Showing papers on "Uranyl published in 2009"
TL;DR: In this paper, the authors describe the synthesis and characterisation of a few kinetically inert complexes containing the f1 [UO2]-cation, and the insight they give into subsequent reactivity of the trans-UO 2 unit.
197 citations
TL;DR: The origins and near-surface distributions of the ~250 known uranium and/or thorium minerals elucidate principles of mineral evolution as discussed by the authors, which can be divided into four phases: the first, from 4.5 to 3.5 Ga, involved successive concentrations of uranium and thorium from their initial uniform trace distribution into magmatic-related fluids from which the first U4+ and Th4+ minerals, uraninite (ideally UO2), thorianite (ThO2) and coffinite (USiO4), precipitated in the crust.
Abstract: The origins and near-surface distributions of the ~250 known uranium and/or thorium minerals elucidate principles of mineral evolution. This history can be divided into four phases. The first, from ~4.5 to 3.5 Ga, involved successive concentrations of uranium and thorium from their initial uniform trace distribution into magmatic-related fluids from which the first U4+ and Th4+ minerals, uraninite (ideally UO2), thorianite (ThO2), and coffinite (USiO4), precipitated in the crust. The second period, from ~3.5 to 2.2 Ga, saw the formation of large low-grade concentrations of detrital uraninite (containing several wt% Th) in the Witwatersrand-type quartz-pebble conglomerates deposited in a highly anoxic fluvial environment. Abiotic alteration of uraninite and coffinite, including radiolysis and auto-oxidation caused by radioactive decay and the formation of helium from alpha particles, may have resulted in the formation of a limited suite of uranyl oxide-hydroxides.
Earth’s third phase of uranium mineral evolution, during which most known U minerals first precipitated from reactions of soluble uranyl (U6+O2)2+ complexes, followed the Great Oxidation Event (GOE) at ~2.2 Ga and thus was mediated indirectly by biologic activity. Most uraninite deposited during this phase was low in Th and precipitated from saline and oxidizing hydrothermal solutions (100 to 300 °C) transporting (UO2)2+-chloride complexes. Examples include the unconformity- and vein-type U deposits (Australia and Canada) and the unique Oklo natural nuclear reactors in Gabon. The onset of hydrothermal transport of (UO2)2+ complexes in the upper crust may reflect the availability of CaSO4- bearing evaporites after the GOE. During this phase, most uranyl minerals would have been able to form in the O2-bearing near-surface environment for the first time through weathering processes. The fourth phase of uranium mineralization began ~400 million years ago, as the rise of land plants led to non-marine organic-rich sediments that promoted new sandstone-type ore deposits.
The modes of accumulation and even the compositions of uraninite, as well as the multiple oxidation states of U (4+, 5+, and 6+), are a sensitive indicator of global redox conditions. In contrast, the behavior of thorium, which has only a single oxidation state (4+) that has a very low solubility in the absence of aqueous F-complexes, cannot reflect changing redox conditions. Geochemical concentration of Th relative to U at high temperatures is therefore limited to special magmatic-related environments, where U4+ is preferentially removed by chloride or carbonate complexes, and at low temperatures by mineral surface reactions.
The near-surface mineralogy of uranium and thorium provide a measure of a planet’s geotectonic and geobiological history. In the absence of extensive magmatic-related fluid reworking of the crust and upper mantle, uranium and thorium will not become sufficiently concentrated to form their own minerals or ore deposits. Furthermore, in the absence of surface oxidation, all but a handful of the known uranium minerals are unlikely to have formed.
179 citations
TL;DR: The Kratos Axis Ultra X-ray Photoelectron Spectrometer with a magnetic-confinement charge-compensation system was used to resolve the fine structure of the O 1s envelope as discussed by the authors.
160 citations
TL;DR: Clusters containing 20 uranyl pentagonal triperoxides have been isolated and characterized that assume the smallest possible fullerene topology consisting only of 12 pentagons, indicating that the U-O(2)-U dihedral angle is inherently bent.
Abstract: Uranyl peroxide polyhedra are known to self-assemble into complex closed clusters with fullerene and other topologies containing as many as 60 polyhedra. Here clusters containing 20 uranyl pentagonal triperoxides have been isolated and characterized that assume the smallest possible fullerene topology consisting only of 12 pentagons. Oxalate has been used to crystallize fragments of larger uranyl peroxide clusters, and these fragments and other known structures indicate that the U−O2−U dihedral angle is inherently bent. Such bending is thought to be essential in directing the self-assembly of uranyl peroxide polyhedra into closed clusters.
117 citations
TL;DR: This paper presents the first spectroscopic evidence of this ternary surface complex, which has significant implications for immobilization of uranyl in carbonate-rich aqueous environments.
Abstract: Previous spectroscopic research suggested that uranium(VI) adsorption to iron oxides is dominated by ternary uranyl−carbonato surface complexes across an unexpectedly wide pH range. Formation of such complexes would have a significant impact on the sorption behavior and mobility of uranium in aqueous environments. We therefore reinvestigated the identity and structural coordination of uranyl sorption complexes using a combination of U LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and iterative transformation factor analysis, which enhances the resolution in comparison to conventional EXAFS analysis. A range of conditions (pH, CO2 partial pressure, ionic strength) made it possible to quantify the variations in surface speciation. In the resulting set of spectral data (N = 11) the variance is explained by only two components, which represent two structurally different types of surface complexes: (1) a binary uranyl surface complex with a bidentate coordination to edges of Fe(O,OH)6...
114 citations
TL;DR: The prevalence of site specific U incorporation under both abiotic and biotic conditions and the fact that the produced solids were shown to be resistant to both extraction and oxidation suggest the potential importance of sequestration in Fe oxides as a stable and immobile form of U in the environment.
Abstract: The form of solid phase U after Fe(II) induced anaerobic remineralization of ferrihydrite in the presence of aqueous and absorbed U(VI) was investigated under both abiotic batch and biotic flow conditions. Experiments were conducted with synthetic ground waters containing 0.168 mM U(VI), 3.8 mM carbonate, and 3.0 mM Ca2+. In spite of the high solubility of U(VI) under these conditions, appreciable removal of U(VI) from solution was observed in both the abiotic and biotic systems. The majority of the removed U was determined to be substituted as oxidized U (U(VI) or U(V)) into the octahedral position of the goethite and magnetite formed during ferrihydrite remineralization. It is estimated that between 3 and 6% of octahedral Fe(III) centers in the new Fe minerals were occupied by U. This site specific substitution is distinct from the nonspecific U coprecipitation processes in which uranyl compounds, e.g., uranyl hydroxide or carbonate, are entrapped within newly formed Fe oxides. The prevalence of site sp...
113 citations
TL;DR: Ion imprinted polymer (IIP) material of mesoporous nature was prepared in two steps: (i) by forming binary/ternary complexes of uranyl imprint ion with a suitable nonvinylated uranophile, formamidoxime and/or vinylated ligand, 4-vinyl pyridine (VP) and (ii) by thermally copolymerizing them with 2-hydroxy ethyl methacrylate (HEMA) as the functional monomer and ethylene glycol dimethacrylated (EGDMA)
100 citations
TL;DR: In this paper, a charge distribution model was used to evaluate the adsorption of uranyl (UO22+) on ferrihydrite for a very large range of conditions, including pH, ionic strength, CO2 pressure, U(VI) concentration, and loading.
97 citations
TL;DR: This poster presents a probabilistic simulation of the response of the immune system to EMT and shows clear patterns in response to EMMARM, including high levels of “good” and “bad” EMT.
Abstract: Reference EPFL-ARTICLE-203028doi:10.1002/anie.200903457View record in Web of Science Record created on 2014-11-07, modified on 2017-05-12
97 citations
TL;DR: In this paper, the reaction of UO3 with cucurbit[5]uril (CB5) under hydrothermal conditions and in the presence of perrhenic acid to give [UO2(CB5)](ReO4)2·2H2O (1) in which the uranyl ion is encompassed by the five oxygen atoms of one CB5 portal, giving an open molecular capsule.
Abstract: Uranium trioxide UO3 reacts with cucurbit[5]uril (CB5) under hydrothermal conditions and in the presence of perrhenic acid to give [UO2(CB5)](ReO4)2·2H2O (1) in which the uranyl ion is encompassed by the five oxygen atoms of one CB5 portal, giving an open molecular capsule. When uranyl nitrate is reacted with CB5 in the presence of alkali metal salts, mixed capsules, capped by one uranyl ion at one portal and K+ or Cs+ at the other, are obtained either as discrete dicationic species in [UO2(CB5)K(NO3)][UO2(NO3)4]·H2O (2) or as part of pentanuclear dicationic assemblages in {[UO2(CB5)Cs(NO3)]2[UO2(NO3)4]}[UO2(NO3)4]·2H2O (3). Finally, the reaction of UO3 with CB5 in the presence of KOH or CsOH, with addition of formic acid, resulted in the formation of the compounds [K2(CB5)(H2O)][(UO2)2(HCOO)(OH)4]2·6H2O (4) and [Cs2(CB5)(H2O)2][(UO2)2(HCOO)(OH)4]2·3H2O (5). In these cases, the uranyl ions are separated from CB5 to form a uranyl/formate/hydroxide two-dimensional assemblage; CB5 capsules capped by K+ or Cs...
95 citations
TL;DR: A new bis(tridentate NO2) Schiff base ligand, H(4)L, was prepared by the reaction of the bifunctional carbonyl compound; 4,6-diacetylresorcinol (DAR) with ethanolamine to yield mono- and bi-nuclear complexes with different coordinating sites.
TL;DR: A marine, unicellular cyanobacterium, Synechococcus elongatus strain BDU/75042 was found to sequester uranium from aqueous systems at pH 7.8 and the potential of this cyanobacteria for harvesting uranium from natural aquatic environments was revealed.
TL;DR: Solid-state luminescent measurements on these monometallic complexes showed that BPM is an efficient sensitizer of the luminescence of both the lanthanide and the uranyl ions emitting visible light, as well as of the Yb(III) ion emitting in the near-IR.
Abstract: Treatment of Ln(NO3)3.nH2O with 1 or 2 equiv 2,2-bipyrimidine (BPM) in dry THF readily afforded the monometallic complexes [Ln(NO3)3(bpm)2] (Ln=Eu, Gd, Dy, Tm) or [Ln(NO3)3(bpm)2]THF (Ln=Eu, Tb, Er, Yb) after recrystallization from MeOH or THF, respectively. Reactions with nitrate salts of the larger lanthanide ions (Ln=Ce, Nd, Sm) yielded one of two distinct monometallic complexes, depending on the recrystallization solvent: [Ln(NO3)3(bpm)2].THF (Ln=Nd, Sm) from THF, or [Ln(NO3)3(bpm)(MeOH)2].MeOH (Ln=Ce, Nd, Sm) from MeOH. Treatment of UO2(NO3)2.6H2O with 1 equiv BPM in THF afforded the monoadduct [UO2(NO3)2(bpm)] after recrystallization from MeOH. The complexes were characterized by their crystal structure. Solid-state luminescence measurements on these monometallic complexes showed that BPM is an efficient sensitizer of the luminescence of both the lanthanide and the uranyl ions emitting visible light, as well as of the YbIII ion emitting in the near-IR. For Tb, Dy, Eu, and Yb complexes, energy transfer was quite efficient, resulting in quantum yields of 80.0, 5.1, 70.0, and 0.8 %, respectively. All these complexes in the solid state were stable in air.
TL;DR: In this article, the authors used batch sorption/desorption experiments combined with U LIII-edge X-ray absorption near-edge structure (XANES) spectroscopy, extended Xray absorption fine structure (EXAFS), scanning and transmission electron microscopy, synchrotron-based microdiffraction, and surface complexation modeling to investigate the dominant sorption process(es) governing uranyl uptake by chlorite.
TL;DR: The geometric and electronic structures of the aqua, chloro, acetato, hydroxo and carbonato complexes of U, Np and Pu in both their (VI) and (V) oxidation states and in an aqueous environment are studied using density functional theory methods.
Abstract: The geometric and electronic structures of the aqua, chloro, acetato, hydroxo and carbonato complexes of U, Np and Pu in both their (VI) and (V) oxidation states, and in an aqueous environment, have been studied using density functional theory methods. We have obtained micro-solvated structures derived from molecular dynamics simulations and included the bulk solvent using a continuum model. We find that two different hydrogen bonding patterns involving the axial actinyl oxygen atoms are sometimes possible, and may give rise to different An–O bond lengths and vibrational frequencies. These alternative structures are reflected in the experimental An–O bond lengths of the aqua and carbonato complexes. The variation of the redox potential of the uranyl complexes with the different ligands has been studied using both BP86 and B3LYP functionals. The relative values for the four uranium complexes having anionic ligands are in surprisingly good agreement with experiment, although the absolute values are in error by ∼1 eV. The absolute error for the aqua species is much less, leading to an incorrect order of the redox potentials of the aqua and chloro species.
TL;DR: Solubility and drop-solution calorimetry measurements are used to determine the thermodynamic properties of the uranyl phosphate phases autunite, uranyl hydrogen phosphate, and uranyl orthophosphate to help optimize and quantitatively assess the effect of phosphate amendment remediation technologies for uranium contaminated systems.
Abstract: In this study, we use solubility and drop-solution calorimetry measurements to determine the thermodynamic properties of the uranyl phosphate phases autunite, uranyl hydrogen phosphate, and uranyl orthophosphate. Conducting the solubility measurements from both supersaturated and undersaturated conditions and under different pH conditions rigorously demonstrates attainment of equilibrium and yields well-constrained solubility product values. We use the solubility data and the calorimetry data, respectively, to calculate standard-state Gibbs free energies of formation and standard-state enthalpies of formation for these uranyl phosphate phases. Combining these results allows us also to calculate the standard-state entropy of formation for each mineral phase. The results from this study are part of a combined effort to develop reliable and internally consistent thermodynamic data for environmentally relevant uranyl minerals. Data such as these are required to optimize and quantitatively assess the effect of phosphate amendment remediation technologies for uranium contaminated systems.
TL;DR: In this article, the authors show that Uranium(VI) mobility in groundwater is strongly affected by sorption of mobile U(VI)-species (e.g., uranyl, UO22+) to mineral surfaces, precipitation of U (VI) compounds, such as schoepite (UO2)(4)O(...
TL;DR: The perrhenate bound to Ln is included in the CB6 cavity, thus providing the first case of inclusion of a tetrahedral oxoanion in this macrocycle.
Abstract: The reaction of uranyl and lanthanide nitrates with cucurbit[6]uril (CB6) in the presence of perrhenic acid and under hydrothermal conditions yields the novel heterometallic uranyl-lanthanide molecular complexes [UO2Ln(CB6)(ReO4)2(NO3)(H2O)7](ReO4)2 (Ln = Sm, Eu, Gd, Lu). Both metal cations are bound to carbonyl groups of the same CB6 portal, one for UO22+ and two for Ln3+. The uranium atom is also bound to one monodentate perrhenate ion and three aquo ligands, while the lanthanide is bound to one monodentate perrhenate and one nitrate ions, and four aquo ligands. Not only are these complexes rare examples of ReO4− bonding to f element ions, but the perrhenate bound to Ln is included in the CB6 cavity, thus providing the first case of inclusion of a tetrahedral oxoanion in this macrocycle.
TL;DR: The enzyme folds into a bulged three‐way‐junction structure with catalytically important nucleotides residing in the bulge and a highly conserved G⋅A mismatch is also crucial for the enzyme's activity.
Abstract: Uranyl ion-specific DNAzyme: A DNAzyme (lower strand) cleaves the substrate (upper strand) in the presence of the uranyl ion. The enzyme folds into a bulged three-way-junction structure with catalytically important nucleotides residing in the bulge. A highly conserved GA mismatch is also crucial for the enzyme's activity.The biochemical characterization of a DNAzyme that is highly specific for uranyl (UO(2) (2+)) ions is described. Sequence alignment, enzyme truncation, and mutation studies have resulted in a conserved sequence that folds into a bulged stem-loop structure. Interestingly, a GA pair next to the scissile site is important for the uranyl ion-specific DNAzyme; this is reminiscent of the GT wobble base pair adjacent to the cleavage site that is crucial for the Pb(II)-specific 8-17 DNAzyme activity. Therefore wobble pairs might be important for formation of metal-specific metal-binding sites in DNAzymes. The DNAzyme binds the uranyl ion with a dissociation constant of 469 nM, which is among the strongest metal-binding affinities in nucleic acid enzymes reported to date. This explains why a catalytic beacon fluorescent sensor based on this enzyme has a detection limit (45 pM) that rivals the most-sensitive analytical instrument. It also has over 1 000 000-fold specificity for the uranyl ion over other metal ions. The DNAzyme can carry out multiple turnover reactions that follow the Michaelis-Menten equation, with a k(cat) of 1.46 min(-1) and a K(M) of 463 nM, similar to that of the 8-17 DNAzyme. The pH profile shows a bell-shaped curve that reaches a maximum at pH 5.5, at which the in vitro selection was carried out; this suggests that in vitro selection can be performed to obtain DNAzymes with optimal performance under specific conditions under which practical applications are required. These findings enrich our fundamental understanding of metal-binding sites in nucleic acids and allow the design of sensors with better performance.
TL;DR: The present multitechnique approach suggests the formation of two intermediate U(VI) species, a 5-fold mononitrato complex ([U( VI)O(2)(H(2)O)(3)(eta(2)-NO(3)))](+)) and a 6-fold dinitratocomplex ([U (VI)O (2)( H(2]O)(2)(eta-NO( 3)))(0), involving an increase in
Abstract: density functional theory calculations. In 1.0 M HClO4 ,U IV exists as a spherical cation of U 4þ , which is surrounded by 9-10 water molecules in the primary coordination sphere, while it forms a colloidal hydrous oxide, U IV O23 nH2O, at a lower acidic concentration of 0.1 M HClO4 .U VI exists as a transdioxo uranyl cation, UO2 2þ , and forms a 5-fold pure hydratecomplexof[U VI O2(H2O)5] 2þ in1.0MHClO4.WithincreasingHNO3concentration,thewatermoleculesoftheU IV and U VI hydrate complexes are successively replaced by planar bidentate coordinating nitrate ions (NO3 - ), forming dominant species of [U IV (H2O)x(NO3)5] - in 9.0 M HNO3 and [U VI O2(NO3)3] - in 14.5 M HNO3, respectively. The present multitechnique approach also suggests the formation of two intermediate U VI species, a 5-fold mononitrato complex ([U VI O2(H2O)3(η2-NO3)] þ ) and a 6-fold dinitrato complex ([U VI O2(H2O)2(η2-NO3)2] 0 ), involving an increase in the total coordinationnumberonthe uranyl(VI) equatorialplane from 5 to 6 with increasingHNO3concentration. The presenceof unidentate coordinate nitrato complexes or tetranitrato U VI complexes is less probable in the present HNO3 system.
TL;DR: The first uranyl-selective DNA-binding protein is designed using the E. coli nickel(II)-responsive protein NikR as the template and selectively binds to DNA in the presence of uranyl.
Abstract: A new pick-up line: The first uranyl-selective DNA-binding protein is designed using the E. coli nickel(II)-responsive protein NikR as the template. The resulting NikR' protein binds uranyl (see picture) with a dissociation constant K(d) = 53 nM and selectively binds to DNA in the presence of uranyl.
TL;DR: The imprinted polymer formed with ternary complex of UO(2)(2+)-SALO-VP (1:2:2, IIP3) showed quantitative enrichment of uranyl ion from dilute aqueous solution and hence was chosen for detailed studies.
TL;DR: Both 3 and 4 have been fully characterized, while the structure of 4 has also been determined by X-ray crystallography, in moderate to good yields.
Abstract: Reaction of Li(ArNC(Ph)CHC(Ph)O) (Aracnac; Ar = 2,4,6-Me3C6H2) or Na(ArNC(Ph)CHC(Ph)O) (Ar = 3,5-tBu2C6H3) with 0.5 equiv of UO2Cl2(THF)3 results in the formation of UO2(Aracnac)2 (Ar = 2,4,6-Me3C6...
TL;DR: In this article, the structure of uranyl sorption complexes on the U-LIII edge was investigated by two independent methods, density functional theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) spectroscopy.
TL;DR: Results on the potential energy differences between U(V)- and U(IV)-carbonate complexes suggest that the cause of slower disproportionation in this system is electrostatic repulsion between UO2 [CO3]35- ions that must approach one another to form U(VI) andU(IV) rather than a change in thermodynamic stability.
Abstract: Quantum mechanical calculations were performed on a variety of uranium species representing U(VI), U(V), U(IV), U-carbonates, U-phosphates, U-oxalates, U-catecholates, U-phosphodiesters, U-phosphorylated N-acetyl-glucosamine (NAG), and U-2-Keto-3-doxyoctanoate (KDO) with explicit solvation by H2O molecules. These models represent major U species in natural waters and complexes on bacterial surfaces. The model results are compared to observed EXAFS, IR, Raman and NMR spectra. Agreement between experiment and theory is acceptable in most cases, and the reasons for discrepancies are discussed. Calculated Gibbs free energies are used to constrain which configurations are most likely to be stable under circumneutral pH conditions. Reduction of U(VI) to U(IV) is examined for the U-carbonate and U-catechol complexes. Results on the potential energy differences between U(V)- and U(IV)-carbonate complexes suggest that the cause of slower disproportionation in this system is electrostatic repulsion between UO2 [CO3]35- ions that must approach one another to form U(VI) and U(IV) rather than a change in thermodynamic stability. Calculations on U-catechol species are consistent with the observation that UO22+ can oxidize catechol and form quinone-like species. In addition, outer-sphere complexation is predicted to be the most stable for U-catechol interactions based on calculated energies and comparison to 13C NMR spectra. Outer-sphere complexes (i.e., ion pairs bridged by water molecules) are predicted to be comparable in Gibbs free energy to inner-sphere complexes for a model carboxylic acid. Complexation of uranyl to phosphorus-containing groups in extracellular polymeric substances is predicted to favor phosphonate groups, such as that found in phosphorylated NAG, rather than phosphodiesters, such as those in nucleic acids.
TL;DR: In this paper, the effects of simultaneous adsorption of aqueous arsenate and uranyl onto aluminum oxide over a range of pH and concentration conditions were examined by combining batch experiments, speciation calculations, X-ray absorption spectroscopy, and Xray diffraction.
TL;DR: The surface reactivity of biogenic, nanoparticulate UO2 with respect to sorption of aqueous Zn(II) and particle annealing is different from that of bulk uraninite because of the presence of surface-associated organic matter as discussed by the authors.
TL;DR: The results indicate the formation of mononuclear complexes at the edges of montmorillonite platelets, with the orientation of the uranyl axis equal to the magic angle, as constrained by the edges' structural properties.
Abstract: The mechanism of U(VI) retention on montmorillonite and hectorite at high ionic strength (0.5 M NaCl) was investigated by solution chemistry and, at near-neutral pH, polarized EXAFS spectroscopy. Uranium(VI) sorption increases from pH 3 to 7 on the two clays, but with a steeper edge for hectorite. Uranium(VI) is no longer retained at pH > 9, presumably owing to the formation of soluble anionic complexes. Polarized EXAFS showed that U(VI) retains its uranyl conformation on montmorillonite (U_mont) and hectorite (U_hect), with uranyl O at 1.79(2) A for U_mont and 1.82(2) A for U_hect, and split equatorial O shells at 2.29(2) and 2.47(2) A (U_mont), or 2.35(2) and 2.53(2) A (U_hect). An additional atomic shell of ∼0.5 Al/Si at 3.3 A is detected for U_mont, but neither the oxygen nor the cationic shell exhibit clear angular dependence. These results indicate the formation of mononuclear complexes at the edges of montmorillonite platelets, with the orientation of the uranyl axis equal to the magic angle, as co...
TL;DR: This technique has potential applications in the field of nuclear waste management for extracting other actinides and by fluorescence spectroscopy and neutron activation analysis.
Abstract: Uranyl ions (UO2)2+ in aqueous nitric acid solutions can be extracted into supercritical CO2 (sc-CO2) via an imidazolium-based ionic liquid using tri-n-butylphosphate (TBP) as a complexing agent. The transfer of uranium from the ionic liquid to the supercritical fluid phase was monitored by UV/Vis spectroscopy using a high-pressure fiberoptic cell. The form of the uranyl complex extracted into the supercritical CO2 phase was found to be UO2(NO3)2(TBP)2. The extraction results were confirmed by UV/Vis spectroscopy and by neutron activation analysis. This technique could potentially be used to extract other actinides for applications in the field of nuclear waste management.
TL;DR: In this article, seven compounds containing the uranyl tetrachloride anion ([UO2Cl4 ]2−) have been synthesized through room temperature reactions of uranium (VI) oxyacetate with several pyridinium cations in highly acidic Cl− solutions.
Abstract: Seven compounds containing the uranyl tetrachloride anion ([UO2Cl4 ]2−) have been synthesized through room temperature reactions of uranium (VI) oxyacetate with several pyridinium cations in highly acidic Cl− solutions. The resulting compounds have been characterized viasingle-crystal X-ray diffraction and fluorescence spectroscopy. These compounds represent an importat step in the synthesis of novel uranium-bearing materials in that their assembly explicitly employs the use of non-covalent bonds, specifically through a systematic pairing of [UO2Cl4]2− with protonated pyridyl species. Four of these compounds exhibit a bifurcated hydrogen bond (NH⋯Cl2U) that leads to the formation of a linear “ribbon motif” which has been previously explored in similar perhalometallate systems. The remaining three compounds exhibit different bonding motifs, that likely result from the non-linear geometry of their organic cations.