Structure of uranium(VI) oxide dihydrate, UO3 center dot 2H(2)O; syntheticmeta-schoepite (UO2)(4)O(OH)(6)center dot 5H(2)O

The structure of uranium oxide dihydrate, also known as meta-schoepite (UO2 )(4)O(OH)(6). 5H(2)O, has been determined from a synthetic single crystal. The structure, at 150 K, space group Pbcn, lattice constants a = 14.6861 (4 ), b = 13.9799 (3) and c = 16.7063 (5) Angstrom, consists of layers of stoi chiometry (UO2)(4)O(OH)(6), formed from edge-sharing UO7 pentagonal bipyram ids, interleaved with hydrogen-bonded water molecules. Three of the layer h ydroxyl groups are linked through hydrogen bonding to single water molecule s and the three remaining OH units form interactions with water molecules t hat each act as acceptors in two hydrogen bonds. One of the water molecules in the inter-layer region is disordered over two symmetry-related sites an d forms hydrogen-bonded interactions only within the layer and with the ura nyl O atoms. The relationship of the structure of meta-schoepite to that of schoepite is discussed in detail.