Actinide Chemistry Research Articles

Continuous Shape Measures Study of the Coordination Spheres of Actinide Complexes – Part 1: Low Coordination Numbers

AbstractStructural analyses of a large set of molecular structures of actinide compounds allow us to establish trends for stereochemical preferences, common distortion paths, geometrical constraints imposed by different ligand topologies, and the existence of incipient bonds or of Van der Waals intramolecular interactions on purportedly vacant coordination sites. In this study the relative abundance of coordination numbers in actinide chemistry appears to be on average higher than that among the lanthanides. The detailed continuous shape measures study of normalized coordination polyhedra with coordination numbers between 1 and 6 presented here is based on more than 1,800 solid state and gas phase structural data sets.

Gas-phase structure, bonding, and fragmentation chemistry of the An (IV)-TMPDCAM complexes studied using mass spectrometry and theoretical calculation (An = Th and U).

Pyridine-2,6-dicarboxamides (PDCAMs) exhibit a certain extraction ability for tetravalent actinide ions, but quite limited information regarding the structures and reactivities of the corresponding An4+ -PDCAMs complexes is available. Neutral diamides can form multiply charged complexes with lanthanide and actinide cations, which are well suited for gas-phase investigations using electrospray ionization (ESI) mass spectrometry in conjunction with theoretical calculation. Binary Th (TMPDCAM)3 4+ /U (TMPDCAM)3 4+ (TMPDCAM =N,N,N',N'-tetramethylpyridine-2,6-dicarboxamide) complexes were generated in the gas phase via ES) of Th (ClO4 )4 /U (ClO4 )4 and TMPDCAM mixtures in acetonitrile; collision-induced dissociation (CID) was employed to reveal their fragmentation behaviors; the structure and bonding were investigated by density functional theory (DFT) calculation. An (TMPDCAM)3 4+ (An = Th and U) tetracations dominated the ESI mass spectra of An (ClO4 )4 and TMPDCAM mixtures in acetonitrile. DFT calculations indicate that the two An (TMPDCAM)3 4+ complexes have C3 geometry, and the bonding analyses demonstrate that the thorium or uranium center interacts with both Ocarbonyl and Npyridine , but the latter is weaker. CID of Th (TMPDCAM)3 4+ generated a series of multiply charged thorium-containing products via bond cleavages of the TMPDCAM ligand, whereas U (TMPDCAM)3 4+ yielded only oxygen extraction product UO (TMPDCAM)2+ and hydrolysis product UO (OH)+ . An4+ (An = Th and U) can form stable tetrapositive complexes in the gas phase on coordination of three neutral TMPDCAM ligands. The structure and bonding analyses indicate that the two An (TMPDCAM)3 4+ complexes possess twisted tricapped trigonal prismatic geometry and the An4+ centers are coordinated by six Ocarbonyl and three Npyridine atoms while the interactions between An4+ and Ocarbonyl are stronger. The fragmentation chemistry of Th (TMPDCAM)3 4+ and U (TMPDCAM)3 4+ is quite different from each other, which reveals that the gas-phase chemistry of quadruply charged actinide-diamide complexes is affected by the metal centers with distinct properties.

Determination of lanthanide and actinide elements by energy dispersive x-ray fluorescence spectrometry applying DLLME preconcentration and dried spot

This work describes an analytical procedure to determination of trace amount of lanthanide and actinide chemistry elements (LAEs) in water samples by energy dispersive x-ray fluorescence spectrometry (EDXRF) with the prepare of the samples using simultaneous preconcentration procedure based on the dispersive liquid-liquid microextraction (DLLME). Critical study of the analytical procedure occurred the following way: ions of Eu, Er, Ho, Th, U and Yb presents in 5.0 mL of aqueous sample have been complexed with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) in a mixture contained solvents (disperser and extractant). After centrifugation, 30 μL of the sedimented organic phase has been removed and deposited on membrane disk and submitted to EDXRF analysis. The optimization step was performed by: i) screening factor with mixture design for the disperser solvent (acetone, acetonitrile and ethanol) and extractant solvent (carbon tetrachloride, trichlorethylene and 1,2-dichloroethane); ii) Box-Behnken design for the independents variables: pH, Br-PADAP concentration, volume of disperser solvent and volume of extractant solvent. The optimized conditions were: 500 μL of disperser solvent (ethanol), 60 μL extractant solvent (carbon tetrachloride and trichlorethylene, 1: 1 ratio), Br-PADAP 1.8 × 10−5 mol L−1 and pH 8.0. In these conditions, the procedure allows the determination of Eu, Ho, Er, Yb, Th and U with quantification limits of 10.5; 8.6; 4.3; 7.0; 6.6 and 1.1 μg L−1, respectively; preconcentration factor between 18 and 74, and precision (RSD%) below that 6%. Salting out effect, presence of other ions, and additions/recoveries of analytes in real samples was verified and the recovery values were between of 90 to 107%. Analytical method has been applied in waters samples and groundwater from uranium mining region.

Norm-Conserving Pseudopotentials and Basis Sets to Explore Actinide Chemistry in Complex Environments.

We have developed a new set of norm-conserving pseudopotentials and companion Gaussian basis sets for the actinide (An) series (Ac-Lr) using the Goedecker, Teter, and Hutter (GTH) formalism with the Perdew, Burke, and Ernzerhof (PBE) exchange-correlation functional of generalized gradient approximation. To test the accuracy and reliability of the newly parameterized An-GTH pseudopotentials and basis sets, a variety of benchmarks on actinide-containing molecules were carried out and compared to all-electron and available experimental results. The new pseudopotentials include both medium- ([Xe]4f14) and large-core ([Xe]4f145d10) options that successfully reproduce the structures and energetics, particularly redox processes. The medium-core size set, in particular, reproduces all-electron calculations over multiple oxidation states from 0 to VII, whereas the large-core set is suitable only for the early series elements and low oxidation states. The underlying reason for these transferability issues is discussed in detail. This work fills a critical void in the literature for studying the chemistry of 5f-block elements in the condensed phase.

Interplay between London Dispersion, Hubbard U, and Metastable States for Uranium Compounds.

High-throughput computational studies of lanthanide and actinide chemistry with density-functional theory are complicated by the need for Hubbard U corrections, which ensure localization of the f-electrons, but can lead to metastable states. This work presents a systematic investigation of the effects of both Hubbard U value and metastable states on the predicted structural and thermodynamic properties of four uranium compounds central to the field of nuclear fuels: UC, UN, UO2, and UCl3. We also assess the impact of the exchange-hole dipole moment (XDM) dispersion correction on the computed properties. Overall, the choice of Hubbard U value and inclusion of a dispersion correction cause larger variations in the computed geometric properties than result from metastable states. The weak dependence of structure optimization on metastable states should simplify future high-throughput calculations on actinides. Conversely, addition of the dispersion correction is found to offset the repulsion introduced by the Hubbard U term and provides greatly improved agreement with experiment for both cell volumes and heats of formation. The XDM dispersion correction is largely invariant to the chosen U value, making it a robust dispersion correction for actinide systems.

Insights into the thermal decomposition of plutonium(IV) oxalate – a DFT study of the intermediate structures

The thermal decomposition of plutonium oxalate to oxide is one of the most studied reactions in actinide chemistry but the intermediates have been the subject of debate for decades. Recent experimental data suggest that the decomposition of Pu(IV) oxalate in air undergoes dehydration first, then reduction to Pu(III) oxalate. The precise structural modifications that take place are unknown as experiments have not been able to fully characterize the intermediates at the microscopic level. To rectify this, we employed solid state density functional theory calculations at the PBE-D3 level with a Hubbard U correction to model the structures and energetics of potential dehydrated Pu(IV) and Pu(III) oxalate intermediate compounds. Based on the theoretical study presented here, the anhydrous analogues of the known hydrated Pu(IV) and Pu(III) oxalates are the preferred crystal structures formed through an overall exothermic reaction process. However, decomposition could proceed through the formation of a higher energy, more complicated 3D lattice structure with frustrated oxalate binding. It is expected that the intermediates presented here could be identified using spectroscopic techniques to enable further insight into the reaction mechanism.

Recent developments in highly basic N-heterocyclic iminato ligands in actinide chemistry.

In the last decade, major conceptual advances in the chemistry of actinide molecules and materials have been made to demonstrate their distinct reactivity profiles as compared to lanthanide and transition metal compounds, but some difficult questions remain concerning the intriguing stability of low-valent actinide complexes, and the importance of the 5f-orbitals in reactivity and bonding. The imidazolin-2-iminato moiety has been extensively used in ligands for the advancement of actinide chemistry owing to its unique capability of stabilizing the reactive and highly electrophilic metal ions by virtue of its strong electron donation and steric tunability. The current review article describes recent developments in the chemistry of light actinide metal ions (thorium and uranium) bearing these N-heterocyclic iminato moieties as supporting ligands. In addition, the effect of ring expansion of the N-heterocycle on the catalytic aptitude of the organoactinides is also described herein. The synthesis and reactivity of actinide complexes bearing N-heterocyclic iminato ligands are presented, and promising apposite applications are also presented. The current review focuses on addressing the catalytic behavior of actinide complexes with oxygen-containing substrates such as in the Tishchenko reaction, hydroelementation processes, and polymerization reactions. Actinide complexes have also found new catalytic applications, as demonstrated by the potent chemoselective carbonyl hydroboration and tandem proton-transfer esterification (TPTE) reaction, featuring coupling between an aldehyde and alcohol.

Stabilization of hydrated AcIII cation: the role of superatom states in actinium-water bonding.

225Ac-based radiopharmaceuticals have the potential to become invaluable in designated cancer therapy. However, the limited understanding of the solution chemistry and bonding properties of actinium has hindered the development of existing and emerging targeted radiotherapeutics, which also poses a significant challenge in the discovery of new agents. Herein, we report the geometric and electronic structural properties of hydrated AcIII cations in the [AcIII(H2O)n]3+ (n = 4–11) complexes in aqueous solution and gas-phase using density functional theory. We found that nine water molecules coordinated to the AcIII cation is the most stable complex due to an enhanced hydration Gibbs free energy. This complex adopts a closed-shell 18-electron configuration (1S21P61D10) of a superatom state, which indicates a non-negligible covalent character and involves H2O → AcIII σ donation interaction between s-/p-/d-type atomic orbitals of the Ac atom and 2p atomic orbitals of the O atoms. Furthermore, potentially existing 10-coordinated complexes need to overcome an energy barrier (>0.10 eV) caused by hydrogen bonding to convert to 9-coordination. These results imply the importance of superatom states in actinide chemistry generally, and specifically in AcIII solution chemistry, and highlight the conversion mechanism between different coordination numbers.

Decisive Role of 5f-Orbital Covalence in the Structure and Stability of Pentavalent Transuranic Oxo [M6O8] Clusters.

Actinide metal oxo clusters are of vital importance in actinide chemistry, as well as in environmental and materials sciences. They are ubiquitous in both aqueous and nonaqueous phases and play key roles in nuclear materials (e.g., nuclear fuel) and nuclear waste management. Despite their importance, our structural understanding of the actinide metal oxo clusters, particularly the transuranic ones, is very limited because of experimental challenges such as high radioactivity. Herein we report a systematic theoretical study on the structures and stabilities of seven actinide metal oxo-hydroxo clusters [AnIV6O4(OH)4L12] (1-An; An = Th-Cm; L = O2CH-) along with their group 4 (Ti, Zr, Hf, Rf) and lanthanide (Ce) counterparts [MIV6O4(OH)4L12] (1-M). The work shows the Td-symmetric structures of all of the 1-An/M clusters and suggests the positions of the -OH functional groups, which are experimentally challenging to determine. Furthermore, by removing six electrons from 1-An, we found that oxidation could happen on the AnIV metal ions, producing [AnV6O4(OH)4L12]6+ (2-An; An = Pa, U, Np), or on the O2- and OH- ligands, producing [AnIV6(O•-)4(OH•)2(OH)2L12]6+ (3-An; An = Pu, Am, Cm). On the basis of 2-An, we constructed a series of tetravalent and pentavalent actinide metal oxo clusters [AnIV6O14]4- (4-An) and [AnV6O14]2+ (5-An), which proves the feasibility of the highly important pentavalent actinyl clusters, demonstrates the f orbital's structure-directing role in the formation of linear [O≡AnV═O]+ actinyl ions, and expands the concept of actinyl-actinyl interaction into pentavalent transuranic actinyl clusters.

Heavy-Element Reactions Database (HERDB): Relativistic ab Initio Geometries and Energies for Actinide Compounds.

Actinide chemistry appears to be a challenge for both experimentalists and theoreticians. Radioactivity and computational obstacles lead to a lack of heterogeneous data describing actinide compounds. Here we present a description of the first database devoted to ab initio actinide calculations. The database contains information about the structures and electronic properties of 87 actinide and 17 other compounds in the gas phase and is ready-to-use for benchmarking computational and experimental results or building new semiempirical models.

Coordination Chemistry of Actinide Nitrates with Cyclic Amide Derivatives for the Development of the Nuclear Fuel Materials Selective Precipitation (NUMAP) Reprocessing Method

Nuclear fuel recycling is one of promising options to resolve current issues arising from energy security and nuclear wastes. Chemical separation called reprocessing aims to recover recyclable nuclear fuel materials from spent fuels, and also to reduce the volume of high‐level radioactive wastes. Even today, solvent extraction is extensively employed as a principal method for reprocessing, while there are also several safety and security concerns arising from use of large amount of organic solvents and potential isolation of highly purified (namely “decontaminated”) Pu. To resolve these issues, we propose selective precipitation of nuclear fuel materials as an alternative principle for the spent fuel reprocessing. In this minireview, we outlined history of our development of precipitation‐based reprocessing methods for spent nuclear fuels from serendipitous discovery of N‐cyclohexyl‐2‐pyrrolidone to current status reaching our simple and versatile reprocessing concept, NUclear fuel MAterials selective Precipitation (NUMAP).

Reaction mechanism of synthetic thorium sulfides: theoretical calculation study.

Actinide sulfides are especially significant in actinide chemistry because of their potentials that are used as nuclear fuel and the wide variety of their stoichiometries and physical properties. It is essential for studying the synthesis mechanism of actinide sulfides. In this study, the reactions of thorium cation Th2+ with the facile sulfur-atom donor OCS to produce thorium sulfides have been systematically explored by using density functional. The detailed insights of the primary reaction and secondary reaction paths are reported. We investigated that the multiple bonding characters and complexes involved in reaction exhibit significant covalent character. The reaction rate indicated that the tunneling effect is small compared with the effect of temperature on the rate. This study addresses some of the current limitation in understanding the detailed reaction information of Th2++OCS.

Transforming lanthanide and actinide chemistry with nanoparticles.

Lanthanides and actinides are used in a wide variety of applications, from energy production to life sciences. To address toxicity issues due to the chemical, and often radiological, properties of these elements, methods to quantify and recover them from industrial waste are necessary. When used in biomedicine, lanthanides and actinides are incorporated in compounds that show promising therapeutic and/or bioimaging properties, but lack robust strategies to target cancer and other pathologies. Furthermore, current decorporation protocols to respond to accidental actinide exposure rely on intravenous injections of soluble chelating agents, which are inefficient for treatment of inhaled radionuclides trapped in lungs. In recent years, nanoparticles have emerged as powerful tools in both industry and clinical settings. Because some inorganic nanoparticles are sensitive to external stimuli, such as light and magnetic fields, they can be used as building blocks for sensitive bioassays and separation techniques. In addition, nanoparticles can be functionalized with multiple ligands and act as carriers for selective delivery of therapeutic and contrast agents. This review summarizes and discusses recent progress on the use of nanoparticles in lanthanide and actinide chemistry. We examine different types of nanoparticles based on composition, functionalization, and properties, and we critically analyze their performance in a comparative mode. Our focus is two-pronged, including the nanoparticles free of lanthanides and actinides that are used for the detection, separation, or decorporation of f-block elements, as well as the nanoparticles that enhance the inherent properties of lanthanides and actinides for therapeutics, imaging and catalysis.

Compounds of Xenon in the Chemistry of Actinides

Published evidence on the reactions of XeF2, Na4XeO6, and XeO3 with ions of uranium, neptunium, plutonium, and americium in aqueous acid, carbonate, and alkaline solutions is analyzed. The reaction mechanisms are considered and suggested.

Carbon-sulfur bond strength in methanesulfinate and benzenesulfinate ligands directs decomposition of Np(v) and Pu(v) coordination complexes.

Gas-phase coordination complexes of actinyl(v) cations, AnO2+, provide a basis to assess fundamental aspects of actinide chemistry. Electrospray ionization of solutions containing an actinyl cation and sulfonate anion CH3SO2- or C6H5SO2- generated complexes [(AnVO2)(CH3SO2)2]- or [(AnVO2)(C6H5SO2)2]- where An = Np or Pu. Collision induced dissociation resulted in C-S bond cleavage for methanesulfinate to yield [(AnVO2)(CH3SO2)(SO2)]-, whereas hydrolytic ligand elimination occurred for benzenesulfinate to yield [(AnVO2)(C6H5SO2)(OH)]-. These different fragmentation pathways are attributed to a stronger C6H5-SO2-versus CH3-SO2- bond, which was confirmed for both the bare and coordinating sulfinate anions by energies computed using a relativistic multireference perturbative approach (XMS-CASPT2 with spin-orbit coupling). The results demonstrate shutting off a ligand fragmentation channel by increasing the strength of a particular bond, here a sulfinate C-S bond. The [(AnVO2)(CH3SO2)(SO2)]- complexes produced by CID spontaneously react with O2 to eliminate SO2, yielding [(AnO2)(CH3SO2)(O2)]-, a process previously reported for An = U and found here for An = Np and Pu. Computations confirm that the O2/SO2 displacement reactions should be exothermic or thermoneutral for all three An, as was experimentally established. The computations furthermore reveal that the products are superoxides [(AnVO2)(CH3SO2)(O2)]- for An = Np and Pu, but peroxide [(UVIO2)(CH3SO2)(O2)]-. Distinctive reduction of O2- to O22- concomitant with oxidation of U(v) to U(vi) reflects the relatively higher stability of hexavalent uranium versus neptunium and plutonium.

Liquid interfaces related to lanthanide and actinide chemistry studied using vibrational sum frequency generation spectroscopy

Liquid interfaces related to lanthanide and actinide chemistry studied using vibrational sum frequency generation spectroscopy

Experimental and computational study of particle formation kinetics in UF6 hydrolysis

The formation and growth of UO2F2 particles by gas-phase UF6 hydrolysis remains of interest to actinide chemistry researchers.

Polyoxometalate-based complexes as ligands for the study of actinide chemistry.

The complexation of actinide cations by polyoxometalates (POMs) has been extensively studied over the past 50 years. In this perspective article, we present the rich structural diversity of actinide-POM complexes and their contribution to the extension of our knowledges of actinide chemistry, especially regarding aspect of their redox chemistry, as well as application for the capture and separation of these cations in the context of nuclear fuel remediation. These heterometallic assemblies have also proven highly valuable as model for heterogeneous systems based on actinides supported by metal oxide surfaces. In particular, activation of the An-O bond of actinyl fragments upon complexation with lacunary POMs has been reported, creating opportunities for future developments regarding the reactivity of these heterometallic assemblies.

In silico design of pseudo D5h actinide based molecular magnets: role of covalency in magnetic anisotropy

Actinide molecular magnets are of great interest in the area molecular magnetism as they possess strong covalency and spin-orbit coupling that their 4f congeners lack. Despite these known advantages, the actinide based molecular magnets have not been explored in detail due to the limited availability of actinide salts. While theoretical tools are proven to be useful in lanthanide chemistry towards prediction, they are still at an infant stage in actinide chemistry. In this manuscript, we have attempted to utilise CASSCF/RASSI-SO calculations to predict suitable pseudo D5h molecules possessing attractive magnetic properties. To begin with, we have undertaken an extensive benchmarking of the methodology employed by studying two sets of isostructural, [NdTp3], [UTp3], [Nd(COT″)2]-, [U(COT″)2]- {Tp− = trispyrazolylborate, COT″ = bis(trimethylsilyl)cyclooctatetraenyl dianion} complexes. The method assessment reveals that the methodology employed is reliable as this has reproduced the experimental observables. With this, we have moved forward with prediction where pseudo-D5h symmetric [L2M(H2O)5][I]3L2.(H2O) {M = Nd, U, Pu; L = tBuPO(NHiPr)2} systems are modelled from their Nd(III) X-ray structure. Our calculations reveal that the Uranium complex studied possess superior SIM characteristics compared to its lanthanide analogue. Plutonium complex has prolate electron density at the ground state, and hence the ligand environment is unsuitable for yielding SIM behaviour. The role of solvent molecules, counter anions and equatorial and axial ligand are explored and tantalizing prediction with a barrier height of 1403.3 and 989.5 cm−1 are obtained for [tBuPO(NHiPr)2-U-tBuPO(NHiPr)2]3+ and [Pu(H2O)5]3+ models, respectively and this paves the way for synthetic chemist to target such geometries in actinide based SIMs. Is pseudo D5h geometry suitable for Actinide SIMs? In this article, we have extensively studied uranium complex and compared it with its lanthanide analogue. The pseudo D5h symmetric uranium complex possesses oblate electron density which is favourable in the axial ligand field and henceforth it is predicted to have attractive SIM behaviour. Studies on models suggest the low-coordinate actinide chemistry may hold the key to further the blocking temperature beyond liquid N2 temperatures.

Ground-state actinide chemistry with scalar-relativistic multiconfiguration pair-density functional theory.

We have examined the performance of Multiconfiguration Pair-Density Functional Theory (MC-PDFT) for computing the ground-state properties of actinide species. Specifically, we focused on the properties of UN2 and various actinyl species. The properties obtained with MC-PDFT at the scalar-relativistic level are compared to Kohn-Sham DFT (KS-DFT); complete active space self-consistent field theory, CASSCF; coupled-cluster theory, CCSD(T) and CCSDT; as well as multireference perturbation theory (CASPT2). We examine the degree to which MC-PDFT improves over KS-DFT and CASSCF while aligning with CASPT2, CCSD(T), and CCSDT. All properties that we considered were for the CASPT2 electronic ground states. For structural parameters, MC-PDFT confers very little advantage over KS-DFT, especially the B3LYP density functional. For NpO2 3+, MC-PDFT and local KS-DFT functionals excessively favor the bent structure, whereas CCSDT and CASPT2 predict the bent and linear structures as isoenergetic. For this special case, hybrid KS-DFT functionals like PBE0 and B3LYP provide results closer to CASPT2 and CCSDT than MC-PDFT. On a more positive note, MC-PDFT is very close to CASPT2 and CCSD(T) for the redox potentials, energetics of redox chemical reactions, as well as ligand-binding energies. These are encouraging results since MC-PDFT is more affordable. The best MC-PDFT functional is ft-PBE. Our findings suggest that MC-PDFT can be used to study systems and excited states with larger strong electron correlation effects than were considered here. However, for the systems and properties considered here, KS-DFT functionals do well, justifying their usage as the bulwark of computational actinyl chemistry over the last two to three decades.