K1.4P4W14O50: An odd-m member (m = 7) of the monophosphate tungsten bronze series KxP4O8(WO3)2m

The crystal structure of K_xP₄W₁₄O₅₀ (x = 1.4) has been solved by three-dimensional single crystal X-ray analysis. The refinement in the cell of symmetry $\text{A2}\text{m}$, with a = 6.660(2) Å, b = 5.3483(3) Å, c = 27.06(5) Å, and β = 97.20(2)°, Z = 1, has led to R = 0.036 and R_w = 0.039 for 2436 reflections with $\text{σ(I)}\text{I}\text{≤ 0.333}$. This structure belongs to the structural family K_xP₄O₈(WO₃)_2m, called monophosphate tungsten bronzes (MPTB), which is characterized by ReO₃-type slabs of various widths connected through PO₄ single tetrahedra. This bronze corresponds to the member m = 7 of the series and its framework is built up alternately of strands of three and four WO₆ octahedra. The structural relationships with the P₄O₈(WO₃)_2m series, called M′PTB, are described and the possibility of intergrowth between these two structures is discussed.     

Hexagonal tungsten bronze-type FeIII fluoride: (H2O)0.33FeF3; crystal structure,magnetic properties,dehydration to a new form of iron trifluoride

(H₂O)_0.33FeF₃, grown by hydrothermal synthesis, crystallizes in the orthorhombic system with cell dimensions a = 7.423(3) Å, b = 12.730(4) Å, c = 7.526(3)Å, and space group Cmcm, Z = 12. The structure, derived from single crystal X-ray diffraction data (605 independent reflections) is refined to R = 0.019 (R_ω = 0.021). The framework of the Fe^IIIF₆ octahedra is related to that of hexagonal tungsten bronze (HTB) Rb_0.29WO₃. At 122°C, zeolithic water is evolved from hexagonal tunnels without any noticeable change of the fluorine skeleton. The related anhydrous compound represents a new form of iron trifluoride which is denoted HTBFeF₃; at 525°C, it transforms into the cubic form of ReO₃-type. (H₂O)_0.33FeF₃ and HTBFeF₃ are antiferromagnetic, with Néel temperatures of T_N = 128°7 ± 0.5 K and T_N = 97 ± 2 K, respectively.     

Structural chemistry of Sr3Cr2WO9, Ca3Cr2WO9, and Ba3Cr2WO9

We have studied the preparation and crystallographic structure of three perovskite-type compounds: Sr₃Cr₂WO₉, cubic, the lattice parameter of which is a = 7.812Å; Ca₃Cr₂WO₉, tetragonal, the lattice parameters of which are a = 5.408 Å and c = 7.635Å; and Ba₃Cr₂WO₉, hexagonal, the lattice parameters of which are a = 5.691 Å and c = 13.957Å. We have compared these three structures and shown the relationship between the dimensions of the alkaline-earth metal and the existence of the different structures.     

Phase transformations in Li2WO4 at high pressure

The phase diagram of Li₂WO₄ has been determined at high pressure up to 160 kbars and a temperature of 800°C. Three new high-pressure phases have been found in the present study. Crystallographic data are given for Li₂WO₄ III and Li₂WO₄ IV by means of single crystal and powder X-ray analyses. Li₂WO₄ III is orthorhombic with the large unit cell containing 16 molecules and having the edges: a₀ = 10.12(4) Å, b₀ = 10.07(1) Å, c₀ = 11.68(6) Å. Li₂WO₄ IV has an orthorhombic unit cell with the parameters: a₀ = 4.96(7) Å, b₀ = 9.72(8) Å, c₀ = 5.93(8)Å and Z = 4. The total volume decrease is estimated to be 24.8% through the high pressure transformations in Li₂WO₄. No spinel-like structure could be found in the present study.     

A new tungsten trioxide hydrate, WO3 · 13H2O: Preparation,characterization, and crystallographic study

A new hydrate of tungsten trioxide, $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$ has been obtained by hydrothermal treatment at 120°C of an aqueous suspension of either tungstic acid gel or crystallized dihydrate. This hydrate has been characterized by different methods. A crystallographic study was carried out from X-ray powder diffraction. The hydrate crystallizes in the orthorhombic system: a = 7.359(3) Å, b = 12.513(6) Å, c = 7.704(5) Å, Z = 12. The existence of structural relationships between the hydrate, $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$, and the product of dehydration, hexagonal WO₃, has permitted us to propose a structural model in agreement with the experimental data. $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$ must be regarded as an interesting compound because its dehydration leads to a new anhydrous tungsten trioxide, hexagonal WO₃.     

L'oxyde double Fe2WO6. I. Structure cristalline et filiation structurale

The authors have found a new structural type, related to α-PbO₂, called tri-α-PbO₂. The oxide Fe₂WO₆ is the prototype. It crystallizes in the orthorhombic system with the following cell parameters: a = 4.576 Å, b = 16.766 Å, and c = 4.967Å. The space group is Pbcn. The structure has been determined by X-ray single-crystal methods and refined by least-squares procedures (R = 0.065).The structure consists of zig-zag chains parallel to the c-axis. Each such chain is built up by MO₆ (M = Fe or W) octahedra-sharing edges. The chains are linked together by corner sharing. There are two types of chains: one containing only iron atoms, the other being an ordered 1-1 arrangement of iron and tungsten atoms.     

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.     

Nouveaux échangeurs cationiques avec une structure à tunnels entrecroisés: les niobates et tantalates A10M29.2O78 et A10M29.2O78·1OH2O

New oxides with formula A₁₀M_29.2O₇₈ (A = Rb, Cs; M = Ta, Nb) have been synthesized. They crystallize in the hexagonal system with cell parameters: a = 7.5 Å, c = 36.4Å. Structural study on powders shows that the framework can be described by hexagonal tungsten bronze and A₂M₇O₁₈ phases intergrowth. Cationic ion exchange properties of these compounds are shown in aqueous solution. Thus, new hydrated oxides have been prepared.     

The stability of the perovskite-type zirconium tungsten bronze ZrxWO3

It has been found that a perovskite-related zirconium tungsten bronze Zr_xWO₃ (with 0 < x ? 0.08) forms readily at temperatures between 973 and 1573° K. Prolonged heating causes the bronze to decompose to other oxide products at all the temperatures investigated. These results are summarized in phase diagrams. Possible reasons for the decomposition of the bronze are discussed.     

Thermochemistry of ammonium tungsten bronze, (NH4)0.25WO3

The enthalpy of formation of ammonium tungsten bronze, (NH₄)_0.25WO₃(s), at 298.15 K has been determined by solution calorimetry. The value obtained for formation from NH₃(g), H₂(g) and WO₃(s) was ?25.7 ± 0.8 k¹ mol^?1. The stability of the bronze towards decomposition and oxidation is discussed.     

Structure and Thermal Stability of La0.10WO3+y; A Hexagonal Tungsten Bronze Related Phase Formed at High Pressure

The structure and thermal stability of a hexagonal tungsten bronze (HTB) related compound, La_xWO_3+y with x≈0.10 and y≈0.15, has been studied by X-ray diffraction, thermal analysis, and electron microscopy. The structure was refined by the Rietveld method from X-ray powder diffractometer data of a La_0.10WO₃ sample prepared at T=1250°C and P=25 kbar, which consisted of two tungsten bronze related phases in 1:1 proportion. The unit cell dimensions are as follows: La_0.108WO_3+y (y≈0.16), a=7.40890(5), and c=3.79329(4) Å (HTB-related structure); La_0.091WO₃, a=3.82458(6) Å (cubic perovskite tungsten bronze (PTB) structure). The lanthanum atoms in La_0.108WO_3+y are located on the hexagonal axis and statistically distributed on two sites close to the tungsten atom plane. Thermal stability studies of the La_0.10WO₃ sample in an argon atmosphere under ambient pressure conditions revealed that the HTB-related compound is metastable, decomposing to the stable PTB-type structure and WO₃. It was also found from the TG experiments in argon and oxygen that additional oxygen atoms (y) are present in the structure, thus forming a lanthanum tungsten oxide of the above composition. The electron diffraction and microanalysis studies confirmed that crystals of the HTB- and PTB-type structures were formed, with a lanthanum content of x≈0.1.     

Phase equilibria,thermal analysis,and reactivity of tin tungsten bronzes and related phases

Crystal chemistry and phase relations of the bronze forming region of the SnWO system have been investigated. Above 780°C the tin bronzes Sn_xWO₃ are shown to be thermally unstable and an equilibrium diagram is established at 700°C which shows that the composition limits of the tetragonal phase are 0.21 ? x ? 0.29. Below x = 0.21 a series of single and two phase regions containing orthorhombic bronzes exists for which the composition limits have been established. In the range 0.29 ? x ? 0.76 the system comprises the tetragonal bronze, Sn₂W₃O₈ and SnWO₄, while above 0.76 there is no bronze, only Sn₂W₃O₈, SnWO₄ and free Sn. The phase Sn₂W₃O₈ has been isolated and shown to have a hexagonal unit cell, a = 7.696 Å, c = 18.654 Å. The evidence of differential thermal analysis and X-ray studies suggests that this hexagonal phase arises from the decomposition of the tungsten bronze phase and is itself decomposed to cubic SnWO₄ above 700°C. Small thermal effects observed in the DTA scans of tin-containing tetragonal bronzes are interpreted in terms of an order-disorder phenomenon arising from asymmetric tunnel occupancy by Sn²⁺ ions caused by the presence of the lone pair of electrons. Hydrogen reduction of Sn_xWO₃ has been shown to result in complete removal of oxygen, producing Sn + α-W in the range 600–850°C. Some activation energy data are given for the reduction process.     

Une nouvelle famille structurale: Les titanoniobates et titanotantalates A2Nb6TiO18 et A2Ta6TiO18

New ternary oxides A₂M₆TiO₁₈ (A = Rb, Cs; M = Ta, Nb) have been synthesized by reaction between M₂O₅ and TiO₂ oxides and A₂CO₃ carbonates. They crystallize in the hexagonal system in a cell of dimensions a and c near 7.5 and 8.2 Å, respectively. There is one formula unit in the cell, in good agreement with the observed densities 4.38 and 4.78 for A₂Nb₆TiO₁₈, 6.62 and 6.93 for A₂Ta₆TiO₁₈. The structure has been determined from powder diffraction patterns, from the 64 first reflections (i.e., 190 hkl), and refined to R₁ values ranging from 0.06 and 0.08. It can be described from a basic unit of composition (M₆O₂₄) formed of 3 × 2 octahedra of oxygen atoms, sharing edges and corners, with MO distances ranging from 1.8 and 2.2 Å. Relations with the hexagonal tungsten bronze and pyrochlore-type structures are discussed.     

X-ray crystal structure of azoxybenzene oxotetrachlorotungsten(VI), (C6H5N)2OWVIOCl4

The crystal and molecular structure of azoxybenzene oxotetrachlorotungsten(VI) has been determined from X-ray diffractometer data. The structure was solved by Patterson and Fourier methods and refined by least-squares techniques to R = 0.058 for 1869 independent reflections.The crystals are monoclinic, space group P2₁/c, with Z = 4, in a unit cell of dimensions: a = 8.314(3), b = 15.100(5), c = 12.901(7) Å, α = 95.31(5)°. The azoxybenzene residue, the structure of which resembles that of free trans azobenzene, is linked to the tungsten atom through its oxygen atom. The coordination at the metal (two oxygen atoms and four chlorine atoms) corresponds to a distorted octahedron.This distortion is very similar to those observed in similar tungsten compounds. There is a intramolecular C?O distance of 2.77 Å between two atoms four bonds apart, of the azoxybenzene residue.     

Thermochemistry of hydrogen tungsten bronze phases HxWO3

The enthalpies of formation of two hydrogen tungsten bronze phases H_0.35WO₃ and H_0.18WO₃ have been determined by solution calorimetry. Values obtained for formation from H₂(g) and WO₃(s) at 298.15 K were H_0.35WO₃(s), ?9.6 ± 0.8 kJ mole^?1 and H_0.18WO₃(s), ?4.8 ± 0.6 kJ mole^?1. The stabilities of these phases towards decomposition, disproportionation and oxidation are discussed.     

Crystal chemistry of lithium in octahedrally coordinated structures. I. Synthesis of Ba8(Me6Li2)O24 (Me = Nb or Ta) and Ba10(W6Li4)O30. II. The tetragonal bronze phase in the system BaONb2O5Li2O

The preparation, single crystal growth, and crystallographic properties of a close-packed, eight-layer, hexagonal (a = 5.803 Å, c = 19.076 Å) modification having the stoichiometry Ba₈Nb₆Li₂O₂₄ and of a close-packed, ten-layer, hexagonal (a = 5.760 Å, c = 23.742 Å) phase with Ba₁₀W₆Li₄O₃₀ stoichiometry are discussed. The isostructural Ba₈Ta₆Li₄O₂₄ form of the eight-layer phase was also prepared (a = 5.802 Å, c = 19.085 Å). Proposed crystal structures involve the pairing of lithium and metal (Nb, Ta, or W) octahedra to yield face-sharing units. The relationship of this phenomenon to other known close-packed phases containing Li is demonstrated. An investigation of the Ba₈Nb₆Li₂O₂₄Ba₁₀W₆Li₄O₃₀ system is reported.A tetragonal bronze phase homogeneity region was delimited at 1200°C in the BaONb₂O₅Li₂O system. A new orthorhombic phase (a = 10.197 Å, b = 14.882 Å, c = 7.942 Å) was prepared with the stoichiometry Ba₄Li₂Nb₁₀O₃₀.     

Crystal structure studies of tetragonal sodium tungsten bronzes,NaxWO3. I. Na0.33WO3 and Na0.48WO3

The crystal structures of two sodium tungsten bronzes, Na_0.33WO₃ and Na_0.48WO₃, have been determined by three-dimensional single-crystal X-ray analysis. They were found to crystallize in the tetragonal space groups $P\overline{4}{2}_{1}m(a=12.097,c=3.754\AA ,Z=10)$ and P4/mbm (a = 12.150,c = 3.769Å, Z = 10), respectively. The structures were solved by standard Patterson and Fourier techniques and refined by full-matrix least-squares to final conventional discrepancy indices of 8.9% for Na_0.33WO₃ and 8.4% for Na_0.48WO₃. In general, the oxygen atoms were found to be either twofold or fourfold disordered, suggesting that the WO₆ octahedra do not have axes exactly aligned parallel to the crystallographicc-axis. The structure found can be viewed as a composite of two kinds of domain structures. These domain structures would require a doubling of thec-axis along with selection of newa- andb-axes along the [1 1 0] and [$[\overline{1}10]$] directions. There exist pentagonal and tetragonal sites in both these sodium tungsten bronzes for sodium atoms occupancy. In Na _xWO₃, x = 0.48, all the pentagonal sites are filled and 40% of the smaller tetragonal sites are also occupied. As x decreases to 0.33 though, only the pentagonal sites are occupied. A relation between the x value and the Na _xWO₃ crystal structures is postulated, extrapolating from the results found in these structure determinations.     

铂-氢钨青铜电极的制备及对氢氧化的电催化

采用电化学还原法在表面改性的碳布上,通过改变催化剂沉积顺序及氢钨青铜沉积时间制备铂-氢钨青铜复合催化剂,所得电极作为质子交换膜燃料电池(PEMFC)阳极。利用X射线衍射(XRD)、热重分析(TG)、扫描电子显微镜(SEM)、循环伏安(CV)及单电池极化性能测试研究了催化剂的组成、沉积量、分散性及其对氢氧化的电催化活性。实验结果表明,氢钨青铜沉积时间及催化剂沉积顺序对电极催化性能有显著影响,当氢钨青铜沉积时间为10 min,先沉积氢钨青铜、后沉积铂所得Pt/HxWO3电极对氢氧化具有最佳的催化活性。适量的氢钨青铜才能与铂形成较好的协同催化效应。     

The formation of a series of barium tungsten bronzes

The phases occurring in samples of gross composition Ba_xWO₃ (0.01 < x < 0.33) heated at temperatures between 1073 and 1373°K have been determined using X-ray diffraction and electron microscopy. At all temperatures a tetragonal tungsten bronze phase with a narrow homogeneity range of x = 0.20?0.21 was observed to form. In addition, at temperatures up to 1273°K, a series of orthorhombic intergrowth bronzes forms within a restricted composition range around x = 0.04. The latter phases are unstable at higher temperatures and were not found in preparations made at 1323°K. Similarly a new type of bronze phase forms at x = 0.14?0.16 at temperatures up to 1323°K, but not at 1373°K. The structure of this phase is unknown. Aspects of the crystal chemistry of the barium bronzes and the relationships to other bronze phases are discussed.     

The crystal and molecular structure of Rh2(CH3CO2)4[HCON(CH3)]2—effect of ligands on metalmetal bonding

The structure of Rh₂(CH₃CO₂)₄(DMF)₂ {DMF = HCON(CH₃)₂} has been determined by single crystal X-ray methods. The compound crystallizes with eight formula units in a cell of dimensions: a = 29.438(7) Å, b = 7.978(2) Å, c = 20.279(5) Å, β = 113.20(4)°, V = 4377.5 ų, space group C2/c. The structure has been refined by full-matrix least-squares method to a final R = 0.030 for the 4156 observed data. Two Rh(II) atoms are linked by four acetate groups forming a dimeric unit, where the RhRh distance is 2.383(1) Å. The coordination sphere about each Rh atom is completed by a DMF molecule; the average RhO(DMF) distance is 2.296(3) Å.