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 (Me 4 Ubbp), [(CH3CH2)4N]{(UO2)[C6H4(PO3H)(PO3H1.5)]2(H2O)} (Et 4 Ubbp), and [(CH3CH2)2N(CH3)2][(UO2)3(O3PC6H4PO3H)2F(H2O)] (Et 2 Me 2 Ubbp). All these new compounds have layered structures, but the structures of Me 4 Ubbp and Et 2 Me 2 Ubbp 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 Et 4 Ubbp 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.