Uranyl Oxygen Research Articles

Crystal structure and Hirshfeld surface analysis of bis(benzoylacetonato)(ethanol)dioxidouranium(VI)

A new uranium metal–organic complex salt, [U(C10H9O2)2O2(C2H6O)], with benzoyl acetone, namely, bis(benzoylacetonato)(ethanol)dioxidouranium(VI), was synthesized. The compound has monoclinic P21/n symmetry. The geometry of the seven-coordinate U atom is pentagonal bipyramidal, with the uranyl oxygen atoms in apical positions. In the complex, the ligands bind to the metal through oxygen atoms. Additional weak O—H...O contacts between the cations and anions consolidate the three-dimensional arrangement of the structure. On the Hirshfeld surface, the largest contributions come from the short contacts such as van der Waals forces, including H...H, O...H and C...H. Interactions including C...C and O...C contacts were also observed; however, their contribution to the overall cohesion of the crystal structure is minor. A packing analysis was performed to check the strength of the crystal packing.

A New Molybdenum Blue Structure Type: How Uranium Expands this Family of Polyoxometalates.

The assembly of molybdenum polyoxometalates (POMs) has afforded large discrete nanoclusters with varied degrees of reduction such as the ~20 % reduced molybdenum blues. While many heterometals have been incorporated into these clusters to afford new properties, uranium has yet to be reported. Here we report the first uranium containing molybdenum blue clusters and the unique properties exhibited by this incorporation. The uranyl ion (UO2 2+) directs formation of Mo72U8, a square POM comprised of two faces connected by eight edge-sharing molybdenum dimers. Mo72U8, a chiral cluster, crystallizes as a racemic mixture and, in the solid state, has a 'negative' charge localized on one face of the cluster opposite the 'positively' charged face of another cluster. Using U(IV) as both heterometal and molybdenum reductant afforded crystals of Mo97U10, a wheel cluster with a heptamolybdate cap on one face. Mo97U10 dissociates in solution, losing the heptamolybdate, to form Mo90U10. Using more solvent during synthesis afforded crystals of Mo90U10S4 which, instead of heptamolybdate, contains four sulfate ions. Crystals of Mo90U10S4 undergo a dehydration induced phase change where clusters form a sheet through oxide bridges. Half of the bridges are cation-cation interactions between the uranyl oxygen atom and molybdenum, the first reported of this kind.

Towards tailoring hydrophobic interaction with uranyl(VI) oxygen for C-H activation.

Bovine serum albumin (BSA) has a uranyl(VI) binding hotspot where uranium is tightly bound by three carboxylates. Uranyl oxygen is "soaked" into the hydrophobic core of BSA. Isopropyl hydrogen of Val is trapped near UO22+ and upon photoexcitation, C-H bond cleavage is initiated. A unique hydrophobic contact with "yl"-oxygen, as observed here, can be used to induce C-H activation.

Chemical and Redox Speciation of Uranyl with Three Environmentally Relevant Bifunctional Chelates: Multi-Technique Approach Combined with Theoretical Estimations.

Carbon and phosphorous are two primary elements common to the bio-geosphere and are omnipresent in both biotic and abiotic arenas. Phosphonate and carboxylate are considered as building blocks of glyphosate and humic substances and constituents of the cellular wall of bacteria and are the driving functionalities for most of the chemical interactions involving these two elements. Phosphonocarboxylates, a combination of both the functionalities in one moiety, are ideal models to dig deep into for understanding the chemical interactions of the two functional groups with metal ions. Phosphorous and carbon majorly exist as inorganic/organic phosphate and carboxylate, respectively, in the bio-geosphere. Aquatic contamination is a major concern for uranium, and the presence of complexing agents would alter the uranium concentrations in aquifers. Determination of solution thermodynamic parameters, speciation plots, redox patterns, Eh-pH diagrams, coordination structures, and molecular-level understanding by density functional theory calculations was carried out to interpret the uranyl (UO22+) interaction with three environmentally relevant phosphonocarboxylates, namely, phosphono-formic acid (PFA), phosphono-acetic acid (PAA), and phosphono-propanoic acid (PPA). UO22+ forms 1:1 complexes with the three phosphonocarboxylates in the monoprotonated form, having nearly the same stability, and the complexes [UO2(PFAH)], [UO2(PAAH)], and [UO2(PPAH)] involve chelate formation of five, six, and seven membered rings, respectively, through the participation of an oxygen each from the carboxylate and phosphonate, strengthened by an intra-molecular hydrogen bonding through the proton of the phosphonate moiety with uranyl oxygen. The complex formations are favored both enthalpically and entropically, with the latter being more contributive to the overall free energy of formation. The redox speciation showed an aqueous soluble complex formation over a wide pH range of 1-8. Electrospray ionization mass spectrometry and extended X-ray absorption fine structure established the coordination modes, which are further corroborated by density functional calculations. The knowledge gained from the present studies provide potential inputs in framing the cleanup, sequestering, microbial, and bio-remediation strategies for uranyl from aquatic environments.

Uranium (VI) Adsorbate Structures on Portlandite [Ca(OH)2] Type Surfaces Determined by Computational Modelling and X-ray Absorption Spectroscopy

Portlandite [Ca(OH)2] is a potentially dominant solid phase in the high pH fluids expected within the cementitious engineered barriers of Geological Disposal Facilities (GDF). This study combined X-ray Absorption Spectroscopy with computational modelling in order to provide atomic-scale data which improves our understanding of how a critically important radionuclide (U) will be adsorbed onto this phase under conditions relevant to a GDF environment. Such data are fundamental for predicting radionuclide mass transfer. Surface coordination chemistry and speciation of uranium with portlandite [Ca(OH)2] under alkaline groundwater conditions (ca. pH 12) were determined by both in situ and ex situ grazing incidence extended X-ray absorption fine structure analysis (EXAFS) and by computational modelling at the atomic level. Free energies of sorption of aqueous uranyl hydroxides, [UO2(OH)n]2–n (n = 0–5) with the (001), (100) and (203) or (101) surfaces of portlandite are predicted from the potential of mean force using classical molecular umbrella sampling simulation methods and the structural interactions are further explored using fully periodic density functional theory computations. Although uranyl is predicted to only weakly adsorb to the (001) and (100) clean surfaces, there should be significantly stronger interactions with the (203/101) surface or at hydroxyl vacancies, both prevalent under groundwater conditions. The uranyl surface complex is typically found to include four equatorially coordinated hydroxyl ligands, forming an inner-sphere sorbate by direct interaction of a uranyl oxygen with surface calcium ions in both the (001) and (203/101) cases. In contrast, on the (100) surface, uranyl is sorbed with its axis more parallel to the surface plane. The EXAFS data are largely consistent with a surface structural layer or film similar to calcium uranate, but also show distinct uranyl characteristics, with the uranyl ion exhibiting the classic dioxygenyl oxygens at 1.8 Å and between four and five equatorial oxygen atoms at distances between 2.28 and 2.35 Å from the central U absorber. These experimental data are wholly consistent with the adsorbate configuration predicted by the computational models. These findings suggest that, under the strongly alkaline conditions of a cementitious backfill engineered barrier, there would be significant uptake of uranyl by portlandite to inhibit the mobility of U(VI) from the near field of a geological disposal facility.

Three-dimensional-printed hierarchical reduced graphene oxide/ethylenediamine filter with super-high uranyl ions with recycling capacity and unique selectivity

Highly efficient and selective adsorption materials for the removal and recycling of U(VI) from radioactive wastewater or seawater are increasingly in demand due to the severe scarcity of strategic uranium sources for nuclear engineering. In this study, a three-dimensional (3D) hierarchical reduced graphene oxide/ethylenediamine scaffold (3D rGOE) was constructed using a direct-ink-writing-based 3D printing method. This technique contained orderly aligned microstructures, good hydrophilicity, mechanical robustness, and a high specific surface area. The optimized 3D rGOE structure obtained by multiscale and rational chemical modification exhibited a significantly higher U(VI) adsorption capacity (908 mg/g at pH = 5.8) compared to other previously reported amino/graphene-oxide-based composites. Additionally, the 3D rGOE mostly retained its high adsorption capacity (decay rate < 3.8%) after 11 cyclical adsorption processes. The adsorbed U(VI) could be eluted in acid through a protonation mechanism, allowing for further enrichment and recovery of U(VI). Characterization and simulations demonstrated that the U(VI) adsorption behaviors of 3D rGOE were due to the synergistic effects of electrostatic adsorption between uranyl ions and oxygen functional groups and the chelation between uranyl ions and amino functional groups. Thus, 3D rGOE shows promise for U(VI) recovery applications because of its high selectivity and adsorption capacity for uranyl ions due to its optimized microstructure and chemical composition.

Saccharified Uranyl Ions: Self-Assembly of UO2 2+ into Trinuclear Anionic Complexes by the Coordination of Glucosamine-Derived Schiff Bases.

The reaction of UO2(OAc)2 ⋅ 2H2O with the biologically inspired ligand 2‐salicylidene glucosamine (H2 L1) results in the formation of the anionic trinuclear uranyl complex [(UO2)3(μ3‐O)(L1)3]2− (1 2−), which was isolated in good yield as its Cs‐salt, [Cs]2 1. Recrystallization of [Cs]2 1 in the presence of 18‐crown‐6 led to formation of a neutral ion pair of type [M(18‐crown‐6)]2 1, which was also obtained for the alkali metal ions Rb+ and K+ (M=Cs, Rb, K). The related ligand, 2‐(2‐hydroxy‐1‐naphthylidene) glucosamine (H2 L2) in a similar procedure with Cs+ gave the corresponding complex [Cs(18‐crown‐6)]2[(UO2)3(μ3‐O)(L2)3 ([Cs(18‐crown‐6)]2 2). From X‐ray investigations, the [(UO2)3O(Ln)3]2− anion (n=1, 2) in each complex is a discrete trinuclear uranyl species that coordinates to the alkali metal ion via three uranyl oxygen atoms. The coordination behavior of H2 L1 and H2 L2 towards UO2 2+ was investigated by NMR, UV/Vis spectroscopy and mass spectrometry, revealing the in situ formation of the 1 2− and 2 2−dianions in solution.

Bimetallic uranyl/cobalt(II) isothiocyanates: structure, property and spectroscopic analysis of homo- and heterometallic phases.

We report the synthesis and characterization of a family of UO22+/Co2+ isothiocyanate materials containing [UO2(NCS)5]3- and/or [Co(NCS)4]2- building units charged balanced by tetramethylammonium cations and assembled via SS or SOyl non-covalent interactions (NCIs), namely (C4H12N)3[UO2(NCS)5], (C4H12N)2[Co(NCS)4], and (C4H12N)5[Co(NCS)4][UO2(NCS)5]. The homometallic uranyl phase preferentially assembles via SS interactions, whereas in the heterometallic phase SOyl interactions are predominant. The variation in assembly mode is explored using electrostatic surfaces potentials, revealing that the pendant -NCS ligands of the [Co(NCS)4]2- anion is capable of outcompeting those of the [UO2(NCS)5]3- anion. Notably, the heterometallic phase displays atypical blue shifting of the uranyl symmetric stretch in the Raman spectra, which is in contrast to many other compounds featuring non-covalent interactions at uranyl oxygen atoms. A combined experimental and computational (density functional theory and natural bond orbital analyses) approach revealed that coupling of the uranyl symmetric stretch with isothiocyanate modes of equatorial -NCS ligands was responsible for the atypical blue shift in the heterometallic phase.

Trimeric uranyl(vi)-citrate forms Na+, Ca2+, and La3+ sandwich complexes in aqueous solution.

M. Basile, et al., Chem. Commun., 2015, 51, 5306-5309, showed that a sodium ion is sandwiched by uranyl(vi) oxygen atoms of two 3 : 3 uranyl(vi)-citrate complex molecules in single-crystals. By means of NMR spectroscopy supported by DFT calculations we provide unambiguous evidence for this complex to persist in aqueous solution above a critical concentration of 3 mM uranyl citrate. Unprecedented Ca2+ and La3+ coordination by a bis-(η3-uranyl(vi)-oxo) motif advances the understanding of uranium's aqueous chemistry. As determined from 17O NMR, Ca2+ and more distinctly La3+ cause strong O[double bond, length as m-dash]U[double bond, length as m-dash]O polarization, which opens up new ways for uranyl(vi)-oxygen activation and functionalization.

Reductive silylation of uranyl mediated by iminosemiquinone ligands

Stoichiometric silylation of the uranyl species, (dippisq)2UO2THF, which features two reduced iminosemiquinone ligands, is reported. These ligand radicals facilitate the reduction of uranium 6+ to 4+, which is accompanied by silylation of the uranyl moiety with two equivalents of Me3SiBr and release of the oxidized ligand. The intermediate, (Me3SiO)2UBr2(OPPh3)2, is isolated prior to U–O bond cleavage by further addition of Me3SiBr, producing UBr4(OPPh3)2. U–O bond scission can also be performed in a one-pot reaction, by treating (dippisq)2UO2THF with Me2SiCl2, forming UCl4(OPPh3)2 and polymeric silyl products, (OSiMe2)n, with concomitant loss of oxidized ligand. In each case, isotopic 18O labeling experiments highlight the incorporation of the uranyl oxygen atoms into the resulting siloxanes released in the reactions.

Structural features of uranium-protein complexes

Uranium toxicity depends on its chemical properties rather than on its radioactivity and involves its interaction with macromolecules. Here, a systematic survey of the structural features of the uranyl sites observed in protein crystal structures deposited in the Protein Data Bank is reported. Beside the two uranyl oxygens, which occupy the axial positions, uranium tends to be coordinated by five other oxygen atoms, which occupy the equatorial vertices of a pentagonal bipyramid. Even if one or more of these equatorial positions are sometime empty, they can be occupied only by oxygen atoms that belong to the carboxylate groups of Glu and Asp side-chains, usually acting as monodentate ligands, to water molecules, or to acetate anions. Although several uranium sites appear undefined or unrefined, with a single uranium atom that lacks the two uranyl oxygen atoms, this problem seems to become less frequent in recent years. However, it is clear that the crystallographic refinements of the uranyl sites are not always well restrained and a better parametrization of these restraints seems to be necessary.

Dioxidouranium(IV) complexes with Schiff bases possessing an ONO donor set: Synthetic, structural and spectroscopic studies

Tridentate Schiff bases derived from the condensation of salicylaldehyde and o-aminophenol or its derivatives have rarely been used in 5f-metal chemistry. Synthetic investigations of the UO2(O2CMe)2·2H2O/4MesaphH2 and UO2(O2CMe)2·2H2O/4ClsaphH2 systems, where 4MesaphH2 is N-salicylidene-4-methyl-o-aminophenol and 4ClsaphH2 is N-salicylidene-4-chloro-o-aminophenol, have provided access to the complexes [(UO2)2(4Mesaph)2(EtOH)2] (1) and [(UO2)2(4Clsaph)2(EtOH)2] (2), respectively, in moderate to good yields. The structures of the isomorphous complexes have been determined by single-crystal X-ray crystallography. In the dinuclear molecules, the two UVI atoms are bridged by two phenoxido oxygen atoms that belong to the methyliminophenolate (1) or chloroiminophenolate (2) parts of the two doubly deprotonated 2.121 ligands. Each UVI center is surrounded by one imine nitrogen and six oxygen atoms in a distorted pentagonal bipyramidal geometry, in which the two uranyl oxido atoms occupy the axial positions. H-bonding interactions build the 3D architectures of the compounds; the H-bond donors are the coordinated ethanol oxygen and aromatic carbon atoms, while the acceptors are the terminal oxygen atoms of the salicylaldehyde parts of the ligands and one of the uranyl oxygen atoms. IR data are discussed in terms of the coordination modes of the ligands. 1H NMR spectra in DMSO‑d6 provide evidence that the structures of the complexes are retained in solution. Upon maximum excitation at 445 nm, a green light emission with a maximum at 563 nm has been recorded for solid 2 at room temperature.

The effect of iron binding on uranyl(v) stability.

Here we report the effect of UO2 +···Fe2+ cation-cation interactions on the redox properties of uranyl(v) complexes and on their stability with respect to proton induced disproportionation. The tripodal heptadentate Schiff base trensal3- ligand allowed the synthesis and characterization of the uranyl(vi) complexes [UO2(trensal)K], 1 and [UO2(Htrensal)], 2 and of uranyl(v) complexes presenting UO2 +···K+ or UO2 +···Fe2+ cation-cation interactions ([UO2(trensal)K]K, 3, [UO2(trensal)] [K(2.2.2crypt)][K(2.2.2crypt)], 4, [UO2(trensal)Fe(py)3], 6). The uranyl(v) complexes show similar stability in pyridine solution, but the presence of Fe2+ bound to the uranyl(v) oxygen leads to increased stability with respect to proton induced disproportionation through the formation of a stable Fe2+-UO2 +-U4+ intermediate ([UO2(trensal)Fe(py)3U(trensal)]I, 7) upon addition of 2 eq. of PyHCl to 6. The addition of 2 eq. of PyHCl to 3 results in the immediate formation of U(iv) and UO2 2+ compounds. The presence of an additional UO2 + bound Fe2+ in [(UO2(trensal)Fe(py)3)2Fe(py)3]I2, 8, does not lead to increased stability. Redox reactivity and cyclic voltammetry studies also show an increased range of stability of the uranyl(v) species in the presence of Fe2+ with respect both to oxidation and reduction reactions, while the presence of a proton in complex 2 results in a smaller stability range for the uranyl(v) species. Cyclic voltammetry studies also show that the presence of a Fe2+ cation bound through one trensal3- arm in the trinuclear complex [{UO2(trensal)}2Fe], 5 does not lead to increased redox stability of the uranyl(v) showing the important role of UO2 +···Fe2+ cation-cation interactions in increasing the stability of uranyl(v). These results provide an important insight into the role that iron binding may play in stabilizing uranyl(v) compounds in the environmental mineral-mediated reduction of uranium(vi).

Cleaving Off Uranyl Oxygens through Chelation: A Mechanistic Study in the Gas Phase

Recent efforts to activate the strong uranium-oxygen bonds in the dioxo uranyl cation have been limited to single oxo-group activation through either uranyl reduction and functionalization in solution, or by collision induced dissociation (CID) in the gas-phase, using mass spectrometry (MS). Here, we report and investigate the surprising double activation of uranyl by an organic ligand, 3,4,3-LI(CAM), leading to the formation of a formal U6+ chelate in the gas-phase. The cleavage of both uranyl oxo bonds was experimentally evidenced by CID, using deuterium and 18O isotopic substitutions, and by infrared multiple photon dissociation (IRMPD) spectroscopy. Density functional theory (DFT) computations predict that the overall reaction requires only 132 kJ/mol, with the first oxygen activation entailing about 107 kJ/mol. Combined with analysis of similar, but unreactive ligands, these results shed light on the chelation-driven mechanism of uranyl oxo bond cleavage, demonstrating its dependence on the presence of ligand hydroxyl protons available for direct interactions with the uranyl oxygens.

UO2 Cl2 (phen)2 ], a Simple Uranium(VI) Compound with a Significantly Bent Uranyl Unit (phen=1,10-phenanthroline).

A simple synthesis based on UO2 Cl2 ⋅n H2 O and 1,10-phenanthroline (phen) resulted in the formation of a new uranyl(VI) complex [UO2 Cl2 (phen)2 ] (1), revealing a unique dodecadeltahedron coordination geometry around the uranium center with significant bending of the robust linear arrangement of the uranyl (O-U-O) unit. Quantum chemical calculations on complex 1 indicated that the weak but distinct interactions between the uranyl oxygens and the adjacent hydrogens of phen molecules play an important role in forming the dodecadeltahedron geometry that fits to the crystal structure of 1, resulting in the bending the uranyl unit. The uranyl oxygens in 1 are anticipated to be activated as compared with those in other linear uranyl(VI) compounds.

Effect of solvents in mixed-ligand supramolecular self-assembly architectures

Seven new uranyl isothiosemicarbazone complexes with the general formula UO2L(hmb)X (X; 1: ethanol, 2: 1-propanol 3: 1-butanol, 4: 1-pentanol, 5: ethylene glycol, 6: propane-1,2-diol, 7: DMSO) were synthesized by the template reaction of allyl N′-2-hydroxy-3-methoxybenzylidenecarbamohydrazonothioate.hydrobromide (H2L·HBr), 2-hydroxy-4-methoxybenzaldehyde (hmb), a U(VI) salt and the appropriate solvent or by recrystallization of 1 from the aforementioned solvents. These compounds were characterized by FT-IR, 1H and 13C NMR, mass spectrometry, elemental and TGA analyses. Single-crystal X-ray diffraction analyses of the complexes reveal distorted pentagonal bipyramidal geometries in which the N2O2 compartment and the oxygen atom of the coordinated solvent form the equatorial plane and the two uranyl oxygen atoms occupy the apical positions. Compounds 1–6 form dimers through pairwise bifurcated hydrogen bonds between solvent molecules and phenoxy oxygen atoms. Moreover, the self-assembly along the c axis with C–H⋯O and C–H⋯πring interactions generates a one-dimensional topology. The aromatic rings play the most important role in constructing the second dimension while different interactions are responsible for the formation of the third dimension in each of compounds 1–6. Classical and non-classical van der Waals interactions in compound 7 generate a one-dimensional expansion of two woven ribbons along the c direction and these woven chains join together to complete the supramolecular architecture, which resembles a set of bricks. The thermal decomposition of all the complexes occurs in three steps, starting with the removal of the coordinated solvent, followed by loss of the S-allyl group and finally the residual ligand fragment. U3O8 is obtained as the final residue.

Uranyl Carbonate Complexes in Aqueous Solution and Their Ligand NMR Chemical Shifts and 17O Quadrupolar Relaxation Studied by ab Initio Molecular Dynamics.

Dynamic structural effects, NMR ligand chemical shifts, and 17O NMR quadrupolar relaxation rates are investigated in the series of complexes UO22+, UO2(CO3)34-, and (UO2)3(CO3)66-. Car-Parrinello molecular dynamics (CPMD) is used to simulate the dynamics of the complexes in water. NMR properties are computed on clusters extracted from the CPMD trajectories. In the UO22+ complex, coordination at the uranium center by water molecules causes a decrease of around 300 ppm for the uranyl 17O chemical shift. The final value of this chemical shift is within 40 ppm of the experimental range. The UO2(CO3)34- and (UO2)3(CO3)66- complexes show a solvent dependence of the terminal carbonate 17O and 13C chemical shifts that is less pronounced than that for the uranyl oxygen atom. Corrections to the chemical shift from hybrid functionals and spin-orbit coupling improve the accuracy of chemical shifts if the sensitivity of the uranyl chemical shift to the uranyl bond length (estimated at 140 ppm per 0.1 Å from trajectory data) is taken into consideration. The experimentally reported trend in the two unique 13C chemical shifts is correctly reproduced for (UO2)3(CO3)66-. NMR relaxation rate data support large 17O peak widths, but remain below those noted in the experimental literature. Comparison of relaxation data for solvent-including versus solvent-free models suggest that carbonate ligand motion overshadows explicit solvent effects.

Can uranyl complexes encapsulate to carbon nanotubes? A periodic DFT study

Periodic density functional theory (DFT)-based calculations were carried out on a series of uranyl complexes encapsulated within single walled (SW)-CNT to understand their encapsulation affinities. We find that uranyl-aqua complex $$([\hbox {UO}_{2}(\hbox {H}_{2}\hbox {O})_{5}]^{2+}$$ ) binds stronger as compared to uranyl-hydroxo-complex $$([\hbox {UO}_{2}(\hbox {OH})_{4}]^{2-}$$ ) due to the variable overall charge of the complex. Further, binding affinities of uranyl formate complexes with different formate stoichiometries (1:1, 1:2 and 1:3) with SW-CNT are considered. Here again, due to variable charges, cationic mono-‘formate-uranyl $$([\hbox {UO}_{2}(\hbox {FM})(\hbox {H}_{2}\hbox {O})_{3}]^{1+})$$ complex binds stronger as compared to anionic tri-formate uranyl $$([\hbox {UO}_{2}(\hbox {FM})_{3}]^{1-})$$ . Further, due to the very weak binding commonly found in $$[\hbox {UO}_{2}(\hbox {FM})_{3}]^{1-}$$ to CNT, the tubular ends of SW-CNT are sealed with functionalized $$\hbox {C}_{36}$$ fullerene. The binding affinity of uranyl complex is not improved when $$\hbox {C}_{36}$$ fullerene is used to seal to the SW-CNT as compared to its unsealed counterpart. However, upon functionalizing (at the hub carbon) the $$\hbox {C}_{36}$$ cork, the binding affinity of $$[\hbox {UO}_{2}(\hbox {FM})_{3}]^{1-}$$ is larger inside the CNT due to favorable hydrogen bonding interactions with the uranyl oxygens. Our findings are consistent with the experimental observations which will help to design novel nanomaterials for nuclear waste management processes. The use of functionalized fullerene as removable corks which can seal single walled carbon nanotubes has the ability to bind uranyl complexes very efficiently is revealed through density functional theory based calculations.

Unusual intramolecular CHO hydrogen bonding interaction between a sterically bulky amide and uranyl oxygen.

The selective separation of toxic heavy metals such as uranyl can be accomplished using ligands with stereognostic hydrogen bonding interactions to the uranyl oxo group, as proposed by Raymond and co-workers (T. S. Franczyk, K. R. Czerwinski and K. N. Raymond, J. Am. Chem. Soc., 1992, 114, 8138-8146). Recently, several ligands possessing this weak interaction have been proposed involving the hydrogen bonding of NH and OH based moieties with uranyl oxygen. We herein report the structurally and spectroscopically characterized CHO hydrogen bonding using a sterically bulky amide based ligand. In conjunction with experiments, electronic structure calculations are carried out to understand the structure, binding and the strength of the CHO hydrogen bonding interactions. This weak interaction is mainly due to the steric effect caused by a bulky substituent around the donor group which has direct relevance in designing novel ligands in nuclear waste management processes. Although the kinetics are very slow, the ligand is also highly selective to uranyl in the presence of other interfering ions such as lanthanides.

X-ray diffraction refinement of the structure of diaquadinitratouranyl tetrahydrate [UO2(NO3)2(H2O)2] • 4H2O

Single crystals of diaquadinitratouranyl tetrahydrate [UO2(NO3)2(H2O)2] • 4H2O (I) have been synthesized by evaporating an aqueous [UO2(NO3)2(H2O)2] • 2H2O solution containing nitric acid under air at room temperature. An experimental X-ray diffraction intensity set has been obtained from a single crystal of I. Crystals are ortorhombic, a = 13.113(2) A, b = 7.9847(12) A, c = 11.3323(17) A, space group Cmc21, Z = 4, V = 1186.5(3) A3. The structural units of a crystal of complex I are neutral molecular complexes [UO2(NO3)2(H2O)2] and crystal water molecules linked by a network of hydrogen bonds. The uranium atom is in a hexagonal bipyramidal surrounding. Axial positions are occupied by uranyl oxygen atoms, and two nonequivalent bidentate cyclic nitrato groups and two equivalent water molecules are coordinated in the equatorial plane in trans-positions to each other. Coordinated and outer-sphere water molecules in the molecular structure of complex I are linked by hydrogen bonds as O-H(H2Ocoord)⋯O(H2Oout). Outer-sphere water molecules are linked to each other and the terminal oxygen atoms of nitrato groups by hydrogen bonds as O-H(H2Oout)⋯O(H2Oout) and O-H(H2Oout)⋯O(ONO2-). Hydrogen bonds of the first type are stronger than those of the second and third types.