydrous perrhenates of strontium, barium, cadmium, and lead have been investigated. The DTA of anhydrousM[ReO₄]₂ (M =Sr, Ba, Cd) compounds exhibit three reversible phase transitions with considerable thermal hysterisis for the first phase transformation. A single reversible phase transition occurs for Pb[ReO₄]₂. The parent phases of Ba[ReO₄]₂, Pb[ReO₄]₂, and Cd[ReO₄]₂ behave as semiconductors at elevated temperatures. The dielectric constants measured for Sr[ReO₄]₂ in the temperature range 30 to −160°C give a broad inflection between −40 and −70°C, which probably indicates a phase transition.     

Preparation and Crystal Structure of Re3O10

Trirheniumdecaoxide, Re₃O₁₀, was obtained by the reaction of ReO₂ and ReO₃ in an arc-melting furnace. X-ray powder diffraction revealed a tetragonal structure with space group I m2 and lattice constants a=5.171(1) and c=13.371(6) Å. The crystal structure is built up by layers of corner-sharing [ReO₅] square pyramids perpendicular to [001] with the apical oxygen pointing up and down alternatingly. These layers are interconnected by disordered [ReO₆] octahedra. Early reports on Re₂O₅ are reviewed in the light of our results.     

Bronzes with a tunnel structure KxP4O8(WO3)2m: The tenth member of the series—KP8W40O136

The crystal structure of KP₈W₄₀O₁₃₆, the tenth member of the series K_xP₄O₈(WO₃)_2m, has been resolved by three-dimensional single-crystal X-ray analysis. The space group is $\text{P2}{}_1\text{c}$ and the cell parameters are a = 19.589(3) Å, b = 7.5362(4) Å, c = 16.970(3) Å and β = 91.864(14)°. The framework is built up from ReO₃-type slabs connected through pyrophosphate groups. The structure is compared to those of the other members of the series: although the ReO₃-type slabs show a different type of tilting of the WO₆ octahedra, the dispersion of WO distances is always higher for the octahedra linked to one or two P₂O₇ groups and decreases in proportion as W is farther from these groups. The perovskite cages of the slabs are described and compared to those encountered in the structures of WO₃ and of the bronzes A_xWO₃.     

Synthesis and characterization of rhenium(VII) oxide complexes of phenothiazines

Summary Five complexes of rhenium(VII) oxide with N-alkylphenothiazines have been synthesized and characterized on the basis of elemental analyses, molar conductances, and u.v.-vis., i.r. and n.m.r. spectral data. The molecular formulas of the new ionic complexes are: [ReO₃(PTZ)₂(H₂O)][ReO₄], PTZ = chlorpromazine, promethazine or ethopropazine; [ReO₃(TF)(H₂O)][ReO₄], TF = trifluoperazine; and [ReO₃(TR)₃][ReO₄(H₂O)₂]·H₂O, TR = thioridazine. Tentative structures have been proposed.     

Structural relationships in the series AxP4O8(WO3)2m (A = K,Rb): A high-resolution electron microscopy study

The first members of the series A_xP₄O₈(WO₃)_2m were studied by means of electron microscopy. These bronzes can be classified into two groups on the basis of ReO₃-type block composition: even- and odd-m members. High-resolution lattice images of tungstophosphate crystals (m ≤ 10) allow us to establish a correlation between the image contrast and the framework of the structure. The structural mechanism proposed for this series is discussed and compared to the possibility of intergrowth, and to the crystallographic shear phenomena observed in tungsten and molybden oxides.     

Rare earth tungsten bronzes: a new method of synthesis. Perspectives for their application as inert matrices for transmutation of long-life actinide elements

A new method of synthesis of oxide tungsten bronzes containing lanthanide (Ln) Nd and Eu, based on thermal degradation of polyoxotungstate compounds, is proposed. The simplicity of the method allows to consider this class of compounds with chemical formula, Ln_xWO₃, as potential inert target for incineration or transmutation of minor actinides, Am and Cm, in neutron reactors. Nd and Eu were used as analogues of transplutonium elements. Powder X-ray diffraction patterns of compounds synthesized reveal a cubic perovskite structure. The lanthanide content in bronzes was determined by optical spectroscopy analysis. The experimental density of the pressed bronze samples was estimated at 6.58 g cm⁻³, i.e., 89% of the crystallographic value. The thermal stability of the bronzes synthesized was checked up to 900°C in an inert atmosphere. Leaching tests were performed for europium bronzes in nitric acid solutions using luminescence technique.     

Über Perrhenate. 2. Zur Kenntnis von Li5ReO6 und Na5ReO6 – mit einer Bemerkung über Na5IO6

On Perrhenates. 2. On Li₅ReO₆ and Na₅ReO₆ — with a Note on Na₅IO₆ The crystal structures of Li₅ReO₆ and Na₅ReO₆ were determined for the first time in full detail from four-circle diffractometer data (AgKα radiation). They and Na₅IO₆, also (according to powder data) crystallize with the monoclinic system (C2/m, Z = 2). The structure may be described as a distorted derivative of the NaCl type; data see ?Inhaltsübersicht”?. Effective Coordination Numbers, ECoN, and the Madelung Parts of the Lattice Energy, MAPLE, have been calculated and are discussed.     

Der Chemische Transport von Re,ReO2 ReO3 und ReS2

The Chemical Transport of Re, ReO₃, ReO₃, and ReS₂ Chemical transport of Re, ReO₂, ReO_y and ReS, in the presence of J₂, of H₂O, and of both, J₂ + H₂O has been investigated experimentally. Experiments concerning the systems Re/J₂ and ReS₂/J₂ showed the importance of water traces, which could be diminished by reaction with graphite. The composition of the gas phases of the multicomponent systems involved have been calculated thermodynamieally. On this basis a discussion of the transport properties has been made. The important Re-containing moleculs are ReO₃J and ReO₃(OH). Gaseous rhenium iodides are insignificant. Favourable transport properties are found in the systems Re/H₂O Re/H₂O, J₂ ReO₂/H₂O, J₂ ReO₃/Re₂O₇, J₂ ReO₃/J₂ ReS₃/H₂O ReS₂/H₃O, J₂     

The crystal structures of two Mercury Perrhenates

The mercury perrhenates with the empirical formulas HgReO₄ and Hg₂ReO₅ were prepared by annealing powdered mixtures of mercury(II)oxide and mercury(II)metaperrhenate Hg(ReO₄)₂ in sealed silica tubes. Their crystal structures were determined from single-crystal X-ray data. HgReO₄ crystallizes dimeric with nearly linear O₃Re? O? Hg? Hg? O? ReO₃ molecular units and Hg₂ReO₅ has a solid state structure, where Hg(I) and Hg(II) together with oxygen atoms form 14-membered rings, which are condensed to two-dimensionally infinite polycationic nets of composition (Hg₂²⁺ · 2 HgO)_n. These nets are separated from each other by tetrahedral ReO₄^? anions.     

Infrared and X-ray studies of hydrogen intercalation in different tungsten trioxides and tungsten trioxide hydrates

Hydrogen intercalation via spillover reaction in various tungsten trioxides leads to the formation of blue hydrogen bronzes. These reversible reactions induce changes in the W-O bond system while maintaining the W-O skeleton. The effect of the intercalation process on the host crystalline structure has been studied with respect to the ν(O-W-O) stretching vibration changes and lattice parameter variations by means of infrared and X-ray diffraction measurements. Among the main results, the intercalation process is shown to be strongly influenced by the structural type of the host compound as well as its amorphous versus crystalline nature. For instance, for the ReO₃ type oxides (monoclinic and cubic WO₃) and hexagonal WO₃, ν(O-W-O) shifts to higher frequency are assigned to a shortening effect of W-O bonds. A W-O bond system arrangement is also measured for the crystallized and amorphous hydrates WO₃ · H₂O, but no detectable changes could be found in the pyrochlore WO₃ and in the hydrate WO₃·1/3 H₂O. Received: 5 March 1997 / Accepted: 21 May 1997     

Crystal structure of [CuL](NO<Subscript>3</Subscript>)(ReO<Subscript>4</Subscript>) and [CuL](ReO<Subscript>4</Subscript>)<Subscript>2</Subscript> (L = 4,6,6-trimethyl-1,9-diamino-3,7-diazanon-3-en)

The crystal structures of [CuL](NO₃)(ReO₄) and [CuL](ReO₄)₂ (L is 4,6,6-trimethyl-1,9-diamino-3,7-diazanon-3-en) are studied. The square coordination of the copper atom in [CuL](NO₃)(ReO₄) is completed to a distorted octahedron by two oxygen atoms: Cu…O (ReO ₄ ^? ) 2.393 Å and Cu…O (NO ₃ ^? ) 2.685 Å, and that in [CuL](ReO₄)₂, by Cu…O(ReO ₄ ^? ) 2.468 Å and 2.697 Å. The products of thermolysis of the salts in a hydrogen atmosphere at 800°C are mixtures of nanocrystalline metal powders with coherent scattering regions of ～45 nm.     

Thermal expansion of phases formed in the system Nb2O5-MoO3

Studies on thermal expansion of phases formed in the system Nb₂O₅-MoO₃ (WO₃) have been carried out in the high-temperature X-ray diffraction attachment. In the case of Nb₁₄Mo₃O₄₄, Nb₁₂MoO₃₃ and Nb₁₂WO₃₃ the structure that consists of ReO₃ type blocks, the direction of minimal thermal expansion is consistent with direction in which the chains of corner-sharing polyhedra spread to infinity. On the contrary, for Nb₂Mo₃O₁₄, the structure of which resembles the structure of tetragonal tungsten bronzes, the maximal thermal expansion direction is consistent with above mentioned direction. This revised version was published online in July 2006 with corrections to the Cover Date.