Hydrothermal synthesis and crystal chemistry of the new strontium uranyl selenites, Sr[(UO2)3(SeO3)2O2]•4H2O and Sr[UO2(SeO3)2]

The reaction of UO3 with SeO2 in the presence of SrCl(2)(.)6H(2)O and Sr(OH)(2)(.)8H(2)O in supercritical water at 425 degreesC for 3 d results in the formation of the new strontium uranyl selenites, Sr[(UO2)(3)(SeO3)(2)O-2](.)4H(2)O (1) and Sr[UO2(SeO3)(2)] (2). The single crystal X-ray structures of type 1 and type 2 were solved by direct methods and refined by full-matrix least-squares methods. Crystallographic data (193 K): (1), monoclinic, space group C2/m, a = 17.014(2), b = 7.0637(7), and c = 7.1084(7) Angstrom, beta = 100.544(2)degrees, Z = 2, R(F) = 0.0361 for 79 parameters with 1132 reflections with I > 2sigma(I), wR(2) = 0.0998 for all data; (2), triclinic, space group P (1) over bar, a = 5.6722(4), b = 6.7627(5), and c = 11.2622(8) Angstrom, alpha = 104.698(1)degrees, beta = 93.708(1)degrees, gamma = 109.489(1)degrees, Z = 2, R(F) = 0.0373 for 110 parameters with 1902 reflections with I > 2sigma(I), wR(2) = 0.0856 for all data. The structure of type 1 contains two-dimensional (2)(infinity)[(UO2)(3)(SeO3)(2)O-2](2-) sheets with the same topology as those found in guilleminite, (1)(infinity)[(UO2)(3)(SeO3)(2)O](.)3H(2)O, and marthozite, Cu[(UO2)(3)(SeO3)(2)O-2](H2O)(8). Sr2+ cations and H2O groups occur between the layers. In contrast, the structure of type 2 contains one-dimensional (1)(infinity)[UO2(SeO3)(2)](2-) ribbons with Sr2+ cations residing between them. This compound is isostructural with its Ca2+-containing analog.