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.     

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.     

The thallium tungstate Tl2W4O13: A tunnel structure related to the hexagonal tungsten bronze

The crystal structure of thallium tungstate Tl₂W₄O₁₃ (a = 7.327Å; b = 37.864 Å; c = 3.840 Å; space group Pmab) has been resolved by three-dimensional single-crystal X-ray analysis. The average structure was resolved by standard Patterson and Fourier techniques and refined by full-matrix least squares to final agreement indices R = 0.087 and R_w = 0.100. Superstructure reflections referred to a supercell (a, b, 2c; space group Pcab) led to a framework model which is described. The structure consists of corner-sharing chains of WO₆ octahedra parallel to a and c axes. Hexagonal and pentagonal tunnels, bound by these chains, are filled by thallium atoms. The atomic arrangement is closely related to the hexagonal bronze structure. The tungstate Tl₂W₄O₁₃ can thus be considered as a member of a series of phases (TlB₃X₉)_n · Tl₆B₁₀X₃₄ (X = O, F) involving hexagonal tungsten bronze ribbons.     

Formation of Co octahedra and tetrahedra in YBaCo4O8.1

High-resolution neutron and synchrotron X-ray powder diffraction experiments were performed, at 300 and 10 K, for the determination of the structure of YBaCo₄O_8.1, which was prepared by controlled oxidation of the Kagomé lattice compound YBaCo₄O₇. Our diffraction data demonstrate that YBaCo₄O_8.1 crystallizes in the orthorhombic Pbc2₁ space group with the formation of a large superstructure (a=12.790 Å, b=10.845 Å, c=10.149 Å), with respect to the parent trigonal YBaCo₄O₇ material. The Co ions occupy both corner-sharing tetrahedral and edge-sharing octahedral sites, in contrast to YBaCo₄O₇, which has only corner-sharing tetrahedra. The octahedral sites form by the addition of two extra oxygen atoms and the drastic displacements of some of the original O atoms relative to the parent. The edge-sharing octahedra form isolated zigzag chains parallel to the c-axis linked to one another via tetrahedra. While found in a few phosphates, silicates and germanates, this motif appears unique to YBaCo₄O_8.1 among mixed-metal oxides. No structural phase transition or long range antiferromagnetic ordering are observed at 10 K.     

A new lead Mo(IV) phosphate with a tunnel structure: Pb2Mo2O(PO4)2P2O7

A molybdenum (IV) phosphate containing lead, Pb₂Mo₂(PO₄)2P₂O₇, has been synthesized for the first time. It crystallizes in the space group C2/c with a=14.098(1) Å, b=14.187(2) Å, c=6.5592(4) Å and β=102.08(1)°. Its original tunnel structure, built up of Mo₂O₁₁ bioctahedra, P₂O₇ and PO₄ phosphate groups can be described from the assemblage of [Mo₄P₄O₂₄]_∞ ribbons interconnected through monophosphate groups. The stereoactivity of the 6s² lone pair of Pb²⁺, which is surrounded by nine oxygen atoms, is discussed.     

A novel cesium hydroxygallophosphate with a layered structure built up of rutile ribbons: CsGa2(OH)2[(PO4)H(PO4)]

A new cesium gallophosphate, CsGa₂(OH)₂[(PO₄)H(PO₄)], with an original layer structure has been synthesized by hydrothermal route and characterized by single-crystal X-ray diffraction (R=0.0344, R_w=0.0319). Its structure crystallizes in the monoclinic space group P2₁/a with cell parameters , , , β=93.36(4)° and Z=2. It consists of [Ga(OH)PO₄]_∞ layers built up of rutile ribbons interconnected through PO₄ tetrahedra. The structure of CsGa₂(OH)₂[(PO₄)H(PO₄)] is closely related to those of (NH₄)Ga(OH)PO₄ and (en)Ga₂(OH)₂(PO₄)₂ (en=ethylenediamine [H₃N(CH₂)₂NH₃]²⁺). The three structures differ mainly from each other by the relative positions and the spacing of the successive layers, which are governed by different hydrogen bonding modes between [Ga(OH)PO₄]_∞ layers and the interleaved species. The title compound presents strong symmetric hydrogen bonds O---H---O which bridge two PO₄ tetrahedra of two successive layers. As a consequence, the distance between the layers is significantly shorter than in the two other amine compounds.     

Phase relations in the K2W2O7-K2WO4-KPO3-Bi2O3 system and structure of K6.5Bi2.5W4P6O34

The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory.     

Mixed valence tungsten oxides with a tunnel structure,P4W4nO12n+8: A nonintegral member P4W10O38 (n = 2.5)

The mixed-valence oxide P₄W₁₀O₃₈, which can be considered as the nonintegral member n = 2.5 of the series P₄W_4nO_12n+8, crystallizes in the monoclinic system with unit-cell dimensions a = 6.5656(25), b = 5.2850(15), c = 20.573(15) Å, β = 96.18(4)°, and space group P2₁. The crystal structure was solved by conventional Patterson and Fourier techniques using 2339 counter-measured reflections that obeyed the condition I > 3σ(I) and refined to an R factor of 0.074 (R_w = 0.077). Basically, the framework of the structure built up from ReO₃-type slabs connected through PO₄ tetrahedra looks like that of P₄W₈O₃₂ previously described. Unlike P₄W₈O₃₂, two successive ReO₃-type slabs have a different width corresponding to two and three WO₆ octahedra so that the structure can be considered as an intergrowth of the integral members n = 2 and n = 3 of the series P₄W_4nO_12n+8.     

n-Hexane cracking over heteropoly acids, 2. Catalytic activity and thermal stability of H4SiW12O40, H6P2W18O62 and H6P2W21O71(H2O)3

The catalytic activity of three heteropoly acids has been studied in n-hexane cracking. Only H₄SiW₁₂O₄₀ does not decompose into oxides at the reaction temperature. Its acidic form is active in cracking but its dehydration leads to an inactive compound.

---

-. H₄SiW₁₂O₄₀ . , .

     

Thermochemistry of the mixed calcium phosphate Ca8P2O7(PO4)4

The calcium mixed phosphate Ca₈P₂O₇(PO₄)₄ has been synthesized by thermal decomposition of octacalcium phosphate previously prepared by precipitation in ammoniacal phosphate solution. The enthalpy of formation at 298.15 K referenced to β-tricalcium phosphate and calcium pyrophosphate is determined. β-Tricalcium phosphate was prepared by two methods: precipitation in ammoniacal aqueous medium and high temperature solid-state reaction. Calcium pyrophosphate was prepared by high temperature solid-state reaction. All the compounds are characterized by chemical analysis, X-rays diffraction and IR spectroscopy. The enthalpy of formation +10.83 ± 0.63 kJ mol⁻¹ is obtained by solution calorimetry at 298.15 K in nitric acid.     

A niobium phosphate with a tunnel structure: Ca0.5+xCs2Nb6P3O24

A new niobium phosphate, Ca_0.5+xCs₂Nb₆P₃O₂₄ has been isolated. It crystallizes in the R32 space group, with the following parameters of the hexagonal cell: a_H = 13.379 Å, c_H = 10.371 Å. The determination of the structure by a single crystal X-ray diffraction study shows that its host lattice [Nb₆P₃O₂₄]_∞ can be described as the assemblage of mixed chains [Nb₂PO₁₃]_∞ running along c_H in which one PO₄ tetrahedron alternates with two NbO₆ octahedra. This framework delimits huge tunnels where the cesium cations are located and cages formed by [Nb₆P₃O₃₆] units occupied by calcium. The most striking feature of this framework deals with its similarity with the hexagonal tungsten bronze of Magnéli (HTB). The latter is discussed here by considering the stacking along c of [Nb₂PO₈]_∞ layers whose geometry is closely related to that of the HTBs. The possibility of nonstoichiometry leading to a mixed valency of niobium is considered.     

Crystal structure of Fe2P2O7

Fe₂P₂O₇ crystallizes in the $\text{C}\text{1}$ space group with lattice parameters a = 6.649(2)Å, b = 8.484(2)Å, c = 4.488(1)Å, α = 90.04°, β = 103.89(3)°, γ = 92.82(3)°, and ?_cal = 3.86 g/cc. It is essentially isostructural with β-Zn₂P₂O₇. As in the Zn compound, the bridging oxygen atom in the P₂O₇ group shows a high anisotropic thermal motion. It appears that the P-O-P bond angle is linear as a result of extensive π bonding with the p orbitals on the bridging oxygen atom. The high thermal motion is vibration of the atom into cavities in the structure.     

Ta4P4S29: A new tunnel structure with inserted polymeric sulfur

Ta₄P₄S₂₉ was prepared from the elements heated together in stoichiometric proportions in an evacuated Pyrex tube for 10 days at 500°C. The crystal symmetry is tetragonal, space group P4₃2₁2, with the cell parameters: a = b = 15.5711(7) Å, c = 13.6516(8) Å, V = 3309.9(5) ų, and Z = 4. The structure calculations were conducted from 2335 reflections and 146 variables, leading to R = 0.033. The structure basic framework, corresponding to the chemical composition [TaPS₆], is made of biprismatic bicapped [Ta₂S₁₂] units (average d_TaS = 2.539 Å), including sulfur pairs (average d_SS = 2.039 Å), bonded to each other through [PS₄] tetrahedral groups (average d_PS = 2.044 Å) sharing sulfurs. This framework leaves large tunnels running along the c axis of the cell and in which (S₁₀)_∞ sulfur chains are found to be inserted (average d_SS = 2.052 Å and SSS = 105.75°). Diamagnetic and semiconducting Ta₄P₄S₂₉ can be formulated: Ta^V₄P^V₄(S^?II)₁₆(S^?II₂)₄(S⁰₅).     

A sodium gallophosphate with an original tunnel structure: NaGa2(OH)(PO4)2

A new sodium gallophosphate, NaGa₂(OH)(PO₄)₂, has been obtained by hydrothermal synthesis under autogeneous pressure at 473 K. It crystallizes in the P2₁/n space group with the cell parameters a=8.9675(8) Å, b=8.9732(5) Å, c=9.2855(7) Å, β=114.812(6)°, V=678.2 Å³ (Z=4). In its original three-dimensional framework, monophosphate groups share their apices with [Ga₄O₁₆(OH)₂] tetrameric units, which are built from two GaO₅(OH) octahedra and two GaO₄(OH) trigonal bipyramids. The sodium cations are located in tunnels running along a, whereas the tunnels running along b are empty.     

The phase equilibria study in the system Na4P2O7Mg2P2O7

The phase equilibria in the system Na₄P₂O₇Mg₂P₂O₇ were studied by means of DTA, hot stage microscopy and X-ray diffraction analysis. There is one intermediate compound in the system which melts congruently at 832°C of chemical composition Na₇Mg_4.5(P₂O₇)₄. It crystallizes in the triclinic system with unit cell constants: a = 10.882(1), b = 9.734(1), c = 6.372(1) Å; α = 112.49(1), β = 99.63(1), γ = 107.40(1)°.     

Single-crystal growth and structure determination of Ag16I12P2O7

Single crystals of the fast-ion conductor Ag₁₆I₁₂P₂O₇ were prepared and their structure ($\text{P6}\text{mcc}\text{, a = 12.054, c = 7.504}$ Å) was determined by X-ray diffraction (r = 0.08). The I atoms form a close-packed array leaving channels occupied by P₂O^4?₇ ions running along the c axis. The Ag atoms are disordered over four different types of site with occupation numbers ranging from 0.12 to 0.52. Each Ag⁺ ion coordination polyhedron shares several faces with adjacent polyhedra providing ready paths for Ag⁺ ion conduction.     

H_6P_2W_(18)O_(62)/SiO_2:用模板剂制备及光催化降解二甲酚橙的性能

分别采用非离子表面活性剂(C_3H_6OC_2H_4O)_x(P123),阴离子表面活性剂C_(12)H_(25)NaO_4S(SDS)和C_(18)H_(29)NaO_3S(SDBS)作为模板剂,通过溶胶-凝胶再结合程序升温溶剂热一步法制备了一系列固载杂多酸光催化材料-H_6P_2W_(18)O_(62)/SiO_2。通过傅立叶-红外光谱(FTIR)、X-射线衍射(XRD)、电感耦合等离子体原子发射光谱(ICP-AES)、氮气吸附-脱附测定、透射电子显微镜(TEM)以及扫描电子显微镜配合X-射线能量色散谱仪(SEM-EDS)等测试手段对不同模板剂作用下合成产物进行了对比表征分析。结果表明,不同模板剂作用下的系列固载杂多酸-H_6P_2W_(18)O_(62)/SiO_2产物中母体多酸的Dawson基本结构均未发生明显变化,但固载后比表面积显著不同,其中,经模板剂P123和SDS作用合成的H_6P_2W_(18)O_(62)/SiO_2(P123)和H_6P_2W_(18)O_(62)/SiO_2(SDS)的比表面积高达916和634m~2·g~(-1),且显示为有序介孔材料。以二甲酚橙为模型分子,在微波场作用下,该系列固载多酸光催化性能研究结果显示,它们的光催化活性可被微波显著增强,其中,采用P123作用合成产物的光催化活性最高,60 min内对二甲酚橙的降解率达99%以上。     

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.     

Topotactic insertion of lithium in the layered structure Li4VO(PO4)2: The tunnel structure Li5VO(PO4)2

A new V(III) lithium phosphate Li₅VO(PO₄)₂ has been synthesized by electrochemical insertion of lithium into Li₄VO(PO₄)₂. This phase, which crystallizes in the space group I4/mcm, exhibits a tunnel structure closely related to the layered structure of Li₄VO(PO₄)₂ and to the tunnel structure of VO(H₂PO₄)₂. The topotactic reactions that take place during lithium exchange and intercalation, starting from VO(H₂PO₄)₂ and going to the final phase Li₅VO(PO₄)₂ are explained on the basis of the flexible coordinations of V⁴⁺ and V³⁺ species. The electrochemical and magnetic properties of this new phase are also presented and explained on the basis of the structure dimensionality.     

A novel germanate, Cu2Fe2Ge4O13, with a four tetrahedra oligomer

The structure of Cu₂Fe₂Ge₄O₁₃, previously thought to be CuFeGe₂O₆, has been determined from single-crystal X-ray diffraction data to be monoclinic, P2₁/m, a=12.1050(6), b=8.5073(4), c=4.8736(2) Å, β=96.145(1)°, Z=2, with R1=0.0231 and wR2=0.0605. The unique structure has an oligomer of four germanate tetrahedra, cross-linked laterally by square-planar copper ions, joined end-to-end by a zigzag chain of edge-sharing iron oxide octahedra. Running along the a-direction the metal oxide chain consists of alternating Cu-Cu and Fe-Fe dimers. A hypothetical series of homologous structures (Cu_n−2Fe₂Ge_nO_3n+1 with n=3,4,…,∞) with different length germanate oligomers is proposed, where as n increases, the infinite chain of the CuGeO₃ is approached. In this context, Cu₂Fe₂Ge₄O₁₃ is viewed as being built from blocks of CuGeO₃ and the Fe oxide chains. This material has significance to the study of low-dimensional mixed-spin systems.