Synthesis, structure and characterization of uranium(IV) phenyl phosphonate, U(O3PC6H5)(2), and uranium(IV) pyro phosphate, UP2O7

Two tetravalent uranium compounds have been characterized. The structure of a new uranium(IV) phosphonate, U(O3PC6H5)(2), has been solved from laboratory X-ray powder diffraction data by using ab initio methodology. U(O3PC6H5)(2) crystallizes in the space group C2/m with a = 9.4559(7) A, b = 5.6769(5) Angstrom, c = 14.9687(12) Angstrom, beta = 96.539(5) Angstrom, V = 798.3(1) Angstrom(3), Z = 2. The reliability factors were R(WP) = 8.0%, R(p) = 6.04%, and R(F) = 3.0%. The structure is lamellar, and the framework of the U(O3P)(2) layers is similar to that of the alpha-Zr(HPO4)(2) . H2O-type structure, although the symmetry of the phosphonate group is higher than that of the phosphate groups in alpha-Zr(HPO4)(2) . H2O and the phosphonate group in Zr(O3PC6H5)(2). The phenyl groups are located in the interlamellar space, being inclined 10 degrees to the c-axis. The phenyl rings are tilted out 53 degrees from the ac plane, and they are disordered. We have also characterized this compound by UV-VIS-IR spectroscopies and thermal analysis. The thermal decomposition product is uranium(IV) pyre phosphate. This compound was identified through its X-ray powder diffraction pattern. UP2O7 crystallizes in the Pa(3) over bar space group (a = 8.6311(2) Angstrom, V = 642.99(4) Angstrom(3), Z = 4). The structure belongs to the cubic ZrP2O7-type structure. The reliability factors were R(WP) = 11.7%, R(P) = 8.6%, and R(F) = 10.4%. Disorder has been found in the oxygen that bridges the pyrophosphate groups, leading to an angular P-O-P arrangement. The VIS-near-IR adsorption spectra revealed the uranium(IV) presence and the oxygen environment. (C) 1996 Academic Press, Inc.