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Paul Arthur Giesting, Nathan J. Porter, Peter Carman Burns
A series of sheet-structured alkali metal uranyl oxalate hydrates: structures and IR spectra
Keywords: Uranyl oxalate, Crystal structure refinement, Hydrothermal synthesis, Infrared spectra
The novel compounds K[(UO2)2(C2O4)2OH] · 2 H2O (KUrOx), Rb[(UO2)2(C2O4)2OH] · 2 H2O (RbUrOx), and Cs[(UO2)2(C2O4)2OH] · H2O (CsUrOx) have been synthesized by mild hydrothermal methods. Single crystal diffraction data collected at 125 K using MoKα radiation and a CCD-based area detector were used to solve and refine the crystal structures by full-matrix least-squares techniques to agreement indices (KUrOx, RbUrOx, CsUrOx) wR2 = 0.045, 0.062, 0.042 for all data, and R1 = 0.023, 0.030, 0.022 calculated for 1834, 1863, 1821 unique reflections respectively. The compounds KUrOx, RbUrOx, and CsUrOx are all monoclinic, space group P21/m, Z = 2. The unit cell of KUrOx has the dimensions a = 5.6427(4), b = 13.7123(9), c = 9.2669(6) Å, β = 98.7490(10)°, V = 708.68(8) Å3. The unit cell of RbUrOx has the dimensions a = 5.6225(4), b = 13.8339(9), c = 9.3308(6) Å, β = 98.1590(10)°, V = 718.41(8) Å3. The unit cell of CsUrOx has the dimensions a = 5.4688(3), b = 13.5710(8), c = 9.5408(5) Å, β = 97.5830(10)°, V = 701.90(7) Å3. The structures consist of chains of uranyl pentagonal bipyramids connected by oxalate groups and hydroxyl groups, and are isotypic with the compound NH4[(UO2)2(C2O4)2OH] · 2 H2O studied by Artem’eva et al. (2003); all four of these compounds are structurally composed of sheets made by polymerizing the chains of UO2C2O4(H2O) · 2 H2O (Jayadevan and Chackraburtty, 1972; Mikhailov et al., (1999), this being achieved by removing a H atom from an H2O group in the coordination sphere of the uranyl ion to form a hydroxyl vertex that is shared by two uranyl ions. Compensating positive charges are provided by the inclusion of large monovalent cations in channels that run through the sheets; these channels also contain hydrogen-bound H2O groups. The positions of the cations and H2O groups change in relation to the uranyl oxalate sheets and to each other through the series. The infrared spectra of these materials collected at room temperature are also presented and compared with previous work.
Zeitschrift für Kristallographie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0044-2968
Volume: 221, 08/2006
Pages: 589 - 599