Theoretical Study on the Coordination and Separation Capacity of Macrocyclic N-Donor Extractants for Am(III)/Eu(III)

Designing ligands that can effectively separate actinide An(III)/lanthanide Ln(III) in the solvent extraction process remains one of the key issues in the treatment of accumulated spent nuclear fuel. Nitrogen donor ligands are considered as promising extractants for the separation of An(III) and Ln(III) due to their environmental friendliness. Four new macrocyclic N-donor hexadentate extractants were designed and their coordination with Am(III) and Eu(III), as well as their extraction selectivity and separation performance for Am(III) and Eu(III), were investigated by scalar relativistic density functional theory. A variety of theoretical methods have been used to evaluate the properties of the four ligands and the coordination structures, bonding properties, and thermodynamic properties of the complexes formed by the four ligands with Am(III) and Eu(III). The results of various wavefunction analysis methods including NBO analysis, quantum theory of atoms in molecules (QTAIM) analysis, and so on show that Am(III) has a stronger coordination ability with the ligands than Eu(III) due to the Am 5f orbitals more involved in bonding with the ligands than the Eu 4f orbitals, and the bonding environment of the N-donor in the ligand has a significant effect on its coordination ability of the metal ions. Thermodynamic analysis of the solvent extraction process shows that all of the four N-containing macrocyclic ligands have good extraction selectivity and separation performance for Am(III) and Eu(III). This study provides theoretical support for designing potential nitrogen-containing macrocyclic extractants with excellent separation performance.

Theoretical Insights into the Selectivity of Hydrophilic Sulfonated and Phosphorylated Ligands to Am(III) and Eu(III) Ions

The separation of lanthanides and actinides has attracted great attention in spent nuclear fuel reprocessing up to date. In addition, liquid-liquid extraction is a feasible and useful way to separate An(III) from Ln(III) based on their relative solubilities in two different immiscible liquids. The hydrophilic bipyridine- and phenanthroline-based nitrogen-chelating ligands show excellent performance in separation of Am(III) and Eu(III) as reported previously. To profoundly explore the separation mechanism, herein, we first of all designed four hydrophilic sulfonated and phosphorylated ligands L¹, L², L³, and L⁴ based on the bipyridine and phenanthroline backbones. In addition, we studied the structures of these ligands and their neutral complexes [ML(NO₃)₃] (M = Am, Eu) as well as the thermodynamic properties of complexing reactions through the scalar relativistic density functional theory. According to the changes of the Gibbs free energy for the back-extraction reactions, the phenanthroline-based ligands L² and L⁴ have stronger complexing capacity for both Am(III) and Eu(III) ions while the phosphorylated ligand L³ with the bipyridine framework has the highest Am(III)/Eu(III) selectivity. In addition, the charge decomposition analysis revealed a higher degree of charge transfer from the ligand to Am(III), suggesting stronger donor-acceptor interactions in the Am(III) complexes. This study can provide theoretical insights into the separation of actinide(III)/lanthanide(III) using hydrophilic sulfonated and phosphorylated N-donor ligands.

Chelating decorporation agents for internal contamination by actinides: Designs, mechanisms, and advances

During the wide utilization of the actinides in medicine, energy, military, and other fields, internal contaminations can profoundly endanger human health and public security. Chelating decorporation agents are the most effective therapies to reduce internal contamination that includes radiological and chemical toxicities. This review introduces the structures of chelating decorporation agents including inorganic salts, polyaminocarboxylic acids, peptides, polyphosphonates, siderophores, calixarenes, polyethylenimines, and fullerenes, and highlights ongoing advances in their designs and mechanisms. However, there are still numerous challenges that block their applications including coordination properties, pharmacokinetic properties, oral bioavailability, limited timing of administration, and toxicity. Therefore, additional efforts are needed to push novel decorporation agents with high efficiency and low toxicity for the treatment of internal contamination by actinides.

Theoretical Insights into Phenanthroline-Based Ligands toward the Separation of Am(III)/Eu(III)

The bistriazinyl-phenanthroline representative ligand, BTPhen, shows excellent extraction and separation ability for trivalent actinides and lanthanides. Herein, we first designed three phenanthroline-based nitrogen-donor ligands (L¹, L², and L³), and then studied the structural and bonding properties as well as thermodynamic properties of the probable complexes, ML(NO₃)₃ (M = Am or Eu and L = L¹, L², or L³), using scalar relativistic density functional theory. Our charge decomposition analysis revealed an obviously higher charge transfer from the ligand to Am(III) compared with the Eu(III) case for the studied complexes. Spin density analysis further showed a more significant degree of Am-to-ligand spin delocalization and the corresponding spin polarization on the ligands. According to the thermodynamic analysis, ligand L³ has the strongest complexation capacity for both Am(III) and Eu(III) ions, while ligand L¹ has the highest Am(III)/Eu(III) selectivity in binary octanol/water solutions. We expected that this work can provide valuable theoretical support for the design of effective ligands for actinide(III)/lanthanide(III) separation in high level liquid waste.

Insights into the Coordination Behavior of Methyl-Substituted Phosphinic Acids with Actinides

The electronic structure and complexation behavior of methyl-substituted phosphinic acids with U(VI) and Pu(IV) were explored by applying quantum chemical methods. In contrast to Ingold's classification, our results indicate that the methyl group is electron-withdrawing, reducing the phosphoryl group electron density in substituted phosphinic acids. The magnitude of the computed complexation energy values increases along with the series, PA → MPA → DMPA, and MP → MMP → MDMP, implying an increasing complexation tendency upon methyl group substitution for both U(VI) and Pu(IV) complexes. One of the nitrate groups in UO₂(NO₃)₂•2L complexes (L = PA, MPA, and DMPA) is in monodentate coordination mode due to the additional stability gained from O₂N-O···H hydrogen bonding interactions with the acidic H atoms of respective ligands. The calculation indicates marginally stronger metal-ligand interactions in Pu(IV) complexes compared to that in U(VI), which is supported by the computed complexation energies, M-O_P bond lengths, ν(P═O), the extent of metal-ligand charge transfer, and properties of M-O_P bond critical points. The energy landscape of substituted phosphinic acid ligands is further analyzed within the framework of the activation strain model to explain the energetic preference of certain conformers.

Porphyrinoid actinide complexes

The diverse coordination modes and electronic features of actinide complexes of porphyrins and related oligopyrrolic systems (referred to as "porpyrinoids") have been the subject of interest since the 1960s. Given their stability and accessibility, most work with actinides has focused on thorium and uranium. This trend is also seen in the case of porphyrinoid-based complexation studies. Nevertheless, the diversity of ligand environments provided by porphyrinoids has led to the stabilization of a number of unique complexes with the early actinides that are often without structural parallel within the broader coordination chemical lexicon. This review summarizes key examples of prophyrinoid actinide complexes reported to date, including the limited number of porphyrinoid systems involving transuranic elements. The emphasis will be on synthesis and structure; however, the electronic features and reactivity pattern of representative systems will be detailed as well. Coverage is through December of 2021.

Cyclopentadienyl coordination induces unexpected ionic Am-N bonding in an americium bipyridyl complex

Variations in bonding between trivalent lanthanides and actinides is critical for reprocessing spent nuclear fuel. The ability to tune bonding and the coordination environment in these trivalent systems is a key factor in identifying a solution for separating lanthanides and actinides. Coordination of 4,4'-bipyridine (4,4'-bpy) and trimethylsilylcyclopentadienide (Cp') to americium introduces unexpectedly ionic Am-N bonding character and unique spectroscopic properties. Here we report the structural characterization of (Cp'₃Am)₂(μ - 4,4'-bpy) and its lanthanide analogue, (Cp'₃Nd)₂(μ - 4,4'-bpy), by single-crystal X-ray diffraction. Spectroscopic techniques in both solid and solution phase are performed in conjunction with theoretical calculations to probe the effects the unique coordination environment has on the electronic structure.

Involvement of 5f Orbitals in the Covalent Bonding between the Uranyl Ion and Trialkyl Phosphine Oxide: Unraveled by Oxygen K-Edge X-ray Absorption Spectroscopy and Density Functional Theory

Monodentate organophosphorus ligands have been used for the extraction of the uranyl ion (UO₂²⁺) for over half a century and have exhibited exceptional extractability and selectivity toward the uranyl ion due to the presence of the phosphoryl group (O═P). Tributyl phosphate (TBP) is the extractant of the world-renowned PUREX process, which selectively recovers uranium from spent nuclear fuel. Trialkyl phosphine oxide (TRPO) shows extractability toward the uranyl ion that far exceeds that for other metal ions, and it has been used in the TRPO process. To date, however, the mechanism of the high affinity of the phosphoryl group for UO₂²⁺ remains elusive. We herein investigate the bonding covalency in a series of complexes of UO₂²⁺ with TRPO by oxygen K-edge X-ray absorption spectroscopy (XAS) in combination with density functional theory (DFT) calculations. Four TRPO ligands with different R substituents are examined in this work, for which both the ligands and their uranyl complexes are crystallized and investigated. The study of the electronic structure of the TRPO ligands reveals that the two TRPO molecules, irrespective of their substituents, can engage in σ- and π-type interactions with U 5f and 6d orbitals in the UO₂Cl₂(TRPO)₂ complexes. Although both the axial (O_yl) and equatorial (O_eq) oxygen atoms in the UO₂Cl₂(TRPO)₂ complexes contribute to the X-ray absorption, the first pre-edge feature in the O K-edge XAS with a small intensity is exclusively contributed by O_eq and is assigned to the transition from O_eq 1s orbitals to the unoccupied molecular orbitals of 1b_1u + 1b_2u + 1b_3u symmetries resulting from the σ- and π-type mixing between U 5f and O_eq 2p orbitals. The small intensity in the experimental spectra is consistent with the small amount of O_eq 2p character in these orbitals for the four UO₂Cl₂(TRPO)₂ complexes as obtained by Mulliken population analysis. The DFT calculations demonstrate that the U 6d orbitals are also involved in the U-TRPO bonding interactions in the UO₂Cl₂(TRPO)₂ complexes. The covalent bonding interactions between TRPO and UO₂²⁺, especially the contributions from U 5f orbitals, while appearing to be small, are sufficiently responsible for the exceptional extractability and selectivity of monodentate organophosphorus ligands for the uranyl ion. Our results provide valuable insight into the fundamental actinide chemistry and are expected to directly guide actinide separation schemes needed for the development of advanced nuclear fuel cycle technologies.

Experimental evaluation of the stabilization of the COT orbitals by 4f orbitals in COT2Ce using a Hubbard model

Significant orbital mixing is rare in lanthanide complexes because of the limited radial extent of the 4f orbitals, which results in a generally small stabilization due to 4f orbital interactions. Nevertheless, even a small amount of additional stabilization could enhance lanthanide separations. One lanthanide complex in which orbital mixing has been extensively studied both experimentally and computationally is cerocene, COT₂Ce, where COT is cyclooctatetraene. This compound has a singlet ground state with a low-lying, triplet excited state. Previous fluorescence studies on trimethylsilyl-substituted cerocenes indicate the triplet state is 0.4 eV higher in energy than the singlet state. In addition, computational studies predict that the triplet is 0.3 to 1 eV higher in energy than the singlet. The synthesis of highly pure COT₂Ce by Walter and Andersen allowed its physical properties to be accurately measured. Using these measurements, we evaluate the stabilization of the 4f orbitals using two, independent approaches. A Hubbard model is used to evaluate the stabilization of the ground state due to orbital mixing. This stabilization, which is also the singlet-triplet gap, is -0.29 eV using this model. This gap was also from the temperature independent paramagnetism of COT₂Ce, which yielded a value of -0.32 eV.

Tailoring the selectivity of phenanthroline derivatives for the partitioning of trivalent Am/Eu ions – a relativistic DFT study

Preferential binding of actinides over lanthanides using tailored phenanthroline derivative ligands through relativistic DFT calculations.

Analysis of charge density in nonaaquagadolinium(III) trifluoromethanesulfonate - insight into GdIII-OH2 bonding

The experimental charge-density distribution in [Gd(H₂O)₉](CF₃SO₃)₃ has been analysed and compared with the theoretical density functional theory calculations. Although the Gd-OH₂ bonds are mainly ionic, a covalent contribution is detectable when inspecting both the topological parameters of these bonds and the natural bond orbital results. This contribution originates from small electron transfer from the lone pairs of oxygen atoms to empty 5d and 6s spin orbitals of Gd³⁺.

Ligand architectural effect on coordination, bonding, interaction, and selectivity of Am(iii) and Ln(iii) ions with bitopic ligands: synthesis, solvent extraction, and DFT studies

The isolation of Am(iii) ion from Ln(iii) ions is very crucial for the safe disposal of nuclear wastes and thus, studies are being continuously pursued to accomplish this goal. In view of this, herein, a new conformationally rigid bitopic ligand, N,N,N',N'-tetra(2-ethylhexyl)piperazine-di-methylenecarboxamide (PIPDA) has been synthesized and studied for the separation of Am(iii) from Ln(iii) ions. The effect of structural rigidification on the selectivity of Am(iii) over Ln(iii) was compared with an open chain flexible compound, namely, N,N,N',N'-tetra(2-ethylhexyl)-3,6-(N'',N'''-dibutyl)diaza-octane-1,8-diamide (DADA). Two oxygen atoms of the diamide moiety seem to be responsible for controlling the metal ion extraction ability of PIPDA, whereas two nitrogen atoms of the piperazine moiety most probably dictate the separation factor between the Am(iii) and Eu(iii) ions in PIPDA. In addition, scalar relativistic density functional theory (DFT) in conjunction with Born-Haber thermodynamics was used herein to compliment the experimental selectivity. The experimentally observed preferential selectivity of PIPDA for Am(iii) ion over the Ln(iii) ion was corroborated by the computed extraction free energy, ΔG_ext. The covalent nature of bonding between the metal ions and the ligand was confirmed by analyzing the Mayer bond order and bond character analysis using the atom in molecule concept. Though the conformational rigidity of PIPDA gives stronger interaction than DADA, it does not offer a significant advantage over DADA in terms of the separation factor. The marginal increase in the separation factor for PIPDA over DADA might be attributed to the piperazine nitrogen and to the ligand architecture during complex formation.

Role of Ligand Straining in Complexation of Eu3+-Am3+ Ions by TPEN and PPDEN, Scalar Relativistic DFT Exploration in Conjunction with COSMO-RS

To search for new ligands suitable for the separation of minor actinides (MA) from lanthanides (Ln) in nuclear waste reprocessing, theoretical (density functional theory) studies were carried out on the complexation (structures, bonding, and thermodynamics) of La³⁺, Sm³⁺, Eu³⁺, and Am³⁺ complexes with moderately soft donor ligands TPEN [N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine] and PPDEN [N,N,N',N″,N″-pentakis(2-pyridylmethyl) diethylenetriamine] in aqueous and nitrobenzene solutions. B3LYP level of theory was used in conjunction with the conductor-like screening model for real systems (COSMO-RS). The metal ions in [M(NO₃)₂(TPEN)]NO₃ and [M(NO₃)(PPDEN)](NO₃)₂ complexes were deca-coordinated with both TPEN and PPDEN. The enthalpy of the complexation with TPEN in an aqueous solution was found to be negative, indicating the exothermic nature of the reaction as observed in the experiments. The calculated values of free energy of complexation follow the experimental trend: Am³⁺ > Sm³⁺ > La³⁺. Furthermore, the calculated free energy with PPDEN is reduced compared to that with TPEN, which may be attributed to the ligand straining during complex formation, which is also reflected in greater residual charges on both the Eu³⁺ and Am³⁺ central ions in the complexes of octadentate PPDEN compared to hexadentate TPEN. The experimental complexation selectivity of Am³⁺ over Eu³⁺ with TPEN is established by employing COSMO-RS. Furthermore, TPEN is Am³⁺-selective, whereas PPDEN is Eu³⁺-selective, which could be exploited for the efficient separation of MA from Ln.

Decomposition of d- and f-Shell Contributions to Uranium Bonding from the Quantum Theory of Atoms in Molecules: Application to Uranium and Uranyl Halides

The electronic structures of a series of uranium hexahalide and uranyl tetrahalide complexes were simulated at the density functional theoretical (DFT) level. The resulting electronic structures were analyzed using a novel application of the Quantum Theory of Atoms in Molecules (QTAIM) by exploiting the high symmetry of the complexes to determine 5f- and 6d-shell contributions to bonding via symmetry arguments. This analysis revealed fluoride ligation to result in strong bonds with a significant covalent character while ligation by chloride and bromide species resulted in more ionic interactions with little differentiation between the ligands. Fluoride ligands were also found to be most capable of perturbing an existing electronic structure. 5f contributions to overlap-driven covalency were found to be larger than 6d contributions for all interactions in all complexes studied while degeneracy-driven covalent contributions showed significantly greater variation. σ-contributions to degeneracy-driven covalency were found to be consistently larger than those of individual π-components while the total π-contribution was, in some cases, larger. Strong correlations were found between overlap-driven covalent bond contributions, U–O vibrational frequencies, and energetic stability, which indicates that overlap-driven covalency leads to bond stabilization in these complexes and that uranyl vibrational frequencies can be used to quantitatively probe equatorial bond covalency. For uranium hexahalides, degeneracy-driven covalency was found to anti-correlate with bond stability.

Synthesis and characterization of a novel aminopolycarboxylate complexant for efficient trivalent f-element differentiation: N-butyl-2-acetamide-diethylenetriamine-N,N',N'',N''-tetraacetic acid

The novel metal ion complexant N-butyl-2-acetamide-diethylenetriamine-N,N',N'',N''-tetraacetic acid (DTTA-BuA) uses an amide functionalization to increase the total ligand acidity and attain efficient 4f/5f differentiation in low pH conditions. The amide, when located on the diethylenetriamine platform containing four acetate pendant arms maintains the octadentate coordination sphere for all investigated trivalent f-elements. This compact coordination environment inhibits the protonation of LnL^- complexes, as indicated by lower K₁₁₁ constants relative to the corresponding protonation site of the free ligand. For actinide ions, the enhanced stability of AnL^- lowers the K₁₁₁ for americium and curium beyond the aptitude of potentiometric detection. Density functional theory computations indicate the difference in the back-donation ability of Am³⁺ and Eu³⁺ f-orbitals is mainly responsible for stronger proton affinity of EuL^- compared to AmL^-. The measured stability constants for the formation of AmL^- and CmL^- complexes are consistently higher, relative to ML^- complexes with lanthanides of similar charge density. When compared with the conventional aminopolycarboxylate diethylenetriamine pentaacetic acid (DTPA), the modified DTTA-BuA complexant features higher ligand acidity and the important An³⁺/Ln³⁺ differentiation when deployed on a liquid-liquid distribution platform.

Spectroscopic and Computational Characterization of Diethylenetriaminepentaacetic Acid/Transplutonium Chelates: Evidencing Heterogeneity in the Heavy Actinide(III) Series

The chemistry of trivalent transplutonium ions (Am³⁺ , Cm³⁺ , Bk³⁺ , Cf³⁺ , Es³⁺ …) is usually perceived as monotonic and paralleling that of the trivalent lanthanide series. Herein, we present the first extended X-ray absorption fine structure (EXAFS) study performed on a series of aqueous heavy actinide chelates, extending past Cm. The results obtained on diethylenetriaminepentaacetic acid (DTPA) complexes of trivalent Am, Cm, Bk, and Cf show a break to much shorter metal-oxygen nearest-neighbor bond lengths in the case of Cf³⁺ . Corroborating those results, density functional theory calculations, extended to Es³⁺ , suggest that the shorter Cf-O and Es-O bonds could arise from the departure of the coordinated water molecule and contraction of the ligand around the metal relative to the other [M^III DTPA(H₂ O)]^2- (M=Am, Cm, Bk) complexes. Taken together, these experimental and theoretical results demonstrate inhomogeneity within the trivalent transplutonium series that has been insinuated and debated in recent years, and that may also be leveraged for future nuclear waste reprocessing technologies.

Structural, luminescence, thermodynamic and theoretical studies on mononuclear complexes of Eu(III) with pyridine monocarboxylate-N-oxides in aqueous solution

The mononuclear complexes formed by Eu(III) with three isomeric pyridine monocarboxylate-N-oxides namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO) in aqueous solutions were studied by potentiometry, luminescence spectroscopy and isothermal titration calorimetry (ITC) to determine the speciation, coordination, luminescence properties and thermodynamic parameters of the complexes formed during the course of the reaction. More stable six membered chelate complexes with stoichiometry (ML_i, i=1-4) are formed by Eu(III) with PANO while non chelating ML and ML₂ complexes are formed by NANO and IANO. The stability of Eu(III) complexes follow the order PANO>IANO>NANO. The ITC studies inferred an endothermic and innersphere complex formation of Eu(III)-PANO and Eu(III)-IANO whereas an exothermic and outer-sphere complex formation for Eu(III)-NANO. The luminescence life time data further supported the ITC results. Density functional theoretical calculations were carried out to optimize geometries of the complexes and to estimate the energies, structural parameters (bond distances, bond angles) and charges on individual atoms of the same. Theoretical approximations are found to be in good agreement with the experimental observations.

Theoretical studies on the synergistic extraction of Am3+ and Eu3+ with CMPO–HDEHP and CMPO–HEH[EHP] systems

Synergistic extraction and separation of Eu³⁺/Am³⁺ with CMPO–HDEHP and CMPO–HEH[EHP] systems have been theoretically investigated.

Enhanced free energy of extraction of Eu3+ and Am3+ ions towards diglycolamide appended calix[4]arene: insights from DFT-D3 and COSMO-RS solvation models

Density functional theory in conjunction with COSMO and COSMO-RS solvation models employing dispersion correction (DFT-D3) has been applied to gain an insight into the complexation of Eu³⁺/Am³⁺ with diglycolamide (DGA) and calix[4]arene appended diglycolamide (CAL4DGA) in ionic liquids by studying structures, energetics, thermodynamics and population analysis. The calculated Gibbs free energy for both Eu³⁺ and Am³⁺ ions with DGA was found to be smaller than that with CAL4DGA. The entropy of complexation was also found to be reduced to a large extent with DGA compared to complexation with CAL4DGA. The solution phase free energy was found to be negative and was higher for Eu³⁺ ion. The entropy of complexation was not only found to be further reduced but also became negative in the case of DGA alone. Though the entropy was found to be negative it could not outweigh the high negative enthalpic contribution. The same trend was observed in the solution where the free energy of extraction, ΔG, for Eu³⁺ ions was shown to be higher than that for Am³⁺ ions towards free DGA. But the values of ΔG and ΔΔG(= ΔG_Eu-ΔG_Am) were found to be much higher with CAL4DGA (-12.58 kcal mol^-1) in the presence of nitrate ions compared to DGA (-1.69 kcal mol^-1) due to enhanced electronic interaction and positive entropic contribution. Furthermore, both the COSMO and COSMO-RS models predict very close values of ΔΔΔG (= ΔΔG_CAL4DGA - ΔΔG_nDGA), indicating that both solvation models could be applied for evaluating the metal ion selectivity. The value of the reaction free energy was found to be higher after dispersion correction. The charge on the Eu and Am atoms for the complexes with DGA and CAL4DGA indicates the charge-dipole type interaction leading to strong binding energy. The present theoretical results support the experimental findings and thus might be of importance in the design of functionalized ligands.

Diglycolic acid modified zirconium phosphate and studies on the extraction of Am(III) and Eu(III) from dilute nitric acid medium

Diglycolic acid modified zirconium phosphate (ZrP-DGA) was prepared and studied for the extraction of Am(III) and Eu(III) from dilute nitric acid medium. The distribution coefficient (Kd, mL·g−1) of Am(III) and Eu(III) was measured as a function of time, pH and concentration of Eu(III) ion etc. The Kd of Am(III) and Eu(III) increased with increase of pH, reached a maximum value of distribution coefficient at pH 1.5 – 2, followed by decrease in Kd values. Rapid extraction of Am(III) and Eu(III) in ZrP-DGA was observed followed by the establishment of equilibrium occurred in 100 min. Kinetics of extraction was fitted in to pseudo second order rate equation. The amount of Eu(III) loaded in ZrP-DGA increased with increase in the concentration of Eu(III) ion in aqueous phase and the isotherm was fitted in to Langmuir and Freundlich adsorption models. The extraction of Am(III) in ZrP-DGA was higher as compared to Eu(III) and the interference of Eu(III) on the extraction of Am(III) was studied. The distribution coefficient of some lanthanides in ZrP-DGA was measured and the Kd of lanthanides increased across the lanthanide series. The extracted trivalent metal ions were recovered in three contacts of loaded ZrP-DGA with 0.5 M nitric acid.

Ligand size dependence of U–N and U–O bond character in a series of uranyl hexaphyrin complexes: quantum chemical simulation and density based analysis

A quantum chemical and density based analysis of bonding in uranyl hexaphyrin complexes, looking for trends in stability and covalency.

Assessing covalency in equatorial U–N bonds: density based measures of bonding in BTP and isoamethyrin complexes of uranyl

N-donor complexes of uranyl have been investigated with density-based analytical methods in order to quantify equatorial bond covalency and its effect on axial U–O_yl bonding.

Theoretical prediction of coordination environments and stability constants of lanthanum lactate complexes in solution

Using Density Functional Theory calculations in combination with explicit solvent and a continuum solvent model, this work sets out to understand the coordination environment and relevant thermodynamics of La(iii)-lactate complexes.

Complexation thermodynamics of diglycolamide with f-elements: solvent extraction and density functional theory analysis

Optimized complexes of Lu³⁺ with TMDGA in 1 : 1, 1 : 2 and 1 : 3 stoichiometric ratios and plots of theoretically calculated stepwise binding energy.

Theoretical prediction of Am(iii)/Eu(iii) selectivity to aid the design of actinide-lanthanide separation agents

Selective extraction of minor actinides from lanthanides is a critical step in the reduction of radiotoxicity of spent nuclear fuels. However, the design of suitable ligands for separating chemically similar 4f- and 5f-block trivalent metal ions poses a significant challenge. First-principles calculations should play an important role in the design of new separation agents, but their ability to predict metal ion selectivity has not been systematically evaluated. In this work, we examine the ability of several density functional theory methods to predict selectivity of Am(iii) and Eu(iii) with oxygen, mixed oxygen-nitrogen, and sulfur donor ligands. The results establish a computational method capable of predicting the correct order of selectivities obtained from liquid-liquid extraction and aqueous phase complexation studies. To allow reasonably accurate predictions, it was critical to employ sufficiently flexible basis sets and provide proper account of solvation effects. The approach is utilized to estimate the selectivity of novel amide-functionalized diazine and 1,2,3-triazole ligands.

Actinide selectivity of 1,10-phenanthroline-2,9-dicarboxamide and its derivatives: a theoretical prediction followed by experimental validation

Selectivities of 1,10-phenanthroline based mixed hard and soft donor ligands towards Am(iii) over the Eu(iii) ion have been predicted theoretically and validated experimentally through synthesis and solvent extraction techniques.

Theoretical insights into the separation of Am(iii) over Eu(iii) with PhenBHPPA

Due to the similar chemical properties of actinides An(iii) and lanthanides Ln(iii), their separation in spent nuclear fuel reprocessing is extremely challenging.

The selectivity of diglycolamide (TODGA) and bis-triazine-bipyridine (BTBP) ligands in actinide/lanthanide complexation and solvent extraction separation – a theoretical approach

Charge transfer from the ligand to valence hybrid (mainly d) metal orbitals nearly equally stabilizes cationic Eu^III and Am^III TODGA complexes.