Uranyl Complexes Research Articles

Interactions of CyMe4 -BTBP ligand with lanthanides and actinides: Insights from ESI-MS and DFT calculations.

Electrospray Ionization Mass Spectrometry (ESI-MS) technique and density functional theory (DFT) calculations were combined to study the formation of the complexes of lanthanides (Ln = La, Ce, Nd, Sm, Eu, Yb) and actinides (UO2 2+ , Th4+ ) with CyMe4 -BTBP (6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4-]triazin-3-yl)-[2,2']bipyridine) to understand the mechanisms during the extraction process. Mass spectrometry titrations showed the formation of the complexation in acetonitrile. For lanthanides, only 1:2 complexes ([Ln(L)2 ]3+ , [Ln(L)2 (CH3 CN)]3+ ), [Ln(L)2 (NO3 )]2+ ) were found at low [Ln]/[L] concentration ratios, whereas the 1:1 complexes ([Ln(L)(NO3 )2 ]+ ) were observed when the [Ln]/[L] concentration ratio reached 1.0. For uranyl complexes, 1:1 complex ([UO2 L(NO3 )]+ ) was the only species within the measuring range. Th4+ complexes had two compositions: 1:1 and 1:2, in which 1:2 species was the dominant complex. Collision-induced dissociation (CID) was employed to characterize the fragmentation process. The fragmentation process was unfolded sequentially on both sides of CyMe4 -BTBP ligand with the loss of alkyl groups and cleavage of triazinyl rings. The CID results of CyMe4 -BTBP complexes revealed a slight difference depending on the metal center. The DFT calculations showed that the stable complexes formed in acetonitrile solution were consistent with the ESI-MS results.

Evidence for Uranium(VI/V) Redox Supported by 2,2'-Bipyridyl-6,6'-dicarboxylate.

The 2,2'-bipyridyl-6,6'-dicarboxylate ligand (bdc) has been shown in prior work to effectively capture the uranyl(VI) ion, UO22+, from aqueous solutions. However, the redox properties of the uranyl complex of this ligand have not been addressed despite the relevance of uranium-centered reduction to the nuclear fuel cycle and the presence of a bipyridyl core in bdc, a motif long recognized for its ability to support redox chemistry. Here, the bdc complex of UO22+ (1-UO2) has been synthetically prepared and isolated under nonaqueous conditions for the study of its reductive chemical and electrochemical behavior. Spectrochemical titration data collected using decamethylcobaltocene (Cp*2Co) as the reductant demonstrate that 1e- reduction of 1-UO2 is accessible, and companion near-infrared and infrared spectroscopic data, along with theoretical findings from density functional theory, provide evidence that supports the accessibility of the U(V) oxidation state. Data obtained for control ruthenium complexes of bdc and related polypyridyl dicarboxylate ligands provide a counterpoint to these findings; ligand-centered reduction of bdc in these control compounds occurs at potentials more negative than those measured for reduction of 1-UO2, further supporting the generation of uranium(V) in 1-UO2. Taken together, these results underscore the usefulness of bdc as a ligand for actinyl ions and suggest that it could be useful for further studies of the reductive activation of these unique species.

Constructing stable uranyl-copper(II) bimetallic organic frameworks using rigid thiophenedicarboxylic acid

By introducing Cu(II) ions as additional connecting nodes to construct stable heterometallic uranyl-organic frameworks (UOFs) with thiophene-2,5-dicarboxylic acid (H2TDC) and N-donor auxiliary ligands, three new uranyl complexes, namely, [Cu(phen)(UO2)(TDC)2] (1), [Cu(phen-NO2)2(UO2)(TDC)2]·3H2O (2), and [Cu(phen-NH2)(H2O)2(UO2)(TDC)2]·4H2O (3) (phen = 1,10-phenanthroline) have been successfully synthesized by hydrothermal reaction. Complex 1 exhibits a rare three-dimensional (3D) network structure of cds topology connected by UO2, Cu(phen), and TDC units. Both complexes 2 and 3 feature similar one-dimensional chain structures based on UO2, TDC, Cu(Phen-NO2)2 and UO2, TDC, Cu(phen-NH2)(H2O)2 respectively. The N-donor auxiliary ligands play a key role in determining their structural dimensionalities and bandgaps formation. Among the three uranyl complexes, phen with a smaller size than its derivatives, phen-NO2 and phen-NH2, was found to be favorable for constructing 3D UOFs. Moreover, complexes with both phen-NO2 and phen-NH2 showed varying degrees of redshift on optical spectra. The UV–Visible diffuse-reflectance spectra, analyzed with Tauc’s fitting in considering Urbach tailing, revealed an indirect bandgap of 2.94 eV, an indirect bandgap of 2.67 eV, and a direct bandgap of 2.45 eV for 1, 2 and 3, respectively. Moreover, thermogravimetric analyses indicate that 3D anhydrous uranyl complex 1 possessed a robust structure and excellent thermal stability above 250 ℃.

Uranium Speciation in a Chalky Soil.

In this article, the speciation and behavior of anthropogenic metallic uranium deposited on natural soil are approached by combining EXAFS (extended X-ray absorption fine structure) and TRLFS (time-resolved laser-induced fluorescence spectroscopy). First, uranium (uranyl) speciation was determined along the vertical profile of the soil and bedrock by linear combination fitting of the EXAFS spectra. It shows that uranium migration is strongly limited by the sorption reaction onto soil and rock constituents, mainly mineral carbonates and organic matter. Second, uranium sorption isotherms were established for calcite, chalk, and chalky soil materials along with EXAFS and TRLFS analysis. The presence of at least two adsorption complexes of uranyl onto carbonate materials (calcite) could be inferred from TRLFS. The first uranyl tricarbonate complex has a liebigite-type structure and is dominant for low loads on the carbonate surface (<10 mgU/kg(rock)). The second uranyl complex is incorporated into the calcite for intermediate (∼10 to 100 mgU/kg(rock)) to high (high: >100 mgU/kg(rock)) loads. Finally, the presence of a uranium-humic substance complex in subsurface soil materials was underlined in the EXAFS analysis by the occurrence of both monodentate and bidentate carboxylate (or/and carbonate) functions and confirmed by sorption isotherms in the presence of humic acid. This observation is of particular interest since humic substances may be mobilized from soil, potentially enhancing uranium migration under colloidal form.

Probing the interaction of uranyl(VI) complex with bovine serum albumin via in-depth experimental and computational perspectives

Interaction aspects of uranyl(VI) complexes as well as the coordinated ONNO-donor ligand with bovine serum albumin (BSA) were investigated by the fluorescence spectroscopy and computational insights. Under optimal physiological condition, it was observed that there was significant decrease in fluorescence intensity of BSA upon interaction with uranyl(VI) complexes as well as the ligand. The mechanism of interaction between the uranyl(VI) complex and BSA protein was examined by fluorescence measurement. The Stern-Volmer constant, binding affinity, binding constant, standard free energy, and fluorescence lifetime decay profile of BSA in the absence as well as in the presence of uranyl(VI) complex were determined. Furthermore, the conformational binding of uranyl(VI) complexes with BSA protein was explored via molecular docking studies, and confirmed that there is a strong affinity between the Trp-213 residue in the binding pocket of sub-domain IIA and uranyl(VI) complex.

Synthetic and Structural Chemistry of Uranyl-Amidoxime Complexes: Technological Implications

Resource shortage is a major problem in our world. Nuclear energy is a green energy and because of this and its high energy density, it has been attracting more and more attention during the last few decades. Uranium is a valuable nuclear fuel used in the majority of nuclear power plants. More than one thousand times more uranium exists in the oceans, at very low concentrations, than is present in terrestrial ores. As the demand for nuclear power generation increases year-on-year, access to this reserve is of paramount importance for energy security. Water-insoluble polymeric materials functionalized with the amidoxime group are a technically feasible platform for extracting uranium, in the form of {UO2}2+, from seawater, which also contains various concentrations of other competing metal ions, including vanadium (V). An in-depth understanding of the coordination modes and binding strength of the amidoxime group with uranyl and other competing ions is a key parameter for improving extraction efficiency and selectivity. Very limited information on the complexation of {UO2}2+ with amidoximes was available before 2012. However, significant advances have been made during the last decade. This report reviews the solid-state coordination chemistry of the amidoxime group (alone or within ligands with other potential donor sites) with the uranyl ion, while sporadic attention on solution and theoretical studies is also given. Comparative studies with vanadium complexation are also briefly described. Eight different coordination modes of the neutral and singly deprotonated amidoxime groups have been identified in the structures of the uranyl complexes. Particular emphasis is given to describing the reactivity of the open-chain glutardiamidoxime, closed-ring glutarimidedioxime and closed-ring glutarimidoxioxime moieties, which are present as side chains on the sorbents, towards the uranyl moiety. The technological implications of some of the observed coordination modes are outlined. It is believed that X-ray crystallography of small uranyl-amidoxime molecules may help to build an understanding of the interactions of seawater uranyl with amidoxime-functionalized polymers and improve their recovery capacity and selectivity, leading to more efficient extractants. The challenges for scientists working on the structural elucidation of uranyl coordination complexes are also outlined. The review contains six sections and 95 references.

How Does Bending the Uranyl Unit Influence Its Spectroscopy and Luminescence?

Bent uranyl complexes can be formed with chloride ligands and 1,10-phenanthroline (phen) ligands bound to the equatorial and axial planes of the uranyl(VI) moiety, as revealed by the crystal structures, IR and Raman spectroscopy, and quantum-chemical calculations. With the goal of probing the influence of chloride and phenanthroline coordination enforcing the bending on the absorption and emission spectra of this complex, spin-orbit time-dependent density functional theory calculations for the bare uranyl complexes as well as for the free UO2Cl2 subunit and the UO2Cl2(phen)2 complex were performed. The emission spectra have been fully simulated by ab initio methods and compared to experimental photoluminescence spectra, recorded for the first time for UO2Cl2(phen)2. Notably, the bending of uranyl in UO2Cl2 and UO2Cl2(phen)2 triggers excitations of the uranyl bending mode, yielding a denser luminescence spectrum.

Modeling Uranyl Adsorption on MoS2/Mo2CTx Heterostructures Using DFT and BOMD Methods.

Uranium-bearing wastewaters exert a great threat to the ecological environment due to its high radiotoxicity level. The designing and fabrication of novel adsorption materials can be promoted for radionuclide elimination from wastewater. In this work, results from density functional theory and Born-Oppenheimer molecular dynamics simulations are reported for the uranyl adsorption behavior on the MoS2/Mo2CTx heterostructure in the gas phase and in an aqueous environment. Uranyl ions prefer to be adsorbed at deprotonated O sites on the Mo2COH surface and S sites on the MoS2 side of the heterojunctions, resulting in the formation of bidentate configurations. In addition to coordination interaction, H-bond and van der Waals interactions can also play an important role in binding configurations. More importantly, the oxidation state U(VI) can be reduced to U(V) and then to U(IV) caused by the strong reducibility of the Mo2COH surface at room temperature, whereas the uranyl complex can move freely on the MoS2 surface. However, the coordination number of U with respect to H2O in the first hydration shell on the Mo2COH surface remains unchanged and is found to be 3, which is similar to that on the MoS2 surface. This work provides novel nanosorbents for the removal of uranyl from wastewater. The present viewpoint provides valuable mechanistic interpretations for uranyl adsorption and will give a supplement to the experimental research.

Spectroscopic investigation of the hydrolysis of benzil bis(isonicotinoyl hydrazone) ligand and its uranyl(VI) complexes: Highly efficient sequential extraction of uranyl(VI) ions from aqueous phase

Spectroscopic investigation of the hydrolysis of benzil bis(isonicotinoyl hydrazone) ligand and its uranyl(VI) complexes: Highly efficient sequential extraction of uranyl(VI) ions from aqueous phase

Periodic Trends in the Stabilization of Actinyls in Their Higher Oxidation States Using Pyrrophen Ligands.

Owing to the prominent existence and unique chemistry of actinyls, their complexation with suitable ligands is of significant interest. The complexation of high-valent actinyl moieties (An = U, Np, Pu and Am) with the acyclic sal-porphyrin analogue called "pyrrophen" (L(1)) and its dimethyl derivative (L(2)) with four nitrogen and two oxygen donor atoms was studied using relativistic density functional theory. Based on the periodic trends, the [UVO2-L(1)/L(2)]1- complexes show shorter bond lengths and higher bond orders that increase across the series of pentavalent actinyl complexes mainly due to the localization of the 5f orbitals. Among the hexavalent complexes, the [UVIO2-L(1)/L(2)] complexes have the shortest bonds. Following the uranyl complex, due to the plutonium turn, the [AmVIO2-L(1)/L(2)] complexes exhibit comparable properties with those of the former. Charge analysis suggests the complexation to be facilitated through ligand-to-metal charge transfer (LMCT) mainly through σ donation. Thermodynamic feasibility of complexation was modeled using hydrated actinyl moieties in aqueous medium and was found to be spontaneous. The dimethylated pyrrophen (L(2)) shows higher magnitudes of thermodynamic parameters indicating increased feasibility compared to the unsubstituted ligand (L(1)). Energy decomposition analysis (EDA) along with extended transition-state-natural orbitals for chemical valence theory (ETS-NOCV) analysis shows that the dominant electrostatic contributions decrease across the series and are counteracted by Pauli repulsion. Slight but considerable covalency is provided to hexavalent actinyl complexes by orbital contributions; this was confirmed by molecular orbital (MO) analysis that suggests strong covalency in americyl (VI) complexes. In addition to the pentavalent and hexavalent actinyl moieties, heptavalent actinyl species of neptunyl, plutonyl, and americyl were studied. Beyond the influence of the charges, the geometric and electronic properties point to the stabilization of neptunyl (VII) in the pyrrophen ligand environment, while the others shift to a lower (+VI) and relatively stable OS on complexation.

The role of uranyl complex decomposition and redox conditions in the precipitation of hydrothermal uranium deposits: Insights from chlorite mineralogy and geochemistry in the Shazhou uranium deposit, Xiangshan, SE China

Uranium precipitation involves the decomposition of uranyl complexes and the reduction of hexavalent uranium, which can occur sequentially or simultaneously within one redox reaction. The redox condition of hydrothermal fluid plays a vital role in controlling the migration and precipitation of uranium in hydrothermal uranium deposits. However, little attention has been paid to the role of uranyl complex decomposition in uranium precipitation. In this study, chlorite mineralogy and geochemistry were examined to clarify the process of uranium precipitation in the Shazhou deposit, Xiangshan uranium orefield, Southeast China. Based on comprehensive petrographic and mineral chemistry studies of chlorites obtained from altered granite porphyries and uranium ores, five types of chlorites were identified: (1) chlorite present in the form of pseudomorphous biotite, which was produced by the hydrothermal alteration of biotite in rocks that underwent hematitization and chloritization (Chl-I); (2) chlorite filling the cleavage cracks in biotite in rocks that underwent hematitization and chloritization (Chl-II); (3) chlorite occurring in pyrite veins (Chl-III); (4) chlorite intergrown with pitchblende in ore veins (Chl-IV); and (5) chlorite occurring in calcite veins (Chl-V). Chlorite geothermometry revealed that the formation temperatures of the five types of chlorites ranged from 219 °C to 254 °C. Mineral chemistry analyses revealed that the five types of chlorites formed in a reductive fluid environment, where the oxygen fugacity at different stages is similar, with log fO2 values ranging from −41.6 to −39.1. Uranium precipitation started only in stage Chl-IV. The examination of the mineral assemblage revealed that the ore-forming fluid was rich in F−, HPO32−, and CO32−. Comprehensive investigation of chemistry and physicochemical conditions of the ore-forming fluid revealed that oxidized uranium (UO22+) could be complexed with HPO42− and F−, and uranyl phosphate and the uranyl fluoride complexes were the main uranium species when uranium precipitation and the decomposition occurred at stage Chl-IV. However, the assessment of oxygen fugacity of the solution equilibria between the UO2(s) and the uranyl phosphate and uranyl fluoride complexes revealed that the reducibility of the fluid favoring the reduction of uranyl ions (UO22+) to U4+ was insufficient to reduce the uranyl phosphate and uranyl fluoride complexes. This indicates that the breakup of uranyl phosphate and the uranyl fluoride complexes to release uranyl ions should occur first at stage Chl-IV, reducing uranyl ions to U4+, and leading to uranium precipitation. Hence, the decomposition of uranyl complexes played an important role in uranium precipitation. With the increase in pH, uranyl phosphate and the uranyl fluoride complexes gradually decomposed and became reducible. Moreover, the decrease in ligand concentration was conducive to the decomposition of uranyl phosphate and the uranyl fluoride complexes. During the formation of the Shazhou deposit, the fluid boiling process induced the loss of volatiles, such as CO2, CH4, HF, and H2S, leading to an increase in pH and decrease in HPO42−, F−, and CO32− concentrations in the fluid. These factors also led to the decomposition of uranyl fluoride and the uranyl phosphate complexes and the precipitation of fluorapatite and calcite. Uranium was then reduced by the action of Fe2+ and S− (pyrite) from a hexavalent to a tetravalent, and finally, uranium was precipitated to form uranium ores.

New Barium Fluorosuccinato and Fluoroglutarato Uranylates

Two new coordination polymers: Ba2[(UO2)3(suc)3F4]⋅5H2O (I) and Ba[(UO2)2(glt)2(Hglt)F]⋅8H2O (II), where suc is C4H4O2−442− (succinate ion) and glt is C5H6O2−442− (glutarate ion), were synthesized, and their structure was studied. The uranium-containing structural units of crystals I are the [(UO2)3(C4H4O4)3F4]4– layers belonging to the crystal-chemical group A3(Q02)3M22M22M12M21 of uranyl complexes, where A = UO2+2UO22+, Q02 = C4H4O2−442−, М1 and М2 = F–. Structure II contains the uranium-containing 3D complex [(UO2)2(C5H6O4)2(C5H7O4)F]2–, which corresponds to the crystal-chemical formula A2(Q02)2B01M2, where A = UO2+2UO22+, Q02 = C5H6O2−442−, B01 = C5H7O−44−, and М2 = F–.

Trends in the Electronic Structure and Chemical Bonding of a Series of Porphyrinoid-Uranyl Complexes.

In this paper, we have explored the relativistic density functional theory study on a series of deprotonated porphyrinoid (Ln) complexes of uranyl to investigate the geometrical structures and chemical bonding. The ligands bound with uranyl in the 1:1 complexes [UO2(Ln)]x (n = 4, 5, 6; x = 0, -1, -2), showing more thermodynamic stability for "in-cavity" structures of L5 and L6 than that of the "side-on" structure of L4 and an increase in stability with the increase of negative charges, L2- < L3- < L4-. Among the six ligands, the cyclo[6]pyrrole presents the best selectivity toward uranyl. Based on chemical bonding analyses, the U-NL bond in the in-cavity complexes adopts a typical dative NL → U bond with mainly ionic bonding and significant covalency, which comes from the significant orbital interaction of U 5fϕ6dδ7s hybrid AOs and NL 2p-based MOs. This work provides a systematic understanding of the coordination chemistry in uranyl pyrrole-containing macrocycle complexes and the nature of chemical bonding in such systems, which may provide inspirations for the future design of synthetic targets that could be relevant to actinide separations or in the remediation of spent nuclear fuel.

Examining Interactions of Uranyl(VI) Ions with Amino Acids in the Gas Phase

Gas-phase experiments, using electrospray ionization quadrupole ion trap mass spectrometry (ESI-QIT/MS), were conducted to probe basic interactions of the uranyl(VI) ion, UO22+, with selected natural amino acids, namely, L-cysteine (Cys), L-histidine (His), and L-aspartic acid (Asp), which strongly bind to metal ions. The simplest amino acid, glycine (Gly), was also studied for comparison. Cys, His, and Asp have additional potentially coordinating groups beyond the amino and carboxylic acid functional groups, specifically thiol in Cys, imidazole in His, and a second carboxylate in Asp. Gas-phase experiments comprised collision-induced dissociation (CID) of uranyl–amino acid complexes and competitive CID to assess the relative binding strength of different amino acids in the same uranyl complex. Reactivity of selected uranyl–amino acid complexes with water provided further insights into relative stabilities. In positive ion mode, CID and ensuing reactions with water suggested that uranyl–neutral AA binding strength decreased in the order His &gt; Asp &gt; Cys &gt; Gly, which is similar to amino acid proton affinities. In negative ion mode, CID revealed a decreasing dissociation tendency in the order Gly &gt;&gt; His ≈ Cys &gt; Asp, presumably reflecting a reverse enhanced binding to uranyl of the doubly deprotonated amino acids formed in CID.

Highly efficient sorption of U(VI) on TiO2 nanosheets supported by amidoxime polyacrylonitrile in a variety of multi-carbonate solutions

Natural carbonate-rich uranium-containing water contributes to the formation of multi-carbonate solutions, including U(VI)–CO3, Mg/Ca–U(VI)–CO3, U(VI)–P–CO3, and U(VI)–X–CO3 (X = F, Cl, Br, I) systems. Herein, a novel composite of TiO2 nanosheets supported by amidoxime polyacrylonitrile (TNSs-PAN-AO) was newly prepared to study the U(VI) sorption in various multi-carbonate solutions. The results showed that the composite achieved the maximum sorption capacity (qe) of 108.4 mg·g−1 in U(VI)–CO3 solution, which was monolayer chemisorption. The competitive complexation of CO32– with U(VI) and the enhanced electrostatic repulsion caused by the transformation of (UO2)2CO3(OH)3– to UO2(CO3)34– species resulted in the relatively low qe values at high pH and [CO3]Total. The U(VI) sorption was suppressed in Mg/Ca–U(VI)–CO3, U(VI)–P–CO3, and U(VI)–X–CO3 solutions, especially in U(VI)–F–CO3, possibly due to the formation of dominant ternary complexes that can preempt the sorption sites of U(VI) on the composite. The desorption experiments showed that the highest desorption rate was 93.78% obtained by 0.1 mol∙L−1 HNO3. The XPS test and DFT calculations indicated that the –C(NH2)=N–OH and Ti–OH groups were the main sorption sites, which can scramble for U(VI) from the formed uranyl complex anions in multi-carbonate solutions. This work presented new insights into the understanding of uranium extraction from multi-carbonate solutions based on the practical U(VI) species, which may be of great significance for the recovery of uranium from natural water.

Hydrothermal Alteration and Element Migration Patterns in the Zhangjiawu Uranium Deposit, Northern Zhejiang Province, China

The Zhangjiawu uranium deposit is the largest volcanic rock-type uranium deposit in the northern Zhejiang Province, China. The deposit has developed hydrothermal alteration, with obvious alternating zoning phenomena from the mineralized center to the fresh surrounding rocks. Based on detailed field and petrographic observations of typical ore bodies, the uranium mineralized section of the Zhangjiawu uranium deposit was divided into mineralized central, ore-side alteration, near-ore alteration and far-ore alteration zones, whose hydrothermal alteration intensity decreases sequentially. Using the standardized Isocon diagram method, the results show that CaO, MgO, Na2O, P2O5, LOI, Zn, Co, Cu, Pb and heavy rare earth elements (HREE) show gain during uranium mineralization, while K2O, Cs, Rb and Tl show loss, which is consistent with the development of hematite mineralization, sodic feldsparization and carbonation in the mine area. A negative correlation of MnO and MgO in the alteration zone indicates a possible elemental convective equilibrium migration mode in the ore zone. The migration mechanism of the elements indicates that the migration of P2O5 and HREE indicates the deep source nature of the mineralizing fluids, and that alteration can lead to a reduction in the activity of uranyl complexes, the formation of a reducing environment and a neutral to weak alkaline environment favorable for uranium precipitation, which can lead to uranium precipitation and enrichment of mineralization. The study of hydrothermal alteration and elemental migration patterns of the deposit provides supporting evidence for a better understanding of the process of uranium mineralization in Zhangjiawu, and also provides a basis for the next step of mineral search and exploration.

Uranyl(VI) Mixed-ligand complex synthesis and characterization using 4-acylhydrazone-5-pyrazolone and 4-acylpyrazolone: Covalency, crystal assay, DFT study and Hirshfeld analysis

Newly prepared bidentate HLA and tridentate Bz-HLA ligands were used to synthesize the novel uranyl mixed ligand [UO2(HLA)(Bz-HLA)] complex with pentagonal bipyramidal geometry. HLA ligand was prepared via the common acylation method, and the Bz-HLA ligand was prepared using the Schiff base reaction of HLA with a benzohydrazide molecule. FTIR, 1H and 13C NMR, SCXRD, molar conductance, and TG-DTA were mainly implemented to examine the structure of produced compounds. The combined covalency effect of complex due to both ligands has been studied, which was discovered to be influenced by the average bond length values on the pentagonal plane, uranyl axial bond lengths, ligand coordination, and donor ability of various atoms. To demonstrate that solvents have no impact on the covalency of the synthesised complex, Sinha's covalency parameters were computed using UV–vis data. DFT calculations were performed in order to validate experimental findings in comparison to theoretical findings, and theoretical bond characteristics were also investigated through the recognition of global index values. Hirshfeld surface analysis was used to examine the crystal strength, energy characteristics and non-covalent surface interactions. Analysis using cyclic voltammetry(CV) shows that the complex is irreversibly reducing. Understanding the Schiff base of acylpyrazolones and their covalency in uranyl complexes allow for the investigation of a wide range of chemical properties and applications.

Dual-Ligand Strategy for the Preparation of Gas-Phase Uranyl(VI) Benzyne Complexes from Uranyl(VI) Benzoates.

The uranyl(VI) benzyne complex (η2-C6H4)UO2Cl- was prepared in the gas phase by electrospray ionization mass spectrometry coupled with collision-induced dissociation. It was formed via a dual-ligand strategy that requires the elimination of benzoic acid or benzene/CO2 from the uranyl dibenzoate precursor (C6H5CO2)2UO2Cl-. This contrasts the known strategy for the formation of gas-phase benzyne complexes that would result from CO2/HCl elimination from (C6H5CO2)UO2Cl2-, during which only one benzoate ligand is involved. Such dual-ligand strategy can be extended to the preparation of a series of methyl- and halo-substituted benzyne complexes of uranyl(VI). Density functional theory calculations at the B3LYP level reveal that the benzyne complex (η2-C6H4)UO2Cl- features a metallacyclopropene structure with the C6H42- ligand coordinated to uranium(VI) through two polarized U-Cbenzyne σ bonds, in accordance with the reactivity test toward water. Dehydrochlorination of the benzyne complex (η2-C6H4)UO2Cl- from (C6H5)UO2Cl2- that originates from decarboxylation of (C6H5CO2)UO2Cl2- with a single benzoate ligand is neither kinetically nor thermodynamically favorable than simple C6H5 radical loss to give UVO2Cl2-. This arises from the presence of an accessible V oxidation state for uranium and accounts for the necessity for the dual-ligand strategy in the preparation of uranyl(VI) benzyne complexes from uranyl benzoate precursors.

Theoretical Study of the Excited States and Luminescent Properties of (H2O)nUO2Cl2 (n = 1–3)

The low-lying excited-state properties of the water-solvated UO2Cl2 complexes, i.e., (H2O)nUO2Cl2 (n = 1-3), below 33,000 cm-1, are investigated based on the ab initio NEVPT2 and CCSD(T) with inclusion of scalar relativistic and spin-orbit coupling effects. The simulated luminescence spectral curves agree well with the experimental spectrum in aqueous solution at -120 °C. Water coordination is found to significantly affect the character of luminescent state, which is changed from the 3Φg state in UO2Cl2 to the 3Δg state in (H2O)2,3UO2Cl2. This is distinctly different from the observed unchanged nature of luminescent state in the cases of Ar coordination to UO2Cl2 and H2O coordination to UO2F2 in the previous work. Furthermore, by combining with the theoretical results for the solvated UO2F2 system, the reason why water coordination does not remarkably change the spectral shape of UO2Cl2, as opposed to UO2F2, was explained based on the analysis of two key spectral parameters, O-U-O symmetrical vibrational frequency and U-O bond length elongation. The roles of ligand field and spin-orbit coupling in the determination of luminescent state character and spectral shape in uranyl dihalide complexes are deeply discussed and summarized. These results deepen our understanding of the luminescent properties of uranyl complexes in aqueous solution.

Guest molecular guided syntheses of 2-dimensional uranyl complexes with rigid benzenedicarboxylate ligands

Two new heterometallic uranyl-organic frameworks (UOFs), [Cd(phen)2(H2O)2][(UO2)2(BDC)3]·2H2O (1) and [Ni(phen)3][(UO2)2(BDC)3]·2H2O (2), were obtained under hydrothermal conditions. Both crystal structures were characterized by single-crystal X-ray diffraction analyses and the results indicate that both complexes feature a similar 2D honeycomb framework that is connected by rigid benzenedicarboxylate (BDC) ligands and uranyl units. BDC works as a linker to bridge neighboring UO2 2+ units, where UO2 2+ is tris-chelated. Different guest molecules guided the stacking of 2D layers and lead into their 3D supramolecular crystal structures with different space groups. As a result, 1 crystallized in a polar space group Cc, whereas 2 belongs to a chiral space group P6122. Thermogravimetric measurements were performed to study their thermal stability. UV-visible diffuse reflectance spectroscopy measurements indicate an experimental optical bandgap of 3.87 eV and 3.63 eV, respectively, for 1 and 2. Luminescent studies of both samples show strong green light emissions.