Nanotubular materials have unique water transport and storage properties that have the potential to advance separations, catalysis, drug delivery, and environmental remediation technologies. The development of novel hybrid materials, such as metal-organic nanotubes (MONs), is of particular interest, as these materials are amenable to structural engineering strategies and may exhibit tunable properties based upon the presence of inorganic components. A novel metal-organic nanotube, (C4H12N2)(0.5)[(UO2)(Hida)(H2ida)]·2H2O (UMON) (ida = iminodiacetate), that demonstrates the possibilities of these types of hybrid compounds has been synthesized via a supramolecular approach. Single-crystal X-ray diffraction of the compound revealed stacked macrocyclic arrays that contain highly ordered water molecules with structural similarities to the "ice channels" observed in single-walled carbon nanotubes. Nanoconfinement of the water molecules may be the cause of the unusual exchange properties observed for UMON, including selectivity to water and reversible exchange at low temperature (37 °C). Similar properties have not been reported for other inorganic or hybrid compounds and indicate the potential of MONs as advanced materials.

Uranyl citrate forms trimeric species at pH > 5.5, but exact structural characteristics of these important oligomers have not previously been reported. Crystallization and structural characterization of the trimers suggests the self-assembly of the 3 : 3 and 3 : 2 U : Cit complexes into larger sandwich and macrocyclic molecules. Raman spectroscopy and ESI-MS have been utilized to investigate the relative abundance of these species in solution under varying pH and citrate concentrations. Additional dynamic light scattering experiments indicate that self-assembly of the larger molecules does occur in aqueous solution.

The interplay of hydrolysis and chelation by organic ligands results in the formation of novel uranium species in aqueous solutions. Many of these molecular complexes have been identified by spectroscopic and potentiometric techniques, but a detailed structural understanding of these species is lacking. Identification of possible uranyl hydrolysis products in the presence of organic functional groups has been achieved by the crystallization of molecular species into a solid-state compound, followed by structural and chemical characterization of the material. The structures of three novel molecular complexes containing either iminodiacetate (ida) (Na3[(UO2)3(OH)3(ida)3]·8H2O (1)) or malate (mal) (K(pip)2[(UO2)3O(mal)3]·6H2O (2a) (pip = C4N2H12), (2b) (pip)3[(UO2)3O(mal)3]·H2O, and (pip)6[(UO2)11(O)4(OH)4(mal)6(CO3)2]·23H2O (3)) ligands have been determined by single-crystal X-ray diffraction and have been chemically characterized by IR, Raman, and NMR spectroscopies. A major structural component in compounds 1 and 2 is a trimeric 3:3 uranyl ida or mal species, but different bridging groups between the metal centers create variations in the structural topologies of the molecular units. Compound 3 contains a large polynuclear cluster with 11 U atoms, which is composed of trimeric and pentameric building units chelated by mal ligands and linked through hydroxyl groups and carbonate anions. The characterized compounds represent novel structural topologies for U(6+) hydrolysis products that may be important molecular species in near-neutral aqueous systems.

Supramolecular assembly of U(VI) materials can be limited by the passivation of the uranyl oxo group and the propensity of the metal center to hydrolyze, resulting in the formation of extended two-dimensional (2D) structures. To overcome these barriers, the use of charge-assisted Hbonding was explored using amino acids (glycine [Gly] and Lalanine [Ala]), resulting in the formation of three novel(3)} that have been characterized by X-ray diffraction, elemental analysis, TGA, and vibrational spectroscopy. Hydrolysis of the uranyl cation (UO 2 2+ ) chelated by bridging zwitterionic amino acids results in the formation of infinite chains when synthesized from mildly acidic aqueous solutions. While positively charged chains form densely packed structures, the neutral UO 2 -glycine chains support a nanoporous (internal diameter ∼1.35 nm) supramolecular architecture through multifurcated charge-assisted hydrogen bonding. These interactions occur directly between the protonated amine of glycine and the uranyl's oxo moiety, representing a unique supramolecular synthon for the assembly of hybrid porous uranyl materials. The zwitterionic glycine ligands also assist in the helical assembly of water molecules that are hydrogen bonded to the interior walls of the nanopores, resulting in the formation of an empty 0.85 nm channel through the pore space.