Uranyl Ion Complexes Research Articles

Effects of aqueous uranyl speciation on the kinetics of microbial uranium reduction

The ability to predict the success of the microbial reduction of soluble U(VI) to highly insoluble U(IV) as an in situ bioremediation strategy is complicated by the wide range of geochemical conditions at contaminated sites and the strong influence of aqueous uranyl speciation on the bioavailability and toxicity of U(VI) to metal-reducing bacteria. To determine the effects of aqueous uranyl speciation on uranium bioreduction kinetics, incubations and viability assays with Shewanella putrefaciens strain 200 were conducted over a range of pH and dissolved inorganic carbon (DIC), Ca2+, and Mg2+ concentrations. A speciation-dependent kinetic model was developed to reproduce the observed time series of total dissolved uranium concentration over the range of geochemical conditions tested. The kinetic model yielded the highest rate constant for the reduction of uranyl non-carbonate species (i.e., the ‘free’ hydrated uranyl ion, uranyl hydroxides, and other minor uranyl complexes), indicating that they represent the most readily reducible fraction of U(VI) despite being the least abundant uranyl species in solution. The presence of DIC, Ca2+, and Mg2+ suppressed the formation of more bioavailable uranyl non-carbonate species and resulted in slower bioreduction rates. At high concentrations of bioavailable U(VI), however, uranium toxicity to S. putrefaciens inhibited bioreduction, and viability assays confirmed that the concentration of non-carbonate uranyl species best predicts the degree of toxicity. The effect of uranium toxicity was accounted for by incorporating the free ion activity model of metal toxicity into the bioreduction rate law. Overall, these results demonstrate that, in the absence of competing terminal electron acceptors, uranium bioreduction kinetics can be predicted over a wide range of geochemical conditions based on the bioavailability and toxicity imparted on U(VI) by solution composition. These findings also imply that the concentration of uranyl non-carbonate species, despite being extremely low, is a determining factor controlling uranium bioreduction at contaminated sites.

Solvent effects in solvo-hydrothermal synthesis of uranyl ion complexes with 1,3-adamantanediacetate

Uranyl ion complexes with 1,3-adamantanediacetate display different topologies arising from variations in coordination mode and the presence of additional ligands.

Complexation of uranyl ions by N-(sulfoethyl)-iminodiacetic acid: Hydrothermal synthesis, luminescence, and uranyl sequestration

Reported here is a water-soluble ligand, N-(sulfoethyl)-iminodiacetic acid (H3SEIDA), used for the complexation of uranyl ions. A coordination compound composed of uranyl cation and N-(sulfonatoethyl)-ammoniodiacetate (SEADA2−) zwitterion was synthesized from an acidic aqueous solution. This compound features a 2D undulating fes (4.82) coordination layer that is stacked and linked by hydrogen-bonding interaction to form a 3D supramolecular framework with a 1D larger-cycle channel. Thermal analysis demonstrates the relatively weak bonding between uranyl cation and SEADA2− zwitterion. The monomeric uranyl-based fluorescence emission is red-shifted by about 5 nm compared to that of uranyl nitrate hexahydrate. The hydrothermal synthesis of this uranyl compound was successfully applied to the sequestration of uranyl ions.

Crystal structure of bis(4-benzoyl-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazol-5-onato)-(ethanol)-dioxourane(VI) ethanol solvate

The crystal structure of bis(4-benzoyl-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazol-5-onato)-(ethanol)-dioxourane(VI) ethanol solvate [UO2L2(C2H5OH)]·C2H5OH (I), where HL is 4-benzoyl-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazol-5-one, is determined. The asymmetric part on the unit cell of the crystal structure of I contains the complex of uranyl ion with two bidentately coordinated L− ions and coordinated molecule of ethanol. In the outer coordination sphere of the central atom, the solvated ethanol molecule is located. The coordination polyhedron of the uranium atom in complex I is a pentagonal bipyramid. Its equatorial plane is composed of oxygen atoms of HL and ethanol. In the axial positions of the metal coordination polyhedron the oxygen atoms are located. In the crystal, the complexes of the studied compound are linked together via hydrogen bonds of the outer-sphere ethanol molecule in chains along the [100] direction. Between the chains in the crystal, the van der Waals interaction occurs.

Synthetic and structural studies of piperidine carboxamide uranyl ion complexes

New piperidine based ligands of the type [C5H10NCONR2] (where R=CH3 (L1), C2H5 (L2) and iC3H7 (L3)) have been prepared and characterized. The complex chemistry of these ligands with uranyl chloride, bromide, nitrate and β-diketonates has been studied using IR and NMR spectroscopic methods. Crystal structures for the complexes [UO2Cl2(L3)2] (1), [UO2Br2(L3)2] (2) [UO2(NO3)2(L3)2] (5) and [UO2(C4H3SCOCHCOCF3)2(L3)] (8) have been determined by the X-ray diffraction method. The structures of 1 and 2 show that the uranyl ion is surrounded by two of the ligands and two halogen atoms in an octahedral geometry. The structure of 5 shows that the uranyl group is surrounded by two nitrate groups and two ligands in a hexagonal bipyramidal geometry. The structure of 8 shows that the uranyl group is surrounded by two β-diketonates and one ligand in a pentagonal bipyramidal geometry. The structures show that the carboxamide ligands are strongly bonded to the uranyl group, showing a near linear geometry for the U–O–C bond (angle 150–159°). The prepared chloro and bromo compounds are air and moisture stable and show good solubility in normal organic solvents.

A Highly Adjustable Coordination System: Nanotubular and Molecular Cage Species in Uranyl Ion Complexes with Kemp’s Triacid

A unique example of topology tailoring in a uranyl–organic system is provided by the three-pronged Kemp’s tricarboxylate ligand. While unexceptional one-dimensional polymers are formed with uranyl alone under solvo-hydrothermal conditions, addition of Ni2+ ions yields the nanotubular species [(UO2)2Ni(L)2(H2O)4]∞, with a hydrophilic inner cavity lined by hydrated Ni2+ ions, and a hydrophobic outer surface. The further presence of 2,2′-bipyridine brings about the trapping of Ni2+ ions into counterions and formation of the octanuclear pseudocubic cage [(UO2)8(L)6(H2O)6]2–.

Molecular and Polymeric Uranyl and Thorium Complexes with Sulfonate‐Containing Ligands

AbstractSix uranyl and one thorium(IV) cation complexes with ligands involving either only sulfonate or both sulfonate and carboxylate groups as complexing sites were obtained, mainly under hydrothermal conditions, and their crystal structures were determined. The uranyl ion complex with the 2‐sulfobenzoate (2‐SB2–) anion synthesized in the presence of pyridine, [pyH]4[(UO2)2(2‐SB)2O]2·4H2O (1), is a molecular, tetranuclear complex in which 2‐SB2– is chelating through its two functional groups, while [Th(2‐SB)2(H2O)3]·2H2O (2) is a 1D polymer with monodentate sulfonate and bridging bidentate carboxylate groups. Complex [(UO2)3K(4‐SB)O(OH)3(H2O)1.5]·0.5H2O (3), with the 4‐sulfobenzoate ligand, crystallizes as a 3D framework in which uranyl oxo/hydroxo 1D subunits are connected to one another by 4‐SB2– and potassium cation bridges, the latter being involved in as much as five bonds with uranyl oxo groups (“cation–cation” bonds). Complex [UO2(5‐SSH2)(H2O)3]2·2(5‐SSH2)·3H2O (4), with 5‐sulfosalicylic acid (5‐SSH3), is a dinuclear species in which the ligand is only coordinated through its bridging bidentate sulfonate group, an unusual occurrence. 5‐Sulfosalicylic acid undergoes partial desulfonation and carboxylation under hydrothermal conditions, yielding the heterometallic, tetranuclear complex [UO2Ni(5‐SHIPH)(4‐HIPH2)(bipy)2(H2O)]2·(4‐HIPH3) (5), 5‐sulfonato‐2‐hydroxyisophthalic acid (5‐SHIPH4) and 4‐hydroxyisophthalic acid (4‐HIPH3) being generated in situ. The all‐sulfonate ligand 1,2‐ethanedisulfonate (EDS2–) acts as a divergent linker in both [UO2(EDS)(H2O)3] (6) and [(UO2)2(EDS)(OH)2(phen)2]·4H2O (7). 1D polymers are formed in both cases, the doubly monodentate EDS2– ligand bridging isolated uranyl ions in 6 or hydroxo‐bridged uranyl dimers in 7. Sulfonate coordination to the 5f cation is present in all these complexes but 5, even in the absence of synergistic effects exerted by the stronger carboxylate ligating groups, and the variety of structures obtained in this as well as in previous work demonstrates that, together with the more investigated phosphonates, sulfonates are anions of great potential for the synthesis of actinide–organic coordination polymers and frameworks.

Optimization of the arsenazo-III method for the determination of uranium in water and plant samples

This work reports a reliable, fast and optimized photometric technique based on the specific chemical complexation of uranyl ion with arsenazo-III. In the case of solid samples (plant samples), for which mineralization under acidic and oxidative conditions was used, addition of ascorbic acid led to stabilization of the arsenazo–uranyl complex over time. The results, in total agreement with data obtained from α and γ spectrometries, demonstrate that the present technique is able to precisely quantify uranium in water as well as in plant samples, within the μg/L and mg/g ranges respectively.

Complexation of Uranyl and Rare-Earth Ions by a Fluorinated Tetracarboxylate. Formation of a Layered Assembly and Three-Dimensional Frameworks

The reaction of uranyl and rare-earth nitrates with 4,4′-(1,1,1,3,3,3-hexafluoroisopropylidene)diphthalic acid (H4L) under hydro-/solvo-thermal conditions (2:1 water/acetonitrile at 180 °C) gives a series of complexes, most of which have been crystallographically characterized. In the lattice of the uranyl complex [(UO2)2(L)(H2O)2]·2H2O (1), the metal atoms are chelated by two adjacent carboxylate groups, each of the latter being bridging bidentate, and the resulting coordination polymer is two-dimensional. The ∼14 Å thick layers comprise two uranyl-covered faces linked to one another by L4– pillars, a claylike architecture likely due to the hydrophobic interactions between the organic ligands. The complexes [Ce(HL)(H2O)]·1.5H2O (2) and [Nd(HL)(H2O)]·2.5H2O (3) are isomorphous and they display a high degree of connectivity, with the metal atoms in ten- or eleven-coordinate environments being bound to five or six HL3– ligands. The three-dimensional (3D) framework formed contains one-dimensional subunits of adjacent metal ions with each coordination polyhedron sharing two triangular faces with its neighbors. The hydrophobic CF3 groups are oriented divergently from the exterior of wide channels (∼22 × 8 Å), which are occupied by the solvent water molecules. The complexes with rare-earth ions of smaller ionic radii, [M4(L)3(H2O)9]·7H2O with M = Er (4), Yb (5), and Y (6), are isomorphous to the previously reported terbium(III) complex, and they crystallize as 3D frameworks containing di- and tetra-nuclear subunits. In the visible region, only the uranyl and europium (and terbium) complexes display significant solid-state luminescence.

Identification of F− and SO42− as the radiolytic products of the ionic liquid C4mimNTf2 and their effect on the extraction of UO22+

A precipitate was found at the interface between the aqueous phase and the ionic liquid (IL) phase during the separation of UO22+/Eu3+ using irradiated IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides (C4mimNTf2), and was analyzed by SEM, EDS, XPS and PXRD. The anions F− and SO42− were identified as the radiolytic products of C4mimNTf2. The radiation effect on the extraction of UO22+ from aqueous solution by tri-n-butyl phosphate (TBP) in C4mimNTf2 was studied. For the presence of F− and SO42−, the utilization of irradiated C4mimNTf2 as diluent reduced the extraction efficiency of UO22+. The EXAFS measurement showed that the degradation of C4mimNTf2 insignificantly influenced the coordination environment of UO22+ in the IL phase. Furthermore, it was suggested that the complex of uranyl ion with four TBP molecules is predominant during the extraction of UO22+ by TBP in C4mimNTf2 from aqueous solution in the absence of nitric acid. This work gives a further assessment for the application of ILs in the processing of spent nuclear fuel.

Uranyl ion interaction at the water/NiO(100) interface: A predictive investigation by first-principles molecular dynamic simulations

The behavior of the UO(2)(2+) uranyl ion at the water/NiO(100) interface was investigated for the first time using Born-Oppenheimer molecular dynamic simulations with the spin polarized DFT + U extension. A water/NiO(100) interface model was first optimized on a defect-free five layers slab thickness, proposed as a reliable surface model, with an explicit treatment of the solvent. Water molecules are adsorbed with a well-defined structure in a thickness of about 4 Å above the surface. The first layer, adsorbed on nickel atoms, remains mainly in molecular form but can partly dissociate at 293 K. Considering low acidic conditions, a bidentate uranyl ion complex was characterized on two surface oxygen species (arising from water molecules adsorption on nickel atoms) with d(U-O(adsorption))=2.39 Å. This complex is stable at 293 K due to iono-covalent bonds with an estimated charge transfer of 0.58 electron from the surface to the uranyl ion.

Sequential recovery of uranium oxides by electrolysis of M2WO4-M2W2O7-UO2WO4 melts (M = Li, Na, K, Cs)

The effect of the electrolyte composition and solvent salt cation on the oxygen coefficient of the cathode product (O/U atomic ratio) and on the main characteristics of potentiostatic electrolytic deposition of UO2 (cathode current efficiency, current density, product deposition rate) in sequential recovery of uranium oxides from electrolytes of the system M2WO4-M2W2O7-UO2WO4 (M = Li, Na, K, Cs) in air was examined. The dependence of the oxygen coefficient of the cathode product on the electrolyte composition and solvent salt cation does not differ essentially from that observed previously in short experiments with low melt depletion of U. The current efficiency, initial current density, and product deposition rate decrease with the electrolyte depletion of U. The results obtained are satisfactorily accounted for in terms of the model of ionic composition of uranyl-containing oxide salt electrolytes, based on the concept of complexation and stepwise solvolysis of uranyl ions, taking into account formation of lower valence forms of U due to chemical corrosion of the cathode product.

New complexes of heteroaromatic N-oxides with europium, uranyl and zinc ions

New solid complexes of europium, uranyl and zinc ions with N-oxides of 4-chloro-2,6-dimethylpyridine, quinoline and 4-methoxyquinaldinic acid in presence different anions were obtained and characterized by elemental and TG analyses, IR and luminescence spectra. The compounds are crystalline, hydrated or anhydrous salts with colours typical of metal ions. Thermal studies showed that in hydrated salts lattice or coordination water molecules are present. A role of different anions in the formation of various types of the complexes is presented.

Design of an efficient uranyl ion optical sensor based on 1′-2,2′-(1,2-phenylene)bis(ethene-2,1-diyl)dinaphthalen-2-ol

A new optical uranyl (IV) selective sensor by incorporation of 1,1′-2,2′-(1,2-phenylene)bis(ethene-2,1-diyl)dinaphthalen-2-ol (PBED), dibutyl phthalate (DBP) and sodium tetraphenylborate (Na-TPB) in the plasticized poly vinyl chloride membrane matrices has been constructed. In the proposed optode, PBED functions as both ionophore and chromoionophore while DBP has synergistic effect on the complexation of uranyl ion (UO22+) by PBED. Following the optimization of influences of variables, the proposed sensor due to its high stability, reproducibility and relatively long lifetime has good selectivity and sensitivity for uranyl ion over a large number of alkali, alkaline earth, transition, and heavy metal ions. The response of the proposed optode is linear over the concentration range of 3.99×10−6 up to 8.06×10−5molL−1 of UO22+ within a detection limit of 9.99×10−7molL−1 and response time less than 10min. The proposed optical sensor was applied successfully for the determination and evaluation of UO22+ ion content in water samples.

Uranyl Ion Complexes with Ammoniobenzoates as Assemblers for Cucurbit[6]uril Molecules

The crystal structures of the complexes formed under hydrothermal conditions by uranyl ions with 4-aminobenzoic (HL1), 4-amino-3-methylbenzoic (HL2), 4-(aminomethyl)benzoic (HL3), and 3-amino-5-hydroxybenzoic (HL4) acids, in the presence of cucurbit[6]uril (CB6), have been determined. These ligands have been chosen because, in their zwitterionic form, they display both a metal-complexing carboxylate group and an ammonium group able to associate with CB6 through ion-dipole and hydrogen bonding interactions. The complexes [H2NMe2]2[(UO2)2(L1)2O(OH)(H2O)]2·CB6·15H2O (1) and [H2NMe2]2[(UO2)2(L2)2O(OH)(H2O)]2·CB6·17H2O (2) were obtained in the presence of dimethylformamide, which gives dimethylammonium ions in situ. The latter are held at the CB6 portals, while the tetranuclear uranyl complex with the aminobenzoate anions is not bound to CB6. The neutral, ammonium-containing form of the ligand is present in [UO2(HL3)(OH)(HCOO)(H2O)]2·2CB6·2DMF·14H2O (3), in which the di(μ2-hydroxo)-bridged, dinuclear uranyl complex displays two diverging, monodentate HL3 ligands. The latter are associated with two CB6 molecules to give a dumbbell-shaped supramolecular assembly. Three CB6 molecules are assembled around a tetranuclear uranyl complex in [(UO2)4(HL3)2(L3)O2(OH)2(H2O)4]·2CB6·0.5CB8·HL3·NO3·20H2O (4), with two of them being bridging and giving rise to a one-dimensional, linear supramolecular architecture. Finally, the 3-amino substituted ligand HL4 gives the highly symmetric complex [UO2(HL4)(L4)2]·3CB6·16H2O (5), in which the uranyl ion is chelated by three carboxylate groups. Three CB6 molecules are assembled around the planar complex to give a triangular, discrete species. In compounds 3–5, the usual packing of CB6 molecules into columns or layers is not retained as it is frequently in the presence of uranyl complexes. This is due to the CB6-assembling role of the heterodifunctional ligands, which hold the CB6 molecules at the periphery of mono-, di-, or tetranuclear uranyl complexes of quite usual, planar geometry.

Coordination Polymers and Frameworks in Uranyl Ion Complexes with Sulfonates and Cucurbit[6]uril

The complexes formed by uranyl nitrate with the three positional isomers of sulfobenzoate and with ethanedisulfonate anions in the presence of cucurbit[6]uril (CB6) under hydrothermal conditions we...

Uranyl Ion Complexation by Aliphatic Dicarboxylic Acids in the Presence of Cucurbiturils as Additional Ligands or Structure-Directing Agents

A series of nine complexes has been obtained from the hydrothermal reaction of uranyl nitrate with long-chain alkyldicarboxylic acids (HOOC-(CH2)n–2-COOH, denoted H2Cn) in the presence of cucurbit[6]uril (CB6), dimethylformamide (DMF), which generates dimethylammonium cations in situ, and additional alkaline-earth metal ions in some cases. The crystal structures of the three complexes [H2NMe2]2[(UO2)4O2(OH)2(C8)2(CB6)]·8H2O (1), [H2NMe2]2[(UO2)4O2(OH)2(C9)2(CB6)]·5H2O (2), and [H2NMe2]2[(UO2)4O2(OH)2(C9)2(CB6)]·8H2O (3) are closely related, since all contain the same tetranuclear motif held by two μ3-oxo and two μ2-hydroxo ions, and attached to CB6 by uranyl-O-carbonyl bonds. Two-dimensional assemblies are formed in 1 and 2 and a three-dimensional framework in 3. The cucurbituril molecule is not coordinated in compounds 4–9 but is present as a structure-directing agent. The complex [H2NMe2]2[(UO2)4O2(C6)3]·CB8·8H2O (4), in which cucurbit[8]uril (CB8) comes from the initial CB6, displays a stacking of plan...

Coordination of uranium(vi) with functional groups of bacterial lipopolysaccharide studied by EXAFS and FT-IR spectroscopy

The complexation of uranyl ions with lipopolysaccharide (LPS), the main component of the cell wall of Gram-negative bacteria, was investigated on a molecular level with U L(III)-edge extended X-ray absorption fine structure (EXAFS) and attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy over a wide pH range (2.6 to 7.0). For the first time, structural determinations of uranyl complexes with cell wall compounds were extended from acidic up to neutral pH. The main functionalities responsible for uranyl binding are phosphoryl and carboxyl groups. At an excess of LPS, related to environmental conditions, the uranyl ion is mainly complexed by phosphoryl groups four-fold monodentately coordinated in the equatorial plane of the uranyl dioxo cation UO(2)(2+) showing great homologies to the uranyl mineral phase meta-autunite in the EXAFS spectra. At equimolar ratios of uranyl and functional groups of LPS, according to a slight deficit of phosphoryl groups, additional carboxyl coordination in a bidentate manner becomes important as it is shown by IR spectroscopy. From the vibrational spectra, a mixed coordination of UO(2)(2+) with both phosphoryl and carboxyl groups is derived. The coordination of uranyl ions to the LPS molecule is obviously mainly controlled by the U/LPS concentration ratio, and the influence of pH is only of minor significance at the investigated range.

Influence of Nitric Acid on Uranyl Nitrate Association in Aqueous Solutions: A Molecular Dynamics Simulation Study

Uranyl ion complexation with water and nitrate is a key aspect of the uranium/plutonium extraction process. We have carried out a molecular dynamics simulation study to investigate this complexation process, including the molecular composition of the various complex species, the corresponding structure, and the equilibrium distribution of the complexes. The observed structures of the complexes suggest that in aqueous solution, uranyls are generally hydrated by 5 water molecules in the equatorial plane. When associating with nitrate ions, a water molecule is replaced by a nitrate ion, preserving the five‐fold coordination and planar symmetry. Analysis of the pair correlation function between uranyl and nitrate suggests that nitrates bind to uranyl in aqueous solution mainly in a monodentate mode, although a small portion of bidentates occur. Dynamic association and dissociation between uranyls and nitrates take place in aqueous solution with a substantial amount of fluctuation in the number of various uranyl nitrate species. The average number of the uranyl mono‐nitrate complexes shows a dependence on acid concentration consistent with equilibrium‐constant analysis, namely, the concentration of [UO2NO3]+ increases with nitric acid concentration.

Cluster control in oligouranyl complexes of p-t-butylcalix[8]arene

Formation of uranyl ion complexes of p-t-butylcalix[8]arene by reaction of the calixarene with [UO(2)(dmso)(5)](2+) in the presence of various bases leads to the crystallisation of solids with interestingly different stoichiometry, involving both di- and tri-uranate oligomers bound to the calixarene in anionic species. In all, the calixarene hexa-anion is present in a virtually identical conformation, suggesting that conformational preferences of the ligand must be a major factor controlling the form of the bound oxo-metal complex. Hydrogen bonding to the anions does not appear to be prominent even in the presence of protonated amines and this may explain the formation of some remarkable cation/solvent/simple anion clusters found within the lattices.