Crystal structures of Rb{sub 2}U{sub 2}O{sub 7} and Rb{sub 8}U{sub 9}O{sub 31}, a new layered rubidium uranate
- Laboratoire de Cristallochimie et Physicochimie du Solide, UMR CNRS 8012, ENSCL-USTL, B.P. 90108, 59652 Villeneuve d'Ascq Cedex (France)
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.
- OSTI ID:
- 20784754
- Journal Information:
- Journal of Solid State Chemistry, Vol. 178, Issue 11; Other Information: DOI: 10.1016/j.jssc.2005.07.017; PII: S0022-4596(05)00334-8; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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