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

摘要

The reaction of UO₃ with SeO₂ in the presence of SrCl₂• 6H₂O and Sr(OH)₂• 8H₂O in supercritical water at 425 °C for 3 d results in the formation of the new strontium uranyl selenites, Sr[(UO₂)₃(SeO₃)₂O₂]•4H₂O (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) Å, ß = 100.544(2)°, Z = 2, R(F) = 0.0361 for 79 parameters with 1132 reflections with I > 2(I), wR₂ = 0.0998 for all data; (2), triclinic, space group P, a = 5.6722(4), b = 6.7627(5), and c = 11.2622(8) Å, = 104.698(1)°, ß = 93.708(1)°, = 109.489(1)°, Z = 2, R(F) = 0.0373 for 110 parameters with 1902 reflections with I > 2(I), wR₂ = 0.0856 for all data. The structure of type 1 contains two-dimensionalsheets with the same topology as those found in guilleminite, Ba[(UO₂)₃(SeO₃)₂O₂]•3H₂O, and marthozite, Cu[(UO₂)₃(SeO₃)₂O₂](H₂O)₈. Sr2+ cations and H₂O groups occur between the layers. In contrast, the structure of type 2 contains one-dimensional ribbons with Sr2+ cations residing between them. This compound is isostructural with its Ca2+-containing analog.