Structural and Spectroscopic Comparison of Soft-Se vs. Hard-O Donor Bonding in Trivalent Americium/Neodymium Molecules

Covalency is often considered to be an influential factor in driving An³⁺ vs. Ln³⁺ selectivity invoked by soft donor ligands. This is intensely debated, particularly the extent to which An³⁺ /Ln³⁺ covalency differences prevail and manifest as the f-block is traversed, and the effects of periodic breaks beyond Pu. Herein, two Am complexes, [Am{N(E=PPh₂ )₂ }₃ ] (1-Am, E=Se; 2-Am, E=O) are compared to isoradial [Nd{N(E=PPh₂ )₂ }₃ ] (1-Nd, 2-Nd) complexes. Covalent contributions are assessed and compared to U/La and Pu/Ce analogues. Through ab initio calculations grounded in UV-vis-NIR spectroscopy and single-crystal X-ray structures, we observe differences in f orbital involvement between Am-Se and Nd-Se bonds, which are not present in O-donor congeners.

Enabling Circular Economy: The Overlooked Role of Inorganic Materials Chemistry

Circular economy is considered a new chance to build a more sustainable world from both the social and the economic point of view. In this Essay, the possible contribution of inorganic chemistry towards a smooth transition to circularity in inorganic materials design and production is discussed by adopting an interdisciplinary approach.

Enhancing the Am3+/Cm3+ separation ability by weakening the binding affinity of N donor atoms: a comparative theoretical study of N, O combined extractants

Mutual separation of trivalent americium (Am3+) and curium (Cm3+) ions through liquid-liquid extraction is challenging due to the similarity in their chemical properties. Three N, O combined extractants 2,6-pyridinedicarboxylic acid di(N-ethyl-4-fluoroanilide) (Et(pFPh)DPA), diphenyl(2-pyridyl)phosphine oxide (Ph2PyPO), and alkyldiamide amine with 2-ethylhexylalkyl chains (ADAAM(EH)) have been identified to exhibit selectivity for Am3+ over Cm3+. In this work, the structures, bonding nature, and thermodynamic behaviors of a series of representative Am- and Cm-complexes with these ligands have been systematically investigated using density functional theory (DFT) calculations. Based on our calculations, the ONO angle formed by three donor atoms of the ligand in the Am-complex is slightly larger than that in its Cm-analogue. The studied ligands show their preference toward Am3+ by opening their "mouths" slightly wider. According to the Mayer bond order and the quantum theory of atoms in molecules (QTAIM) analyses, the interactions between the O donor atoms of these ligands and Am3+ and Cm3+ ions show some weak partial covalent character, and compared to the Am-O bond, there is relatively more covalency in the Cm-O bond in the corresponding complex. However, opposite results can be found in the Am-N and Cm-N bonding for the first two ligands. Particularly, for the better separation ligand ADAAM(EH), the Am-N and Cm-N interactions are extremely weak and no covalent character exists in the bonding. Nevertheless, the difference between the very weak Am-N and Cm-N interactions still leads to a better performance of ADAAM(EH). Based on the comparison of these ligands, we can find that weakening the binding ability of N atoms in the ligand may increase the difference between the Am-N and Cm-N interactions, thus enhancing the Am3+/Cm3+ separation ability of the ligand. Our study might provide new insights into understanding the selectivity of these three N, O combined ligands toward minor actinides and pave the way for designing efficient Am3+/Cm3+ extraction and separation ligands.

Comparative uptake studies on trivalent f-cations from acidic feeds using two extraction chromatography resins containing a diglycolamide in molecular diluent and ionic liquid

Low molecular weight diglycolamide (DGA) extractants were tested for the extraction of europium(III) and americium(III) from nitric acid solutions in n-dodecane, a molecular diluent and 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide (C₄mim⋅NTf₂), a room temperature ionic liquid, as the diluents. N,N,N',N'-tetra-n-butyl diglycolamide (TBDGA) was selected for extraction chromatography (XC) studies involving Eu(III) and Am(III). While the TBDGA resin containing n-dodecane gave reasonably high K_d values, that containing the ionic liquid showed higher Eu(III) uptake values. Compared to Eu(III), Am(III) was extracted by the resins to a lower extent. The loaded Eu(III) was back extracted from the resin using 0.05 M EDTA solutions in a buffered medium containing 1 M guanidine carbonate. Reusability studies indicated that, while the ionic liquid-based resin can be conveniently recycled five times with very marginal decrease in the percentage extraction values, there was a sharp decrease in the percent extraction after three cycles with the n-dodecane-based resin. The uptake data was fitted into different isotherm models and the results conformed to the Langmuir model. Based on the batch uptake studies, columns were prepared and the breakthrough as well as elution profiles were obtained. The elution profiles were found to be sharp without any significant tailing.

Radiation-induced effects on the extraction properties of hexa-n-octylnitrilo-triacetamide (HONTA) complexes of americium and europium

The candidate An(iii)/Ln(iii) separation ligand hexa-n-octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions (n-dodecane/0.1 M HNO3) using a solvent test loop in conjunction with cobalt-60 gamma irradiation. The extent of HONTA radiolysis and complementary degradation product formation was quantified by HPLC-ESI-MS/MS. Further, the impact of HONTA radiolysis on process performance was evaluated by measuring the change in 243Am and 154Eu distribution ratios as a function of absorbed gamma dose. HONTA was found to decay exponentially with increasing dose, affording a dose coefficient of d = (4.48 ± 0.19) × 10-3 kGy-1. Multiple degradation products were detected by HPLC-ESI-MS/MS with dioctylamine being the dominant quantifiable species. Both 243Am and 154Eu distribution ratios exhibited an induction period of ∼70 kGy for extraction (0.1 M HNO3) and back-extraction (4.0 M HNO3) conditions, after which both values decreased with absorbed dose. The decrease in distribution ratios was attributed to a combination of the destruction of HONTA and ingrowth of dioctylamine, which is capable of interfering in metal ion complexation. The loss of HONTA with absorbed gamma dose was predominantly attributed to its reaction with the n-dodecane radical cation (R˙+). These R˙+ reaction kinetics were measured for HONTA and its 241Am and 154Eu complexes using picosecond pulsed electron radiolysis techniques. All three second-order rate coefficients (k) were essentially diffusion limited in n-dodecane indicating a significant reaction pathway: k(HONTA + R˙+) = (7.6 ± 0.8) × 109 M-1 s-1, k(Am(HONTA)2 + R˙+) = (7.1 ± 0.7) × 1010 M-1 s-1, and k(Eu(HONTA)2 + R˙+) = (9.5 ± 0.5) × 1010 M-1 s-1. HONTA-metal ion complexation afforded an order-of-magnitude increase in rate coefficient. Nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived (<100 ns) HONTA radical cation and a second long-lived (μs) species identified as the HONTA triplet excited state. The latter was confirmed by a series of oxygen quenching picosecond pulsed electron measurements, affording a quenching rate coefficient of k(3[HONTA]* + O2) = 2.2 × 108 M-1 s-1. Overall, both the HONTA radical cation and triplet excited state are important precursors to the suite of measured HONTA degradation products.

Support loading effects on the performance of an extraction chromatographic resin: Toward improved separation of trivalent lanthanides

Changes in the level of impregnation of an Amberchrom CG-71m support with bis(2-ethylhexyl)phosphoric acid (HDEHP) are shown to alter the column efficiency, peak tailing, and metal ion uptake capacity associated with the resulting extraction chromatographic resins. Optimum efficiency and minimum peak tailing are observed at intermediate levels (ca. 20% (w/w)) of support loading. Metal ion uptake capacity is reduced relative to a commercial (loaded to 40% (w/w)) resin under the same conditions, however. The utility of the improved efficiency arising from reduced support loading is illustrated in the separation of selected trivalent lanthanide ions, including Gd(III) and Eu(III), whose resolution is unsatisfactory using commercial extraction chromatographic materials.

An Approach to Nonsymmetric Bis(tertiary phosphine oxides) Comprising Heterocyclic Fragments via the Pd-Catalyzed Phosphorylation

Nonsymmetric tertiary phosphine oxides with different five- and six-membered heterocyclic fragments such as pyridine, 2,2′-bipyridine, 1,10-phenantroline, quinoline, imidazole, and thiazole were synthesized in good yields via the successive introduction of phosphine oxide groups into the initial dihalogenated heterocycles by means of Pd-catalyzed phosphorylation reaction. The synthesis of pyridine-type compounds is hindered by competing double coupling, while for five-membered heterocycles the principal difficulty is the dehalogenation. Both side processes were successfully suppressed by the use of an excess of a dihalide (which can be easily recovered during the product purification step), proper phosphine ligand for palladium, and nonpolar solvent such as toluene.

Separation and recovery of exotic radiolanthanides from irradiated tantalum targets for half-life measurements

The current knowledge of the half-lives (T_1/2) of several radiolanthanides is either affected by a high uncertainty or is still awaiting confirmation. The scientific information deriving from this imprecise T_1/2 data has a significant impact on a variety of research fields, e.g., astrophysics, fundamental nuclear sciences, and nuclear energy and safety. The main reason for these shortcomings in the nuclear databases is the limited availability of suitable sample material together with the difficulties in performing accurate activity measurements with low uncertainties. In reaction to the urgent need to improve the current nuclear databases, the long-term project “ERAWAST” (Exotic Radionuclides from Accelerator Waste for Science and Technology) was launched at Paul Scherrer Institute (PSI). In this context, we present a wet radiochemical separation procedure for the extraction and purification of dysprosium (Dy), terbium (Tb), gadolinium (Gd), and samarium (Sm) fractions from highly radioactive tantalum specimens, in order to obtain ¹⁵⁴Dy, ^157-158Tb, ^148,150Gd, and ¹⁴⁶Sm samples, needed for T_1/2 determination studies. Ion-exchange chromatography was successfully applied for the separation of individual lanthanides. All separations were conducted in aqueous phase. The separation process was monitored via γ-spectrometry using suitable radioactive tracers. Both the purity and the quantification of the desired radiolanthanides were assessed by inductively coupled plasma mass spectrometry. Test experiments revealed that, prior to the Dy, Tb, Gd, and Sm separation, the removal of hafnium, lutetium, and barium from the irradiated tantalum material was necessary to minimize the overall dose rate exposure (in the mSv/h range), as well to obtain pure lanthanide fractions. With the herein proposed separation method, exotic ¹⁵⁴Dy, ^157-158Tb, ^148,150Gd, and ¹⁴⁶Sm radionuclides were obtained in sufficient amounts and purity for the preparation of samples for envisaged half-life measurements. During the separation process, fractions containing holmium, europium, and promethium radionuclides were collected and stored for further use.