作者:Andrew J. Locock、Peter C. Burns
DOI:10.1016/s0022-4596(03)00299-8
日期:2003.11
Two homeotypic hydrated uranyl arsenates, (UO2)[(UO2)(AsO4)](2)(H2O)(4), UAs4, and (UO2)[(UO2)(AsO4)](2)(H2O)(5), UAs5 were synthesized by hydrothermal methods. Intensity data were collected at room temperature using MoKalpha X-radiation and a CCD-based area detector. Their crystal structures were solved by direct methods and refined by full-matrix least-squares techniques on the basis of F-2 to agreement indices (UAs4, UAs5) wR(2) = 0.116, 0.060, for all data, and R-1 = 0.046, 0.033, calculated for 3176, 5306 unique observed reflections (\F-o\ > 4sigma(F)) respectively. UAs4 is monoclinic, space group P2(1)/c, Z = 4, a = 11.238(1), b = 7.152(1), c = 21.941(2) Angstrom, beta = 104.576(2)degrees, V = 1706.8(1) Angstrom(3), D-calc = 4.51 g/cm(3). UAs5 is orthorhombic, space group Pca2(1), Z = 4, a = 20.133(2), b = 11.695(1), c = 7.154(1) Angstrom, V = 1684.4(1) Angstrom(3), D-calc = 4.65 g/cm(3). Both structures contain sheets of arsenate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO2)(AsO4)](1-) and the uranophane sheet anion-topology. The sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with an arsenate tetrahedron on each of two adjacent sheets, resulting in open-frameworks with isolated H2O groups in the larger cavities of the structures. The uranyl arsenate sheet in UAs4 is relatively planar, and is topologically identical with the uranyl phosphate sheet in (UO2)[(UO2)(PO4)](2) (H2O)(4). The uranyl arsenate sheet in UAs5 is the same geometrical isomer as in UAs4, but is highly corrugated, exhibiting approximately right angle bends of the sheet after every second uranyl arsenate chain repeat. (C) 2003 Elsevier Inc. All rights reserved.