Nanotubular bells: A simple route to a uranyl diphosphonate with an elliptical nanotubular structure has been developed (see picture; C black, O red, Cs blue, F yellow, UO7 green pentagonal bipyramids, phosphonate violet tetrahedra). The interior of the nanotubules provides a different chemical environment than the exterior with regards to the exchange of Cs+ cations for Ag+ cations, thus demonstrating that uranyl nanotubules are functional materials.

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 A(2){(UO(2))(2)F(PO(3)HC(6)H(4)C(6)H(4)PO(3)H)(PO(3)HC(6)H(4)C(6)H(4)PO(3))}·2H(2)O (A = Cs(+), Rb(+)), revealed that A(+) cations can be exchanged for Ag(+) ions. The uranyl phenyldiphosphonate nanotubules, Cs(3.62)H(0.38)[(UO(2))(4){C(6)H(4)(PO(2)OH)(2)}(3){C(6)H(4)(PO(3))(2)}F(2)]·nH(2)O, 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 Cs(3.62)H(0.38)[(UO(2))(4){C(6)H(4)(PO(2)OH)(2)}(3){C(6)H(4)(PO(3))(2)}F(2)]·nH(2)O, as might be expected for exchange through a diffusion mechanism.

The hydrothermal reactions of thorium nitrate and uranyl acetate with carboxyphenylphosphonic acid and HF result in the formation of ThF(2)(PO(3)C(6)H(4)CO(2)H) and UO(2)(PO(3)HC(6)H(4)CO(2)H)(2).2H(2)O, respectively. ThF(2)(PO(3)C(6)H(4)CO(2)H) adopts a pillared structure constructed from thorium oxyfluoride layers built from [ThO(4)F(4)] units that are bridged by carboxyphenylphosphonate to yield a three-dimensional network. UO(2)(PO(3)HC(6)H(4)CO(2)H)(2).2H(2)O forms one-dimensional chains of UO(6) tetragonal bipyramids that are bridged by the phosphonate moiety of the ligand. The carboxylate portion of the structure links the chains together into layers via a hydrogen-bonding network. The higher effective charge and more isotropic coordination of the Th(IV) centers versus the uranium centers contained within uranyl cations allow for coordination by the protonated carboxylate portions of the ligands to the thorium cations, which does not occur with uranium in carboxyphosphonates. UO(2)(PO(3)HC(6)H(4)CO(2)H)(2).2H(2)O displays vibronically coupled fluorescence and the potential for energy transfer from the ligand to the charge-transfer bands of the uranyl cations. The main fluorescence by the ligand is quenched in ThF(2)(PO(3)C(6)H(4)CO(2)H).

The hydrothermal reactions of uranyl nitrate with diethyl(2-ethoxycarbonylphenyl)phosphonate, 3-carboxyphenylphosphonic acid, or diethyl(3-ethoxycarbonylphenyl)phosphonate with HF result in the formation of [Cu(H2O)]2Cu(H2O)2[(UO2)(PO3C6H4CO2H)(PO3C6H4CO2)]2 (UCuCPPE-1) and [H3O]2[Cu(H2O)]2[(UO2)3(PO3C6H4CO2)4]·3H2O (UCuCPPE-2). UCuCPPE-1 is constructed from the UO2 2+ moiety coordinated by four additional oxygen donor atoms from the phosphonate moiety, resulting in a tetragonal bipyramidal geometry. The phosphonate groups span between the uranyl cations to create chains that are in turn linked into sheets by square planar and square pyramidal Cu(II) units. The phenyl groups separate the sheets from one another. The structure of UCuCPPE-2 consists of a three-dimensional network of tetragonal bipyramidal and pentagonal bipyramidal U(VI) centers. These units form chains that the phosphonate groups link into sheets. The sheets are then joined together by square pyramidal CuO5 units to create the three-dimensional network. In UCuCPPE-1, the phosphonate group coordinates to both uranium and copper, while the carboxylate moiety binds exclusively to the copper(II) centers. In contrast, the oxygen atoms from the phosphonate and carboxylate moieties in UCuCPPE-2 coordinate exclusively to the uranium and copper centers, respectively. Despite the presence of Cu(II) ions in these compounds, they both fluoresce, showing characteristic vibronically coupled charge-transfer based emission.

The hydrothermal reactions of either uranyl nitrate or uranium trioxide with 4-carboxyphenylphosphonic acid and HF/CsOH in the presence of Cs þ or Ba 2þ cations result in the formation of Cs 2 {(UO 2 ) 2 (PO 3 HC 6 H 4 CO 2 H) 3 - -3). All these compounds contain the UO 2 2þ moiety coordinated by five additional donor atoms resulting in a pentagonal bipyramidal coordination environment. CsUcpp-1, CsUcpp-2, and BaUcpp-1 were isolated at low pH, whereas CsUcpp-3 was synthesized at high pH giving rise to complete elimination of protonation of phosphonic and carboxylic acid moieties. The pH of the reaction is playing a vital role in the formation of the pillared structures in which the carboxylate and phosphonate moieties are coordinated to uranium center in CsUcpp-3, while in the other three compounds, the carboxylate moiety coordinate exclusively to the Cs þ or Ba 2þ cations.