The crystal and molecular structure of sodium uranyl triperoxide

The crystal structure of sodium uranyl triperoxide nonahydrate, Na4[UO2(O2)3],9H2O, has been determined by single-crystal X-ray diffraction, by the heavy-atom method. The main structural feature is the uranyl triperoxide anion consisting of three co-planar peroxide groups equatorially surrounding a linear uranyl group, in approximately D3h symmetry. The mean U–O(uranyl) distance is 1·86, the U–O(peroxide) is 2·28 and the peroxide O–O 1·5 Å. The water molecules are co-ordinated in octahedra around the sodium atoms. The crystals are monoclinic, space group P21/c, a= 6·413, b= 17·292, c= 14·186 Å, β= 98·52°. The i.r. and Raman spectra of this and some related compounds are reported, with tentative assignments.