X-ray diffraction refinement of the structure of diaquadinitratouranyl tetrahydrate [UO2(NO3)2(H2O)2] • 4H2O

Abstract

Single crystals of diaquadinitratouranyl tetrahydrate [UO2(NO3)2(H2O)2] • 4H2O (I) have been synthesized by evaporating an aqueous [UO2(NO3)2(H2O)2] • 2H2O solution containing nitric acid under air at room temperature. An experimental X-ray diffraction intensity set has been obtained from a single crystal of I. Crystals are ortorhombic, a = 13.113(2) A, b = 7.9847(12) A, c = 11.3323(17) A, space group Cmc21, Z = 4, V = 1186.5(3) A3. The structural units of a crystal of complex I are neutral molecular complexes [UO2(NO3)2(H2O)2] and crystal water molecules linked by a network of hydrogen bonds. The uranium atom is in a hexagonal bipyramidal surrounding. Axial positions are occupied by uranyl oxygen atoms, and two nonequivalent bidentate cyclic nitrato groups and two equivalent water molecules are coordinated in the equatorial plane in trans-positions to each other. Coordinated and outer-sphere water molecules in the molecular structure of complex I are linked by hydrogen bonds as O-H(H2Ocoord)⋯O(H2Oout). Outer-sphere water molecules are linked to each other and the terminal oxygen atoms of nitrato groups by hydrogen bonds as O-H(H2Oout)⋯O(H2Oout) and O-H(H2Oout)⋯O(ONO2-). Hydrogen bonds of the first type are stronger than those of the second and third types.