European Journal of Solid State and Inorganic Chemistry最新文献

A new microporous iron (III) phosphate, [H₃N(CH₂)₄NH₃]₃[Fe₈(HPO₄)₁₂(PO₄)₂(H₂O)₆], has been prepared using low temperature hydrothermal methods and characterized by single-crystal X-ray diffraction, EDAX, infrared spectroscopy, thermogravimetric analysis and bond valence sums. The title compound crystallizes as light pink hexagonal-shaped tabs in the centrosymmetric hexagonal space group 3¯ (No.147) with a = b = 13.495(2) Å, c = 9.396(2) Å, V = 1481.9(4) ų and Z = 4 with R/R_w = 0.044/0.048. The compound exhibits a complicated three-dimensional microporous structure with quaternary ammonium ions acting as a template for the framework. It is similar to previously reported [HN(CH₂CH₂)₃NH]₃[Fe₈(HPO₄)₁₂(PO₄)₂(H₂O)₆].

Cs₂Au₂Se₃ was obtained as red platelike crystals by reacting a stoichiometric mixture of Cs₂Se, Au and Se at 670K. It crystallizes in space group C2/c, Z = 4 with a = 9.769(5) Å, b = 13.44(1) Å, c = 7.178(3) Å, β = 90.69(1)°. The crystal structure was determined from single crystal data and refined to a conventional R of 0.042 for 674 Fo's and 34 variables. The characteristic structural feature of this new selenoaurate is the formation of infinite helical anionic chains, _∞¹-[AuSeAuSe₂]²⁻ which run parallel to [001] and are separated by the alkali cations. The average Au-Se bond length is 2.402 Å, the bond length in the Se₂-unit is 2.436 Å. Au…Au contacts of 3.200 Å, are formed within the anionic chains. The cesium atoms are coordinated to seven Se in an irregular configuration.

New compounds, Sr₂Ga(HPO₄)(PO₄)F₂ and Sr₂Fe₂(HPO₄)(PO₄)₂F₂, have been prepared by hydrothermal synthesis (700°C, 180 MPa, 24 h) and characterized by single-crystal X-ray diffraction. Sr₂Ga(HPO₄)(PO₄)F₂ crystallizes in the monoclinic space group P2₁/n with a = 8.257(1) Å, b = 7.205(1) Å, c = 13.596(2) Å, β = 108.02(1)°, V = 769.2(2) ų and Z = 4 and Sr₂Fe₂(HPO₄)(PO₄)₂F₂ in the triclinic space group P2₁/n with a = 8.072(1) Å, b = 8.794(1) Å, c = 8.885(1) Å, α = 102.46(1)°, β = 115.95(1)°, γ = 89.95(1)°, V = 550.6(1) ų and Z = 2. Structures are both based on different sheets involving corner-linkage between octahedra and tetrahedra. The sheets are linked by Sr²⁺ cations. Structural relationships exist between the descloizite mineral and the title compounds.

Two synthesis methods for preparing Pr₄Ni₃O_10±δ are compared : a modified sol — gel route and a nitrate — citrate one. It is shown that the autoignition involved in the nitrate — citrate route provides good conditions ressembling the Rapid Thermal Annealing procedure. The oxygen stoichiometry of Pr₄Ni₃O_10±δ phases is measured according to the method of synthesis and thermal treatment. The compounds are metallic as seen by electrical resistivity measurements and thermoelectric power. We show that the adjustment of δ in this series is an important parameter of the transport properties that change from metallic for −0.1 <δ < 0.1 to insulating for Pr₄Ni₃O_8.25. An electronic anomaly is evidenced at 160 K, which intensity is more marked for the stoichiometric Pr₄Ni₃O₁₀. Our results are consistent with the existence of a charge density wave instability.

Bi₂Te₂O₇ is orthothobic, space group Pbcn. The lattice parameters derived from a Guinier powder pattern (Si standard) are: a= 22.794 ± 0.005, b= 5.526 ± 0.001, c= 22.065 ± 0.005Å, z= 16. The structure was solved by analysis of single crystal X-ray data and refined on the basis of neutron powder diffraction data. It is an anion-deficient 4: 1: 4 superstructure of fluorite in which the electron lone-pairs of tellurium are stereochemically active. The structural relationships with fluorite and with Bi₂TeO₅ (and other anion-deficient fluorite-related superstructures) have been shown and discussed.

When heated, yellow goethite dehydrates and transforms to red hematite. Both iron oxides were used by the Palaeolithic artists as pigments, one question being whether those people took advantage of the phase transformation. To answer this question, the dehydration of synthetic goethite was studied by XRD coupled to Rietveld refinement. It was shown that no hydroxylated hematite is formed during the early stages of dehydration, the presence of hydroxyl ions in materials treated at high temperatures being explained by trapped water inside porous microstructure (TEM). Archaeological samples from the south of France were investigated. Some of them exhibit distinctive features of heating which, supports the idea that Palaeolithic people used both natural and ex-goethite hematite.

The T₁ and T₂ crystalline varieties of the ternary carbide Al₂MgC₂ were synthesized by reacting graphite particles with Mg-Al melts at 930–1020 K. Below 1000 K, the T₁ variety was predominant but little amounts of T₂ were also present. At 1000 K and above, only the T₂ variety was obtained. Assuming a hexagonal close packing of the metal atoms, the crystal structure of T₂-Al₂MgC₂ was determined by Rietveld refinemenent from X-ray powder diffraction data.

Ba₄Cu₂Al₃F₂₁ is orthorhombic : a = 5.299(1) Å, b = 7.318(1) Å, c = 41.529(7) Å, Z = 4. The crystal structure was solved in the space group P2₁2₁2₁ (n^o19) from X-ray single crystal data using 5682 unique reflections (3698 with F_O/σ(F) > 4). It consists in a succession along c of 8 layers of 2 different types of sheets. The first layer, formulated [Cu₂AlF₁₁]⁴⁻ in which copper-fluorine octahedra are linked by edges to form infinite distorted chains connected together by aluminium-fluorine octahedra, is followed by two [Al₂F₁₀]⁴⁻ layers of infinite cischains of aluminium-fluorine octahedra linked by two vertices and another [Cu₂AlF₁₁]⁴⁻ layer. These 4 layers are doubled along c by one of the screw-axes 2₁. The barium ions, 12-coordinated, are inserted between the sheets.

Ba₂La₄Ti₅O₁₈ crystallizes in the trigonal system (space group R3) with the unit-cell parameters: a = 5.584 (1) Å; c = 41.176 (8) Å; Z= 3.

The structure has been solved from single crystal X-ray diffraction data to a final R₁ = 0.0285. Ba and La atoms are twelve-fold coordinated and Ti atoms six-fold coordinated. The structure can be described as consisting of identical perovskite-like blocks, five corner-sharing TiO₆ octahedra thick, separated by layers of vacant octahedra. The distortion of the cation and anion sublattices has been analysed and a Ba/La order has been evidenced.

Hydrothermal syntheses between 120 and 200 °C have been performed to determine the chemical variability of semiconducting microporous materials with cetineite structure. The syntheses were based on the general formula A₆[B₁₂O₁₈][CX₃]₂[D_x(H₂O,OH,O)_6−y], (0≤×≤2; 0≤y≤6), which was derived from X-ray crystal structure refinements. A = Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Tl⁺, NH₄⁺, Ca²⁺, Sr²⁺, and Ba²⁺ were introduced as hydroxides, in some cases as carbonates, B = C = As³⁺, Sb³⁺, and Bi³⁺, and X = S²⁻, Se²⁻, and Te²⁻ as elements. Only syntheses with B = C = Sb³⁺ and X = S²⁻ and Se²⁻ were successfull. Known cetineite-type phases now include the element combinations A/Sb³⁺/S²⁻ with A = Na⁺ and K⁺, and A/Sb³⁺/Se²⁻ with A = Na⁺, K⁺, Rb⁺, Sr²⁺, Ba²⁺, and probably Tl⁺. Variable amounts of Na⁺, Sb³⁺ and C⁴⁺ were found to occupy the D position of the cetineite-type structure. The chemical variability can be described by the coupled substitutions A⁺ + H₂OA²⁺ + OH⁻ mH₂OD^m+ + mOH, and nOH⁻Dⁿ⁺ + nO²⁻. The crystals obtained are orange to dark red, in agreement with their semiconducting properties.