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Abstract: The reaction of triuranyl diphosphate tetrahydrate precursor (UO2)3(PO4)2(H2O)4 with a CsI flux at 750°C yields a yellow single crystals of new compound Cs3(UO2)2(PO4)O2. The crystal structure (monoclinic, space group C2/c, a=13.6261 (13)Å, b=8.1081(8)Å, c=12.3983(12)Å, β=114.61(12)°, V=1245.41(20)Å3 with Z=4) has been solved using direct methods and Fourier difference techniques. A full-matrix least-squares refinement on the basis of F 2 yielded R1=0.028 and wR2=0.071 for 79 parameters and 1352 independent reflections with I≥2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a charge-coupled device detector. The crystal structure is built by two independent uranium atoms in square bipyramidal coordination, connected by two opposite corners to form infinite chains and by one phosphorus atom in a tetrahedral environment PO4. The two last entities and PO4 are linked by sharing corners to form a three-dimensional structure presenting different types of channels occupied by Cs+ alkaline cations. Their mobility within the tunnels were studied between 280 and 800°C and compared with other tunneled uranyl minerals. The infrared spectrum shows a good agreement with the values inferred from the single crystal structure analysis of uranyl phosphate compound. [Copyright &y& Elsevier]

Abstract: Two alkali metal uranates Rb2U2O7 and Rb8U9O31 have been synthesized by solid state reaction at high temperature and their crystal structures determined from single crystal X-ray diffraction data, collected with a three circles Brucker SMART diffractometer equipped by Mo(Kα) radiation and a charge-coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least-square method on the basis of F 2 for all unique reflections, with for 53 parameters and 746 independent reflections with for Rb2U2O7, monoclinic symmetry, space group P21/c, , , , , , , and for 141 parameters and 2065 independent reflections with for Rb8U9O31, orthorhombic, space group Pbna, , , , , , . The Rb2U2O7 structure presents a strong analogy with that of K2U2O7 and can be described by layers of distorted UO2(O4) octahedra built from dimeric units of edge shared octahedra further linked together by opposite corners. In Rb8U9O31 puckered layers are formed by the association of two different uranium polyhedra, pentagonal bipyramids and distorted octahedra. The structure of Rb8U9O31 is built from a regular succession of infinite ribbons similar to those observed in diuranates M 2U2O7 (M d infinite three polyhedra wide ribbons , to create an original undulated sheets . For both compounds Rb+ ions occupy the interlayer space and exhibit comparable mobility with conductivity measurements indicating an Arrhenius-type behavior. [Copyright &y& Elsevier]

Two new lithium uranyl tangstates Li2(UO2)(WO4)2 and Li2(UO2)4(WO4)4O have been prepared by high-temperature solid state reactions of Li2CO3, U3O8 and WO3. For each compound, the crystal structure was determined by single crystal X-ray diffraction data, using a Brucker diffractometer, equipped with a SMART CCD detector and MoKα radiation. The crystal structures were solved at room temperature by direct methods followed by Fourier difference techniques, and refined by a least square procedure on the basis of F2 for all independent reflections, to R1=0.035 for 65 refined parameters and 807 reflections with I⩾2σ(I) for Li2(UO2)(WO4)2 and to R1=0.051 for 153 refined parameters and 1766 reflections with I⩾2σ(I) for Li2(UO2)4(WO4)4O.The crystal structure of Li2(UO2)(WO4)2 is formed by perovskite sheets of WO6 octahedra, one octahedron thickness, connected together by (UO5)∞ infinite chains, and creating tunnels parallel to the c-axis. The lithium atoms are localized in the tunnels. The structure can be deduced from that of UMO5 (M=Mo, V, Nb) compounds by the replacement of half U atoms by Li. The crystal structure of Li2(UO2)4(WO4)4O consists of UO7 pentagonal bipyramids, UO6 tetragonal bipyramids and WO6 distorted octahedra linked together to form a three-dimensional framework creating paralleled channels filled with lithium cations. The structure can also be described by the stacking of layers with the uranophane sheet anion topology similar to those obtained in UMO5 (M=Mo, V, Nb, Sb) compounds with an ordered population of pentagons by U and Li and of squares by U and W. The measured conductivities are comparable to those of the better Li+ ion conductor solid electrolytes such as Lisicon or Li-β-alumina.Crystallographic data: Li2(UO2)(WO4)2, orthorhombic symmetry, space group Pbcn and unit cell parameters a=7.9372(15) A˚, b=12.786(2) A˚, c=7.4249(14) A˚, ρcal=6.87(2) g/cm3, ρmes=6.89(1) g/cm3 and Z=4. Li2(UO2)4(WO4)4O, monoclinic symmetry, space group C2/c and unit cell parameters a=14.019(4) A˚, b=6.3116(17) A˚, c=22.296(6) A˚, β=98.86(3)°, ρcal=7.16(2) g/cm3, ρmes=7.25(3) g/cm3 and Z=4. [Copyright &y& Elsevier]

Two new potassium uranyl molybdates K2(UO2)2(MoO4)O2 and K8(UO2)8(MoO5)3O6 have been obtained by solid state chemistry . The crystal structures were determined by single crystal X-ray diffraction data, collected with MoKα radiation and a charge coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least square method on the basis of F2 for all unique reflections, with R1=0.046 for 136 parameters and 1412 reflections with I⩾2σ(I) for K2(UO2)2(MoO4)O2 and R1=0.055 for 257 parameters and 2585 reflections with I⩾2σ(I) for K8(UO2)8(MoO5)3O6. The first compound crystallizes in the monoclinic symmetry, space group P21/c with a=8.250(1) A˚, b=15.337(2) A˚, c=8.351(1) A˚, β=104.75(1)°, ρmes=5.22(2) g/cm3, ρcal=5.27(2) g/cm3 and Z=4. The second material adopts a tetragonal unit cell with a=b=23.488(3) A˚, c=6.7857(11) A˚, ρmes=5.44(3) g/cm3, ρcal=5.49(2) g/cm3, Z=4 and space group P4/n.In both structures, the uranium atoms adopt a UO7 pentagonal bipyramid environment, molybdenum atoms are in a MoO4 tetrahedral environment for K2(UO2)2(MoO4)O2 and MoO5 square pyramid coordination in K8(UO2)8(MoO5)3O6. These compounds are characterized by layered structures. The association of uranyl ions (UO7) and molybdate oxoanions MoO4 or MoO5, give infinite layers [(UO2)2(MoO4)O2]2− and [(UO2)8(MoO5)3O6]8− in K2(UO2)2(MoO4)O2 and K8(UO2)8(MoO5)3O6, respectively. Conductivity properties of alkali metal within the interlayer spaces have been measured and show an Arrhenius type evolution. [Copyright &y& Elsevier]

Abstract: A 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)Åβ=110.59(1)°, P21/c space group and Z=4. The crystal structure was refined to agreement factors R 1=0.049 and wR 2=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 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 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 400–4000cm−1, showed some characteristic bands of uranyl ion and niobium polyhedra. [Copyright &y& Elsevier]

Abstract: Attempts to prepare alkaline metal uranyl niobates of composition A 1− x UNbO6− x /2 by high-temperature solid-state reactions of A 2CO3, U3O8 and Nb2O5 led to pure compounds for x=0 and A=Li (1), Na (2), K (3), Cs (4) and for x=0.5 and A=Rb (5), Cs (6). Single crystals were grown for 1, 3, 4, 5, 6 and for the mixed Na0.92Cs0.08UNbO6 (7) compound. Crystallographic data: 1, monoclinic, P21/c, a=10.3091(11), b=6.4414(10), c=7.5602(5)Å, β=100.65(1), Z=4, R 1=0.054 (wR 2=0.107); 3, 5 and 7 orthorhombic, Pnma, Z=8, with a=10.307(2), 10.272(4) and 10.432(3)Å, b=7.588(1), 7.628(3) and 7.681(2)Å, c=13.403(2), 13.451(5) and 13.853(4)Å, R 1=0.023, 0.046 and 0.036 (wR 2=0.058, 0.0106 and 0.088) for 3, 5 and 7, respectively; 6, orthorhombic, Cmcm, Z=8, and a=13.952(3), b=10.607(2)Å, c=7.748(2)Å, R 1=0.044 (wR 2=0.117). The crystal structure of 1 is characterized by layers of uranophane sheet anion topology parallel to the (100) plane. These layers are formed by the association by edge-sharing of chains of edge-shared UO7 pentagonal bipyramids and chains of corner-shared NbO5 square pyramids alternating along the [010] direction. The Li+ ions are located between two consecutive layers and hold them together; the Li+ ions and two layers constitute a neutral “sandwich” {(UNbO6)−–(Li)2 2+–(UNbO6)−}. In this unusual structure, the neutral sandwiches are stacked one above another with no formal chemical bonds between the neutral sandwiches. The homeotypic compounds 3, 5, 6, 7 have open-framework structures built from the association by edge-sharing in two directions of parallel chains of edge-shared UO7 pentagonal bipyramids and ribbons of two edge-shared NbO6 octahedra further linked by corners. In 3, 5 and 7, the mono-dimensional large tunnels created in the [001] direction by this arrangement can be considered as the association by rectangular faces of two columns of triangular face-shared trigonal prisms of uranyl oxygens. In 3 and 7, all the trigonal prisms are occupied by the alkaline metal, in 5, they are half-occupied. In 6, the polyhedral arrangement is more symmetric and the tunnels created in the [010] direction are built of face-sharing cubes of uranyl oxygens totally occupied by the Cs atoms. This last compound well illustrates the structure-directing effect of the conterion. [Copyright &y& Elsevier]

Abstract: A new lead uranyl divanadate, PbUO2(V2O7), has been synthesized by high temperature solid-state reaction and its crystal structure was solved by direct methods using single-crystal X-ray diffraction data. It crystallizes in the monoclinic system with space group P21/n and following cell parameters: a=6.9212(9)Å, b=9.6523(13)Å, c=11.7881(16)Å, β=91.74(1)°, V=787.01(2)Å3, Z=4, ρmes=5.82(3), ρcal=5.83(1)g/cm3. A full-matrix least-squares refinement on the basis of yielded R1=0.029 and wR2=0.064 for 2136 independent reflections with collected with a Bruker AXS diffractometer (MoKα radiation). The crystal structure of PbUO2(V2O7) consists of a tri-dimensional framework resulting from the association of V2O7 divanadate units formed by two VO4 tetrahedra sharing corner and UO7 uranyl pentagonal bipyramids and creating one-dimensional elliptic channels occupied by the Pb2+ ions. In PbUO2(V2O7), infinite ribbons of four pentagons wide are formed which can be deduced from the sheets with Uranophane type anion-topology that occurs, for example, in the uranyl divanadate (UO2)2(V2O7), by replacement of half-U atoms of the edge-shared UO7 pentagonal bipyramids by Pb atoms. Infrared spectroscopy was investigated at room temperature in the frequency range 400–4000cm-1, showing some characteristic bands of uranyl ion and of VO4 tetrahedra. [Copyright &y& Elsevier]

In this paper, we report the direct chemical synthesis of silicon sheets in gram-scale quantities by chemical exfoliation of pre-processed calcium disilicide (CaSi2). We have used a combination of x-ray photoelectron spectroscopy, transmission electron microscopy and energy-dispersive x-ray spectroscopy to characterize the obtained silicon sheets. We found that the clean and crystalline silicon sheets show a two-dimensional hexagonal graphitic structure.

The title compound, Th(V(2)O(7))(H(2)O)(2), was synthesized by a hydro-thermal reaction. The crystal structure consists of ThO(7)(OH(2))(2) tricapped trigonal prisms that share edges, forming [ThO(5)(OH(2))(2)](n) chains along [010]. The edge-sharing ThO(7)(OH(2))(2) polyhedra share one edge and five vertices with the V(2)O(7) divanadate anions having a nearly ecliptic conformation parallel to [001]. This results in an open framework with the water mol-ecules located in channels. O-H⋯O hydrogen bonding between water molecules and framework O atoms is observed. Bond-valence-sum calculations are in good agreement with the chemical formula of the title compound.