Hydrothermal Synthesis and Structural Characterization of Organically Templated Uranyl Diphosphonate Compounds

The hydrothermal treatment of uranyl nitrate and 1,4-benzenebisphosphonic acid with a variety of aliphatic amines (tetramethylammonium hydroxide, tetraethylammonium hydroxide, and diethyldimethylammonium hydroxide) and small quantities of hydrofluoric acid at 200 °C results in the crystallization of a series of layered uranyl diphosphonate compounds, [(CH3)4N][(UO2)3(O3PC6H4PO3H)2F(H2O)]·0.5H2O (Me4Ubbp), [(CH3CH2)4N]{(UO2)[C6H4(PO3H)(PO3H1.5)]2(H2O)} (Et4Ubbp), and [(CH3CH2)2N(CH3)2][(UO2)3(O3PC6H4PO3H)2F(H2O)] (Et2Me2Ubbp). All these new compounds have layered structures, but the structures of Me4Ubbp and Et2Me2Ubbp are similar in that they both contain UO6F and UO7 pentagonal bipyramids within dimers that are bridged by the phosphonate into a three-dimensional structure. The structure of Et4Ubbp contains a single crystallographically unique UO7 unit. The edge-sharing pentagonal bipyramids are linked into chains formulated as {(UO2)[C6H4(PO3H)(PO3H1.5)]2(H2O)}1−. The voids in these structures are filled with the organic templates so that the overall charge balance is maintained. Intense fluorescence was observed from these compounds at room temperature.