CRYSTAL-STRUCTURE OF URANYL CHLOROMETHYLPHOSPHONATE FROM X-RAY-POWDER DIFFRACTION DATA

The crystal structure of a uranyl phosphonate layer compound was found ab initio by using X-ray powder diffraction data and refined by the Rietveld method. UO2(O3PCH2Cl) crystallizes in the monoclinic space group P2(1)/c with a = 6.74212(2), b =7.11507(2), c = 13.1490(1) Angstrom, beta = 98.808(1)degrees and Z = 4. The positions of the metal, oxygens and that of the chlorine atoms were obtained from an electron density map computed using 71 unambiguously indexed powder diffraction intensities. The position of the P atom was derived from a Patterson map and that of the carbon atom was located from a Fourier difference map. Final agreement factors are: R(wp) = 0.117, R(p) = 0.091 and R(F) = 0.044. The linear uranyl group is coordinated by five oxygens of the phosphonate groups which are located nearly in a plane perpendicular to the uranyl axis. The bridging nature of the phosphonate oxygens leads to a two-dimensional layered structure for the compound. The chloromethyl groups are oriented into the interlayer space.