Molten salt flux synthesis and crystal structure of a new open-framework uranyl phosphate Cs3(UO2)2(PO4)O2: Spectroscopic characterization and cationic mobility studies

The reaction of triuranyl diphosphate tetrahydrate precursor (UO2)(3)(FO4)(2)(H2O)(4) with a CsI flux at 750 degrees C yields a yellow single crystals of new compound Cs-3(UO2)(2)(PO4)O-2. The crystal structure (monoclinic, space group C2/c, a=13.6261 (13) angstrom, b =8.1081(8) angstrom, c=12.3983(12) angstrom, beta=114.61(12)degrees, V=1245.41(20) angstrom(3) 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 >= 2 sigma(I) collected on a BRUKER AXS diffractometer with MoK alpha 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 (1)(infinity)[UO5] and by one phosphorus atom in a tetrahedral environment PO4. The two last entities (infinity UO5)-U-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 degrees 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. (C) 2013 Elsevier Inc. All rights reserved.