Refinement of the crystal structure of rutherfordine

Citation
Rj. Finch et al., Refinement of the crystal structure of rutherfordine, CAN MINERAL, 37, 1999, pp. 929-938
Citations number
40
Categorie Soggetti
Earth Sciences
Journal title
CANADIAN MINERALOGIST
ISSN journal
00084476 → ACNP
Volume
37
Year of publication
1999
Part
4
Pages
929 - 938
Database
ISI
SICI code
0008-4476(199908)37:<929:ROTCSO>2.0.ZU;2-I
Abstract
Rutherfordine, UO2CO3, is orthorhombic, a 4.840(1), b 9.273(2), c 4.298(1) Angstrom, V 192.90(7) Angstrom(3), space group Imm2, Z = 2. The structure w as refined to an R index of 2.2% on the basis of 306 unique data [\F-o\/sig ma(\F-o\) > 5] measured with MoK alpha X-radiation on a single-crystal diff ractometer. The structure consists of neutral sheets of edge- and corner-sh aring (UO8) hexagonal bipyramids and (CO3) triangles, as originally propose d by Christ et al. (1955); our refinement, however, shows that (CO3) groups in alternate layers have the same orientation, not opposite orientations a s originally reported. The refined value of the U-O(uranyl) distance is str ongly affected by the details of the absorption correction, ranging from 1. 71 to 1.80 a as a function of the plate-glancing angle used in an empirical psi-scan absorption correction and as a function of the type of weighting scheme used in the refinement. The Gaussian-quadrature method of integratio n also shows similar problems, but they are less extreme. The preferred val ue for the U-O(uranyl) distance in rutherfordine is similar to 1.745 Angstr om; as rutherfordine contains no H atoms, the O(uranyl) atom is [1]coordina ted, and should have the shortest U-O(uranyl) distance stereochemically pos sible. The current work suggests that U-O(uranyl) values less than 1.745 An gstrom reported in other studies are adversely affected by less-than-optimu m absorption corrections.