Structures and syntheses of framework triuranyl diarsenate hydrates

Two homeotypic hydrated uranyl arsenates, (UO₂)[(UO₂)(AsO₄)]₂(H₂O)₄, UAs4, and (UO₂)[(UO₂)(AsO₄)]₂(H₂O)₅, UAs5 were synthesized by hydrothermal methods. Intensity data were collected at room temperature using MoKα X-radiation and a CCD-based area detector. Their crystal structures were solved by direct methods and refined by full-matrix least-squares techniques on the basis of F² to agreement indices (UAs4, UAs5) wR₂=0.116, 0.060, for all data, and R₁=0.046, 0.033, calculated for 3176, 5306 unique observed reflections (|F_o|>4σ_F) respectively. UAs4 is monoclinic, space group P2₁/c, Z=4, a=11.238(1), b=7.152(1), c=21.941(2)Å, β=104.576(2)°, V=1706.8(1)ų, D_calc=4.51 g/cm³. UAs5 is orthorhombic, space group Pca2₁, Z=4, a=20.133(2), b=11.695(1), c=7.154(1)Å, V=1684.4(1)ų, D_calc=4.65 g/cm³. Both structures contain sheets of arsenate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO₂)(AsO₄)]¹⁻ and the uranophane sheet anion-topology. The sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with an arsenate tetrahedron on each of two adjacent sheets, resulting in open-frameworks with isolated H₂O groups in the larger cavities of the structures. The uranyl arsenate sheet in UAs4 is relatively planar, and is topologically identical with the uranyl phosphate sheet in (UO₂)[(UO₂)(PO₄)]₂(H₂O)₄. The uranyl arsenate sheet in UAs5 is the same geometrical isomer as in UAs4, but is highly corrugated, exhibiting approximately right angle bends of the sheet after every second uranyl arsenate chain repeat.     

Crystal Structures of Three Framework Alkali Metal Uranyl Phosphate Hydrates

Three homeotypic hydrated alkali metal uranyl phosphates, A₂(UO₂)[(UO₂)(PO₄)]₄(H₂O)₂, A=Cs (CsUP), Rb (RbUP), K (KUP), were synthesized by hydrothermal methods. Intensity data were collected at room temperature using MoKα radiation and a CCD-based area detector. Their crystal structures were solved by Patterson (CsUP) and direct (RbUP, KUP) methods and refined by full-matrix least-squares techniques to agreement indices (CsUP, RbUP, KUP) wR₂=0.048, 0.230, 0.072 for all data, and R1=0.023, 0.078, 0.038 calculated for 5338, 4738, 4514 unique observed reflections (∣F_o∣≥4σ_F), respectively. The compound CsUP is orthorhombic, space group Cmc2₁, Z=4, a=14.854(1), b=13.879(1), c=12.987(1) Å, V=2677.5(3) ų. Both RbUP and KUP are monoclinic, space group Cm, but are presented in the unconventional pseudo-orthorhombic space group Fm11 to facilitate comparison with CsUP and to allow a model for RbUP that includes the effects of pseudo-merohedral twinning. RbUP is monoclinic, space group Fm11, Z=4, a=15.72(2), b=13.84(1), c=13.05(1) Å, α=90.39°(2), V=2839(5) ų; KUP is monoclinic, space group Fm11, Z=4, a=15.257(1), b=13.831(1), c=13.007(1) Å, α=91.760°(1), V=2743.4(3) ų. The structures consist of sheets of phosphate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO₂)(PO₄)]⁻, that are topologically identical to the uranyl silicate sheets in uranophane-beta. These sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with two phosphate tetrahedra on each of two adjacent sheets and whose fifth equatorial vertex is an H₂O group, resulting in an open framework with alkali metal cations in the larger cavities of the structures. Where CsUP and RbUP have two alkali metal positions and a H₂O group in these cavities, KUP has four K atoms and two H₂O groups, all of which are partially occupied, in the interstitial sites.     

Structures and synthesis of framework Rb and Cs uranyl arsenates and their relationships with their phosphate analogues

Two hydrated uranyl arsenates, Cs₂(UO₂)[(UO₂)(AsO₄)]₄(H₂O)₂ (CsUAs) and Rb₂(UO₂)[(UO₂)(AsO₄)]₄(H₂O)_4.5 (RbUAs), were synthesized by hydrothermal methods. Intensity data were collected at room temperature using MoKα radiation and a CCD-based area detector. The crystal structure of RbUAs was solved by direct methods, whereas the structure model of the phosphate Cs₂(UO₂)[(UO₂)(PO₄)]₄(H₂O)₂ was used for CsUAs; both were refined by full-matrix least-squares techniques on the basis of F² to agreement indices (CsUAs, RbUAs) wR₂=0.061,0.041, for all data, and R₁=0.032,0.021, calculated for 5098, 4991 unique observed reflections (|F_o|>4σ_F), respectively. The compound CsUAs is orthorhombic, space group Cmc2₁, Z=4, a=15.157(2), b=14.079(2), c=13.439(2) Å, V=2867.9(1) Å³. RbUAs is monoclinic, space group C2/m, Z=4, a=13.4619(4), b=15.8463(5), c=14.0068(4) Å, β=92.311(1)°, V=2985.52(2) Å³. The structures consist of sheets of arsenate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO₂)(AsO₄)]⁻, that are topologically identical to the uranyl silicate sheets in uranophane-beta. These sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with two arsenate tetrahedra on each of two adjacent sheets and whose fifth equatorial vertex is an H₂O group, resulting in an open framework with alkali metal cations in the larger cavities of the structures. CsUAs is isostructural with its phosphate analogue, and has two Cs atoms and a H₂O group in its structural cavities. RbUAs is not isostructural with its phosphate analogue, although it has a homeotypic framework. Its structural cavities are occupied by three Rb atoms and four H₂O groups; one Rb position and three of the interstitial H₂O groups are half-occupied. The partial occupancies of these positions probably result from the accommodation of the larger As atoms (relative to P) in the framework and resultant larger cavities.     

Structures and syntheses of layered and framework amine-bearing uranyl phosphate and uranyl arsenates

Two hydrated uranyl arsenates and a uranyl phosphate were synthesized by hydrothermal methods in the presence of amine structure-directing agents and their structures determined: (N₂C₆H₁₄)[(UO₂)(AsO₄)]₂(H₂O)₃, DabcoUAs, {NH(C₂H₅)₃}[(UO₂)₂(AsO₄)(AsO₃OH)], TriethUAs, and (N₂C₄H₁₂)(UO₂)[(UO₂)(PO₄)]₄(H₂O)₂, PiperUP. Intensity data were collected at room temperature using MoKα X-radiation and a CCD-based area detector. The crystal structures were refined by full-matrix least-squares techniques on the basis of F² to agreement indices (DabcoUAs, TriethUAs, PiperUP) wR₂=5.6%, 8.3%, 7.2% for all data, and R₁=2.9%, 3.3%, 4.0%, calculated for 1777, 5822, 9119 unique observed reflections (|F_o|?4σ_F), respectively. DabcoUAs is monoclinic, space group C2/m, Z=2, a=18.581(1), b=7.1897(4), c=7.1909(4) Å, β=102.886(1)°, V=936.43(9) Å³, D_calc=3.50 g/cm³. TriethUAs is monoclinic, space group P2₁/n, Z=4, a=9.6359(4), b=18.4678(7), c=10.0708(4) Å, β=92.282(1)°, V=1790.7(1) Å³, D_calc=3.41 g/cm³. PiperUP is monoclinic, space group Pn, Z=2, a=9.3278(4), b=15.5529(7), c=9.6474(5) Å, β=93.266(1)°, V=1397.3(1) Å³, D_calc=4.41 g/cm³. The structure of DabcoUAs contains the autunite-type sheet formed by the sharing of vertices between uranyl square bipyramids and arsenate tetrahedra. The triethylenediammonium cations are located in the interlayer along with two H₂O groups and are disordered. Both TriethUAs and PiperUP contain sheets formed of uranyl pentagonal bipyramids and tetrahedra (arsenate and phosphate, respectively) with the uranophane sheet-anion topology. In TriethUAs, triethlyammonium cations are located in the interlayer. In PiperUP, the sheets are connected by a uranyl pentagonal bipyramid that shares corners with phosphate tetrahedra of adjacent sheets, resulting in a framework with piperazinium cations and H₂O groups in the cavities of the structure.     

Combinatorial topology of uranyl molybdate sheets: syntheses and crystal structures of (C6H14N2)3[(UO2)5(MoO4)8](H2O)4 and (C2H10N2)[(UO2)(MoO4)2]

Two new mixed organic-inorganic uranyl molybdates, (C₆H₁₄N₂)₃[(UO₂)₅(MoO₄)₈](H₂O)₄ (1) and (C₂H₁₀N₂)[(UO₂)(MoO₄)₂] (2), have been obtained by hydrothermal methods. The structure of 1 [triclinic, , Z=1, a=11.8557(9), b=11.8702(9), c=12.6746(9) Å, α=96.734(2)°, β=91.107(2)°, γ=110.193(2)°, V=1659.1(2) Å] has been solved by direct methods and refined on the basis of F² for all unique reflections to R1=0.058, which was calculated for the 5642 unique observed reflections (|F_o|?4σ_F). The structure contains topologically novel sheets of uranyl square bipyramids, uranyl pentagonal bipyramids, and MoO₄ tetrahedra, with composition [(UO₂)₅(MoO₄)₈]⁶⁻, that are parallel to (−101). H₂O groups and 1,4-diazabicyclo [2.2.2]-octane (DABCO) molecules are located in the interlayer, where they provide linkage of the sheets. The structure of 2 [triclinic, , Z=2, a=8.4004(4), b=11.2600(5), c=13.1239(6) Å, α=86.112(1)°, β=86.434(1)°, γ=76.544(1)°, V=1203.14(10) Å] has been solved by direct methods and refined on the basis of F² for all unique reflections to R1=0.043, which was calculated for 5491 unique observed reflections (|F_o|?4σ_F). The structure contains topologically novel sheets of uranyl pentagonal bipyramids and MoO₄ tetrahedra, with composition [(UO₂)(MoO₄)₂]²⁻, that are parallel to (110). Ethylenediamine molecules are located in the interlayer, where they provide linkage of the sheets. All known topologies of uranyl molybdate sheets of corner-sharing U and Mo polyhedra can be described by their nodal representations (representations as graphs in which U and Mo polyhedra are given as black and white vertices, respectively). Each topology can be derived from a simple black-and-white graph of six-connected black vertices and three-connected white vertices by deleting some of its segments and white vertices.     

Pb(UO2)(V2O7), a novel lead uranyl divanadate

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, ρ_mes=5.82(3), ρ_cal=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 400-4000 cm⁻¹, showing some characteristic bands of uranyl ion and of VO₄ tetrahedra.     

Synthesis and structure of [C6H14N2][(UO2)4(HPO4)2(PO4)2(H2O)]·H2O: An expanded open-framework amine-bearing uranyl phosphate

A new open-framework compound, [C₆H₁₄N₂][(UO₂)₄(HPO₄)₂(PO₄)₂(H₂O)]·H₂O, (DUP-1) has been synthesized under mild hydrothermal conditions. The resulting structure consists of diprotonated DABCOH₂²⁺ (C₆H₁₄N₂²⁺) cations and occluded water molecules occupying the channels of a complex uranyl phosphate three-dimensional framework. The anionic lattice contains uranophane-like sheets connected by hydrated pentagonal bipyramidal UO₇ units. [C₆H₁₄N₂][(UO₂)₄(HPO₄)₂(PO₄)₂(H₂O)]·H₂O possesses five crystallographically unique U centers. U(VI) is present here in both six- and seven-coordinate environments. The DABCOH₂²⁺ cations are held within the channels by hydrogen bonds to both two uranyl oxygen atoms and a μ₂-O atom. Crystallographic data (193 K, Mo Kα, λ=0.71073 Å): DUP-1, monoclinic, P2₁/n, a=7.017(1) Å, b=21.966(4) Å, c=17.619(3) Å, β=90.198(3)°, Z=4, R(F)=4.76% for 382 parameters with 6615 reflections with I>2σ(I).     

A novel open-framework with non-crossing channels in the uranyl vanadates A(UO2)4(VO4)3 (A=Li, Na)

A new sodium uranyl vanadate Na(UO₂)₄(VO₄)₃ has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the tetragonal symmetry with space group I4₁/amd and following cell parameters: a=7.2267(4) Å and c=34.079(4) Å, V=1779.8(2) Å³, Z=4 with ρ_mes=5.36(3) g/cm³ and ρ_cal=5.40(2) g/cm³. A full-matrix least-squares refinement on the basis of F² yielded R₁=0.028 and wR₂=0.056 for 52 parameters with 474 independent reflections with I?2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a CCD detector. The crystal structure is characterized by _∞²[(UO₂)₂(VO₄)] sheets parallel to (001) formed by corner-shared UO₆ distorted octahedra and V(2)O₄ tetrahedra, connected by V(1)O₄ tetrahedra to _∞¹[UO₅]⁴⁻ chains of edge-shared UO₇ pentagonal bipyramids alternately parallel to the a- and b-axis. The resulting three-dimensional framework creates mono-dimensional channels running down the a- and b-axis formed by face-shared oxygen octahedra half occupied by Na. The powder of Li analog compound Li(UO₂)₄(VO₄)₃ has been synthesized by solid-state reaction. The two compounds exhibit high mobility of the alkaline ions within the two-dimensional network of non-intersecting channels.     

Channels occupancy and distortion in new lithium uranyl phosphates with three-dimensional open-frameworks

Three new lithium uranyl phosphates, Li₂(UO₂)₃(PO₄)₂O (1), Li(UO₂)₄(PO₄)₃ (2) and Li₃(UO₂)₇(PO₄)₅O (3) were synthesized and studied. Powders of 1 and 2 were synthesized via solid state reaction, and single crystals of the three compounds were obtained by melting of 1 and 2 powders. The structures of the three compounds have been solved and refined from single crystal X-ray diffraction data. In the three compounds, the uranium atoms occupy square and pentagonal bipyramids. The uranium square bipyramids and phosphate tetrahedra are connected by vertices to form two types of layers with autunite sheet anion-topology and denoted S and D, respectively. The uranyl pentagonal bipyramids share opposite equatorial edges to form infinite chains. Mutually perpendicular chains are hung on each side of the sheets to build frameworks with non-crossing perpendicular channels that accommodate the lithium ions. Various stacking sequences of the S and D layers, S-S, D-D and S-D, generate three different frameworks in 1, 2 and 3, respectively. These compounds are similar to the recently reported vanadate analogous. However, the phosphate tetrahedra, smaller than the vanadate ones, gives distortion of the layers and a lowering of the symmetry and/or a change of periodicity. The electrical conductivity of 1 and 2 was measured using impedance spectroscopy method. The rather low conductivity of the lithium cations is explained by the crystal structure and the Li⁺ position within the tunnels. These results corroborate those on the analogous three-dimensional alkaline uranyl vanadates. Crystallographic data: 293 K, BRUKER X8-APEX2 X-ray diffractometer, 4 K CCD detector, MoKα, λ=0.71073 Å, full-matrix least-squares refinement on the basis of F. 1, Tetragonal symmetry, space group I4₁/amd, Z=4 with a=7.1109(2) Å and c=25.0407(8) Å, R=0.034 and wR=0.047 for 38 parameters with 479 independent reflections with I?3σ(I). 2, monoclinic symmetry, space group P2₁/c, Z=4 and a=9.8829(2) Å, b=9.8909(2) Å, c=17.4871(4) Å and β=106.198(1)°, R=0.021 and wR=0.031 for 249 parameters with 4201 independent reflections with I?3σ(I). 3, Tetragonal symmetry, space group with a=9.9305(2) Å and c=14.5741(3) Å, R=0.035 and wR=0.038 for 137 parameters with 4527 independent reflections with i?3σ(I).     

[Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3], crystal structure and comparison with uranium minerals with U3O8-type sheets

The new U(VI) compound, [Ni(H₂O)₄]₃[U(OH,H₂O)(UO₂)₈O₁₂(OH)₃], was synthesized by mild hydrothermal reaction of uranyl and nickel nitrates. The crystal-structure was solved in the P-1 space group, a=8.627(2), b=10.566(2), c=12.091(4) Å and α=110.59(1), β=102.96(2), γ=105.50(1)°, R=0.0539 and wR=0.0464 from 3441 unique observed reflections and 151 parameters. The structure of the title compound is built from sheets of uranium polyhedra closely related to that in β-U₃O₈. Within the sheets [(UO₂)(OH)O₄] pentagonal bipyramids share equatorial edges to form chains, which are cross-linked by [(UO₂)O₄] and [UO₄(H₂O)(OH)] square bipyramids and through hydroxyl groups shared between [(UO₂)(OH)O₄] pentagonal bipyramids. The sheets are pillared by sharing the apical oxygen atoms of the [(UO₂)(OH)O₄] pentagonal bipyramids with the oxygen atoms of [NiO₂(H₂O)₄] octahedral units. That builds a three-dimensional framework with water molecules pointing towards the channels. On heating [Ni(H₂O)₄]₃[U(OH,H₂O)(UO₂)₈O₁₂(OH)₃] decomposes into NiU₃O₁₀.     

Hydrothermal syntheses and structures of the uranyl tellurates AgUO2(HTeO5) and Pb2UO2(TeO6)

Two uranyl tellurates, AgUO₂(HTeO₅) (1) and Pb₂UO₂(TeO₆) (2), were synthesized under hydrothermal conditions and were structurally, chemically, and spectroscopically characterized. 1 crystallizes in space group Pbca, a=7.085(2) Å, b=11.986(3) Å, c=13.913(4) Å, V=1181.5(5) Å³, Z=8; 2 is in P2(1)/c, a=5.742(1) Å, b=7.789(2) Å, c=7.928(2) Å, V=90.703(2) Å³, and Z=2. These are the first structures reported for uranyl compounds containing tellurate. The U⁶⁺ cations are present as (UO₂)²⁺ uranyl ions that are coordinated by O atoms to give pentagonal and square bipyramids in compounds 1 and 2, respectively. The structural unit in 1 is a sheet consisting of chains of edge-sharing uranyl pentagonal bipyramids that are one bipyramid wide, linked through the dimers of TeO₆ octahedra. In 2, uranyl square bipyramids share each of their equatorial vertices with different TeO₆ octahedra, giving a sheet with the autunite-type topology. Sheets in 1 and 2 are connected through the low-valence cations that are located in the interlayer region. The structures of 1 and 2 are compared to those of uranyl compounds containing octahedrally coordinated cations.     

New open-framework in the uranyl vanadates A3(UO2)7(VO4)5O (A=Li, Ag) with intergrowth structure between A(UO2)4(VO4)3 and A2(UO2)3(VO4)2O

New 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 and characterization of a cadmium germanium phosphate CdGe(OH)3PO4 with an open framework

A new three-dimensional (3D) framework cadmium germanium phosphate, CdGe(OH)₃PO₄ was synthesized by solvothermal methods. The crystal structure of CdGe(OH)₃PO₄ was established by single-crystal X-ray diffraction: CdGeH₃O₇P, Orthorhombic, Cmca, a=7.1415(7) Å, b=10.9034(1) Å, c=13.1098(1) Å, Z=8, R₁=0.0365 (F²>2σ(F²) and wR₂=0.0985 (all data). The framework of CdGe(OH)₃PO₄ is built by a mixed network of GeO₆, CdO₆ octahedra and PO₄ tetrahedra, which are linked to form a 3-membered ring (3-MR). The GeO₆ and CdO₆ octahedra share common vertexes and edges, respectively, to form one-dimensional (1D) Ge-O-Ge and Cd-O-Cd chains, which are further connected forming corrugated Ge-O-Cd layers. The layers are linked by PO₄ tetrahedra, leading to a 3D open-framework structure with 3- and 6-MR channels.     

Syntheses, structures, characterizations and charge-density matching of novel amino-templated uranyl selenates

Five hybrid organic-inorganic uranyl selenates have been synthesized, characterized and their structures have been determined. The structure of (C₂H₈N)₂[(UO₂)₂(SeO₄)₃(H₂O)] (EthylAUSe) is monoclinic, P2₁, a=8.290(1), b=12.349(2), c=11.038(2) Å, β=104.439(4)°, V=1094.3(3) Å³, Z=2, R₁=0.0425. The structure of (C₇H₁₀N)₂[(UO₂)(SeO₄)₂(H₂O)]H₂O (BenzylAUSe) is orthorhombic, Pna2₁, a=24.221(2), b=11.917(1), c=7.4528(7) Å, V=2151.1(3) Å³, Z=4, R₁=0.0307. The structure of (C₂H₁₀N₂)[(UO₂)(SeO₄)₂(H₂O)](H₂O)₂ (EDAUSe) is monoclinic, P2₁/c, a=11.677(2), b=7.908(1), c=15.698(2) Å, β=98.813(3)°, V=1432.4(3) Å³, Z=4, R₁=0.0371. The structure of (C₆H₂₂N₄)[(UO₂)(SeO₄)₂(H₂O)](H₂O) (TETAUSe) is monoclinic, P2₁/n, a=13.002(2), b=7.962(1), c=14.754(2) Å, β=114.077(2)°, V=1394.5(3) Å³, Z=4, R₁=0.0323. The structure of (C₆H₂₁N₄)[(UO₂)(SeO₄)₂(HSeO₄)] (TAEAUSe) is monoclinic, P2₁/m, a=9.2218(6), b=12.2768(9), c=9.4464(7) Å, β=116.1650(10)°, V=959.88(12) Å³, Z=2, R₁=0.0322. The inorganic structural units in these compounds are composed of uranyl pentagonal bipyramids and selenate tetrahedra. In each case, tetrahedra link bipyramids through vertex-sharing, resulting in chain or sheet topologies. The charge-density matching principle is discussed relative to the orientations of the organic molecules between the inorganic structural units.     

Synthesis and crystal structure of two new uranyl oxychloro-vanadate layered compounds: M7(UO2)8(VO4)2O8Cl with M=Rb, Cs

Two new alkali uranyl oxychloro vanadates M₇(UO₂)₈(VO₄)₂O₈Cl with M=Rb, Cs, have been synthesized by solid-state reactions and their structures determined from single-crystal X-ray diffraction data. They crystallize in the orthorhombic system with space groups Pmcn and Pmmn, respectively. The a and b unit cell parameters are almost identical in both compounds while the c parameter in the Rb compound is doubled: Rb—a=21.427(5) Å, b=11.814(3) Å, c=14.203(3) Å, V=3595.1(1) Å³, Z=4, ρ_mes=5.93(2) g/cm³, ρ_cal=5.82(1) g/cm³; Cs—a=21.458(3) Å, b=11.773(2) Å, c=7.495(1) Å, V=1893.6(5) Å³, Z=2, ρ_mes=6.09(2) g/cm³, ρ_cal=6.11(1) g/cm³. A full-matrix least-squares refinement yielded R₁=0.0221, wR₂=0.0562 for 2675 independent reflections and R₁=0.0386, wR₂=0.1042 for 2446 independent reflections, for the Rb and Cs compounds, respectively. Data were collected with Mo(Kα) radiation and a charge coupled device (CCD) detector of a Bruker diffractometer. Both structures are characterized by [(UO₂)₈(VO₄)₂O₈Cl]_n⁷ⁿ⁻ layers parallel to the (001) plane. The layers are built up from VO₄ tetrahedra, UO₇ and UO₆Cl pentagonal bipyramids, and UO₆ distorded octahedra. The UO₇ and UO₆Cl pentagonal bipyramids are associated by sharing opposite equatorial edges to form infinite chains (UO₅-UO₄Cl-UO₅)_n parallel to the a axis. These chains are linked together by VO₄ tetrahedra, UO₆ octahedra, UO₇ corner sharing and UO₆Cl, Cl sharing. Both structures differ simply by the symmetry of the layers. The unit cell contains one centrosymmetric layer in the Cs compound, whereas in the two-layer unit cell of the Rb compound, two non-centrosymmetric consecutive layers are related by an inversion center. The layers appear to be held together by the alkali ions. The mobility of the M⁺ ions within the interlayer space in M₇(UO₂)₈(VO₄)₂O₈Cl and carnotite analog compounds is compared.     

Crystal chemistry and ion-exchange properties of the layered uranyl iodate K[UO2(IO3)3]

Single crystals of the potassium uranyl iodate, K[UO₂(IO₃)₃] (1), have been grown under mild hydrothermal conditions. The structure of 1 contains two-dimensional sheets extending in the [ab] plane that consist of approximately linear UO₂²⁺ cations bound by iodate anions to yield UO₇ pentagonal bipyramids. There are three crystallographically unique iodate anions, two of which bridge between uranyl cations to create sheets, and one that is monodentate and protrudes in between the layers in cavities. K⁺ cations form long ionic contacts with oxygen atoms from the layers forming an eight-coordinate distorted dodecahedral geometry. These cations join the sheets together. Ion-exchange reactions have been carried out that indicate the selective uptake of Cs⁺ over Na⁺ or K⁺ by 1. Crystallographic data (193 K, MoKα, ): 1, orthorhombic, Pbca, a=11.495(1) Å, b=7.2293(7) Å, c=25.394(2) Å, Z=8, R(F)=1.95% for 146 parameters with 2619 reflections with I>2σ(I).     

Synthesis and crystal structure of new uranyl tungstates M2(UO2)(W2O8) (M=Na, K), M2(UO2)2(WO5)O (M=K, Rb), and Na10(UO2)8(W5O20)O8

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(Kα) 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, β=93.96(2)°, ρ_cal=6.62(2) g/cm³, ρ_mes=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, ρ_cal=6.15(2) g/cm³, ρ_mes=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, β=102.14(1)°, ρ_cal=5.83(2) g/cm³, ρ_mes=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, β=104.59(1)°, ρ_cal=6.13(2) g/cm³,  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, β=94.85(3)°, ρ_cal=6.42(2) g/cm³,  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 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.