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The relationship between extractant stereochemistry and their extraction performance has only poorly been established. In order to address a part of this concern, we investigated the Pu(IV) liquid‐liquid extraction (LLE) by using the N,N‐di‐(2‐ethylhexyl)butyramide (DEHBA), as well as those of its position isomers. DEHBA (ββ‐isomer) and N‐(2‐ethylhexyl)‐N‐(oct‐3‐yl)butyramide (EHOBA or αβ‐isomer) were synthesized as a mixture of stereoisomer or stereoenriched (R,S)‐ and (S,S)‐diastereoisomers, and were all assessed for PuIV LLE. The results showed that both the position and the stereoisomerism of the aliphatic substituents affect PuIV complexation and extraction. We found that Pu extraction is lowered by factor 2 to 4 when the ethyl branching group is closer to the complexing site. UV‐vis spectroscopy showed that this extraction decrease was affected by steric hindrance inducing a deprivation of Pu inner sphere complex. Effect of stereoisomerism is highlighted for branching closer to the complexing site (α‐position). Enantiopure DEHBA stereoisomers provided similar Pu extraction, whereas a slight decrease could be noticed for the more cluttered stereoenriched (αβ)‐isomers, which was also concomitant with a smaller population of inner sphere complex. In contrast, the stereoisomers mixture led to a strong decrease of Pu extraction because of an antagonistic association in the mixed complexes. [ABSTRACT FROM AUTHOR]

A spectroelectrochemical setup has been developed to investigate radioactive elements in small volumes (0.7 to 2 ml) under oxidation–reduction (redox) controlled conditions by X‐ray absorption spectroscopy (XAS). The cell design is presented together with in situ XAS measurements performed during neptunium redox reactions. Cycling experiments on the NpO22+/NpO2+ redox couple were applied to qualify the cell electrodynamics using XANES measurements and its ability to probe modifications in the neptunyl hydration shell in a 1 mol l−1 HNO3 solution. The XAS results are in agreement with previous structural studies and the NpO22+/NpO2+ standard potential, determined using Nernst methods, is consistent with measurements based on other techniques. Subsequently, the NpO2+, NpO22+ and Np4+ ion structures in solution were stabilized and measured using EXAFS. The resulting fit parameters are again compared with other results from the literature and with theoretical models in order to evaluate how this spectroelectrochemistry experiment succeeds or fails to stabilize the oxidation states of actinides. The experiment succeeded in: (i) implementing a robust and safe XAS device to investigate unstable radioactive species, (ii) evaluate in a reproducible manner the NpO22+/NpO2+ standard potential under dilute conditions and (iii) clarify mechanistic aspects of the actinyl hydration sphere in solution. In contrast, a detailed comparison of EXAFS fit parameters shows that this method is less appropriate than the majority of the previously reported chemical methods for the stabilization of the Np4+ ion. [ABSTRACT FROM AUTHOR]

The size and shape of a water‐soluble hexanuclear plutonium cluster were probed by combining synchrotron small‐angle X‐ray scattering (SAXS) and extended X‐ray absorption fine structure (EXAFS). A specific setup coupling both techniques and dedicated to radioactive samples on the MARS beamline endstation at Synchrotron SOLEIL is described. The plutonium hexanuclear cores are well stabilized by the 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid ligands and this allows a good evaluation of the setup to probe the very small plutonium core. The results show that, in spite of the constrained conditions required to avoid any risk of sample dispersion, the flux and the sample environment are optimized to obtain a very good signal‐to‐noise ratio, allowing the detection of small plutonium aggregates in an aqueous phase. The structure of the well defined hexanuclear cluster has been confirmed by EXAFS measurements in solution and correlated with SAXS data processing and modelling. An iterative comparison of classical fit models (Guinier or sphere form factor) with the experimental results allowed a better interpretation of the SAXS signal that will be relevant for future work under environmentally relevant conditions. [ABSTRACT FROM AUTHOR]

[H7O3]4[Tc20O68] ⋅ 4H2O [1] was prepared from an aqueous Tc2O7 solution concentrated over anhydrous H2SO4. [Tc20O68]4− is the first polyanionic species to be reported for Tc. The unit cell contains one centrosymmetric [Tc20O68]4− polyanion as well as hydronium ions and water molecules. The core of the structure consists of four Tc(V)O6 octahedra that form a square Tc4O4 ring. The four Tc(V)O6 octahedra are decorated by sixteen Tc(VII)O4 tetrahedra. Calculations show the bonding within the Tc4O4 ring to consist of a 3‐center bond formed between each neighboring pair of Tc atoms and their bridging oxygen. Calculations also indicate that a strong d→d electronic transition at 513 nm is the origin of the red color of [1]. The characterization of red HTcO4 solutions by X‐ray absorption spectroscopy has complemented the description of this compound in aqueous solution. The formation mechanisms in solution, including the possible role of technetium's radioactivity in the formation of [1], are discussed. [ABSTRACT FROM AUTHOR]

Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and EuIII/EuII electrochemical behavior as a function of water content in 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf2]) was investigated using UV–visible spectrophotometry, time‐resolved laser fluorescence spectroscopy, electrochemistry, and X‐ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, EuIII and EuII were complexed by NTf2, forming Eu−O and Eu−(N,O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of EuII, and in quasi‐reversible oxidation–reduction with an E0' potential of 0.18 V versus the ferrocenium/ferrocene (Fc+/Fc) couple. Upon increasing water content, progressive incorporation of water in the EuIII coordination sphere occurred. This led to reversible oxidation–reduction reactions, but also to a decrease in stability of the +II oxidation state (E0'=−0.45 V vs. Fc+/Fc in RTIL containing 1300 mm water). [ABSTRACT FROM AUTHOR]

The molecular characterization based on multi‐technique approach has led to major highlights on revealing the coordination of americium with citric acid. The structure of the different complexes at pH 1 and 3 are described. These characterizations are made possible by the comparison of the americium‐citric acid system with the americium‐tricarballylic acid (one analogue of the citric acid without the alpha‐hydroxo group). The structural analyses (Vis spectrophotometry, NMR, EXAFS, TRLFS and capillary electrophoresis) were carried out after the establishment of the speciation distribution diagrams, allowing to take into account the species repartition for structural analysis data treatment. For the 1:1 complex the hydroxo group is counter intuitively deprotonated and coordinated to the Am(III) at pH 1 as well as two carboxylate functions, whereas at pH 3 the hydroxo is not coordinated and stays protonated allowing the three carboxylate functions to coordinate the metallic cation. Therefore, the hydroxo group affects the Am complexation differently depending on the pHs: by inductive effect at pH 3, and by direct coordination at pH 1. [ABSTRACT FROM AUTHOR]

The preparation and structural characterization of an original Th peroxo sulfate dihydrate, crystallizing at room temperature in the form of stable 1D polymeric microfibres is described. A combination of laboratory and synchrotron techniques allowed solution of the structure of the Th(O2)(SO4)(H2O)2 compound, which crystallizes in a new structure type in the space group Pna21 of the orthorhombic crystal system. Particularly, the peroxide ligand coordinates to the Th cations in an unusual μ3‐η2:η2:η2 bridging mode, forming an infinite 1D chain decorated with sulfato ligands exhibiting simultaneously monodentate and bidentate coordination modes. [ABSTRACT FROM AUTHOR]

The magnetic properties of LnIII and AnIII complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single‐crystal X‐ray diffraction (XRD) and extended X‐ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal–ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher‐order terms of the dipolar and contact contributions are required, especially for the lightest LnIII and almost all the studied AnIII. Bleaney's parameters a and CaD relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of a and CaD. However, the CaD values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for LnIII. Other parameters, such as the crystal field parameter and the hyperfine constants Fi obtained from the experimental data of the [An(ethyl‐dpa)3]3− complexes (ethyl‐dpa=4‐ethyl‐2,6‐dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory. Valid for Ln, but for An? Is Bleaney's equation for paramagnetic NMR shifts of LnIII valid for AnIII complexes? (see figure) Several methods have been applied to separate the paramagnetic shifts observed in the NMR spectra of LnIII and AnIII complexes formed with dipicolinate ligands. Discrepancies with Bleaney's equation have been found for the AnIII complexes, and some parameters are at odds with the assumptions underlying Bleaney's theory. [ABSTRACT FROM AUTHOR]

Three tetravalent actinide (AnIV) hexanuclear clusters with the octahedral core [An6(OH)4O4]12+ (AnIV=UIV, NpIV, PuIV) were structurally characterized in the solid state and in aqueous solution by using single-crystal X-ray diffraction, X-ray absorption, IR, Raman, and UV/Vis spectroscopy. The observed structure, [An6(OH)4O4(H2O)8(HDOTA)4] ⋅HCl/HNO3 ⋅ n H2O (An=U( I), Np( II), Pu( III)), consists of a AnIV hexanuclear pseudo-octahedral cluster stabilized by DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) ligands. The six actinide atoms are connected through alternate μ3-O2− and μ3-OH− groups. Extended X-ray absorption fine structure (EXAFS) investigations combined with UV/Vis spectroscopy provide evidence for the same local structure in moderate acidic and neutral aqueous solutions. The synthesis mechanism was partially elucidated and the main physicochemical properties (pH range stability, solubility, and protonation constant) of the cluster were determined. The results underline the importance of: 1) considering such polynuclear species in thermodynamic models, and 2) competing reactions between hydrolysis and complexation. It is interesting to note that the same synthesis route with thorium(IV) led to the formation of a dimer, Th2(H2O)10(H2DOTA)2 ⋅4 NO3 ⋅ x H2O ( IV), which contrasts to the structure of the other AnIV hexamers. [ABSTRACT FROM AUTHOR]

To enable the reduction of the environmental impact of nuclear energy generation, in this paper, we link the molecular and macroscopic behaviour of a functionalized material (TR@SBA15) used to extract uranium from sulfuric media. Two organic 3-[ N, N-di(2-ethylhexyl)carbamoyl]-3-[ethoxy(hydroxy)phosphoryl]propanoic acid (TR) molecules grafted onto the solid are involved in the extraction process and form a 2:1 TR-U complex. FTIR and extended X-ray absorption fine structure (EXAFS) spectroscopic analyses show that the TR-U bond is realized through a phosphonate group in a monodentate fashion below pH 3, in agreement with the macroscopic observations. The first coordination sphere of the uranyl ion is completed by two monodentate sulfate ions and one water molecule. Above pH 3, the TR contribution decreases, and other inner-sphere complexes appear, which is consistent with the increased extraction observed on the macroscopic scale. Molybdenum, a competitor element, reduces the uranium extraction capacity but not its speciation, whereas polyoxomolybdates form inside the pores from the molybdenum in solution. [ABSTRACT FROM AUTHOR]

The singular PuIV hexanuclear cluster [Pu6(OH)4O4]12+ stabilized by 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) ligands was structurally characterized for the first time both in the solid state and in water solution by using X-ray diffraction and X-ray absorption and UV/Vis spectroscopy. The stability of this cluster in water and its high solubility over a large pH range are of upmost importance for plutonium environmental speciation with potential applications in a related migration model. [ABSTRACT FROM AUTHOR]

Highlights from the article: Peroxide ligands coordinate to Th cations with a rare SB 3 sb - SP 2 sp : SP 2 sp : SP 2 sp bridging mode, forming infinite 1D chains decorated simultaneously with monodentate and bidentate sulfato ligands. Peroxide, spectroscopic techniques, structure elucidation, sulfate, thorium.

Single crystals of the PuIV hexanuclear cluster [Pu6(OH)4O4]12+ stabilized by 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) ligands are grown from an aqueous protonated DOTA solution to which a HNO3 solution of PuO2 is given (pH 0.5, overnight). [ABSTRACT FROM AUTHOR]