Synthesis, Crystal Structure, Cationic Mobility, Thermal Evolution and Spectroscopic Study of Cs8(UO2)4(WO4)4 (WO5)2 Containing Infinite Uranyl Tungstate Chains.

Abstract The powder samples and single crystals of the cesium uranyl tungstate compound Cs 8 (UO 2 ) 4 (WO 4 ) 4 (WO 5 ) 2 have been synthesized by high temperature solid state reaction and its structure determined from single crystal X-ray diffraction data. The cesium mobility and vibration modes of uranyl and tungstate polyhedrons have been evidenced using pulverulent samples. It crystallizes in the monoclinic symmetry with space group P 2 1 / n and following cell parameters, a  = 11.2460(3) A, b  = 13.8113(3) A, c  = 25.7287(3) A, β  = 90.00(3)°, V  = 3996.23(17) A 3 and Z  = 4 with ρ mes  = 6.079(2) g/cm 3 and ρ cal  = 6.087(2) g/cm 3 . A full-matrix least-squares refinement on the basis of F 2 yielded R 1  = 0.0379 and wR 2  = 0.0624 for 471 parameters with 14,278 independent reflections with I  ≥ 2 σ ( I ) collected on a Bruker X8 CCD 4K diffractometer with Mo Kα radiation. In this structure, the uranium atoms adopt UO 7 pentagonal bipyramid coordination, while tungsten atoms are in two different environments, WO 4 tetrahedral and WO 5 square pyramidal coordinations. The association of uranyl ions (UO 7 ) and tungstate oxoanions WO 4 and WO 5 , gives infinite chains [ ( UO 2 ) 4 ∞ 1 ( WO 4 ) 4 ( WO 5 ) 2 ] 8 − parallel to [100]. These types of chains has not been previously observed. The association of these chains in the (010) plane gives undulated pseudo-layers stacked along [010]. The cohesion between the chains is assured by alkaline Cs + cations. The conductivity measurements, between 200 and 600 °C, show an Arrhenius law evolution. Infrared spectroscopy investigated at room temperature in the 400–4000 cm −1 wave number range, has allowed the identification of the various modes of vibrations of uranyl and tungstate polyhedrons.