Gas-phase reactions of molecular oxygen with uranyl(V) anionic complexes-synthesis and characterization of new superoxides of uranyl(VI).

Gas-phase complexes of uranyl(V) ligated to anions X(-) (X = F, Cl, Br, I, OH, NO3, ClO4, HCO2, CH3CO2, CF3CO2, CH3COS, NCS, N3), [UO2X2](-), were produced by electrospray ionization and reacted with O2 in a quadrupole ion trap mass spectrometer to form uranyl(VI) anionic complexes, [UO2X2(O2)](-), comprising a superoxo ligand. The comparative rates for the oxidation reactions were measured, ranging from relatively fast [UO2(OH)2](-) to slow [UO2I2](-). The reaction rates of [UO2X2](-) ions containing polyatomic ligands were significantly faster than those containing the monatomic halogens, which can be attributed to the greater number of vibrational degrees of freedom in the polyatomic ligands to dissipate the energy of the initial O2-association complexes. The effect of the basicity of the X(-) ligands was also apparent in the relative rates for O2 addition, with a general correlation between increasing ligand basicity and O2-addition efficiency for polyatomic ligands. Collision-induced dissociation of the superoxo complexes showed in all cases loss of O2 to form the [UO2X2](-) anions, indicating weaker binding of the O2(-) ligand compared to the X(-) ligands. Density functional theory computations of the structures and energetics of selected species are in accord with the experimental observations.

The inverse trans influence in a family of pentavalent uranium complexes.

Systematic ligand variation in a structurally conserved framework of pentavalent uranium complexes of the formulas U(V)X2[N(SiMe3)2]3 (X = F, Cl, Br, N3, NCS, 2-naphthoxide) and U(V)OX[N(SiMe3)2]3(-) (X = -CCPh, -CN) allowed an investigation into the role of the inverse trans influence in pentavalent uranium complexes. The -CCPh and -CN derivatives were only stable in the presence of the trans-U═O multiple bond, implicating the inverse trans influence in stabilizing these complexes. Spectroscopic, structural, and density functional theory calculated electronic structural data are explored. Near-IR data of all complexes is presented, displaying vibronic coupling of 5f(1) electronic transitions along the primary axis. Electrochemical characterization allowed assessment of the relative donating ability of the various axial ligands in this framework. Electron paramagnetic resonance data presented display axial spectra, with hyperfine coupling along the primary axis.

Synthesis, structures, and properties of uranyl hybrids constructed by a variety of mono- and polycarboxylic acids.

A series of uranyl-organic coordination polymers have been hydrothermally synthesized by using a variety of carboxylic ligands, 3,3'-((2-((3-carboxyphenoxy)methyl)-2-methylpropane-1,3-diyl)bis(oxy))dibenzoic acid (H3L(1)), 4,4'-(3-(4-carboxyphenethyl)-3-hydroxypentane-1,5-diyl)dibenzoic acid (H3L(2)), chelidamic acid (H2L(3)), and benzoic acid (HL(4)) in the presence of N-bearing coligands, including 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), 1-([1,1'-biphenyl]-4-yl)-1H-imidazole (bpi), and 1,4-di(1H-imidazol-1-yl)benzene (dib). Compounds (UO2)(HL(1)) (1) and Zn(H2O)3(UO2)2(O)(OH)(L(2))·H2O (2) are constructed by semirigid ligands. The former is a one-dimensional ribbon-like structure with UO7 pentagonal bipyramids as the building unit, while the latter adopts a tetramer of UO7 pentagonal bipyramids to build a layered structure. Mononuclear UO7 pentagonal bipyramids are connected by L(3) groups to generate a two-dimensional arrangement of UO2(L(3))(H2dib)0.5 (3), in which the protonated dib molecules provide space filling and form π···π interactions with the layers. Compounds UO2(L(3))(phen) (4), UO2(L(3))2(Hbpi)2 (5), and UO2(L(4))2(bipy) (6) are molecular complexes, in which 4 and 6 are neutral, and 5 comprises protonated bpi as the counterion. The uranyl center in compound 4 is chelated by one phen and one L(3) group to form a UO5N2 pentagonal bipyramid, while in compound 5, two L(3) groups are coordinated to an uranyl center, producing a UO8 polyhedron. Compound 6 consists of a UO6N2 polyhedron of uranyl unit coordinated by one bipy and two benzoate groups. Compounds Zn(phen)3[(UO2)(C2O4)(L(4))]2 (7) and Zn(bpi)2(UO2)(O)(C2O4)0.5(L(4))·H2O (8) feature one-dimensional structures. In 7, UO7 pentagonal bipyramids are alternatively connected by oxalate groups to form the chain, in which unidentate benzoate groups are coordinated to the uranium atoms. Zn(phen)3 cations fill the void space of the chains to compensate the negative charge. Differently, the chain of 8 can be seen as the heterometallic tetramer of UO7 and ZnO2N2 polyhedra connected by oxalate groups, and then bpi and benzoate groups are coordinated to the chain. All of the compounds have been characterized by IR and photoluminescent spectroscopy, and compounds 2, 3, 5, 6, and 8 exhibit characteristic emissions of uranyl cations.

Attitude towards personal protective equipment in the French nuclear fuel industry.

This descriptive cross-sectional study examines the compliance of workers from the European Gaseous Diffusion Uranium Enrichment Consortium (EURODIF) with personal protection equipment (PPE) in view of the various hazards in the nuclear fuel industry. The PPE inventory was drawn up by an industrial hygienist in charge of the PPE at EURODIF. Two hundred and twenty seven (10%) randomly selected, active and retired, EURODIF workers filled in a questionnaire on their attitudes towards PPE. Exposure data from the EURODIF job exposure matrix were used to examine whether PPE usage varies according to exposure level. The study suggests a PPE usage profile that varies depending on the hazards present and PPE available. Anti-uranium PPE and gloves were among the best rated, while anti-spray goggles were the least used. We found that, for most hazards known to cause cancer or irreversible health damage, PPE usage varied according to exposure (homogeneity test, p<0.05; trend test, p<0.05). The continuous use of PPE among workers should be encouraged through improvements to the PPE management system. A precise model of individual exposure can only be designed if the use and efficiency of PPE are taken into consideration.

Polytypism and oxo-tungstate polyhedra polymerization in novel complex uranyl tungstates.

Three new uranyl tungstates, α-, ß-Cs(2)[(UO(2))(2)(W(2)O(9))], and Rb(6)[(UO(2))(7)(WO(5))(2)(W(3)O(13))O(2)], have been obtained by high temperature solid state reactions. All three compounds display novel structure topologies: α- and ß-Cs(2)[(UO(2))(2)(W(2)O(9))] are based upon layers with a new topology that can be related to the uranophane topology; Rb(6)[(UO(2))(7)(WO(5))(2)(W(3)O(13))O(2)] is a rare example of a non-molecular inorganic phase with layers containing oxo-tungstate trimers. The structural relationship between α- and ß-Cs(2)[(UO(2))(2)(W(2)O(9))] can be assigned to polytypism.

Uranium azide photolysis results in C-H bond activation and provides evidence for a terminal uranium nitride.

Uranium nitride [U[triple bond]N](x) is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U[triple bond]N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U-N=N=N) precursor. The transient U[triple bond]N fragment is reactive and undergoes insertion into a ligand C-H bond to generate new N-H and N-C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C(6)F(5))(3). These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C-H bonds.

Polymer complexes: XLX. Novel supramolecular coordination modes of structure and bonding in polymeric hydrazone sulphadrugs uranyl complexes.

Novel five binuclear polymeric dioxouranium(VI) of azosulphadrugs [(azodrug substances) azobenzene sulphonamides] were prepared for the first time. The infrared spectra of the samples were recorded and their fundamental vibration wave number was obtained. The resulting polymeric uranyl complexes were characterized on the basis of their elemental analyses, conductance and spectral (IR, NMR, and electronic spectra) data. The ligation modes of the azosulphadrugs ligands towards uranyl(II) ions were critically assigned and addressed properly on the basis of their IR and their uranyl(II) complexes. The theoretical aspects are described in terms of the well-known theory of 5d-4f transitions. The coordination geometries and electronic structures are determined from a framework for the modeling of novel polymer complexes. The values of nu(3) of the prepared complexes containing UO(2)(2+) were successfully used to calculate the force constant, F(UO) (1n 10(-8)N/A) and the bond length R(UO) of the U-O bond. Wilson's, matrix method, Badger's formula, and Jones and El-Sonbati equations were used to calculate the U-O bond distances from the values of the stretching and interaction force constants. The most probable correlations between U-O force constant to U-O bond distance were satisfactorily discussed in terms of "Badger's rule", "Jones" and "El-Sonbati equations".

Visualizing different uranium oxidation states during the surface alteration of uraninite and uranium tetrachloride.

Low-temperature alteration reactions on uranium phases may lead to the mobilization of uranium and thereby poses a potential threat to humans living close to uranium-contaminated sites. In this study, the surface alteration of uraninite (UO(2)) and uranium tetrachloride (UCl(4)) in air atmosphere was studied by confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy using an excitation wavelength of 408 nm. It was found that within minutes the oxidation state on the surface of the uraninite and the uranium tetrachloride changed. During the surface alteration process U(IV) atoms on the uraninite and uranium tetrachloride surface became stepwise oxidized by a one-electron step at first to U(V) and then further to U(VI). These observed changes in the oxidation states of the uraninite surface were microscopically visualized and spectroscopically identified on the basis of their fluorescence emission signal. A fluorescence signal in the wavelength range of 415-475 nm was indicative for metastable uranium(V), and a fluorescence signal in the range of 480-560 nm was identified as uranium(VI). In addition, the oxidation process of tetravalent uranium in aqueous solution at pH 0.3 was visualized by CLSM and U(V) was fluorescence spectroscopically identified. The combination of microscopy and fluorescence spectroscopy provided a very convincing visualization of the brief presence of U(V) as a metastable reaction intermediate and of the simultaneous coexistence of the three states U(IV), U(V), and U(VI). These results have a significant importance for fundamental uranium redox chemistry and should contribute to a better understanding of the geochemical behavior of uranium in nature.

Synthesis of colloidal uranium-dioxide nanocrystals.

In this paper, we have developed an organic-phase synthesis method for producing size-controlled, nearly monodispersed, colloidal uranium-dioxide nanocrystals. These UO2 nanocrystals are potentially important to applications such as nuclear fuel materials, catalysts, and thermopower materials. In addition, we have systematically mapped out the functions of the solvents (oleic acid, oleylamine, and 1-octadecene) in the synthesis, and we found that N-(cis-9-octadecenyl)oleamide-a product of the condensation of oleic acid and oleylamine-can substantially affect the formation of UO2 nanocrystals. Importantly, these results provide fundamental insight into the mechanisms of UO2 nanocrystal synthesis. Moreover, because a mixture of oleic acid and oleylamine has been widely used in synthesizing a variety of high-quality metal or metal-oxide nanocrystals, the results herein should also be important for understanding the detailed mechanisms of these syntheses.

Determination of the formation constants of ternary complexes of uranyl and carbonate with alkaline earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) using anion exchange method.

The formation constants of ternary complexes (MUO2(CO3)3(2-) and M2UO2(CO3)3(0)) of uranyl and carbonate with alkaline earth metals (M2+ denotes Mg2+, Ca2+, Sr2+, and Ba2+) were determined with an anion exchange method by varying the metal concentrations (0.1-5 mmol/L) at pH 8.1 and a constant ionic strength (0.1 mol/L NaNO3) under equilibrium with atmospheric CO2. The results indicate that the complexes of MUO2(CO3)3(2-) and M2UO2(CO3)3 are simultaneously formed for Ca2+ and Ba2+, while Mg2+ and Sr2+ form only the MUO2(CO3)3(2-) complex under our experimental conditions. The cumulative stability constants for the MUO2(CO3)3(2-) complex obtained at / = 0 are as follows: logbeta113 = 26.11 +/- 0.04, 27.18 +/- 0.06, 26.86 +/- 0.04, and 26.68 +/- 0.04 for Mg2+, Ca2+, Sr2+, and Ba2+, respectively. For M2UO2(CO3)3(0), the value of logbeta213 at / = 0 was measured to be 30.70 +/- 0.05 and 29.75 +/- 0.07 for Ca2+ and Ba2+, respectively. Based on the formation constants obtained in this study, speciation calculations indicate that at low Ca2+ concentration (e.g., <2.2 mmol/L), CaUO2(CO3)3(2-) is more important than Ca2UO2(CO3)3 and that the Ca2UO2(CO3)3 distribution increased with increasing Ca2+ concentration. Uranium sorption onto anion-exchange resins is inhibited by the formation of the neutral Ca2UO2(CO3)3(0) species.

Novel supramolecular assembly of symmetrical mixed-metal-ligand complexes of dioxouranium(VI).

Some binary and ternary novel complexes of dioxouranium(VI) with 8-hydroxy-7-quinolinecarboxaldehyde (OXH) have been prepared and characterized by elemental analyses, magnetic susceptibility measurements and spectral studies. Coordination effects on the vibrational spectra of the ligands have been investigated. The amine exchange reactions of coordinated Schiff bases in these complexes have been also studied, which reveal symmetrical tetradentate Schiff base complexes. Metal exchange reaction of dioxouranium(VI) complexes was obtained when reacted with tetradentate Schiff base complexes of Cu(II) with ZrCl(4)/UO(2)(CH(3)COO)(2) giving heterobinuclear complexes. Magnetic, electronic and IR spectral data suggest the configurations of distorted square planar ligand field copper(II) complexes. The ligands behave as bi-(O,O) and tetradentate (N(2),O(2)) donors. El-Sonbati equation has been used to evaluate the symmetric stretching frequency from which the F(U-O) and F(UO,UO)(-) were calculated. The bond distances of these complexes were also investigated.

Structural model of dioxouranium(VI) with hydrazono ligands.

Synthesis and characterization of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate hydrazono compounds derived from 1-phenyl-3-methyl-5-pyrazolone are described. The ligands and uranayl complexes have been characterized by various physico-chemical techniques. The bond lengths and the force constant have been calculated from asymmetric stretching frequency of OUO groups. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and hydrazo nitrogen donor system. The effect of Hammett's constant on the bond distances and the force constants were also discussed and drawn. Wilson's matrix method, Badger's formula, Jones and El-Sonbati equations were used to determine the stretching and interaction force constant from which the UO bond distances were calculated. The bond distances of these complexes were also investigated.

Spectroscopic evidence for the direct coordination of the pertechnetate anion to the uranyl cation in [UO2(TcO4)(DPPMO2)2]+.

We report the synthesis and structural characterization of [UO(2)(ReO(4))(DPPMO(2))(2)][ReO(4)] and [UO(2)(Cl)(DPPMO(2))(2)][Cl] (where DPPMO(2) = bis(diphenylphosphino)methane dioxide). In both complexes, the linear uranyl dication is coordinated to two bidentate DPPMO(2) ligands in the equatorial plane with one coordinated and one non-coordinated anion (either perrhenate or chloride). We have also prepared the pertechnetate analogue, and, through (31)P and (99)Tc NMR, we have shown that the cation, [UO(2)(TcO(4))(DPPMO(2))(2)](+), is stable in solution.

Uranium complexes supported by an aryloxide functionalised triazacyclononane macrocycle: synthesis and characterisation of a six-coordinate U(III) species and insights into its reactivity.

A reactive low-valent uranium(III) complex supported by an aryloxide functionalised triazacyclononane has been synthesised and provides a platform for enhanced uranium reactivity.

Structure of uranium(VI) oxide dihydrate, UO3.2H2O; synthetic meta-schoepite (UO2)4O(OH)6.5H2O.

Structure of uranium(VI) oxide dihydrate, P03.2H20; synthetic meta-schoepite (UO2)40(OH)6.5H20 f The structure of uranium oxide dihydrate, also known as meta-schoepite (UO2)4O(OH)6.5H2O, has been determined from a synthetic single crystal. The structure, at 150 K, space group Pbcn, lattice constants a = 14.6861 (4), b = 13.9799 (3) and c = 16.7063 (5) A, consists of layers of stoichiometry (UO2)4O(OH)6, formed from edge-sharing UO7 pentagonal bipyramids, interleaved with hydrogen-bonded water molecules. Three of the layer hydroxyl groups are linked through hydrogen bonding to single water molecules and the three remaining OH units form interactions with water molecules that each act as acceptors in two hydrogen bonds. One of the water molecules in the inter-layer region is disordered over two symmetry-related sites and forms hydrogen-bonded interactions only within the layer and with the uranyl O atoms. The relationship of the structure of meta-schoepite to that of schoepite is discussed in detail.