Abstract
The novel compounds K[(UO~2~)~2~(C~2~O~4~)~2~OH] Β· 2 H~2~O (KUrO~x~), Rb[(UO~2~)~2~(C~2~O~4~)~2~OH] Β· 2 H~2~O (RbUrO~x~), and Cs[(UO~2~)~2~(C~2~O~4~)~2~OH] Β· H~2~O (CsUrO~x~) have been synthesized by mild hydrothermal methods. Single crystal diffraction data collected at 125 K using Mo__K__
~Ξ±~ 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 (KUrO~x~, RbUrO~x~, CsUrO~x~) wR
~2~ = 0.045, 0.062, 0.042 for all data, and __R__1 = 0.023, 0.030, 0.022 calculated for 1834, 1863, 1821 unique reflections respectively. The compounds KUrO~x~, RbUrO~x~, and CsUrO~x~ are all monoclinic, space group __P__2~1~/m, Z = 2. The unit cell of KUrO~x~ has the dimensions a = 5.6427(4), b = 13.7123(9), c = 9.2669(6) Γ
, Ξ² = 98.7490(10)Β°, V = 708.68(8) Γ
^3^. The unit cell of RbUrO~x~ has the dimensions a = 5.6225(4), b = 13.8339(9), c = 9.3308(6) Γ
, Ξ² = 98.1590(10)Β°, V = 718.41(8) Γ
^3^. The unit cell of CsUrO~x~ has the dimensions a = 5.4688(3), b = 13.5710(8), c = 9.5408(5) Γ
, Ξ² = 97.5830(10)Β°, V = 701.90(7) Γ
^3^. The structures consist of chains of uranyl pentagonal bipyramids connected by oxalate groups and hydroxyl groups, and are isotypic with the compound NH~4~[(UO~2~)~2~(C~2~O~4~)~2~OH] Β· 2 H~2~O studied by Artemβeva et al. (2003); all four of these compounds are structurally composed of sheets made by polymerizing the chains of UO~2~C~2~O~4~(H~2~O) Β· 2 H~2~O (Jayadevan and Chackraburtty, 1972; Mikhailov et al., (1999), this being achieved by removing a H atom from an H~2~O 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 H~2~O groups. The positions of the cations and H~2~O 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.