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 |
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Authors: | S. Obbade C. Dion S. Yagoubi F. Abraham |
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Affiliation: | a Laboratoire de Cristallochimie et Physicochimie du Solide, UMR CNRS 8012, ENSCL-USTL, BP 108, 59652 Villeneuve d’Ascq Cedex, Franceb Laboratoire de Chimie de Coordination et Analytique, Faculté des Sciences, Université Chouaib Doukkali, B.P. 20, El Jadida, Morocco |
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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(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)°, ρcal=6.62(2) g/cm3, ρmes=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, ρcal=6.15(2) g/cm3, ρmes=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)°, ρcal=5.83(2) g/cm3, ρmes=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)°, ρcal=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)°, ρcal=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. |
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