S. Yagoubi

Université Paris-Sud 11, Orsay, Île-de-France, France

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Publications (19)21.02 Total impact

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    ABSTRACT: The high-pressure structural behavior of californium has been studied experimentally and theoretically up to 100 GPa. A valence change from divalent to trivalent forms was observed under modest pressure revealing californium to be the only actinide to exhibit more than one metallic valence at near to ambient conditions as is the case for cerium in the lanthanide series. Three metallic valencies and four different crystallographic phases were observed in californium as a function of pressure. High-pressure techniques, synchrotron radiation, and ab initio electronic structure calculations of total energies were used to investigate the material and to determine the role which californium's 5f electrons play in influencing these transitions. The crystallographic structures observed are similar to those found in the preceding actinide elements, curium and americium, with the initially localized 5f states becoming completely delocalized under the influence of high pressure.
    Physical Review B 06/2013; 87(21). · 3.66 Impact Factor
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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 F2 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 [UO5]∞1 and by one phosphorus atom in a tetrahedral environment PO4. The two last entities [UO5]∞1 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.
    Journal of Solid State Chemistry 04/2013; 200:13–21. · 2.04 Impact Factor
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    ABSTRACT: The actinide silicides ThSi, USi and USi2 have been studied under high pressure using both theory and experiment. High pressure synchrotron X-ray diffraction experiments were performed on polycrystalline samples in diamond anvil cells at room temperature and for pressures up to 54, 52 and 26 GPa, for ThSi, USi and USi2, respectively. At ambient conditions, the uranium silicides crystallize in tetragonal structures (space groups: I4/mmm for USi and I41/amd for USi2), while ThSi adopts an orthorhombic structure (space group: Pbnm) (including an anharmonic analysis of the silicon). These structures are found to be stable with no structural transitions observed up to the highest pressures achieved. The zero-pressure bulk modulus B0 and its pressure derivative B0′ at ambient pressure are obtained from the measured P–V relations. The experiments are accompanied by first principles calculations using the full-potential linear muffin-tin orbital method within the generalized gradient approximation for exchange–correlation effects. Experimental results are well reproduced by the calculated equation of state and ground state properties.
    Journal of Alloys and Compounds 01/2013; 546:63. · 2.73 Impact Factor
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    ABSTRACT: 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.
    Acta Crystallographica Section E Structure Reports Online 10/2011; 67(Pt 10):i60. · 0.35 Impact Factor
  • S. Yagoubi, S. Obbade, S. Saad, F. Abraham
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    ABSTRACT: Single crystals of the title compound are obtained from a melt of U3O8, MoO3, and excess Cs2CO3 (Pt crucible, 950 °C, 12 h, cooling rate 5 °C/h).
    ChemInform 08/2011; 42(34).
  • S. Yagoubi, S. Obbade, S. Saad, F. Abraham
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    ABSTRACT: A new caesium uranyl molybdate belonging to the M6U2Mo4O21 family has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. Contrary to the other alkali uranyl molybdates of this family (A=Na, K, Rb) where molybdenum atoms adopt only tetrahedral coordination and which can be formulated A6[(UO2)2O(MoO4)4], the caesium compound Cs6U2Mo4O21 should be written Cs6[(UO2)2(MoO4)3(MoO5)] with molybdenum atoms in tetrahedral and square pyramidal environments. Cs6[(UO2)2(MoO4)3(MoO5)] crystallizes in the triclinic symmetry with space group P1̄ and a=10.4275(14) Å, b=15.075(2) Å, c=17.806(2) Å, α=70.72(1)°, β=80.38(1)° and γ=86.39(1)°, V=2604.7(6) Å3, Z=4, ρmes=5.02(2) g/cm3 and ρcal=5.08(3) g/cm3. A full-matrix least-squares refinement on the basis of F2 yielded R1=0.0464 and wR2=0.0950 for 596 parameters with 6964 independent reflections with I≥2σ(I) collected on a BRUKER AXS diffractometer with Mo(Kα) radiation and a CCD detector. The crystal structure of Cs compound is characterized by ∞1[(UO2)2(MoO4)3(MoO5)]6− parallels chains built from U2O13 dimeric units, MoO4 tetrahedra and MoO5 square pyramids, whereas, Na, K and Rb compounds are characterized by ∞1[(UO2)2O(MoO4)4]6− parallel chains formulated simply of U2O13 units and MoO4 tetrahedra.Infrared spectroscopy measurements using powdered samples synthesized by solid-state reaction, confirm the structural results. The thermal stability and the electrical conductivity are also studied. The four compounds decompose at low temperature (between 540 and 610 °C).
    Journal of Solid State Chemistry 05/2011; 184(5):971–981. · 2.04 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 08/2008; 39(32).
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    ABSTRACT: A new cesium uranyl niobate, Cs{sub 9}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}] or Cs{sub 9}U{sub 8}Nb{sub 5}O{sub 41} has been synthesized by high-temperature solid-state reaction, using a mixture of U{sub 3}O{sub 8}, Cs{sub 2}CO{sub 3} and Nb{sub 2}O{sub 5}. 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) A, b=14.933(2) A, c=20.155(2) A{beta}=110.59(1){sup o}, P2{sub 1}/c space group and Z=4. The crystal structure was refined to agreement factors R{sub 1}=0.049 and wR{sub 2}=0.089, calculated for 4660 unique observed reflections with I{>=}2{sigma}(I), collected on a BRUKER AXS diffractometer with MoK{alpha} radiation and a CCD detector. In this structure the UO{sub 7} uranyl pentagonal bipyramids are connected by sharing edges and corners to form a uranyl layer {sub {infinity}}{sup 2}[U{sub 8}O{sub 36}] corresponding to a new anion-sheet topology, and creating triangular, rectangular and square vacant sites. The two last sites are occupied by Nb{sub 2}O{sub 8} entities and NbO{sub 5} square pyramids, respectively, to form infinite uranyl niobate sheets {sub {infinity}}{sup 2}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}]{sup 9-} stacking along the [010] direction. The Nb{sub 2}O{sub 8} entities result from two edge-shared NbO{sub 5} square pyramids. The Cs{sup +} 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{sup +} 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{sup -1}, showed some characteristic bands of uranyl ion and niobium polyhedra. - Graphical abstract: View of the {sub {infinity}}{sup 2}[U{sub 8}O{sub 36}] uranyl infinite layer formed by association of [U{sub 6}O{sub 30}] and [U{sub 2}O{sub 12}] uranyl blocks in Cs{sub 9}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}].
    Journal of Solid State Chemistry 04/2008; 181(4). · 2.04 Impact Factor
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    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) Åbeta=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=>2sigma(I), collected on a BRUKER AXS diffractometer with MoKalpha 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[UO] 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[(UO)O(NbO)(NbO)] 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 polyhedra.
    Journal of Solid State Chemistry - J SOLID STATE CHEM. 01/2008; 181:741-750.
  • ChemInform 01/2008; 39(5).
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    ABSTRACT: The 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 [(UO2)4∞1(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.
    ChemInform 10/2007; 9(10):933–943.
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
    ChemInform 12/2006; 37(52).
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    ABSTRACT: Attempts to prepare alkaline metal uranyl niobates of composition A1−xUNbO6−x/2 by high-temperature solid-state reactions of A2CO3, 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, R1=0.054 (wR2=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, R1=0.023, 0.046 and 0.036 (wR2=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, R1=0.044 (wR2=0.117). The crystal structure of 1 is characterized by ∞2[UNbO6]- layers of uranophane sheet anion topology parallel to the (100) plane. These layers are formed by the association by edge-sharing of ∞1[UO5]4- chains of edge-shared UO7 pentagonal bipyramids and ∞1[NbO4]3- 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)22+–(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 ∞1[UO5]4- chains of edge-shared UO7 pentagonal bipyramids and ∞1[Nb2O8]6- 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.
    Journal of Solid State Chemistry 10/2006; 179(10):3238–3251. · 2.04 Impact Factor
  • S. Yagoubi, S. Obbade, C. Dion, F. Abraham
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    ABSTRACT: Two alkali metal uranates Rb{sub 2}U{sub 2}O{sub 7} and Rb{sub 8}U{sub 9}O{sub 31} 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(K{alpha}) 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{sup 2} for all unique reflections, with R{sub 1}=0.043 for 53 parameters and 746 independent reflections with I>=2{sigma}(I) for Rb{sub 2}U{sub 2}O{sub 7}, monoclinic symmetry, space group P2{sub 1}/c, a=7.323(2)A, b=8.004(3)A, c=6.950(2)A, {beta}=108.81(1){sup o}, {rho}{sub mes}=6.56(3)g/cm{sup 3}, {rho}{sub cal}=6.54(2)g/cm{sup 3}, Z=2 and R{sub 1}=0.036 for 141 parameters and 2065 independent reflections with I>=2{sigma}(I) for Rb{sub 8}U{sub 9}O{sub 31}, orthorhombic, space group Pbna, a=6.9925(9)A, b=14.288(2)A, c=34.062(5)A, {rho}{sub mes}=6.47(3)g/cm{sup 3}, {rho}{sub cal}=6.48(2)g/cm{sup 3}, Z=4. The Rb{sub 2}U{sub 2}O{sub 7} structure presents a strong analogy with that of K{sub 2}U{sub 2}O{sub 7} and can be described by layers of distorted UO{sub 2}(O{sub 4}) octahedra built from dimeric units of edge shared octahedra further linked together by opposite corners. In Rb{sub 8}U{sub 9}O{sub 31} puckered layers are formed by the association of two different uranium polyhedra, pentagonal bipyramids and distorted octahedra. The structure of Rb{sub 8}U{sub 9}O{sub 31} is built from a regular succession of {sub {approx}}{sup 1}[U{sub 4}O{sub 14}]{sup 4-} infinite ribbons similar to those observed in diuranates M{sub 2}U{sub 2}O{sub 7} (M?K, Rb) and infinite three polyhedra wide ribbons {sub {approx}}{sup 1}[U{sub 5}O{sub 21}]{sup 12-}, to create an original undulated sheets {sub {approx}}{sup 2}[U{sub 9}O{sub 31}]{sup 8-}. For both compounds Rb{sup +} ions occupy the interlayer space and exhibit comparable mobility with conductivity measurements indicating an Arrhenius-type behavior.
    Journal of Solid State Chemistry 11/2005; 178(11). · 2.04 Impact Factor
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    ABSTRACT: 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) Å, b=12.786(2) Å, c=7.4249(14) Å, 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) Å, b=6.3116(17) Å, c=22.296(6) Å, β=98.86(3)°, ρcal=7.16(2) g/cm3, ρmes=7.25(3) g/cm3 and Z=4.
    Journal of Solid State Chemistry 04/2004; 177(s 4–5):1681–1694. · 2.04 Impact Factor
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    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 F2 yielded R1=0.029 and wR2=0.064 for 2136 independent reflections with I>2σ(I) 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.
    Membrane Science and Technology 01/2004; 177(11):3909-3917.
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    ABSTRACT: Two new potassium uranyl molybdates K 2(UO 2) 2(MoO 4)O 2 and K 8(UO 2) 8(MoO 5) 3O 6 have been obtained by solid state chemistry . The crystal structures were determined by single crystal X-ray diffraction data, collected with 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 F2 for all unique reflections, with R1=0.046 for 136 parameters and 1412 reflections with I⩾2 σ( I) for K 2(UO 2) 2(MoO 4)O 2 and R1=0.055 for 257 parameters and 2585 reflections with I⩾2 σ( I) for K 8(UO 2) 8(MoO 5) 3O 6. The first compound crystallizes in the monoclinic symmetry, space group P2 1/ c with a=8.250(1) Å, b=15.337(2) Å, c=8.351(1) Å, β=104.75(1)°, ρmes=5.22(2) g/cm 3, ρcal=5.27(2) g/cm 3 and Z=4. The second material adopts a tetragonal unit cell with a= b=23.488(3) Å, c=6.7857(11) Å, ρmes=5.44(3) g/cm 3, ρcal=5.49(2) g/cm 3, Z=4 and space group P4/ n. In both structures, the uranium atoms adopt a UO 7 pentagonal bipyramid environment, molybdenum atoms are in a MoO 4 tetrahedral environment for K 2(UO 2) 2(MoO 4)O 2 and MoO 5 square pyramid coordination in K 8(UO 2) 8(MoO 5) 3O 6. These compounds are characterized by layered structures. The association of uranyl ions (UO 7) and molybdate oxoanions MoO 4 or MoO 5, give infinite layers [(UO 2) 2(MoO 4)O 2] 2- and [(UO 2) 8(MoO 5) 3O 6] 8- in K 2(UO 2) 2(MoO 4)O 2 and K 8(UO 2) 8(MoO 5) 3O 6, respectively. Conductivity properties of alkali metal within the interlayer spaces have been measured and show an Arrhenius type evolution.
    Journal of Solid State Chemistry 08/2003; 174(1):19-31. · 2.04 Impact Factor
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    ABSTRACT: The solid-state reactions of UO3 and WO3 with M2CO3 (M=Na, K, Rb) at 650°C for 5 days result, accordingly the starting stoichiometry, in the formation of M2(UO2)(W2O8) (M=Na (1), K (2)), M2(UO2)2(WO5)O (M=K (3), Rb (4)), and Na10(UO2)8(W5O20)O8 (5). The crystal structures of compounds 2, 3, 4, and 5 have been determined by single-crystal X-ray diffraction using Mo(Kalpha) radiation and a charge-coupled device detector. The crystal structures were solved by direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F2 for all unique reflections. For (1), unit-cell parameters were determined from powder X-ray diffraction data. Crystallographic data: 1, monoclinic, /a=12.736(4)Å, /b=7.531(3)Å, /c=8.493(3)Å, /beta=93.96(2)°, rhocal=6.62(2)g/cm3, rhomes=6.64(1)g/cm3, /Z=4; 2, orthorhombic, space group Pmcn, /a=7.5884(16)Å, /b=8.6157(18)Å, /c=13.946(3)Å, rhocal=6.15(2)g/cm3, rhomes=6.22(1)g/cm3, /Z=8, /R1=0.029 for 80 parameters with 1069 independent reflections; 3, monoclinic, space group P21/n, /a=8.083(4)Å, /b=28.724(5)Å, /c=9.012(4)Å, /beta=102.14(1)°, rhocal=5.83(2)g/cm3, rhomes=5.90(2)g/cm3, /Z=8, /R1=0.037 for 171 parameters with 1471 reflections; 4, monoclinic, space group P21/n, /a=8.234(1)Å, /b=28.740(3)Å, /c=9.378(1)Å, /beta=104.59(1)°, rhocal=6.13(2)g/cm3, rhomes=6.19(3)g/cm3, /Z=8, /R1=0.037 for 171 parameters with 1452 reflections; 5, monoclinic, space group /C2/c, /a=24.359(5)Å, /b=23.506(5)Å, /c=6.8068(14)Å, /beta=94.85(3)°, rhocal=6.42(2)g/cm3, rhomes=6.39(3)g/cm3, /Z=8, /R1=0.036 for 306 parameters with 5190 independent reflections. The crystal structure of 2 contains linear one-dimensional chains formed from edge-sharing UO7 pentagonal bipyramids connected by two octahedra wide (W2O8) ribbons formed from two edge-sharing WO6 octahedra connected together by corners. This arrangement leads to [UW2O10]2- corrugated layers parallel to (001). Owing to the unit-cell parameters, compound 1 probably contains similar sheets parallel to (100). Compounds 3 and 4 are isostructural and the structure consists of bi-dimensional networks built from the edge- and corner-sharing UO7 pentagonal bipyramids. This arrangement creates square sites occupied by W atoms, a fifth oxygen atom completes the coordination of W atoms to form WO5 distorted square pyramids. The interspaces between the resulting [U2WO10]2- layers parallel to /(101¯) plane are occupied by K or Rb atoms. The crystal structure of compound 5 is particularly original. It is based upon layers formed from UO7 pentagonal bipyramids and two edge-shared octahedra units, W2O10, by the sharing of edges and corners. Two successive layers stacked along the [100] direction are pillared by WO4 tetrahedra resulting in sheets of double layers. The sheets are separated by Na+ ions. The other Na+ ions occupy the rectangular tunnels created within the sheets. In fact complex anions W5O2010- are built by the sharing of the four corners of a WO4 tetrahedron with two W2O10 dimmers, so, the formula of compound 5 can be written Na10(UO2)8(W5O20)O8.
    Journal of Solid State Chemistry - J SOLID STATE CHEM. 01/2003; 172:305-318.
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    ABSTRACT: 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 MoKalpha 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>=2sigma(I) for K2(UO2)2(MoO4)O2 and R1=0.055 for 257 parameters and 2585 reflections with /I>=2sigma(I) for K8(UO2)8(MoO5)3O6. The first compound crystallizes in the monoclinic symmetry, space group P21/c with /a=8.250(1)Å, /b=15.337(2)Å, /c=8.351(1)Å, /beta=104.75(1)°, rhomes=5.22(2)g/cm3, rhocal=5.27(2)g/cm3 and /Z=4. The second material adopts a tetragonal unit cell with /a=b=23.488(3)Å, /c=6.7857(11)Å, rhomes=5.44(3)g/cm3, rhocal=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.
    Journal of Solid State Chemistry - J SOLID STATE CHEM. 01/2003; 174:19-31.

Publication Stats

32 Citations
21.02 Total Impact Points

Institutions

  • 2013
    • Université Paris-Sud 11
      Orsay, Île-de-France, France
    • Institute for Transuranium Elements
      Carlsruhe, Baden-Württemberg, Germany
  • 2011
    • University Joseph Fourier - Grenoble 1
      Grenoble, Rhône-Alpes, France
  • 2004–2006
    • French National Centre for Scientific Research
      • Institut Néel
      Lutetia Parisorum, Île-de-France, France
    • Université des Sciences et Technologies de Lille 1
      Lille, Nord-Pas-de-Calais, France