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The stability of many MOFs is not satisfactory, which severely limits the exploration of their potential applications. Given this, we have proposed a strategy to improve the stability of MOFs by introducing alkali metal K+ capable of coordinating with metal nodes, which finally induces the interpenetrating uranyl-porphyrin framework to connect as a whole (IHEP-9). The stability experiments reveal that the IHEP-9 has good thermal stability up to 400 °C and can maintain its crystalline state in the aqueous solution with pH ranging from 2 to 11. The catalytic activity of IHEP-9 as a heterogeneous photocatalyst for CO2 cycloaddition under the driving of visible light at room temperature is also demonstrated. This induced interpenetration and fixation method may be promising for the fabrication of more functional MOFs with improved structural stability.

Diglycolamide-based ligands have recently received increased attention due to their outstanding affinity for trivalent actinides and lanthanides. The structure optimization of the ligands, however, still remains a hot topic to achieve better extraction performance. In this work, we prepare and investigate three multidentate diglycolamide ligands for the selective separation of Eu(III) over Am(III) from a nitric acid solution to explore the effect on the extraction of alkyl groups on the nitrogen atoms in the center of the BisDGA ligands. The introduction of ethyl or isopropyl groups on the central nitrogen atoms greatly increased the distribution ratios of trivalent metal ions and enhanced the separation factor of Eu(III) over Am(III). The complexation behaviors of Eu(III) and Am(III) ions were studied by slope analyses, electrospray ionization mass spectrometry (ESI-MS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The results indicated that the trivalent metal ions were extracted as 1:2 and 1:3 complexes for all three BisDGA ligands during the extraction. Density functional theory (DFT) calculations verified the relevant experimental conclusion that the selectivity of THEE-BisDGA for Eu(III) is better than that for Am(III). The metal-DGA bonds in the ML3(NO3)3 complexes seem to be stronger than those in ML2(NO3)3 complexes.

Recovery of transplutonium elements from adjacent actinides is extremely complicated in spent fuel reprocessing. Uncovering the electronic structures of transplutonium compounds is essential for designing robust ligands for in-group separation of transplutonium actinides. Here, we demonstrate the in-group transplutonium actinides separation ability of the recent developed phenanthroline ligand Et-Tol-DAPhen (

In order to elucidate the coordination structure and bonding properties between Am(III) and carbonate ion (CO32−), the geometric and electronic structures of the Am(III) carbonate complexes were systematically studied by scalar-relativistic density function theory. The bonding nature between Am atom and ligands was explored by the analyses of the natural bond orbital, quantum theory of atoms-in-molecules and electron localization function. These results indicate that the Am–Oc bonds are σ character with ionic interaction. Thermodynamic analysis shows that [Am(CO3)3(H2O)2]3− was the most stable complex. This work can provide insight into the coordination and bonding nature of the Am(III) carbonate complexes.

Nitrogen-donor ligands have been considered to be promising agents for separating trivalent actinides (An(III)) from lanthanides (Ln(III)). Thereinto, how to decorate these ligands for better extraction performance is urgent to design "perfect" separating extractants. In this work, we systematically explored a series of heterocyclic N-donor ligands (L1 = dipyridazino[4,3-c:3',4'-h]acridine, L2 = dipyridazino[3,4-a:4',3'-j]phenazine, L3 = 2,6-di(cinnolin-3-yl)pyridine)), as well as their substituted derivatives, and compared their extraction and complexation ability toward An(III) and Ln(III) ions by using quasi-relativistic density functional theory (DFT). We found that the pyridazine N atoms probably play a notable role in electron donation to metal cations by molecular orbital (MO) and bond order analyses. Besides, the calculated results clearly verified that these N-donor ligands possess higher coordination affinity toward Am(III) over Eu(III). The rigid ligands (L1 and L2) exhibit higher selective abilities for the Am(III)/Eu(III) separation compared with that of the flexible ligand (L3). For each ligand, the 1:2 (metal/ligand) extraction reaction is predicted to be most probable in the separation process. The introduction of an alkyl group on the lateral chain or an electron-donating group on the main chain gives rise to a better extraction performance of the ligands, and the CyMe4 or MeO substituted ligands show higher extraction and separation ability. Simultaneous introduction of CyMe4 and MeO groups can enhance the extraction ability of the ligand to metal ions, but the separating ability depends on the differences of the extraction capacity of An(III) and Ln(III). This work can help to gain a more in-depth understanding the selectivity differences of similar N-donor ligands and provide more theoretical insights into the design of novel extractants for An(III)/Ln(III) separation.

Developing necessary reprocessing techniques to meet the remarkable increase of spent nuclear fuels (SNFs) is crucial for the sustainable development of nuclear energy. This review summarizes recent research progresses related to the SNF reprocessing in China, with an emphasis on actinides separation over lanthanides through three different techniques, hydrometallurgical reprocessing, pyrometallurgical processes, and selective crystallization based separation. Some future perspectives with respect to advanced actinide separation are also given.

Separation of trivalent actinides An(III) from lanthanides Ln(III) is a worldwide challenge owing to their very similar chemical behaviors. It is highly desirable to understand the nature of selectivity for the An(III)/Ln(III) separation with various ligands through theoretical calculations because of their radiotoxicity and experimental difficulties. In this work, we have investigated three dithioamide-based ligands and their extraction behaviors with Am(III) and Eu(III) ions using the scalar-relativistic density functional theory. The results show that the dithioamide-based ligands have stronger electron donating ability than do the corresponding diamide-based ones. All analyses including geometry, Mulliken population, QTAIM (quantum theory of atoms in molecules), and NBO (natural bond orbital) suggest that the Am-S/N bonds possess more covalency compared to the Eu-S/N bonds, and the M-S bonds have more covalent character than the M-N bonds. Thermodynamic results reveal that N2,N9-diethyl-N2,N9-di-p-tolyl-1,10-phenanthroline-2,9-bis(carbothioamide) (L1) has a stronger complexing ability with metal ions owing to its rigid structure and that N6,N6'-diethyl-N6,N6'-di-p-tolyl-[2,2'-bipyridine]-6,6'-bis(carbothioamide) (L2) shows a higher selectivity for the Am(III)/Eu(III) separation. In addition, these dithioamide-based ligands possess Am(III)/Eu(III) selectivity higher than those of the corresponding diamide-based ones, although the former have weaker complexing ability with metal ions, probably due to the greater covalency of the M-S bonds. This theoretical evaluation provides valuable insights into the nature of the selectivity for the Am(III)/Eu(III) separation and information on designing of efficient An(III)/Ln(III) separation with dithioamide-based ligands.

The study of metal–metal bonds is one of the important challenges in organometallic chemistry and of great significance in applied and structural chemistry. We built a series of potential complexes...

The key to effective separation of neptunium from the spent fuel reprocessing process is to adjust and control its valence state. Hydrazine and its derivatives have been experimentally confirmed to be effective salt-free reductants for reducing Np(VI) to Np(V). We theoretically studied the reduction reactions of Np(VI) with three hydrazine derivatives (2-hydroxyethyl hydrazine (HOC

We studied geometric and electronic structures as well as thermodynamic properties of complexes [M(CyMe4–BTBP)2(NO3)]2+ and [M(CyMe4–BTBP)2]3+ with M = Am(III), Cm(III) and Ln(III) (La–Lu) theoretically. The actinide–nitrogen bonding is principally ionic with higher covalency in An–N bonds than in the Ln–N analogues. The selectivity towards An(III) over Ln(III) (La, Ce, Pr, Pm, Sm, Eu and Yb) is influenced by formed complexes to different extents by comparison of changes of Gibbs free energy of reaction, ΔΔGAm/Ln, for formation of [AmL2]3+/[LnL2]3+, [AmL2(NO3)]2+/[LnL2(NO3)]2+, and [AmL2(NO3)]2+/[LnL2]3+. The Am(III) selectivity is enhanced for [AmL2(NO3)]2+/[LnL2]3+ over [AmL2]3+/[LnL2]3+.

On the basis of the first structurally authenticated LArU–FeCp(CO)2 (LAr = deprotonated p-terphenyl bis(aniline) ligand) complex bearing an unsupported U–Fe bond, we expanded the structures of comp...

Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is one of the most important steps in spent nuclear fuel reprocessing. However, it is very difficult and challenging to separate them due to their similar chemical properties. Recently the pyridylpyrazole ligand (PypzH) has been identified to show good separation ability toward Am(III) over Eu(III). In this work, to explore the Am(III)/Eu(III) separation mechanism of PypzH at the molecular level, the geometrical structures, bonding nature, and thermodynamic behaviors of the Am(III) and Eu(III) complexes with PypzH ligands modified by alkyl chains (Cn-PypzH, n = 2, 4, 8) have been systematically investigated using scalar relativistic density functional theory (DFT). According to the NBO (natural bonding orbital) and QTAIM (quantum theory of atoms in molecules) analyses, the M-N bonds exhibit a certain degree of covalent character, and more covalency appears in Am-N bonds compared to Eu-N bonds. Thermodynamic analyses suggest that the 1:1 extraction reaction, [M(NO

Am3+/Cm3+ separation is an extremely hard but important task in nuclear waste treatment. In this study, Am and Cm complexes formed with a back-extraction agent N,N,N′,N′-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylene-diamine (H4TPAEN) and its two derivatives with hydrophilic substituents (methoxy and morpholine groups) were investigated using the density functional theory (DFT). The optimized geometrical structures indicated that the Am3+ cation matched better with the cavities of the three studied ligands than Cm3+, and the Am3+ cations were located deeper in the cavities of the ligands. The bond order and quantum theory of atoms in molecules (QTAIM) analyses suggested that ionic interactions dominated An–N and An–O (An = Cm and Am) bonds. However, weak and different extents of partial covalency could also be found in the Am–N and Cm–N bonds. The O donor atoms in the carboxylate groups preferably coordinated with Cm3+ rather than Am3+, whereas the N atoms preferred Am3+. Therefore, the Am3+/Cm3+ selectivity of H4TPAEN and its two hydrophilic derivatives may be ascribed to the competition between the An–N and An–O interactions and the few dissimilarities in their geometrical structures. Based on our calculations, the methoxy and morpholine groups in the two derivatives can serve as electron-donating groups and enhance the strength of the An–NPY bonds (NPY denotes the nitrogen atom of pyridine ring). When compared with the Am-complex, the Cm-complex exhibited significant strength effect, resulting in the relatively lower Am3+/Cm3+ separation ability of the H4TPAEN's hydrophilic derivatives.

Since the discovery of the first all-boron fullerenes B40−/0, metal-doped borospherenes have received extensive attention. So far, in spite of theoretical efforts on metalloborospherenes, the feasibility of actinide analogues remains minimally explored. Here we report a series of actinide borospherenes AnBn (An = U, Th; n = 36, 38, and 40) using DFT-PBE0 calculations. All the AnBn complexes are found to possess endohedral structures (An@Bn) as the global minima. In particular, U@B36 (C2h, 3Ag) and Th@B38 (D2h, 1Ag) exhibit nearly ideal endohedral borospherene structures. The C2h U@B36 and D2h Th@B38 complexes are predicted to be highly robust both thermodynamically and dynamically. In addition to the actinide size match to the cage, the covalent character of the metal-cage bonding in U@B36 and Th@B38 affords further stabilization. Bonding analysis indicates that U@B36 and Th@B38 can be qualified as 32-electron systems, and Th@B38 exhibits 3D aromaticity with σ plus π double delocalization bonding. The results demonstrate that doping with appropriate actinide atoms is promising to stabilize diverse borospherenes, and may provide routes for borospherene modification and functionalization.

We have investigated M-C bonds in lanthanide and actinide complexes ML2 (M = Ce, Th, U, Np and Pu; L = C(PPh2NMes)2) using scalar-relativistic theory. The M-C bonds possess typical σ and π bonding character, except for the nearly π-only Th-C bonds. The metal valence electrons significantly reside in the valence d and f orbitals for CeL2, UL2, NpL2 and PuL2, while for ThL2 most electron population is in 6d orbitals. The contribution of 6d orbitals to the An-C bonds decreases and that of 5f orbitals increases across the actinide series. QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) analyses confirm that the M-C bonds possess significant covalent character. This work provides insights into the contributions of d and f valence orbitals to M-C bonding. And inclusion of Np and Pu in this evaluation extends understanding to later actinides.

In recent years, there has been a trend to use synergistic systems of neutral and acidic extractants into a single-solvent formulation to achieve Ln3+/An3+ extraction and separation via simplified processing schemes. In this study, geometrical structures, bonding nature, and thermodynamic stabilities of a series of possible extraction complexes of Am3+ and Eu3+ with two neutral-acid synergistic systems (CMPO–HDEHP and CMPO–HEH[EHP]) were theoretically studied using scalar-relativistic density functional theory (DFT). It is found that hydrogen bonds between neutral and acid ligands may greatly influence the Eu3+/Am3+ extraction and separation performance of the two synergistic systems. According to natural bond orbital (NBO) and energy decomposition analyses (EDA), the phosphoryl oxygen atoms of HDEHP or HEH[EHP] have higher affinity for Eu3+ and Am3+ than those of the CMPO ligand. Since weak but different extents of covalency exist in Eu- and Am-complexes, Eu3+/Am3+ separation via these two systems may be attributed to the different compositions of interactions between the metal ions and ligands. Thermodynamic analysis shows that the neutral complexes ML(NO3)2 (M = Eu and Am; L = [CMPO-DEHP]− and [CMPO-EH[EHP]]−) appear to be the most probable species in the complexation process.

Recently, the carbon nanobelt (CNB) comprising a closed loop of fully fused edge-sharing benzene rings has been reported in an experiment. To explore its potential molecular properties and applications, we performed scalar relativistic density functional theory investigations on the interaction mechanisms of the CNB with a series of actinide atoms (An = Th-Am). Computations indicate that doping of actinide (An) atoms onto the surface of the CNB can result in the formation of stable actinide endohedral An@CNB compounds, along with the formation of C-An-C rings as well as a drastic structural transformation of the CNB. Compared to transuranium actinides, Th, Pa, and U exhibit a stronger adsorption affinity to the CNB in terms of the calculated binding energies. The adaptive natural density partitioning analysis shows that there form five 3c-2e bonds and two 5c-2e bonds in An@CNB for An = Th, Pa, and U, with fewer multicenter bonds for An = Np, Pu, and Am. These theoretical results provide a new strategy for chemical modification and functionalization of the CNB by actinide doping in the future.

Two thorium organic frameworks, Th(BDC)2 and Th(OH)(BCPBA) have been hydrothermally synthesized using 1,4-benzenedicarboxylic acid (H2BDC) and 3,5-bi(4-carboxyphenoxy)benzoic acid (H3BCPBA), respectively. The obtained two compounds were determined by single-crystal XRD, and they exhibited two new topologies. Th(BDC)2 shows a 3-dimensional (4,4,8)-connected framework with the Schläfli symbol of (414·612·82)(42·63·8)(44·62), and it is a mononuclear thorium(IV) complex. Th(OH)(BCPBA) possesses a (4,6)-connected topology with the Schläfli symbol of (415)2(46)3, and it has a dinuclear thorium(IV) asymmetric unit with the shortest Th–Th distances. Viewing along suitable directions, channels with different shapes can be found in the obtained two frameworks. Based on calculation with PLATON, the amount of void space is 21.9% and 13.5% in Th(BDC)2 and Th(OH)(BCPBA), respectively. Density functional theory (DFT) studies revealed that the metal-ligand interactions were mainly of ionic character in both compounds and the hydroxyl ions might play an important role in the stability of dinuclear thorium(IV) of Th(OH)(BCPBA).

With the fast development of nuclear energy, the issue related to spent nuclear fuel reprocessing has been regarded as an imperative task, especially for the separation of minor actinides. In fact, it still remains a worldwide challenge to separate trivalent An(iii) from Ln(iii) because of their similar chemical properties. Therefore, understanding the origin of extractant selectivity for the separation of An(iii)/Ln(iii) by using theoretical methods is quite necessary. In this work, three ligands with similar structures but different bridging frameworks, Et-Tol-DAPhen (La), Et-Tol-BPyDA (Lb) and Et-Tol-PyDA (Lc), have been investigated and compared using relativistic density functional theory. The electrostatic potential and molecular orbitals of the ligands indicate that ligand La is a better electron donor compared to ligands Lb and Lc. The results of QTAIM, NOCV and NBO suggest that the Am-N bonds in the studied complexes have more covalent character compared to the Eu-N bonds. Based on the thermodynamic analysis, [M(NO3)(H2O)8]2+ + L + 2NO3- = [ML(NO3)3] + 8H2O should be the most probable reaction in the solvent extraction system. Our results clearly verify that the relatively harder oxygen atoms offer these ligands higher coordination affinities toward both of the An(iii) and Ln(iii) ions compared to the relatively softer nitrogen atoms. However, the latter possess stronger affinities toward An(iii) over Ln(iii), which partly results in the selectivity of these ligands. This work can afford useful information on achieving efficient An(iii)/Ln(iii) separation through tuning the structural rigidity and hardness or softness of the functional moieties of the ligands.

Although the first organoactinide chloride Cp3UCl (Cp=η5-C5H5) was synthesized more than 50 years ago, binuclear uranium halides remain very rare in organoactinide chemistry. Herein, a series of binuclear trivalent and tetravalent uranium halides and cyanides with cyclooctatetraene ligands, (COT)2U2X n (COT=η8-C8H8; X=F, Cl, CN; n=2, 4), have been systematically studied using scalar-relativistic density functional theory (DFT). The structures with bridging halide or cyanide ligands were predicted to be the most stable complexes of (COT)2U2X n , and all the complexes show weak antiferromagnetic interactions between the uranium centers. However, for each species, there is no significant uranium-uranium bonding interaction. The bonding between the metal and the ligands shows some degree of covalent character, especially between the metal and terminal halide or cyanide ligands. The U-5f and 6d orbitals are predominantly involved in the metal-ligand bonding. All the (COT)2U2X n species were predicted to be more stable compared to the mononuclear half-sandwich complexes at room temperature in the gas phase such that (COT)2U2X4 might be accessible through the known (COT)2U complex. The tetravalent derivatives (COT)2U2X4 are more energetically favorable than the trivalent (COT)2U2X2 analogs, which may be attributed to the greater number of strong metal-ligand bonds in the former complexes.

A unique two-dimensional inorganic cationic network with the formula [Th3O2(IO3)5(OH)2]Cl was synthesized hydrothermally. Its crystal structure can best be described as positively charged slabs built with hexanuclear thorium clusters connected by iodate trigonal pyramids. Additional chloride anions are present in the interlayer spaces but surprisingly are not exchangeable, as demonstrated by a series of CrO4(2-) uptake experiments. This is because all chloride anions are trapped by multiple strong halogen-halogen interactions with short Cl-I bond lengths ranging from 3.134 to 3.333 Å, forming a special Cl-centered trigonal-pyramidal polyhedron as a newly observed coordination mode for halogen bonds. Density functional theory calculations clarified that electrons transformed from central Cl atoms to I atoms, generating a halogen-halogen interaction energy with a value of about -8.3 kcal mol(-1) per Cl···I pair as well as providing a total value of -57.9 kcal mol(-1) among delocalized halogen-halogen bonds, which is a new record value reported for a single halogen atom. Additional hydrogen-bonding interaction is also present between Cl and OH, and the interaction energy is predicted to be -8.1 kcal mol(-1), confirming the strong total interaction to lock the interlayer Cl anions.

Novel uranyl coordination polymers, UO2(bqdc)(phen)·H2O (1), [UO2(μ-OH)(bqdc)(H2bpy)0.5(H2O)] (2), Na[(UO2)2(bqdc)3Na(H2O)2] (3), and [Na(bqdc)0.5(bpp)(H2O)] (4) (H2bqdc = 2,2′-biquinoline-4,4′-dicarboxylic acid; phen = 1,10-phenanthroline; bpy = 4,4′-bipyridine; bpp = 1,3-di(4-pyridyl)propane), with bqdc2– ligands have been successfully synthesized by hydrothermal reactions and characterized by single-crystal X-ray diffraction, Infrared spectroscopy (IR), thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). The topological structures feature 1D chain to 3D framework by altering N-donor ancillary ligands. Compound 1 shows a 1D wave-shaped zigzag chain structure and further extends to a two-dimensional (2D) layer through π···π interactions between the quinoline ring of bqdc2– ligand and benzene ring of phen ligand. The uranium adopts an approximate hexagonal bipyramidal coordination geometry with the equatorial plane warped to the unusual chair conformation. Compound 2 features rectangula...

In this work, hydroxylated titanium carbide Ti3C2(OH)2, a representative of the two-dimensional transition metal carbides, has been predicted to be an effective adsorbent for uranyl ions in aqueous environments for the first time using density functional theory simulations. The calculations revealed that the uranyl ion can strongly bind with Ti3C2(OH)2 nanosheet in aqueous solution regardless of the presence of anionic ligands such as OH(-), Cl(-) and NO3(-). The bidentate coordination of uranyl to the surface is energetically more favorable than other adsorption configurations, and the uranyl ion prefers to bind with the deprotonated O adsorption site rather than the protonated one on the hydroxylated surface. During the adsorption process, the chemical adsorption as well as the formation of hydrogen bonds is the dominant factor.

Pyridylpyrazole ligands have shown excellent competence for partitioning actinides from lanthanides. As far as we know, the preorganization structure of the ligand has a great impact on the extraction separation ability. However, the mechanism that works well for some ligands but fails for others needs to be clearly elucidated. In this work, we designed three various pyridylpyrazole ligands, BPP, BPBP, and BPPhen, and further preorganized one or both side pyrazole rings of these ligands. The properties of these ligands and the coordination structures, bonding nature and thermodynamic behaviors of the related Am(III) and Eu(III) complexes have been systematically studied in a theoretical fashion. All analyses of geometries, charge transfer, QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) suggest that the Am-N bonds possess more covalence compared to that of Eu-N bonds. According to the thermodynamic results, increasing the rigidity of the bridging skeleton rather than the side chain can enhance the extraction ability and Am(III)/Eu(III) selectivity of the ligand. This work may identify the reasonability of a useful approach on achieving highly efficient Am(III)/Eu(III) separation through tuning the preorganization level of the ligand and further provide meaningful theoretical basis on the input of preorganization toward ligand design and screening.

To study the coordination modes and the binding affinities of uranyl ions with serine and phosphoserine, 1:1, 1:2 and 1:3 type complexes of a uranyl ion with these ligands were optimized at the B3LYP/ECP60MWB-SEG/6-311+G(d)/SMD level of theory in an aqueous solution. The analyses of the electronic energies show that the uranyl ion tends to adopt a penta-coordination mode and the binding affinity of the uranyl ion toward three functional groups follows the order of –PO42− > –COO− > –PO4H−. The changes of the Gibbs free energy (ΔGsol) for the studied reactions suggest that the uranyl ion prefers to form a 1:3 type complex with these ligands. Moreover, the absolute values of ΔGsol increase for the phosphorylated serine with the same type of reaction. Based on the thermodynamic results, a higher solution pH is more favorable for uranyl ion coordination with phosphoserine. This work could render theoretical insights into the specific coordination modes of uranyl ions with serine/phosphoserine under different conditions and provide useful information for further study on the interactions between actinide cations with peptides and proteins.

Valence state control and adjustment of neptunium in spent fuel reprocessing is very important for improving the separation efficiency of U/Np and Np/Pu. Hydrazine and its derivatives have been experimentally demonstrated to be effective in the reduction of NpVI to NpV. In this work, hydrazine was used as a representative reductant and the reduction mechanisms of NpVI induced by hydrazine were investigated using density functional theory (DFT) calculations. Three reaction pathways were taken into account and characterized by gradually transferring a hydrogen atom from N2H4 to the “yl”-oxygen of [NpVIO2(H2O)5]2+ followed by the valence state adjustment from NpVI to NpV. The calculated results of the potential energy profiles (PEPs) revealed that Pathway I should be the most likely to occur as the process of forming ˙N2H3 is considered to be the rate-determining step with the highest energy barrier of 32.02 kcal mol−1, which is in favor of the experimental results. Pathway II hardly occurs and Pathway III probably occurs. The bonding evolution, along with the reaction pathways, was explored through natural bond orbitals (NBOs), quantum theory of atoms-in-molecules (QTAIM) and electron localization function (ELF) analyses. This work can shed light on the understanding of redox mechanisms of NpVI with N2H4 and its derivatives and help further attempts to design more efficient reductants for the separation of U/Np and Np/Pu in spent nuclear fuel reprocessing in the near future.

The γ-radiation effect on Th4+ extraction by N,N,N′,N′-tetraoctyldiglycolamide (TODGA)/1-ethyl-3-methylimidazoliumbis (trifluoromethylsulfonyl) imide ([C2mim][NTf2]) and TODGA/dodecane was evaluated through the quantitative analysis of TODGA content and identification of the radiolytic products. In addition, the density functional theory (DFT) calculations of extractability for the first time. The Th4+ partitioning of TODGA/[C2mim][NTf2] from 0.01 M HNO3 was near 98.6% at 1000 kGy, which was much higher than that in TODGA/dodecane (16.3%). The content of TODGA in diluent after irradiation was quantified using UPLC-Q-TOF-MS. The results showed that the [C2mim][NTf2] did not have the ability to protect the TODGA molecular comparing with the dodecane. However, TODGA in [C2mim][NTf2] prefers to react with the [C2mim]+ radical under γ-radiation, and that in dodecane prefers degradation according to radiolytic products identification. Moreover, the DFT calculations presented that the substituted compounds formed in TODGA/[C2mim][NTf2] was responsible for partially keeping the extraction ability for Th4+.

Although many heterocyclic N-donor ligands have shown excellent competence for separating actinides from lanthanides, an explanation for why some ligands work whereas others fail is very fundamental but greatly needs to be addressed for designing novel and efficient extractants. In this work, we systematically investigated four phenanthroline-derived ligands, DHDIPhen, BQPhen, Ph2-BTPhen and CyMe4-BTPhen, and their coordination geometrical properties and formation reactions with Am(III) and Eu(III) ions by quasi-relativistic density functional theory. The calculated hardness of ligands, which may help to determine their selectivity toward actinides and lanthanides, yielded an order, from the softest to the hardest, as follows: Ph2-BTPhen < CyMe4-BTPhen < BQPhen < DHDIPhen. It shows that the intramolecular hydrogen bonds and size of a ligand cavity are two dominant factors for metal-ion complexation. Natural population analysis (NPA) reveals that the 5d/6d orbitals of Eu/Am accept significantly more electrons than other orbitals, but partial density of states and molecular orbital analysis prove that the d orbitals with more accepted electrons have little contribution to the metal–ligand bonds. The thermodynamic results suggest that ligand protonation does have a great influence on the complexation of ligands with metal ions but does not change the selectivity of ligands toward metal ions. This work can help in-depth understanding the differences of selectivity of various structurally similar ligands and provide more theoretical insights for designing more innovative ligands for Ln/An separation.

Separation of trivalent lanthanides (Ln(III)) and actinides (An(III)) is a key issue in the advanced spent nuclear fuel reprocessing. In the well-known trivalent actinide lanthanide separation by phosphorus reagent extraction from aqueous komplexes (TALSPEAK) process, the organophosphorus ligand HDEHP (di-(2-ethylhexyl) phosphoric acid) has been used as an efficient reagent for the partitioning of Ln(III) from An(III) with the combination of a holdback reagent in aqueous lactate buffer solution. In this work, the structural and electronic properties of Eu3+ and Am3+ complexes with HDEHP in nitric acid solution have been systematically explored by using scalar-relativistic density functional theory (DFT). It was found that HDEHP can coordinate with M(III) (M=Eu, Am) cations in the form of hydrogen-bonded dimers HL2 - (L=DEHP), and the metal ions prefer to coordinate with the phosphoryl oxygen atom of the ligand. For all the extraction complexes, the metal-ligand bonds are mainly ionic in nature. Although Eu(III) complexes have higher interaction energies, the HL2 - dimer shows comparable affinity for Eu(III) and Am(III) according to thermodynamic analysis, which may be attributed to the higher stabilities of Eu(III) nonahydrate. It is expected that this work could provide insightful information on the complexation of An(III) and Ln(III) with HDEHP at the molecular level.

The reaction of uranyl nitrate with terephthalic acid (H2TP) under hydrothermal conditions in the presence of an organic base, 1,3-(4,4'-bispyridyl)propane (BPP) or 4,4'-bipyridine (BPY), provided four uranyl terephthalate compounds with different entangled structures by a pH-tuning method. [UO2(TP)1.5](H2BPP)0.5·2H2O (1) obtained in a relatively acidic solution (final aqueous pH, 4.28) crystallizes in the form of a noninterpenetrated honeycomb-like two-dimensional network structure. An elevation of the solution pH (final pH, 5.21) promotes the formation of a dimeric uranyl-mediated polycatenated framework, [(UO2)2(μ-OH)2(TP)2]2(H2BPP)2·4.5H2O (2). Another new polycatenated framework with a monomeric uranyl unit, [(UO2)2(TP)3](H2BPP) (3), begins to emerge as a minor accompanying product of 2 when the pH is increased up to 6.61, and turns out to be a significant product at pH 7.00. When more rigid but small-size BPY molecules replace BPP molecules, [UO2(TP)1.5](H2BPP)0.5 (4) with a polycatenated framework similar to 3 was obtained in a relatively acidic solution (final pH, 4.81). The successful preparation of 2-4 represents the first report of uranyl-organic polycatenated frameworks derived from a simple H2TP linker. A direct comparison between these polycatenated frameworks and previously reported uranyl terephthalate compounds suggests that the template and cavity-filling effects of organic bases (such as BPP or BPY), in combination with specific hydrothermal conditions, promote the formation of uranyl terephthalate polycatenated frameworks.

Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is a pivotal step with respect to the treatment of nuclear waste based on the partitioning and transmutation (P&T) strategy, which is also extraordinarily challenging due to their similar coordination chemistry. The diethylenetriaminepentaacetate (DTPA) ligand has been demonstrated to possess selective separation ability toward An(III) over Ln(III) in aqueous media. Nevertheless, the extracted complexes of An(III)/Ln(III) with DTPA, and the origin of selectivity for An(III) are still not well deciphered. In this work, from theoretical perspective and at the molecular level, the geometrical structures, bonding nature as well as thermodynamic behaviors of possible complexes of An(III) (An = Am, Cm, Cf) and Ln(III) (Ln = Nd, Eu) with DTPA in the aqueous phase have been systematically studied using scalar relativistic density functional theory (DFT). All bonding analyses indicate that the metal-ligand bonds possess weak but non-negligible covalent interactions, and An(III)-DTPA species demonstrate more covalency compared to Ln(III) analogues. In addition, the covalency of the metal-ligand bonding of An(III)-DTPA increases across the actinide series from Am to Cf, which stems from the increased orbital degeneracy of the 5f orbitals of actinides and the 2p orbitals of the ligands. According to thermodynamic analysis, the anhydrous species [Cf(HDTPA)]− is the most likely species for Cf(III) in acidic solution, whereas [M(HDTPA)(H2O)]− are more favorable for Am(III) and Cm(III), probably due to the different bonding nature of the transplutonium series. This work affords new theoretical insights into the coordination chemistry of An(III)/Ln(III)-DTPA complexes, and paves the way to further design efficient DTPA-based ligands for An(III)/Ln(III) separation. Moreover, the DTPA ligand may also be applied for in-group separation of trivalent actinides, which is quite meaningful for the extraction of Cf(III).

Two highly symmetrical (3,4)-connected uranyl-organic frameworks (UOFs) were synthesized by a judicious combination of D3h -symmetrical triangular [UO2 (COO)3 ]- and Td symmetrical tetrahedral tetrakis(4-carboxyphenyl)methane (H4 MTB). These two as-synthesized UOFs possess similar structural units and coordination modes but totally different topological structures, namely ctn net and bor net. Solvent-induced interpenetration and a morphology change are observed. The two compounds exhibit crystal transformation via a dissolution-crystallization process. Adsorption experiments in CH3 OH solution indicate that both of them can selectively remove positively charged dyes over negatively charged and neutral dyes. Moreover, the electronic structural and bonding properties of the two compounds were systematically explored by density functional theory (DFT) calculations.