U(UO2)(PO4)2, a New Mixed-Valence Uranium Orthophosphate: Ab Initio Structure Determination from Powder Diffraction Data and Optical and X-ray Photoelectron Spectra

A mixed-valence uranium phosphate, U(UO[sub 2])(PO[sub 4])[sub 2], has been synthesized through dry and wet chemical processes. The crystal structure has been solved ab initio from conventional monochromatic X-ray powder diffraction. The unit cell is triclinic (space group P1, Z = 2) with the cell dimensions a = 8.8212(4) [angstrom], b - 9.2173(5) [angstrom], c = 4772(3) [angstrom], [alpha] = 102.622(4)[degrees], [beta] = 97.748(4)[degrees], [gamma] = 102.459(5)[degrees], and V = 416.55(3) [angstrom][sup 3]. Initial positional parameters for two independent uranium atoms were obtained by solution of the Patterson map resulting from 509 integrated intensities. Phosphorus and oxygen atoms were localized by Fourier methods. The final indicators from the Rietveld refinement was R[sub F] = 0.039 and R[sub wp] = 0.144. The overall quality of the structure was improved from the refinement of atomic coordinates from neutron diffraction data (R[sub F] = 0.029, R[sub wp] = 0.057). 42 refs., 7 figs., 5 tabs.