The crystal structure of cesium biuranyl trisulphate, Cs2(UO2)2(SO4)3

The crystal structure of the new compound Cs(UO₂)₂(SO₄)₃ has been determined by X-ray diffraction methods. The compound is tetragonal, space group P421m">P42₁m (D_2d³), with a = 9·62 ± 0·02, c = 8·13 ± 0·01Å">c = 8·13 ± 0·01Å, and Z = 2; s.g. (calc.) = 4·80 ± 0·03, s.g. (obs.) = 4·74 ± 0·05. The compound forms plates parallel to (001) bounded by the form (110). Intensity data were obtained from Buerger precession photographs of the (hk0) and (0kl) reciprocal lattice nets. No corrections for absorption were made. The co-ordinates of the U and Cs atoms were obtained by interpretation of the Patterson projections normal to (001) and (100) and a plausible structure was derived from electron density projections. The final parameters of the structure were determined from subtraction electron density maps, least squares analysis of the structure factors, and spatial considerations.

The compound has a layer structure consisting of (UO₂)₂(SO₄)₃]_n²ⁿ⁻ sheets paralle to (001), tied together by cesium ions. The UO₂²⁺ group is co-ordinated by five sulphate oxygens which form a nearly plane pentagon approximately normal to the uranyl axis. The Cs₂ atom is co-ordinated by twelve oxygen atoms and the Cs₁ atom by eight oxygen atoms.

X-ray and optical data are also given for the compound Rb₂UO₂(SO₄)₂·2H₂O.