Synthesis, crystal structure, infrared and electrical conductivity of the layered rubidium uranate Rb4U5O17

Single crystals of a new layered rubidium uranate compound Rb4U5O17 have been synthesized by high-temperature solid-state reaction. The crystal structure was determined from single crystal X-ray diffraction data. The title compound crystallizes in the orthorhombic symmetry with space group Pbcn, and the following crystallographic data: a = 18.6762(9) Å, b = 7.0490(4) Å, c = 14.1207(7) Å and Z = 4. A full-matrix least-squares refinement on the basis of F2 yielded R1 = 0.031 and wR2=0.060wR2=0.060 for 120 parameters with 2723 independent reflections with I ≥ 2σ(I  ) collected on a BRUKER X8 Apex II 4K diffractometer with Mo Kα radiation and a CCD detector. The crystal structure contains infinite corrugated layers [(UO2)5O7]4−[(UO2)5O7]4− parallel to (0 0 1), formed by the association by edge- and corner-sharing of (UO2)O5 pentagonal bipyramids and distorted (UO2)O4 square bipyramids. The alkaline cation Rb+ are localized between layers and ensured the cohesion of the structure. Conductivity measurements, between 200 and 700 °C, show an Arrhenius law evolution, with a better electrical conductivity than the two other uranates Rb9U9O31 and Rb2U2O7, recently characterized. Infrared spectroscopy measurements at room temperature have allowed the identification of the various modes of vibrations of the uranyl ions.