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In the Americium selective (AmSEL) process, the N-donor ligand 3,3’,3’’,3’’’-([2,2’-bipyridine]-6,6’-diylbis(1,2,4-triazine-3,5,6-triyl))tetrabenzenesulfonate (SO3-Ph-BTBP) is used to selectively strip Am(III) from a N,N,N’,N’-tetraoctyl diglycolamide (TODGA) containing organic phase loaded with Am(III), Cm(III) and lanthanides (Ln(III)). Fundamental extraction mechanism studies revealed an unusual extraction behavior of heavy Ln(III) and Y(III), which provided the motivation to investigate their complexation with SO3-Ph-BTBP using nuclear magnetic resonance (NMR) spectroscopy and solvent extraction. NMR spectroscopy indicated the formation of the same SO3-Ph-BTBP complex with Lu(III) in 10-3 mol L-1, 1 mol L-1 and 3 mol L-1 DNO3 solution. However, the complexation at high DNO3 concentration is subject to a slower than expected complexation kinetics leading to the conclusion that the unusual extraction behavior is probably related to a kinetics effect rather than an unknown complex species. Kinetics studies using solvent extraction show a slowly increasing extraction of heavy Ln(III) and Y(III) into the organic phase which is attributed to a kinetically inhibited decomplexation of the SO3-Ph-BTBP complexes. This effect is even more pronounced at higher HNO3 concentration. Additionally, combinations of monoand di-methylated TODGA derivatives with SO3-Ph-BTBP were tested, showing a decreasing performance regarding the actinide(III)/lanthanide(III) and Am(III)/Cm(III) separation with increasing degree of methylation.

The actinides possess a complex electronic structure, making their chemical and physical properties among the least understood in the periodic table. Advanced spectroscopic tools, able to obtain deep insights into the electronic structure and binding properties of the actinides, are highly desirable. Here, we introduce two sensitive spectroscopic tools: one determines the number of localized 5f electrons on an actinide atom, and another assesses the covalent character of actinide-ligand bonding. Both tools are based on the multiplet structure present in actinide M 4 edge core-to-core resonant inelastic X-ray scattering (CC-RIXS) maps. The spectral intensity of different many-body final-state multiplets directly depends on the local many-electron ground-state symmetry including the local 5 f spin configuration. By comparing U M 4 edge CC-RIXS data for 21 U, Np, Pu and Am compounds, we demonstrate the ability to compare the number of localized 5 f electrons and bond covalency across the actinide series., Competing Interests: Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

To improve the understanding of the extraction chemistry of An(iii) and Ln(iii) with N-donor ligands 2,6-bis(5-( tert -butyl)-1 H -pyrazol-3-yl)pyridine (C4-BPP) in the presence of 2-bromohexanoic acid was investigated. Extraction studies showed an excellent separation factor of SF Am(III)/Eu(III) ≈ 200 and SF Am(III)/Nd(III) ≈ 60 in comparison with the structurally similar ligand 2,6-bis(5-neopentyl-1 H -pyrazol-3-yl)pyridine C5-BPP (SF Am(III)/Eu(III) ≈ 100), even though C5-BPP showed significantly higher stability constants. Time-resolved laser fluorescence spectroscopy (TRLFS) studies revealed the formation of the ternary 1 : 1 and 1 : 2 complexes [Eu(C4-BPP) n (2-bromohexanoate) m ] (3- m )+ ( n = 1-2) ( and ). [Eu(C4-BPP) 2 (2-bromohexanoate) m ] (3- m )+ was the relevant complex species in solvent extraction. In contrast, Cm(iii) form stable 1 : 3 complexes. The ability of 2-bromohexanoic acid to replace C4-BPP from the inner coordination sphere of Eu(iii) but not from Cm(iii) is due to a more favorable complexation of Cm(iii) over Eu(iii) with C4-BPP. This resulted in a notably more efficient separation of An(iii) and Ln(iii) in comparison with C5-BPP., Competing Interests: No potential conflict of interest was reported by the author(s)., (This journal is © The Royal Society of Chemistry.)

Here, we report the synthesis of the 6-(6-methyl-1,2,4,5-tetrazine-3-yl)-2,2'-bipyridine (MTB) ligand that has been developed for lanthanide/actinide separation. A multimethod study of the complexation of MTB with trivalent actinide and lanthanide ions is presented. Single-crystal X-ray diffraction measurements reveal the formation of [Ce(MTB) 2 (NO 3 ) 3 ], [Pr(MTB)(NO 3 ) 3 H 2 O], and [Ln(MTB)(NO 3 ) 3 MeCN] (Ln = Nd, Sm, Eu, Gd). In addition, the complexation of Cm(III) with MTB in solution was studied by time-resolved laser fluorescence spectroscopy. The results show the formation of [Cm(MTB) 1-3 ] 3+ complexes, which occur in two different isomers. Quantum chemical calculations reveal an energy difference between these isomers of 12 kJ mol -1 , clarifying the initial observations made by time-resolved laser fluorescence spectroscopy (TRLFS). Furthermore, quantum theory of atoms in molecules (QTAIM) analysis of the Cm(III) and Ln(III) complexes was performed, indicating a stronger covalent contribution in the Cm-N interaction compared to the respective Ln-N interaction. These findings align well with extraction data showing a preferred extraction of Am and Cm over lanthanides (e.g., max. SF Am/Eu = 8.3) at nitric acid concentrations <0.1 mol L -1 HNO 3 .

To improve our understanding of the interaction mechanism in trivalent lanthanide and actinide complexes, studies with structurally different hard and soft donor ligands are of great interest. For that reason, the coordination chemistry of An(III) and Ln(III) with 2,6-bis(5-( tert -butyl)-1 H -pyrazol-3-yl)pyridine (C4-BPP) has been explored. Time-resolved laser fluorescence spectroscopy (TRLFS) studies have revealed the formation of [Cm(C4-BPP) n ] 3+ ( n = 1-3) (log β 1 ' = 7.2 ± 0.4, log β 2 ' = 10.1 ± 0.5, and log β 3 ' = 11.8 ± 0.6) and [Eu(C4-BPP) m ] 3+ ( m = 1-2) (log β 1 ' = 4.9 ± 0.2 and log β 2 ' = 8.0 ± 0.4). The absence of the [Eu(C4-BPP) 3 ] 3+ complex shows a more favorable complexation of Cm(III) over that of Eu(III). Additionally, complementary NMR measurements have been conducted to examine the M(III)-N bond in Ln(III) and Am(III) C4-BPP complexes. 15 N NMR data have revealed notable differences in the chemical shifts of the coordinating nitrogen atoms between the Am(III) and Ln(III) complexes. In the Am(III) complex, the coordinating nitrogen atoms have shown a shift by 260 ppm, indicating a higher fraction of covalent bonding in the Am(III)-N bond compared with the Ln(III)-N bond. This observation aligns excellently with the differences in the stability constants obtained from TRLFS studies.

Novel hydrophilic ligands to selectively separate Am(III) are synthesized: 3,3'-([2,2'-bipyridine]-6,6'-diylbis(1 H -1,2,3-triazole-4,1-diyl))bis(propan-1-ol) (PrOH-BPTD) and 3,3'-([2,2'-bipyridine]-6,6'-diylbis(1 H -1,2,3-triazole-4,1-diyl))bis(ethan-1-ol) (EtOH-BPTD). The complexation of An(III) and Ln(III) with PrOH- and EtOH-BPTD is studied by time-resolved laser fluorescence spectroscopy. [ML 2 ] 3+ is found for both Cm(III) and Eu(III), while [ML] 3+ is only formed with Cm(III). Stability constants show a preferential coordination of Cm(III) over Eu(III) with PrOH-BPTD being the stronger ligand. The distribution of Am(III), Cm(III), and Ln(III) between an organic phase containing the extracting agent N , N , N ', N '-tetra- n -octyl-3-oxapentanediamide (TODGA) and aqueous phases containing PrOH-BPTD is studied as a function of time and temperature as well as the TODGA, BPTD, and HNO 3 concentrations. A system composed of 0.2 mol/L TODGA and 0.04 mol/L PrOH-BPTD in 0.33-0.39 mol/L HNO 3 allows for selective Am(III) back-extraction into the aqueous phase while keeping Cm(III) and Ln(III) in the organic phase, marking PrOH-BPTD as an excellent complexant for an optimized AmSel process (Am(III) selective extraction).

In this work, we report a combined NMR spectroscopic and time-resolved laser fluorescence spectroscopic (TRLFS) study of the complexation of N , N , N ', N '-tetraethyl-2,6-carboxamidopyridine (Et-Pic) with Ln(III) (La, Sm, Eu, and Lu), Y(III) and An(III) (Am and Cm). The focal point of this study was the metal-ligand interaction in the [M(Et-Pic) 3 ] 3+ (M = An and Ln) complexes. The NMR analyses found slight differences between the An(III)-N and Ln(III)-N interactions in contrast to the similar properties of the Am(III)-O and Ln(III)-O interactions. These results were supported by TRLFS which shows that the 1 : 3 Cm(III) complex is by one order of magnitude more stable than the respective Eu(III) complex. Thus, the ligand's selectivity lies in between those of pure N- and O-donor ligands. The selectivity results from a small partial covalent bonding between the An(III) ions and Et-Pic.

Ammonium pertechnetate reacts in mixtures of trifluoromethanesulfonic anhydride and trifluoromethanesulfonic acid under final formation of ammonium pentakis(trifluoromethanesulfonato)oxidotechnetate(V), (NH 4 ) 2 [TcO(OTf) 5 ]. The reaction proceeds only at exact concentrations and under the exclusion of air and moisture via pertechnetyl trifluoromethanesulfonate, [TcO 3 (OTf)], and intermediate Tc VI species. 99 Tc nuclear magnetic resonance (NMR) has been used to study the Tc VII compound and electron paramagnetic resonance (EPR), 99 Tc NMR and X-ray absorption near-edge structure (XANES) experiments indicate the presence of the reduced technetium species. In moist air, (NH 4 ) 2 [TcO(OTf) 5 ] slowly hydrolyses under formation of the tetrameric oxidotechnetate(V) (NH 4 ) 4 [{TcO(TcO 4 ) 4 } 4 ] ⋅10 H 2 O. Single-crystal X-ray crystallography was used to determine the solid-state structures. Additionally, UV/Vis absorption and IR spectra as well as quantum chemical calculations confirm the identity of the species., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A combined NMR spectroscopic and theoretical study on the complexation of diamagnetic Th(IV) with 2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine ( n Pr-BTP) was performed. Different ligand configurations were observed for [Th( n Pr-BTP) 3 ] 4+ complexes depending on the solvent's ability to actively form hydrogen bonds. In polar aprotic solvents, a complex is observed, which is isostructural with [M( n Pr-BTP) 3 ] 3+ (M = Am, Ln) complexes studied earlier. In contrast, 1 H, 13 C, and 15 N NMR spectra recorded in polar protic solvents showed twice as many signals, indicating a breakdown of symmetry. Supported by density functional theory (DFT) calculations, this difference is explained by the solvent effect on the steric arrangement of the propyl moieties located on the triazine rings. Important information on bonding properties was obtained by 15 N NMR. In contrast to the respective Am(III) complex showing a significant covalent contribution, the Th(IV)-BTP interaction is mainly electrostatic.

Combination of three radical anionic Ph-BIAN ligands (Ph-BIAN=bis-(phenylimino)-acenaphthenequinone) with lanthanoid ions leads to a series of homoleptic, six-coordinate complexes of the type Ln(Ph-BIAN) 3 . Magnetic coupling data were measured by paramagnetic solution NMR spectroscopy. Combining 1 H NMR with 2 H NMR of partially deuterated compounds allowed a detailed study of the magnetic susceptibility anisotropies over a large temperature range. The observed chemical shifts were separated into ligand- and metal-centered contributions by comparison with the Y analogue (diamagnetic at the metal). The metal-centered contributions of the complexes with the paramagnetic ions could then be separated into pseudocontact and Fermi contact shifts. The latter is large within the Ph-BIAN scaffold, which shows that magnetic coupling is significant between the lanthanide ion and the radical ligand. Pseudocontact shifts were further correlated to structural data obtained from X-ray diffraction experiments. Ligand-field parameters were determined by fitting the temperature dependence of the observed magnetic susceptibility anisotropies. The electronic structure determined by this approach shows, that the Er and Tm analogues are candidates for single molecule magnets (SMM). These results demonstrate the possibilities for the application of NMR spectroscopy in investigations of paramagnetic systems in general and single molecule magnets in particular., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)