Metal-Controlled Assembly of Uranyl Diphosphonates toward the Design of Functional Uranyl Nanotubules

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.