Association d'ions uranyle et d'oxoanions molybdates ou tungstates (nouvelles architectures structurales et mobilité cationique)

LILLE1-BU (590092102) / SudocSudocFranceF

A new uranyl niobate sheet in the cesium uranyl niobate Cs₉[(UO₂)₈O₄(NbO₅)(Nb₂O₈)₂]

International audienceA new cesium uranyl niobate, Cs9[(UO2)8O4(NbO5)(Nb2O8)2] or Cs9U8Nb5O41 has been synthesized by high-temperature solid-state reaction, using a mixture of U3O8, Cs2CO3 and Nb2O5. Single crystals were obtained by incongruent melting of a starting mixture with metallic ratio=Cs/U/Nb=1/1/1. The crystal structure of the title compound was determined from single crystal X-ray diffraction data, and solved in the monoclinic system with the following crystallographic data: a=16.729(2) Å, b=14.933(2) Å, c=20.155(2) Å β=110.59(1)°, P21/c space group and Z=4. The crystal structure was refined to agreement factors R1=0.049 and wR2=0.089, calculated for 4660 unique observed reflections with I ≥ 2σ(I), collected on a BRUKER AXS diffractometer with MoKα radiation and a CCD detector.In this structure the UO7 uranyl pentagonal bipyramids are connected by sharing edges and corners to form a uranyl layer ∞2[U8O36] corresponding to a new anion-sheet topology, and creating triangular, rectangular and square vacant sites. The two last sites are occupied by Nb2O8 entities and NbO5 square pyramids, respectively, to form infinite uranyl niobate sheets ∞2[(UO2)8O4(NbO5)(Nb2O8)2]9- stacking along the [010] direction. The Nb2O8 entities result from two edge-shared NbO5 square pyramids. The Cs+ cations are localized between layers and ensured the cohesion of the structure.The cesium cation mobility between the uranyl niobate sheets was studied by electrical measurements. The conductivity obeys the Arrhenius law in all the studied temperature domains. The observed low conductivity values with high activation energy may be explained by the strong connection of the Cs+ cations to the infinite uranyl niobate layers and by the high density of these cations in the interlayer space without vacant site.Infrared spectroscopy investigated at room temperature in the frequency range 400–4000 cm−1, showed some characteristic bands of uranyl ion and niobium polyhedr

New open-framework in the uranyl vanadates <i>A</i>₃(UO₂)₇(VO₄)₅O (<i>A</i>=Li, Ag) with intergrowth structure between <i>A</i>(UO₂)₄(VO₄)₃ and <i>A</i>₂(UO₂)₃(VO₄)₂O

International audienceNew uranyl vanadates A3(UO2)7(VO4)5O (M=Li (1), Na (2), Ag (3)) have been synthesized by solid-state reaction and their structures determined from single-crystal X-ray diffraction data for 1 and 3. The tetragonal structure results of an alternation of two types of sheets denoted S for ∞2[UO2(VO4)2]4− and D for ∞2[(UO2)2(VO4)3]5− built from UO6 square bipyramids and connected through VO4 tetrahedra to ∞1[U(3)O5-U(4)O5]8− infinite chains of edge-shared U(3)O7 and U(4)O7 pentagonal bipyramids alternatively parallel to a- and b-axis to construct a three-dimensional uranyl vanadate arrangement. It is noticeable that similar ∞[UO5]4− chains are connected only by S-type sheets in A2(UO2)3(VO4)2O and by D-type sheets in A(UO2)4(VO4)3, thus A3(UO2)7(VO4)5O appears as an intergrowth structure between the two previously reported series. The mobility of the monovalent ion in the mutually perpendicular channels created in the three-dimensional arrangement is correlated to the occupation rate of the sites and by the geometry of the different sites occupied by either Na, Ag or Li. Crystallographic data: 293 K, Bruker X8-APEX2 X-ray diffractometer equipped with a 4 K CCD detector, MoKα, λ=0.71073 Å, tetragonal symmetry, space group P4¯m2, Z=1, full-matrix least-squares refinement on the basis of F2; 1, a=7.2794(9) Å, c=14.514(4) Å, R1=0.021 and wR2=0.048 for 62 parameters with 782 independent reflections with I≥2σ(I); 3, a=7.2373(3) Å, c=14.7973(15) Å, R1=0.041 and wR2=0.085 for 60 parameters with 1066 independent reflections with I≥2σ(I)

Synthesis, crystal structure, cationic mobility, thermal evolution and spectroscopic study of Cs₈(UO₂)₄(WO₄)₄(WO₅)₂ containing infinite uranyl tungstate chains

International audienceThe powder samples and single crystals of the cesium uranyl tungstate compound Cs8(UO2)4(WO4)4(WO5)2 have been synthesized by high temperature solid state reaction and its structure determined from single crystal X-ray diffraction data. The cesium mobility and vibration modes of uranyl and tungstate polyhedrons have been evidenced using pulverulent samples. It crystallizes in the monoclinic symmetry with space group P21/n and following cell parameters, a = 11.2460(3) Å, b = 13.8113(3) Å, c = 25.7287(3) Å, β = 90.00(3)°, V = 3996.23(17) Å3 and Z = 4 with ρmes = 6.079(2) g/cm3 and ρcal = 6.087(2) g/cm3. A full-matrix least-squares refinement on the basis of F2 yielded R1 = 0.0379 and wR2 = 0.0624 for 471 parameters with 14,278 independent reflections with I ≥ 2σ(I) collected on a Bruker X8 CCD 4K diffractometer with Mo Kα radiation.In this structure, the uranium atoms adopt UO7 pentagonal bipyramid coordination, while tungsten atoms are in two different environments, WO4 tetrahedral and WO5 square pyramidal coordinations. The association of uranyl ions (UO7) and tungstate oxoanions WO4 and WO5, gives infinite chains 1∞[(UO2)4(WO4)4(WO5)2]8- parallel to [100]. These types of chains has not been previously observed. The association of these chains in the (010) plane gives undulated pseudo-layers stacked along [010]. The cohesion between the chains is assured by alkaline Cs+ cations. The conductivity measurements, between 200 and 600 °C, show an Arrhenius law evolution. Infrared spectroscopy investigated at room temperature in the 400–4000 cm−1 wave number range, has allowed the identification of the various modes of vibrations of uranyl and tungstate polyhedrons

Structural Evolution in the Rare-Earth Uranyl Vanadates Ln 2 [(UO 2 ) 2 V 2 O 8 ] 3 · n H 2 O, Singularity of the Lanthanum Compound, and Single-Crystal to Single-Crystal Partial Dehydration

International audienceThe rare-earth uranyl vanadates Ln2[(UO2)2V2O8]3·nH2O are built from carnotite-type layers connected by Ln atoms through interactions involving vanadyl oxygens. For Ln = La the layers adopt another geometrical isomer and the connection involves vanadyl and uranyl oxygens. Upon dehydration the La compound undergoes a single-crystal to single-crystal transformation

Synthesis, crystal structure, infrared and electrical conductivity of the layered rubidium uranate Rb₄U₅O₁₇

International audienceSingle crystals of a new layered rubidium uranate compound Rb4U5O17 have been synthesized by high-temperature solid-state reaction. The crystal structure was determined from single crystal X-ray diffraction data. The title compound crystallizes in the orthorhombic symmetry with space group Pbcn, and the following crystallographic data: a = 18.6762(9) Å, b = 7.0490(4) Å, c = 14.1207(7) Å and Z = 4. A full-matrix least-squares refinement on the basis of F2 yielded R1 = 0.031 and wR2=0.060 for 120 parameters with 2723 independent reflections with I ≥ 2σ(I) collected on a BRUKER X8 Apex II 4K diffractometer with Mo Kα radiation and a CCD detector. The crystal structure contains infinite corrugated layers [(UO2)5O7]4− parallel to (0 0 1), formed by the association by edge- and corner-sharing of (UO2)O5 pentagonal bipyramids and distorted (UO2)O4 square bipyramids. The alkaline cation Rb+ are localized between layers and ensured the cohesion of the structure. Conductivity measurements, between 200 and 700 °C, show an Arrhenius law evolution, with a better electrical conductivity than the two other uranates Rb9U9O31 and Rb2U2O7, recently characterized. Infrared spectroscopy measurements at room temperature have allowed the identification of the various modes of vibrations of the uranyl ions

Three-dimensional framework of uranium-centered polyhedra with non-intersecting channels in the uranyl oxy-vanadates <i>A</i>₂(UO₂)₃(VO₄)₂O (<i>A</i>=Li, Na)

International audienceThe uranyl vanadates A2(UO2)3(VO4)2O (A=Li, Na) have been synthesized by solid-state reaction and the structure of the Li compound was solved from single-crystal X-ray diffraction. The crystal structure is built from 1∞[UO5]4- chains of edge-shared U(2)O7 pentagonal bipyramids alternatively parallel to a- and b-axis and further connected together to form a three-dimensional (3-D) arrangement. The perpendicular chains are hung on both sides of a sheet 2∞[(UO2(VO4)2]4- parallel to (001), formed by U(1)O6 square bipyramids connected by VO4 tetrahedra, and derived from the autunite-type sheet. The resulting 3-D framework creates non-intersecting channels running down the a- and b-axis formed by empty face-shared oxygen octahedra, the Li+ ions are displaced from the center of the channels and occupy the middle of one edge of the common face. The peculiar position of the Li+ ion together with the full occupancy explain the low conductivity of Li2(UO2)3(VO4)2O compared with that of Na(UO2)4(VO4)3 containing the same type of channels half occupied by Na+ ions in the octahedral sites.Crystallographic data for Li2(UO2)3(VO4)2O: tetragonal, space group I41/amd, a=7.3303(5) Å, c=24.653(3) Å V=1324.7(2) Å3, Z=4, ρmes=5.32(2) g/cm3, ρcal=5.36(3) g/cm3, full-matrix least-squares refinement basis on F2 yielded, R1=0.032, wR2=0.085 for 37 refined parameters with 364 independent reflections with I ≥ 2σ(I

Synthesis and Structural, Electrical, and Magnetic Properties of New Iron–Aluminum Alluaudite Phases β-Na 2 Ni 2 M(PO 4 ) 3 (M = Fe and Al)

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Na/Li substitution effect on the structural, electrical and magnetic properties of LiCr(MoO4)2 and β─Li0.87Na0.13Cr(MoO4)2

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