Showing papers on "Uranyl published in 1990"

Uranium(VI) organoimido complexes

Abstract: Complexes containing multiply bonded alkylidene, alkylidyne, imido, nitrido, and oxo ligands, and selected combinations thereof, are part of the tapestry of tungsten(VI) chemistry. Aside from uranyl complexes, the only reported molecular coordination compounds of U(VI) are UF{sub 6}, UCl{sub 6}, and the binary alkoxides, U(OR){sub 6}. Uranium(VI) compounds containing the other functional groups listed above have never been reported. Here the authors describe the synthesis and structural characterization of the first uranium(VI) systems containing a multiple bond to nitrogen.

Electron transfer from halide ions to uranyl(2+) excited-state ions in aqueous solution: formation and decay of dihalide radical anions

Abstract: The decay of the excited uranyl ion in water in the presence of Cl{sup {minus}}, Br{sup {minus}}, I{sup {minus}}, and SCN{sup {minus}} is studied by laser flash kinetic spectrophotometry. The four anions all quench *UO{sub 2}{sup 2+} by a bimolecular process suggested to involve electron or charge transfer. Steady-state luminescence studies suggest that there is also some static contribution to the quenching. For Br{sup {minus}}, I{sup {minus}}, and SCN{sup {minus}}, radical anions, X{sub 2}{sup {sm bullet}{minus}}, are observed. However, kinetic studies indicate that these are not formed directly from *UO{sub 2}{sup 2+} but probably come by bimolecular reaction of an intermediate uranium(V)/radical pair with the corresponding halide ion. The extinction coefficient for the *UO{sub 2}{sup 2+} absorption is reported, and by use of this and transient absorbance data radical-anion yields are obtained and found to depend linearly upon the halide anion concentration. The variation of the yield in the series I{sup {minus}}, SCN{sup {minus}}, and Br{sup {minus}} is interpreted in terms of the effect of overall free energy change on back-electron-transfer in the uranium(V)/radical pair. With the chloride system no significant yield of radical anion was observed. The decay of X{sub 2}{sup {sm bullet}{minus}} was found to be unaffected bymore » the presence of uranyl ion, supporting the previously suggested mechanism for radical-anion decay in these systems. 68 refs., 6 figs., 2 tabs.« less

Exafs for studying corrosion of glass surfaces

Abstract: The technique of glancing angle EXAFS is introduced and applied to the study of aqueous corrosion at the surface of sodium borosilicate glass. In particular, the structural roles of iron and uranium are compared at loadings typical for nuclear waste disposal. The structural chemistry observed at the surface is rich in detail and adds considerably to the qualitative picture for the leaching of oxide glasses obtained from conventional surface analytical probes. Both metald migrate to the surface as corrosion progresses, iron more rapidly than uranium. There is evidence for mineralisation of the modifiers at the surface following leaching and, in the case of uranium, as a result of polishing. Indeed the uranyl configuration of U 6+ is particularly sensitive to changes just beyond the oxygen ligand. Wet and dry surfaces can be distinguished and square planar clustering can be identified. The sequence of events is interpreted in terms of ion migration and water infusion taking place along percolation channels within the borosilicate network.

Study of luminescent forms of the uranyl ion

Abstract: — Luminescence spectra and luminescence decay kinetics of uranyl sulphate water and uranyl nitrate acetone solutions of different concentrations have been studied. Similar experiments have been done with uranyl sulphate powder under vacuum. It has been experimentally shown that the hydrolysis of uranyl sulphate in water takes place, and under low salt concentrations (0.1-4.0 times 10-4M) a luminescence of a basic form of the photoexcited ion with a tentative structure of UO2OH+* has been observed. The luminescence of the acidic form UO+* has been observed under higher salt concentrations (1–4 times 10-2M) in water and under any salt concentration in acetone. The acidic form has the characteristic emission spectrum possessing vibrational structure. The luminescence concentrational quenching of both photoexcited uranyl forms and exciplex emission have not been observed. The effect of a number of organic quenchers and molecular oxygen on uranyl luminescence has been studied. There is no luminescence quenching by O2 up to 2 times 106 Pa (20 atm) pressure. The low effectiveness of energy transfer from the photoexcited uranyl forms has been explained in terms of strong steric screening of 5f-uranium (VI) orbital by oxygen atoms and by external filled up uranium electronic shells.

DNA Conformational analysis in solution by uranyl mediated photocleavage

Abstract: Uranyl mediated photocleavage of double stranded DNA is proposed as a general probing for DNA helix conformation in terms of minor groove width/electronegative potential. Specifically, it is found that A/T-tracts known to constitute strong distamycin binding sites are preferentially photocleaved by uranyl in a way indicating strongest uranyl binding at the center of the minor groove of the AT-region. The A-tracts of kinetoplast DNA show the highest reactivity at the 3'-end of the tract--as opposed to cleavage by EDTA/Fell--in accordance with the minor groove being more narrow at this end. Finally, uranyl photocleavage of the internal control region (ICR) of the 5S-RNA gene yields a cleavage modulation pattern fully compatible with that obtained by DNase I which also--in a more complex way--senses DNA minor groove width.

Synthesis, properties, and crystal structures of new mono- and homo-binuclear uranyl(VI) complexes with compartmental schiff bases

Abstract: Mono-and homo-binuclear uranyl(VI) complexes of the type [UO2(H2L1)]·solv, [(UO2)2(L1)(solv)], [UO2(H2L2)]·solv, and [(UO2)2(L2)(solv)], where solv is a co-ordinatingsolvent[H2O, dimethylformamide (dmf), or dimethyl sulphoxide (dmso)] and H4L1 and H4L2 are the potentially heptadentate dinucleating ligands derived by the condensation of 2,3-dihydroxybenzaldehyde with 1,5-diamino-3-azapentane or 1,5-diamino-3-thiapentane, have been prepared by a template procedure or by reaction of the preformed ligands with [UO2(CH3CO2)2]·2H2O and characterized by i.r., 1H and 13C n.m.r. spectroscopic and X-ray diffraction techniques. The crystal structures of [UO2(H2L1)]·dmf, [(UO2)2(L1)(dmso)], and [(UO2)2(L1)(dmf)] have been determined by X-ray crystallography and refined to conventional R values of 0.044, 0.054, and 0.039 respectively: [UO2(H2L1)]·dmf is monoclinic, space group P21/n, with a= 21.155(5), b= 11.833(8), c= 9.679(8)A, β= 102.34(3)°, Z= 4; [(UO2)2(L1)(dmso)] is monoclinic, space group P21/c, with a= 14.985(5), b= 16.536(5), c= 19.956(5)A, β= 90.13(3)°, Z= 8; [(UO2)2(L1)(dmf)] is monoclinic, space group P21/c, with a= 9.285(6), b= 16.187(5), c= 17.544(5)A, β= 104.56(3)°, and Z= 4. In [UO2(H2L1)]·dmf the ligand behaves as a quinquedentate dianionic and, using the inner co-ordination chamber, binds equatorially to UO22+ leading to seven-co-ordinated uranium in a distorted bipyramidal co-ordination geometry. A dmf molecule is hydrogen bonded to the phenolic oxygens of the ligand. Selected bond distances for this compound are U–O(uranyl) 1.79 (mean), U–O(ligand) 2.235 (mean), and U–N (mean) 2.59 A. In [(UO2)2(L1)(dmso)] and [(UO2)2(L1)(dmf)] the tetra-anionic chelating ligand co-ordinates the inner UO22+ as in [UO2(H2L1)]·dmf, while the outer UO22+ is co-ordinated by four oxygen atoms of the dinucleating ligand and by the oxygen atom of the solvent molecule. Structural details of the binuclear complexes are comparable. Comparison of the structures in the solid and in solution revealed some conformational differences.

Interactions of large ions with phospholipid monolayers

Abstract: Surface pressure-area isotherms of dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine, dimyristoylphosphatidylethanolamine, and dipalmitoylphosphatidylethanolamine monolayers have been measured at 25°C on buffer solutions from pH 1.5 to 12.5, and the effects of phosphotungstate ions and of uranyl ions in the subphase have been determined. Phosphotungstate causes expansion of the monolayers at low pH values, indicating some penetration into the monolayer region and an associated increase in the bulk phase pH for protonation of the phosphate. Uranyl ions cause contraction of expanded monolayers at low pH, which is attributed to adsorption of the UO22+ drawing neighboring phospholipid molecules together. Hydrolysis of the uranyl ions at higher pH values increases their size and reduces their charge, leading to decreased effects on the monolayers. It is concluded that the use of phosphotungstic acid or uranyl acetate as a "stain" for electron microscopy could lead to significant distortions in membrane or vesicle structure.

Synthesis of 1,3-Bis(benzo-15-crown-5)-2-thioxo-4,5-bis(hydroxyimino)imidazoline and its Complexes with Copper(II), Nickel(II), Cobalt(II), Cobalt(III), Palladium(II), and Uranyl(VI)

Abstract: 1,3-Bis(benzo-15-crown-5-)-2-thioxo-4,5-bis(hydroxyimino)imidazoline (H2L) has been synthesized using N,N'-bis(benzo-15-crown-5) thiourea, which has been prepared from 4′-aminobenzo(15-crown-5) and thiocarbonyldichloride, and cyanogen-di-N-oxide in dichloromethane. Nickel(II), Palladium(II), Copper(II), Cobalt(II), and Cobalt(III) complexes of H2L have a metal:ligand ratio of 1:2 and the ligand coordinates through the two N atoms, as most of the vicinal dioximes. [Co(HL)2(Benzimidazole)Cl. 4NaClO4] has also been prepared using benzimidazole and chloride ion as axial ligands. H2L reacts with UO2(O2CMe)2 2H2O to give complexes with a metal:ligand ratio of 1:1. All these complexes are slightly soluble in water. The ion extraction properties of H2L and N,N'-bis(benzo-15-crown-5)thiourea (BTU) towards lithium, sodium and potassium picrate from aqueous solution to dichlorobenzene have been measured. Extraction values, 1H, 13C n.m.r, i.r, and uv-visible data are presented.

Tetranuclear complexes of 1,3,5,9,11,13-hexaketonates. 2. Synthesis and electrochemistry of a series of heterotetranuclear complexes, bis {1,1'-(1,3-phenylene)bis[7-methyl-1,3,5-octanetrionato(4-)]}hexakis(pyridine)bis[di-oxouranium(VI)dimetal(II), M2(UO2)2(MOB)2(py)6

Abstract: A series of heterotetranuclear complexes was prepared by using a hexaketone ligand. The specific ligand used in this study contains two 1,3,5-triketone groups substituted at the meta positions of a benzene ring. Neutral complexes are formed by binding four dicationic metal species to two tetraanionic ligands. The resulting tetranuclear complexes contain two binuclear moities separated by about 7 A. A series of complexes with two uranyl ions and two metal ions, M 2+ , per molecule was prepared

External surface adsorption of uranyl–hydroxo complexes on zeolite particles in relation to the double-layer potential

Abstract: The natural zeolites used in this study and identified by X-ray diffraction were scolecite, chabazite, heulandite and stilbite. Thermal analysis (TG and DSC) and water adsorption isotherms were also used as characterization techniques. The zeta potential was measured by a microelectrophoretic technique on zeolite suspensions containing dilute uranyl solutions.The external adsorption of the uranyl species started at pH 4 and the highest values were reached between pH 6 and 7, when the adsorption could be ascribed to single (UO2)3(OH)+5 species. The zeta potential of zeolite particles in uranyl-free suspensions became more negative with increasing pH, explained by hydroxylation of the zeolite surface, resulting in a negative electrical double layer. For heulandite and stilbite a similar zeta potential vs. pH curve was obtained in the presence of uranyl species. The curves obtained in uranyl-containing solutions for scolecite and chabazite, which adsorb the greatest amount of uranyl species, showed a spectacular increase of the zeta potential to positive values between pH 4 and 5 but at higher pH the zeta-potential decreased to negative values. This was probably due to complicated electrostatic interactions between the external surface of the zeolite and the uranyl species in solution.

Structure of dibenzoatodioxouranium(VI)

Abstract: [U(C 7 H 5 O 2 ) 2 O 2 ] cristallise dans C2/m avec a=7,604, b=17,408, c=5,296 A, β=95,81 o , Z=2; affinement jusqu'a R=0,058. L'ion uranyl possede une coordination quaternaire. Le polyedre de coordination autour du centre uranium ressemble a un octaedre avec les groupements carboxylates agissant comme donneurs pontants

New uranyl(VI) complexes with hydrazones derived from aliphatic and aromatic acid hydrazides containing dihydroxo bridges

Abstract: Several new uranyl(VI) complexes of hydrazones, derived from formoyl-, acetoyl-, butroyl-, caproyl-, salicyloyl-, oxaloyldi-, malonoyldi-, and adipolyldi-hydrazines and benzaldehyde or salicylaldehyde have been prepared in absolute EtOH and in the presence or absence of AcONa. The complexes have been characterized by elemental analyses, molar conductivities, spectral (u.v., i.r, n.m.r.,) and magnetic measurements. I.r. spectral data suggest that the ligands coordinate in a bi-, tri- and/or tetradentate fashion in the enol form, and that proton displacement proceedsvia the enolized carbonyl oxygen solely in the benzaldehyde hydrazone complexes and through the OH (phenolic) in the salicylaldehyde hydrazone complexes. Moreover, the spectral data show the existence of dihydroxo bridges for benzaldehyde hydrazone complexes. The role of the OH (phenolic) as well as the presence or absence of NaOAc on the properties of the latter complexes is discussed.

Performance for PAN-3 chelate fiber for adsorbing and separating trace uranium—determination by ICP-OES

Abstract: An ICP-OES method is established for polyacrylamidoxime-carboxylic acid chelate fiber (PAN-3) adsorbing and separating trace uranium in waste water. The conditions for quantitative enrichment and desorption uranyl ions are investigated. The stability and the reuse performance of the chelate fiber are discussed. The interference of co-existent ions on uranyl ions as well as the analyses of samples are performed with satisfactory results. The lowest concentration of uranium determined by ICP-OES is 5 μg/l, its RSD is 2.6%.

Spectroscopic investigation of uranium complexation in the reversed micellar system HDEHP-n-heptane-water

Abstract: A spectroscopic investigation of the uranyl ion in the reversed micellar system HDEHP— n -heptane—water (HDEHP = di(2-ethylhexyl) phosphoric acid) was carried out to determine its site of solubilization, microenvironment and complexation with the extractant HDEHP in the apolar phase. The system was studied using absorption and emission spectroscopy. The vibrational interactions were determined using near-IR and IR spectroscopy.

An X-ray and thermogravimetric study of the lanthanum(III) uranyl propionate-acetate systems

Abstract: The structure of the complex [La2(C2H5COO)4 (H2O)6][UO2 (C2H5COO)3· UO2(C2H5COO)2.5(CH3COO)0.5] has been determined by X-ray diffraction techniques. The complex crystallizes in the monoclinic system, space group Pc, with cell dimensions a = 8.165(2) A , b = 21.104(4) A , c = 14.922(3) A , β = 95.06 (3)° and d calc = 2.14 g cm 3 with Z = 2, R = 0.037 and Rw = 0.038 for 4036 observed reflections. The propionate ligands bridge the lanthanide cations in chains developing in the [100] direction. The coordination geometry around each lanthanum ion is a distorted monocapped square antiprism, owing to the presence of three water molecules linked to each lanthanum ion. The cation chains are separated by UO2(propionate)3 and UO2 (propionate)2.5 (acetate)0.5 anions which balance the cation charges. X-ray powder investigations and thermogravimetric analyses complete the characterization of the compound.

Complex formation reactions of uranyl(VI) with neutral N-donors in dimethyl sulfoxide. Influence of small amounts of water

Abstract: Quantitative information about the existence and thermodynamic stability of uranyl(VI) ion complexes based solely upon nitrogen coordination has been obtained in the solvent dimethyl sulfoxide. Calorimetric, potentiometric, and FT-IR investigations, under controlled anhydrous conditions, show that the uranyl(VI) ion can form both mono and bis chelates with the ethylenediamine ligand and only a mono chelate of rather low stability with propylenediamine. With the monodentate ligand n-butylamine only a very weak metal-ligand interaction has been detected. The stability constants and the enthalpy and entropy changes have been calculated for the identified coordinated species. All data refer to 25.0{degree}C and a tetraethylammonium perchlorate medium of ionic strength 0.1 M. All the complexes are enthalpy stabilized whereas the entropy contributions oppose the complex formation. Calorimetric and FT-IR measurements carried out to investigate the effects of small amounts of water present show that a very low water concentration, comparable to that of the coordinating metal ion, can give rise to hydrolysis reactions that may compete with complex formation. This is due to the combined action of different factors that are discussed. 39 refs., 6 figs., 1 tab.

Thermodynamics of complexed aqueous uranyl species. 1. Volume and heat capacity changes associated with the formation of uranyl sulfate from 10 to 55.degree.C and calculation of the ion-pair equilibrium constant to 175.degree.C

Abstract: Apparent molar heat capacities and volumes of aqueous solutions containing UO{sub 2}SO{sub 4} in dilute H{sub 2}SO{sub 4} have been obtained from 10 to 55{degree}C. These results have been analyzed considering the ion-pair-formation reaction of uranyl with sulfate ion, and considering the contributions to the measured heat capacities from chemical relaxation. Young's rule was used to extract apparent molar volumes and heat capacities for the solute species UO{sub 2}SO{sub 4} from 10 to 55{degree}C. The temperature dependence of the standard-state heat capacity and volume functions for UO{sub 2}SO{sub 4}(aq) are represented by the following equations: {bar V}{degree}/(cm{sup 3} mol{sup {minus}1}) = {minus}93.87 + 0.7784T - 0.001 093 T{sup 2} and {bar C}{sub p}{degree}/(J K{sup {minus}1} mol{sup {minus}1}) = {minus} 2,773.1 + 13.636T - 0.015 322T{sup 2}, which are accurate from 10 to 55{degree}C. The volumetric and heat capacity changes associated with the complexation of uranyl ion with sulfate are compared with other results for divalent and trivalent monatomic cations. The results for uranyl sulfate and other metal sulfates have also been examined in reference to the Eigen-Tamm three-step ion-pair-formation model. The highly negative standard heat capacities of this neutral solute along with the structural data for uranyl sulfate provide informationmore » regarding the enhanced solute-water dipole interactions not present in systems containing other neutral solutes.« less

Uranyl(VI) Complexes of Pyridine-Based Pentadentate Acyclic and Macrocyclic Ligands

Abstract: The uranyl(VI) complexes of pyridine-based pentadentate ligands derived from 2,6-diacetylpyridine and semicarbazide (DAPSC) or benzoylhydrazide (DAPBH) are described, characterized on the basis of elemental analysis, electrical conductance, infrared and electronic spectra. The ligands form complexes of the type [(UO2)2(DAPSC)X4] and [(UO2)(DAPBH)X]X (where X = Cl). The template effect of uranyl(VI) has been studied in the cyclization of 2,6-diacetylpyridine with carbohydrazide and 2-phenylenediamine. The complexes obtained from 2,6-diacetylpyridine and 2-phenylenediamine represented as [(UO2Mac1)X2], where Mac1 is a macrocyclic hexadentate (M6) ligand and complexes obtained by the condensation of 2,6-diacetylpyridine and carbohydrazide has been formulated as [(UO2)2(Mac2)X4], where Mac2 is a heptadentate macrocyclic ligand. The formulation as macrocyclic ligand complexes is indicated by the absence of v(C=0) of 2,6-diacetylpyridine and formation of an azomethine linkage. The intense colour of the...

Magnetic Resonance as a Structural Probe of a Uranium (Vi) Sol-Gel Process

Abstract: Nuclear Magnetic Resonance (NMR) investigations on the Oak Ridge National Laboratory process for sol-gel synthesis of microspherical nuclear fuel (UO2), has been extremely useful in sorting out the chemical mechanism in the sol-gel steps. 13C, 15N, and 1H NMR studies on the HMTA gelation agent (hexamethylenetetramine, C6H12N4) has revealed near quantitative stability of this adamantane-like compound in the sol-gel process, contrary to its historical role as an ammonia source for gelation from the worldwide technical literature. 17O NMR of uranyl (UO2 ++) hydrolysis fragments produced in colloidal sols has revealed the selective formation of a uranyl trimer, [(UO2)3 (μ3-O)(μ2-OH)3]+, induced by basic hydrolysis with the HMTA gelation agent. Spectroscopic results will be presented to illustrate that trimer condensation occurs during sol-gel processing leading to layered polyanionic hydrous uranium oxides in which HMTAH+ is occluded as an ‘intercalation’ cation. Subsequent sol-gel processing of microspheres by ammonia washing results in in-situ ion exchange and formation of a layered hydrous ammonium uranate with a proposed structural formula of (NH4)2 [(UO2)8 O4 (OH)10]- 8H2)O. This compound is the precursor to sintered UO2 ceramic fuel.

Uranium(V) as an intermediate in the photochemical reduction of the uranyl ion with dicyclohexylsulphide

Abstract: Formation of uranium(V) was established using electronic absorption studies in the photochemical reduction of the uranyl ion by dicyclohexylsulphide in dry acetone medium. Low values of the quantum yields Φ(U(V)) were found. The Stern-Volmer quenching constant suggests a significant physical quenching contribution of the cyclohexyl group.