Layered Uranyl Coordination Polymers Rigidly Pillared by Diphosphonates

The hydrothermal reaction of uranyl nitrate and 1,4-benzenebisphosphonic acid in the presence of monovalent and divalent metal hydroxides results in the formation of four new uranyl coordination polymers: Ag2{(UO2)­[C6H4(PO3H)2]2} (AgUbbp), Cs­{(UO2)­[C6H4(PO3H0.5)2]} (CsUbbp), [Ba­(H2O)3]­{(UO2)3[C6H4(PO3)2]2(O)}·5­(H2O) (BaUbbp), and [Sr­(H2O)3]­{(UO2)2[C6H4(PO3)2]­(OH)2(H2O)}·3­(H2O) (SrUbbp). AgUbbp and CsUbbp complexes are constructed from UO6 units with tetragonal bipyramidal coordination geometries, whereas BaUbbp and SrUbbp complexes contain UO7 units with pentagonal bipyramidal coordination environments. The pH and the monovalent/divalent metal cations have significant effects on the topology of these structures. These compounds fluoresce at room temperature owing to emission from the uranyl units.