Abstract
Single crystals of the new guanidinium uranyl selenate, [CH6N3]2[(UO2)2(SeO4)3] (1), and methylammonium uranyl sulfate, [CH3NH3]2[(UO2)2(SO4)3] (2) have been prepared by isothermal evaporation from aqueous solutions under room-temperature conditions. The crystal structure of 1 has been solved by direct methods [monoclinic, P2, a = 9.9448(15), b = 9.727(2), c = 10.1508(15) Å, β = 90.213(12)°, V = 981.9(3) Å3, Z = 2] and refined to R1 = 0.0696 (wR2 = 0.1611) for 2511 reflections with |F0| ≥ 4σF using least square techniques. The crystal structure of 2 has been solved by direct methods [triclinic, P1, a = 8.4784(6), b = 9.7873(8), c = 9.8121(7) Å, α = 90.170(2), β = 95.744(2), γ = 90.136(2)°, V = 810.12(10) Å3, Z = 1] and refined to R1 = 0.0146 (wR2 = 0.0336) for 5378 reflections with |F0| ≥ 4σF using least square techniques. The structures of 1 and 2 are based upon the [(UO2)2(TO4)3]2- (T = Se, S) twodimensional uranyl layers formed by linkage of U pentagonal bipyramids and TO4 tetrahedra via common O atoms. The layers consist of two types of 4-membered rings; this topology has previously been observed in the structures of several actinyl compounds that crystallize in tetragonal or orthorhombic space groups. Violation of the higher symmetry is caused by tiltings of the TO4 tetrahedra, associated with displacement of bridging oxygen atoms from their ideal position induced by the formation of moderate hydrogen bonds with the organic cations.
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