The crystal structure of dehydrated wyartite, Ca(CO3)[U5+(U6+O2)2O4(OH)] (H2O)3

Dehydrated wyartite from the Shinkolobwe mine, Shaba, Democratic Republic if Congo, ideally Ca (CO3) [U5+ (U6+O2)(2) O-4(OH)] (H2O)(3), is orthorhoinbic. a 11.2610(6), b 7.0870(4), c16.8359(10) angstrom, V 1313.6(2) angstrom(3), space group Pmcn, Z = 4. The structure was solved by direct methods and refined to all R-1 index of 2.9%, based on 2045 observed reflections measured with MoK alpha X-radiation on a four-circle single-crystal diffractometer equipped with a CCD detector. The sturucture consists of neutral sheets of the form [U5+ (U6+O2)(2) O-4 (OH)] that contains edge- and corner-sharing (U6- phi(7)) polyhedra (phi : O2-, H2O), two of which are pentagonal bipyramids with five equatorial O2- and OH- groups bonded to a central uranyl ion, (U6+O2)(2+). The third U atom is part of a unique U5+phi(7) Polyhedron. in which two O2- anions ale part of an interlayer (CO3)(2-) group and another is the O atom of an H2O group. The plane of the (CO3) groups lies perpendicular to the structural sheets, and each (CO3) group is coordinated to U5+ in the structural sheet and to Ca in the interlayer. The sheet is topologically similar to that found in beta-U3O8, and the sheets are bonded to each other through interlayer Ca atoms and interlayer ((HC)-C-2) groups. The principal difference between the structures of wyartite and dehydrated wyartite is that the sheets in the former are linked only through interstitial hydrogen-bonding, whereas the sheets in the latter are linked directly by Ca-O bonds (plus interstitial hydrogen-bonds).