Structural diversity of sheets in rubidium uranyl oxoselenates:: Synthesis and crystal structures of Rb2[(UO2)(SeO4)2(H2O)](H2O), Rb2[(UO2)2(SeO4)3(H2O)2](H2O)4, and Rb4[(UO2)3(SeO4)5(H2O)]

Single crystals of three rubidium uranyl selenates, Rb-2[(UO2)(SeO4)(2)(H2O]H2O) (1), Rb-2[(UO2)(2)(SeO4)(3)(H2O)(2)]-(H2O)(4) (2), and Rb-4[(UO2)(3)(SeO4)5(H2O)] (3), have been prepared by evaporation from aqueous solutions made out of mixtures of uranyl nitrate, selenic acid and Rb2CO3. The structures of all compounds have been solved by direct methods on the basis of X-ray diffraction data sets. The crystallographic data are as follows: (1): orthorhombic, Pna2(1), a = 13.677(2), b = 11.8707(13), c = 7.6397(9) angstrom, V = 1240.4(3) angstrom(3), R-1 = 0.045 for 2396 independent observed reflections; (2): triclinic, P1, a = 8.4261(12), b = 11.8636(15), c = 13.3279(18) angstrom, alpha = 102.612(10), beta = 107.250(10), gamma = 102.510(10)degrees, V = 1183.7(3) angstrom(3), R, = 0.067 for 4762 independent observed reflections; (3): orthorhombic, Pbnm, a = 11.3761(14), b = 15.069(2), c = 19.2089(17) angstrom, V = 3292.9(7) angstrom(3), R-1 = 0.075 for 3808 independent observed reflections. The structures of the phases 1, 2, and 3 are based upon uranyl selenate hydrate sheets composed from corner-sharing pentagonal [UO7](8-) bipyramids and [SeO4](2-) tetrahedra. In the crystal structure of 1, the sheets have composition [(UO2)(SeO4)2(H2O)](2-) and run parallel to (001). The interlayer contains Rb' cations and additional H2O molecules. In structure of 2, the [(UO2)(2)(SeO4)(3)(H2O)(2)](2-) sheets are oriented parallel to (101). Highly disordered Rb' cations and H2O molecules are located between the sheets. The structure of 3 is based upon [(UO2)(3)(SeO4)(5)(H2O)](4-) sheets stacked parallel to (010) and contains Rb+ cations in the interlayers. The topologies of the uranyl oxoselenate sheets observed in the structures of 1, 2, and 3 are related to the same simple and highly-symmetric graph consisting of 3-connected white and 6-connected black vertices.