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(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 F 2 yielded R 1=0.028 and wR 2=0.071 for 79 parameters and 1352 independent reflections with I ≥2σ (I ) collected on a BRUKER AXS diffractometer with MoK α 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 View the MathML source[UO5]∞1 and by one phosphorus atom in a tetrahedral environment PO4. The two last entities View the MathML source[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.