Metal-Controlled Assembly of Uranyl Diphosphonates toward the Design of Functional Uranyl Nanotubules
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Two uranyl nanotubules with elliptical cross sections were synthesized in high yield from complex and large oxoanions using hydrothermal reactions of uranyl salts with 1,4-benzenebisphosphonic acid or 4,4′-biphenylenbisphosphonic acid and Cs+ or Rb+ cations in the presence of hydrofluoric acid. Disordered Cs+/Rb+ cations and solvent molecules are present within and/or between the nanotubules. Ion-exchange experiments with A2{(UO2)2F(PO3HC6H4C6H4PO3H)(PO3HC6H4C6H4PO3)}·2H2O (A = Cs+, Rb+), revealed that A+ cations can be exchanged for Ag+ ions. The uranyl phenyldiphosphonate nanotubules, Cs3.62H0.38[(UO2)4{C6H4(PO2OH)2}3{C6H4(PO3)2}F2]·nH2O, show high stability and exceptional ion-exchange properties toward monovalent cations, as demonstrated by ion-exchange studies with selected cations, Na+, K+, Tl+, and Ag+. Studies on ion-exchanged single crystal using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS) provide evidence for chemical zonation in Cs3.62H0.38[(UO2)4{C6H4(PO2OH)2}3{C6H4(PO3)2}F2]·nH2O, as might be expected for exchange through a diffusion mechanism.
