Synthesis, crystallographic characterization, and conformational prediction of a structurally unique molecular mixed-ligand U(VI) solid, Na-6[UO2(O-2)(2)(OH)(2)](OH)(2)center dot 14H(2)O

The first mononuclear molecular mixed-ligand U(VI) solid containing hydroxide and peroxide ligands,Na-6[UO2(O-2)(2)(OH)(2)](OH)(2)center dot 14H(2)O (I), was synthesized and structurally characterized using single crystal X-ray diffraction. The crystal structure of I consisted of [UO2(O-2)(2)(OH)(2)](4-) molecular units, with a uranyl(VI) moiety perpendicular to 6 equatorial O atoms belonging to two side-on trans peroxo groups and two terminal trans hydroxo groups. Density functional theory (DFT) calculations determined that the trans-conformer of the [UO2(O-2)(2)(OH)(2)](4-) molecular unit found in I was 24kcal/mol lower in energy than the previously proposed cis-conformer. Crystal data: monoclinic, space group P2(1)/n with a = 13.357(4) angstrom, b 5.8521(15) angstrom, c = 15.948(6) angstrom, beta = 112.292(4)degrees, and Z = 2.