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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 (L

In the advanced spent fuel cycle, the control and adjustment of neptunium valence state is greatly important for the highly efficient separation of neptunium. Hydrazine and its derivatives as salt-free reagents can selectively reduce Np(VI) to Np(V), but their reduction mechanisms are still unclear. We explored the reduction of [NpVIO2(H2O)2(NO3)2] by N2H4 and its two derivatives HOC2H4N2H3 and CHON2H3 using scalar relativistic density functional theory. The thermodynamic energy of the reactions [NpVIO2(H2O)2(NO3)2] with three reductants are sensitive to the substitution group, HOC2H4N2H3 enhances thermodynamic ability of the reaction and CHON2H3 shows contrary result. Both HOC2H4N2H3 and CHON2H3 have lower energy barrier compared to N2H4 based on the potential energy profiles (PEPs), which probably attributes to the intramolecular hydrogen bond of hydrazine derivatives. The nature of these redox reactions is that the hydrogen atom of reductants is gradually transferred to the axis oxygen atom of neptunyl, which accompanies the N–H bond dissociation and Oax–H bond formation. The reduction of Np(VI) with HOC2H4N2H3 is the most favorable reaction based on the thermodynamic and kinetic results. This work provides theoretical perspective into the reduction of Np(VI) to Np(V), which is beneficial to the development of more effective free-salt reductants for the separation of neptunium from uranium and plutonium in spent fuel reprocessing.

Designing ligands with efficient actinide (An(III))/lanthanide (Ln(III)) separation performance is still one of the key issues for the disposal of accumulated radioactive waste and the recovery of minor actinides. Recently, the hydrophilic ligands as promising extractants in the innovative Selective ActiNide Extraction (i-SANEX) process show excellent selectivity for Am(III) over Eu(III), such as hydroxylated-based ligands. In this work, we investigated the selective back-extraction toward Am(III) over Eu(III) with three hydrophilic hydroxylated triazolyl-based ligands (the skeleton of pyridine

Effective separation and recovery of chemically similar transplutonium elements from adjacent actinides is extremely challenging in spent fuel reprocessing. Deep comprehension of the complexation of transplutonium elements and ligands is significant for the design and development of ligands for the in-group separation of transplutonium elements. Because of experimental difficulties of transplutonium elements, theoretical calculation has become an effective means of exploring transplutonium complexes. In this work, we systematically investigated the coordination mechanism between transplutonium elements (An = Am, Cm, Bk, Cf) and two crown ether macrocyclic ligands [

The propensity of uranyl for hydrolysis in aqueous environments prevents precise control of uranyl species in the scenarios of on-demand separation and tailored synthesis. Herein, using cucurbit[7]uril (CB[7]) as the macrocyclic molecule and 4,4'-bipyridine-N,N'-dioxide (DPO) as the string molecule, we propose a new kind of multidentate pseudorotaxane ligand, DPO@CB[7] for capturing uranyl species at different pH's. With the aprotic nature of DPO for metal coordination, the coordination ability of the DPO@CB[7] ligand is less affected by pH and can work in a wide range of pH's. Furthermore, by adaptive uranyl coordination, this aprotic pseudorotaxane ligand achieves effective recognition for different uranyl species ranging from monomeric to tetrameric originating from hydrolysis at varying pH's, and four novel uranyl-rotaxane compounds (URC1-4) are successfully obtained. Single-crystal X-ray diffraction analysis reveals that the DPO@CB[7] ligand coordinates with uranyl centers from monomeric to tetrameric in four different modes, as a result of structural flexibility of the DPO@CB[7] pseudorotaxane ligand. A detailed discussion for conformation flexibility of the DPO@CB[7] ligand has been conducted on the position changes of the DPO ligand trapped in the CB[7], which thus reveals good adaptivity of DPO@CB[7] that is noncovalently bonded as a supramolecular motif. In addition, characterization of the physicochemical properties of URC1 and URC2 with high phase purity, including powder X-ray diffraction (PXRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and luminescence properties, are also provided. This work provides a good case of an adaptive pseudorotaxane ligand for the recognition and capture of different uranyl species and will bring valuable hints to the design of multifunctional supramolecular ligands for actinide separation in the future.

The reduction mechanisms of Np(vi) with hydrazinopropionitrile were theoretically explored and the pathway with water-mediated proton transfer is energetically preferred.

The competition of uranium and vanadium ions is a major challenge in extracting uranium from seawater. In-depth exploration of the complexation of uranium and vanadium ions with promising ligands is essential to design highly efficient ligands for selective recovery of uranium. In this work, we systematically explored the uranyl and vanadium extraction complexes with three tetradentate N,O-mixed donor analogues including the rigid backbone ligands 1,10-phenanthroline-2,9-dicarboxylic acid (PDA, L

Although 1,10-phenanthroline-based ligands have recently shown vast opportunities for the separation of trivalent actinides (Ans(III)) from lanthanides (Lns(III)), the optimization and design of the extractant structure based on the phenanthroline framework remain hotspots for further improving the separation. Following the strategy of hard and soft donor atom combination, for the first time, the quinoline group was attached to the 1,10-phenanthroline skeleton, giving a lipophilic ligand, 2,9-diacyl-bis((3,4-dihydroquinoline-1((2H)-yl)-1),10-phenanthroline (QL-DAPhen)), for Am(III)/Eu(III) separation. In the presence of sodium nitrate, the ligand can effectively extract Am(III) over Eu(III) in HNO3 solution, with the separation factor (SFAm/Eu) ranging from 29 to 44. The coordination chemistry of Eu(III) with QL-DAPhen was investigated by slope analysis, NMR titration, UV-vis titration, Fourier transform infrared spectroscopy, electrospray ionization-mass spectrometry, and theoretical calculations. The experimental results unanimously confirm that the ligand forms both 1:1 and 1:2 complexes with Eu(III), and the stability constants (log β) of each of the two complexes were obtained. Density functional theory calculations show that the Am-N bonds have more covalent characteristics than the Eu-N bonds in the complexes, which reveals the reason why the ligand preferentially bonds with Am(III). Meanwhile, the thermodynamic analysis reveals that the 1:1 complex is more thermodynamically stable than the 1:2 complex. The findings of this work have laid a solid theoretical foundation for the application of phenanthroline-based ligands in the separation of An(III) from practical systems.

A highly flexible uranyl-organic polythreading framework enabled by cucurbit[8]uril-based host–guest complexation exhibits remarkable negative thermal expansion behaviour through a relaxation-related mechanism.

Similar to graphene and fullerene, metal-doping has been considered to be an effective approach to the construction of highly stable boron clusters. In this work, a series of actinide metal-doped boron clusters AnB

The involvement of the 2-phosphaethynolate anion species with ambident nucleophilic properties serves as an essential protocol for synthesizing oxygen-bound or phosphorus-bound complexes. This work mainly describes the synthesis and characterization of U, Th, and Ti phosphaethynolate complexes featuring a preferential O-coordination fashion. Among these complexes, the first examples of a Ti(IV)-OCP complex 3A, Th(IV)-OCP complex 3B, and U(IV)-OCP complex 3C were assembled by a salt metathesis reaction between M(Trapen

Separation of trivalent actinide (An(III)) and lanthanide (Ln(III)) is a worldwide challenge of nuclear waste treatment. Designing ligands with efficient An(III)/Ln(III) separation performance is still one of the key issues for the disposal of accumulated radioactive waste and the recovery of minor actinides. Recently, N-heterocyclic ligands modified with amide groups have shown excellent An(III)/Ln(III) separation performance. The preorganized structure of the ligands has a great impact on the An(III)/Ln(III) separation performance. We theoretically investigated the extraction behaviors of Am(III) and Eu(III) using phenanthroline (L1 and L2) and bipyridine (L3 and L4) based ligands with a completely or partially preorganized structure. The properties of these ligands and their coordination structures, bonding nature and thermodynamic behaviors with the Am(III) and Eu(III) complexes have been systematically studied in a theoretical fashion. The analyses of the bonding nature suggest that the Am-N bonds possess more covalence than the Eu-N bonds. The thermodynamic results indicate that L2 with a completely preorganized structure has the strongest extraction ability and the best Am(III)/Eu(III) selectivity, while L3 with the most flexible skeleton appears to have the weakest extraction ability and the lowest Am(III)/Eu(III) selectivity. And L1 and L4 have similar performances with regard to Am(III)/Eu(III) selectivity. The results suggest that a certain degree of preorganization of the ligand structure can enhance the extraction ability and Am(III)/Eu(III) selectivity. This work provides valuable information for designing efficient ligands for An(III)/Ln(III) separation by the preorganization strategy.

Metal doping has been considered to be an effective approach to stabilize various boron clusters. In this work, we constructed a series of largest metal-centered double-ring tubular boron clusters An@B

In order to optimize the application of Al electrodes in pyrochemical reprocessing of spent nuclear fuel, the feasibility of porous Al electrodes to separate actinides-lanthanides (An-Ln) in LiCl-KCl eutectic melt was explored. The separation efficiencies and rates of U and lanthanides (La, Ce, Sm) on Al electrodes with regular and irregular and without pores were compared. U was selectively recovered in the form of U-Al alloys by controlling the potential (−1.2 V) on both Al rod and porous Al electrodes. X-ray diffraction (XRD) and scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS) showed that the obtained granular alloys were mainly Al3U and Al4U, and inductive coupled plasma optical emission spectrometry (ICP-OES) indicated that there was almost no Ln in the electrolysis products. Positively, the required separation time was greatly shortened, and the separation rate was effectively improved when porous Al electrodes were used. In addition, the Al honeycomb electrode with regular pores has better kinetic performance compared with Al foam electrodes with irregular pores. The results indicate that the specially designed porous Al electrodes may have a good application prospect for the separation of An-Ln in the pyrochemical reprocessing of spent nuclear fuel.

Extraction of uranium from seawater is one of the important ways to solve the shortage of terrestrial uranium resources. Thereinto, the competition between uranyl and vanadium cations is a significant challenge in the commonly used amidoxime-based adsorbents for extracting uranium from seawater. An in-depth understanding of the extraction behaviors of modified amidoxime groups with uranyl and vanadium ions is one of the effective means to design and develop efficient adsorbents for selective uranium sequestration. In this work, we have designed and systematically investigated the alkyl and amino functionalized amidoxime, (

Monitoring and quantification of the photoresponsive behavior of metal-organic frameworks that respond to a light stimulus are crucial to establish a clear structure-activity relationship related to light regulation. Herein, we report the first azobenzene-modified photoresponsive thorium-organic framework (

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.

To evaluate how halogen and actinide atoms affect the electronic structures and bonding nature, we have theoretically investigated a series of the actinide halides An(TRENTIPS)X (An = Th-Pu; X = F-I); several of them have been synthesized by Liddle's group. The An-X bond distances decrease from An = Th to Pu for the same halides, and the harmonic vibrational frequencies for the An-X bonds are more susceptible to being affected by the halogen atoms. The analyses of bonding nature reveal that the An-X bonds have a certain covalency with a polarized character, and the σ-bonding component in the total orbital contribution is greatly larger than the corresponding π-bonding ones based on the analysis of the NOCVs (the natural orbitals for chemical valence). Furthermore, the electronic structures of the thorium complexes are obviously different from those of the uranium and transuranic analogues due to more valence electrons in Th 6d orbitals. In addition, thermodynamic results suggest that the U(TRENTIPS)Br complex is the most stable and U(TRENTIPS)Cl has the highest reactivity based on the halide exchange reaction of U(TRENTIPS)X complexes using Me3SiX. The reduction ability of the tetravalent An(TRENTIPS)X is sensitive to halogen atoms according to the calculated electron affinity of the An(TRENTIPS)X and the reactions An(TRENTIPS)X + K → An(TRENTIPS) + KX. This work presents the effect of the halogen and the actinide atoms on the structures, bonding nature and redox ability of a series of the tetravalent actinide halides with TREN ligand and facilitates our in-depth understanding of f-block elements, which could provide theoretical guidance for experimental work on actinide halides, especially for the synthetic chemistry of transuranic halides.