Variable dimensionality and new uranium oxide topologies in the alkaline-earth metal uranyl selenites AE[(UO2)(SeO3)2] (AE=Ca,Ba) and Sr[(UO2)(SeO3)2] • 2H2O

Three new alkaline-earth metal uranyl selenites, Ca[(UO2) (SeO3)(2)] (1), Sr[(UO2)(SeO3)(2)] . 2H(2)O (2), and Ba[UO2) (SeO3)(2)] (3), have been prepared from the reactions of CaCO3 and Ca(OH)(2), SrCl2 and Sr(OH)(2), or BaCl2 and Ba(OH)(2) with UO3 and SeO2 under mild hydrothermal conditions. Single-crystal X-ray diffraction experiments reveal that the structures of 1-3 differ in both connectivity and dimensionality even though all contain the same fundamental building unit, namely UO2(SeO3)(4)]. This polyhedron consists of a linear uranyl unit that is bound by one chelating and three bridging selenite anions creating a pentagonal bipyramidal environment around the U(VI) center. The crystal structure of 1 contains one-dimensional ribbons where the edges are terminated by monodentate selenite anions. The interior of the ribbons are constructed from edge-sharing pentagonal bipyramidal UO7 units. The structure of 2 is also one-dimensional; however, here there are chains of edge-sharing pentagonal bipyramidal UO7 dimers that are connected by bridging selenite anions. Ba[(UO2)(SeO3)(2)] (3) is two-dimensional, and the highly ruffled anionic sheets present in this structure are formed from both bridging and chelating/bridging selenite anions bound to uranyl moieties. The anionic substructures in 1-3 are separated 2+ 2+ by Ca2+ , Sr2+, or Ba2+ cations. Crystallographic data (193K, MoKalpha, lambda = 0.71073): 1, triclinic, space group P (1) over bar, a = 5.5502(6), b = 6.6415(7) Angstrom, c = 11.013(1)Angstrom, alpha = 104.055(2)degrees, beta = 93.342(2)degrees ' gamma=110.589(2)degrees, Z=2, R(f)=4.56% for 100 parameters with 1530 reflections with I>2a(I);, triclinic, space group P!, a=7.0545(5),, b=7.4656(5)Angstrom, c=10.0484(6)Angstrom, at = 106.995(1)degrees, beta = 108.028(1)degrees, gamma = 98.875(1)degrees, Z= 2, R(F) 2.43% for 128 parameters with 2187 reflections with I > 2sigma(I); monoclinic, space group P21/c, a = 7.3067(6)Angstrom, b = 8.1239(7) Angstrom, c=13.651(1)Angstrom, beta=100.375(2)degrees, Z=4, R(f)=4.31% for 105 parameters with 1824 reflections with I>2sigma(I). (C) 2002 Elsevier Science (USA).