Refinement of the crystal structure of billietite, Ba [(UO2)6 O4 (OH)6] (H2O)8

The crystal structure of billietite, Ba [(UO2)(6)O-4(OH)(6)](H2O)(8), orthorhombic, space group Pbn2(1), a 12.0941(8), b 30.211(2), c 7.1563(5) angstrom, V 2614.7(4) angstrom(3), Z = 4, has been refined to an R-1 index of 3.4% for 4918 unique observed (vertical bar F-o vertical bar > 4 sigma F) reflections measured with MoK alpha X-radiation and a diffractometer fitted with a CCD detector. The structure consists of anionic [(UO2)(6) O-4 (OH)(6)](2-) sheets, linked by interstitial Ba atoms and (H2O) groups. There are two crystallographically distinct structural sheets and eight interlayer (H2O) groups in billietite. Four (H2O) groups are bonded to the interlayer Ba atoms, and the remaining four (H2O) groups are not bonded to a cation, but are held in the structure by a network of hydrogen bonds.