Distinguishing the Geometric and Electronic Structures of Actinide Carbides AnxC8 (An = Th, U; x = 2, 3) through Exchange Interactions.

Global-minimum optimizations combined with relativistic quantum chemistry calculations have been performed to characterize the ground-state stable structures of four titled compounds and to analyze the bonding properties. Th2C8 was identified as being a ThC4-Th(C2)2 structure, U2C8 has been found to favor the U-U(C8) structure, and both Th3C8 and U3C8 adopt the (AnC3)2-(AnC2) structure. Then, the wave function analyses reveal that the interactions between the Th 7s-based orbital and the σg molecular orbital of the C2 unit compensate for the excitation energy of 7s16d1 → 6d2 and lead to the stabilization of two Th(IV)s in the ThC4-Th(C2)2 structure. It also reveals that the U species exhibit magnetic exchange coupling behavior in UxC8, for instance, as seen in the direct interaction of U2C8 and the superexchange pathway of U3C8, which effectively stabilizes their low-spin states. This interpretation indicates that the geometric and electronic structures of AnxC8 species are largely influenced by the local magnetic moment and spin correlation.

Emergence of a Lanthanide Chalcogenide as an Ideal Scintillator for a Flexible X-ray Detector.

The development of high-performance X-ray detectors requires scintillators with fast decay time, high light yield, stability, and X-ray absorption capacity, which are difficult to achieve in a single material. Here, we present the first example of a lanthanide chalcogenide of LaCsSiS4 : 1 % Ce3+ that simultaneously integrates multiple desirable properties for an ideal scintillator. LaCsSiS4 : 1 % Ce3+ demonstrates a remarkably low detection limit of 43.13 nGyair s-1 and a high photoluminescence quantum yield of 98.24 %, resulting in a high light yield of 50480±1441 photons/MeV. Notably, LaCsSiS4 : 1 % Ce3+ exhibits a fast decay time of only 29.35±0.16 ns, making it one of the fastest scintillators among all lanthanide-based inorganic scintillators. Furthermore, this material shows robust radiation and moisture resistance, endowing it with suitability for chemical processing under solution conditions. To demonstrate the X-ray imaging capacity of LaCsSiS4 : 1 % Ce3+ , we fabricated a flexible X-ray detector that achieved a high spatial resolution of 8.2 lp mm-1 . This work highlights the potential of lanthanide chalcogenide as a promising candidate for high-performance scintillators.

Trends in the Electronic Structure and Chemical Bonding of a Series of Porphyrinoid-Uranyl Complexes.

In this paper, we have explored the relativistic density functional theory study on a series of deprotonated porphyrinoid (Ln) complexes of uranyl to investigate the geometrical structures and chemical bonding. The ligands bound with uranyl in the 1:1 complexes [UO2(Ln)]x (n = 4, 5, 6; x = 0, -1, -2), showing more thermodynamic stability for "in-cavity" structures of L5 and L6 than that of the "side-on" structure of L4 and an increase in stability with the increase of negative charges, L2- < L3- < L4-. Among the six ligands, the cyclo[6]pyrrole presents the best selectivity toward uranyl. Based on chemical bonding analyses, the U-NL bond in the in-cavity complexes adopts a typical dative NL → U bond with mainly ionic bonding and significant covalency, which comes from the significant orbital interaction of U 5fϕ6dδ7s hybrid AOs and NL 2p-based MOs. This work provides a systematic understanding of the coordination chemistry in uranyl pyrrole-containing macrocycle complexes and the nature of chemical bonding in such systems, which may provide inspirations for the future design of synthetic targets that could be relevant to actinide separations or in the remediation of spent nuclear fuel.

Li vs Na: Divergent Reaction Patterns between Organolithium and Organosodium Complexes and Ligand-Catalyzed Ketone/Aldehyde Methylenation.

Organosodium chemistry is underdeveloped compared with organolithium chemistry, and all the reported organosodium complexes exhibit similar, if not identical, reactivity patterns to their lithium counterparts. Herein, we report a rare organosodium monomeric complex, namely, [Na(CH2SiMe3)(Me6Tren)] (1-Na) (Me6Tren: tris[2-(dimethylamino)ethyl]amine) stabilized by a tetra-dentate neutral amine ligand Me6Tren. Employing organo-carbonyl substrates (ketones, aldehydes, amides, ester), we demonstrated that 1-Na features distinct reactivity patterns compared with its lithium counterpart, [Li(CH2SiMe3)(Me6Tren)] (1-Li). Based on this knowledge, we further developed a ligand-catalysis strategy to conduct ketone/aldehyde methylenations, using [NaCH2SiMe3]∞ as the CH2 feedstock, replacing the widely used but hazardous/expensive C═O methylenation methods, such as Wittig, Tebbe, Julia/Julia-Kocienski, Peterson, and so on.

XPu(CO)n (X = B, Al, Ga; n = 2 to 4): π Back-Bonding in Heterodinuclear Plutonium Boron Group Compounds with an End-On Carbonyl Ligand.

The bonding situation and the oxidation state of plutonium in heterodinuclear plutonium boron group carbonyl compounds XPu(CO)n (X = B, Al, Ga; n = 2 to 4) were investigated by systematically searching their ground-state geometrical structures and by analyzing their electronic structures. We found that the series of XPu(CO)n compounds show various interesting structures with an increment in n as well as a changeover from X = B to Ga. The first ethylene dione (OCCO) compounds of plutonium are found in AlPu(CO)n (n = 2, 3). A direct Ga-Pu single bond is first predicted in the series of GaPu(CO)n, where the bonding pattern represents a class of the Pu → CO π back-bonding system. There is a trend where the Pu-Ga bonding decreases and the Pu-C(O) covalency increases as the Ga oxidation state increases from Ga(0) to Ga(I). Our finding extends the metal → CO covalence back-bonding concept to plutonium systems and also enriches plutonium-containing bonding chemistry.

Electronic Structures and Unusual Chemical Bonding in Actinyl Peroxide Dimers [An2O6]2+ and [(An2O6)(12-crown-4 ether)2]2+ (An = U, Np, and Pu).

As known, actinyl peroxides play important roles in environmental transport of actinides, and they have strategic importance in the application of nuclear industry. Compared to the most studied uranyl peroxides, the studies of transuranic counterparts are still few, and more information about these species is needed. In this work, experimentally inspired actinyl peroxide dimers ([An2O6]2+, An = U, Np, and Pu) have been studied and analyzed by using density functional theory and multireference wave function methods. This study determines that the three [An2O6]2+ have unique electronic structures and oxidation states, as [(UVIO2)2(O2)2-]2+, [(NpVIIO2)2(O2-)2]2+, and mixed-valent [(PuVI/VO2)2(O2)1-]2+. This study demonstrates the significance of two bridging oxo ligands with at most four electron holes availability in ionically directing actinyl and resulting in the unusual multiradical bonding in [(PuVI/VO2)2(O2)1-]2+. In addition, thermodynamically stable 12-crown-4 ether (12C4) chelated [(An2O6)(12C4)2]2+ complexes have been predicted, that could maintain these unique electronic structures of [An2O6]2+, where the An ← O12C4 dative bonding shows a trend in binding capacity of 12C4 from κ4 (U) to κ3 (Np) and κ4 (Pu). This study reveals the interesting electronic character and bonding feature of a series of early actinide elements in peroxide complexes, which can provide insights into the intrinsic stability of An-containing species.

In Situ Synthesis of MOF-74 Family for High Areal Energy Density of Aqueous Nickel-Zinc Batteries.

Limited by single metal active sites and low electrical conductivity, designing nickel-based metal-organic framework (MOF) materials with high capacity and high energy density remains a challenge. Herein, a series of bi/multimetallic MOF-74 family materials in situ grown on carbon cloth (CC) by doping Mx+ ions in Ni-MOF-74 is fabricated: NiM-MOF@CC (M = Mn2+ , Co2+ , Cu2+ , Zn2+ , Al3+ , Fe3+ ), and NiCoM-MOF@CC (M = Mn2+ , Zn2+ , Al3+ , Fe3+ ). The type and ratio of doping metal ions can be adjusted while the original topology is preserved. Different metal ions are confirmed by X-ray absorption fine structure (XAFS). Furthermore, these Ni-based MOF electrodes are directly utilized as cathodes for aqueous nickel-zinc batteries (NZBs). Among all the as-prepared electrodes, NiCo-MOF@CC-3 (NCM@CC-3), with an optimized Co/Ni ratio of 1:1, exhibits the best electrical conductivity, which is according to the density functional theory (DFT) theoretical calculations. The NCM@CC-3//Zn@CC battery achieves a high specific capacity of 1.77 mAh cm-2 , a high areal energy density of 2.97 mWh cm-2 , and high cycling stability of 83% capacity retention rate after 6000 cycles. The synthetic strategy based on the coordination effect of metal ions and the concept of binder-free electrodes provide a new direction for the synthesis of high-performance materials in the energy-storage field.

Versatile Coordination Modes of Multidentate Neutral Amine Ligands with Group 1 Metal Cations.

This work comprehensively investigated the coordination chemistry of a hexa-dentate neutral amine ligand, namely, N,N',N"-tris-(2-N-diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN), with group-1 metal cations (Li+, Na+, K+, Rb+, Cs+). Versatile coordination modes were observed, from four-coordinate trigonal pyramidal to six-coordinate trigonal prismatic, depending on the metal ionic radii and metal's substituent. For comparison, the coordination chemistry of a tetra-dentate tris-[2-(dimethylamino)ethyl]amine (Me6Tren) ligand was also studied. This work defines the available coordination modes of two multidentate amine ligands (DETAN and Me6Tren), guiding future applications of these ligands for pursuing highly reactive and elusive s-block and rare-earth metal complexes.

12-Membered Ring Carbides with Stabilization of Actinide Atoms.

Actinide (Th and U) carbides as the potential nuclear fuels in nuclear reactors require basic research in order to understand the thermodynamic stability and performance of these substances. Here we report the structural characterization and bonding analyses of [C12], ThC12, and UC12 clusters via a global-minimum search combined with relativistic quantum chemistry calculations to elucidate the stability and bonding nature of An-C bonds. We predict that these [C12], ThC12, and UC12 compounds have a planar structure with C6h, D12h, and D12h symmetry, respectively. [C12] has a hyperconjugation structure containing alternating single and double bonds. The significant stabilization when forming AnC12 predominantly comes from the electrostatic interaction between An4+ and [C12]4- and also from a certain degree of orbital interaction between the An 5f6d7s valence shell and [C12] π orbitals. The covalent character of the An-C bonds exhibits a direct in-plane σ-type overlap of the C 2p-derived MOs of [C12] and the An 5fϕ AO, thus leading to an unprecedented electronic configuration of d1f1 for U in UC12. Our results present an example of the novel properties that can be expected for actinide compounds and would provide the knowledge required to obtain novel structures of AnC12 in future experiments.

Stable copernicium hexafluoride (CnF6) with an oxidation state of VI.

As the heaviest group 12 element known currently, copernicium (Cn) often presents the oxidation states of I+, II+, and rarely IV+ as in its homologue mercury. In this work we systematically studied the stability of some oxides, fluorides, and oxyfluorides of Cn by two-component relativistic calculations and found that the CnF6 molecule with an oxidation state of VI+ has an extraordinary stability. CnF6 may decompose into CnF4 by conquering an energy barrier of about 34 kcal mol-1 without markedly releasing heat. Our results indicate that CnF6 may exist under some special conditions.

Electronic Structures and Properties of Bimetallic Plutonium Group 13 Carbonyl Compounds [XPuCO] (X = B, Al, and Ga).

Bonding features of heterobimetallic complexes containing f-block elements are fundamental content in actinide chemistry. In order to account for the structural periodicity of the X-Pu carbonyls and the formation of chemical bonds between bimetallic plutonium and group 13 carbonyl compounds, we report a comprehensively quantum-chemical study of the electronic structure and properties of XPuCO (X = B, Al, and Ga). With increasing atomic radii of the group 13 elements, the XPuCO structure alternates from cyclic [PuCBO] to linear [AlCPuO] and [GaCPuO]. The bonding analysis indicates that the donor-acceptor model is the best description for bonding interactions of metal and ligands with different donation patterns of CBO → Pu and XC → PuO (X = Al and Ga). The apparent XC ← PuO backdonation increases the C-Pu bond strength markedly and stabilizes the linear geometry of [AlCPuO] and [GaCPuO], while spin-orbit coupling is found to be significant in the stabilization of [PuCBO]. The ground electron configurations and natural orbital analysis indicate that cyclic [PuCBO] and linear [XCPuO] (X = Al and Ga) are considered as complexes of Pu(III) and Pu(V), respectively. The trend presents a valuable insight for the 5f/6d-np bonding interactions, especially for the fundamental understanding of transuranic elements.

Unprecedented neptunyl(V) cation-directed structural variations in Np2Ox compounds.

Studies on transuranic oxides provide a particularly valuable insight into chemical bonding in actinide compounds, in which subtle differences between metal ions and oxygen atoms are of fundamental importance for the stability of these compounds as well as their existence. In the case of neptunium, it is still mainly limited to specific Np oxide compounds without periodicity in the formation of stable structures or different oxidation states. Here, we report a systematic global minimum search of Np2Ox (x = 1-7) clusters and the computational study of their electronic structures and chemical bonding. These studies suggest that Np(V) ion could play the structure-directing role, and thus the mixed-valent Np(III/V) in Np2O4 is predicted accessible. In comparison with lower oxidation state Np analogues, significant 5f-orbital covalent interactions with Np(V)O bonding are observed, which shows that these model neptunium oxides can provide new understandings into the behavior of 5f-electrons in chemical bonding and structural design.

Intrinsic Semiconducting Behavior in a Large Mixed-Valent Uranium(V/VI) Cluster.

We disclose the intrinsic semiconducting properties of one of the largest mixed-valent uranium clusters, [H3 O+ ][UV (UVI O2 )8 (µ3 -O)6 (PhCOO)2 (Py(CH2 O)2 )4 (DMF)4 ] (Ph=phenyl, Py=pyridyl, DMF=N,N-dimethylformamide) (1). Single-crystal X-ray crystallography demonstrates that UV center is stabilized within a tetraoxo core surrounded by eight uranyl(VI) pentagonal bipyramidal centers. The oxidation states of uranium are substantiated by spectroscopic data and magnetic susceptibility measurement. Electronic spectroscopy and theory corroborate that UV species serve as electron donors and thus facilitate 1 being a n-type semiconductor. With the largest effective atomic number among all reported radiation-detection semiconductor materials, charge transport properties and photoconductivity were investigated under X-ray excitation for 1: a large on-off ratio of 500 and considerable charge mobility lifetime product of 2.3×10-4  cm2 V-1 , as well as a high detection sensitivity of 23.4 µC Gyair -1 cm-2 .

Insight into the Mechanism of the CuAAC Reaction by Capturing the Crucial Au4Cu4-π-Alkyne Intermediate.

The classic Fokin mechanism of the CuAAC reaction of terminal alkynes using a variety of Cu(I) catalysts is well-known to include alkyne deprotonation involving a bimetallic σ,π-alkynyl intermediate. In this study, we have designed a CNT-supported atomically precise nanocluster Au4Cu4 (noted Au4Cu4/CNT) that heterogeneously catalyzes the CuAAC reaction of terminal alkynes without alkyne deprotonation to a σ,π-alkynyl intermediate. Therefore, three nanocluster-π-alkyne intermediates [Au4Cu4(π-CH≡C-p-C6H4R)], R = H, Cl, and CH3, have been captured and characterized by MALDI-MS. This Au4Cu4/CNT system efficiently catalyzed the CuAAC reaction of terminal alkynes, and internal alkynes also undergo this reaction. DFT results further confirmed that HC≡CPh was activated by π-complexation with Au4Cu4, unlike the classic dehydrogenation mechanism involving the bimetallic σ,π-alkynyl intermediate. On the other hand, a Cu11/CNT catalyst was shown to catalyze the reaction of terminal alkynes following the classic deprotonation mechanism, and both Au11/CNT and Cu11/CNT catalysts were inactive for the AAC reaction of internal alkynes under the same conditions, which shows the specificity of Au4Cu4 involving synergy between Cu and Au in this precise nanocluster. This will offer important guidance for subsequent catalyst design.

Decisive Role of 5f-Orbital Covalence in the Structure and Stability of Pentavalent Transuranic Oxo [M6O8] Clusters.

Actinide metal oxo clusters are of vital importance in actinide chemistry, as well as in environmental and materials sciences. They are ubiquitous in both aqueous and nonaqueous phases and play key roles in nuclear materials (e.g., nuclear fuel) and nuclear waste management. Despite their importance, our structural understanding of the actinide metal oxo clusters, particularly the transuranic ones, is very limited because of experimental challenges such as high radioactivity. Herein we report a systematic theoretical study on the structures and stabilities of seven actinide metal oxo-hydroxo clusters [AnIV6O4(OH)4L12] (1-An; An = Th-Cm; L = O2CH-) along with their group 4 (Ti, Zr, Hf, Rf) and lanthanide (Ce) counterparts [MIV6O4(OH)4L12] (1-M). The work shows the Td-symmetric structures of all of the 1-An/M clusters and suggests the positions of the -OH functional groups, which are experimentally challenging to determine. Furthermore, by removing six electrons from 1-An, we found that oxidation could happen on the AnIV metal ions, producing [AnV6O4(OH)4L12]6+ (2-An; An = Pa, U, Np), or on the O2- and OH- ligands, producing [AnIV6(O•-)4(OH•)2(OH)2L12]6+ (3-An; An = Pu, Am, Cm). On the basis of 2-An, we constructed a series of tetravalent and pentavalent actinide metal oxo clusters [AnIV6O14]4- (4-An) and [AnV6O14]2+ (5-An), which proves the feasibility of the highly important pentavalent actinyl clusters, demonstrates the f orbital's structure-directing role in the formation of linear [O≡AnV═O]+ actinyl ions, and expands the concept of actinyl-actinyl interaction into pentavalent transuranic actinyl clusters.

The decisive role of 4f-covalency in the structural direction and oxidation state of XPrO compounds (X: group 13 to 17 elements).

Lanthanide oxo compounds are of vital importance in lanthanide chemistry, as well as in environmental and materials sciences. Praseodymium, as an exceptional element in lanthanides which can form a +V formal oxidation state (OSf) besides the dominant +III among the 4f-block element, displays the significant participation of the Pr 4f orbitals in bonding interactions which is commonly crucial in stabilizing the high oxidation state of Pr in PrO2+ and NPrO species. Here, we report a systematic theoretical study on the structures and stabilities of a series of XPrO (X: B, Al, C, Si, N, P, As, O, S, F, Cl) compounds along with [XPrO]+ cation (X: O, S) and [X3PrO] complexes (X: F and Cl). This work reveals that Pr is able to achieve the lowest and highest OSf and the OSf exhibits periodic variation from +I in BOPr and AlOPr to +II in SiOPr to +III in CPrO, FPrO, ClPrO and AsPrO to +IV in OPrO and SPrO and even to +V in NPrO, [OPrO]+, [SPrO]+, F3PrO and Cl3PrO. We found that the molecular structures are correlated to the Pr oxidation state due to the highly important 4f orbital in the chemical bonding of the high oxidation state compounds. Thus, not only the electronegativity of the ligand but also the quasi-degenerate Pr valence 4f orbitals, namely energetic covalency, control the oxidation state and play a fundamental role in affecting the electronic structural stability of Pr(v) compounds as well. This work demonstrates the structurally directing role of the f-orbital in the formation of the linear structure and is constructive for achieving the higher oxidation state of a given element by tuning the ligand.

Evaluation of Chemical Bonding in Actinyl(VI/V) Oxo-Crown-Ether Complexes for Actinide Series from Uranium to Curium.

The separation and management of nuclear waste is one of the problems that needs to be solved urgently, so finding a new radiation-proof and durable extractant to deal with nuclear waste is a difficult but desirable task. Since the successful isolation of the first pentavalent plutonium crown ether complex recently (Wang et al. CCS Chem. 2020, 2, 425-431), complexes with actinyl(V/VI) inserted into the cavity of 18-crown-6 ether (oxo-18C6), as well as their bonding character, need to be explored. Here we present a series of novel crown ether complexes containing actinyl(V/VI) and oxo-18C6 via computational prediction and analysis. On the basis of the calculations, actinyl(V/VI) are thermodynamically feasible and can be stabilized by oxo-18C6 ligand via six dative bonds between An ions and the oxo-18C6 O atoms in the "insertion" structure of [AnO2(18C6)]2+/+ complexes. The stability of actinyl(VI) species generally falls at minor actinides, ascribed to the reduced highest possible oxidation states of curium, which is mainly attributed to the mixing of bonding orbitals and non-bonding orbitals as well as the increase of occupation on partially 5f antibonding orbitals. It is found that the interactions between the actinyl(V/VI) and oxo-18C6 are mainly electronic interactions, with the well-known covalency contributions generally decreasing from uranium to curium due to energy degeneracy and spatial orbital contraction. This work would give a basic understanding of the coordination chemistry of actinyl(V/VI), which also provides inspirations on the design of new extractants for actinide separations.

Solar-Driven Nitrogen Fixation Catalyzed by Stable Radical-Containing MOFs: Improved Efficiency Induced by a Structural Transformation.

Herein we present a new viologen-based radical-containing metal-organic framework (RMOF) Gd-IHEP-7, which upon heating in air undergoes a single-crystal-to-single-crystal transformation to generate Gd-IHEP-8. Both RMOFs exhibit excellent air and water stability as a result of favorable radical-radical interactions, and their long-lifetime radicals result in wide spectral absorption in the range 200-2500 nm. Gd-IHEP-7 and Gd-IHEP-8 show excellent activity toward solar-driven nitrogen fixation, with ammonia production rates of 128 and 220 µmol h-1 g-1 , respectively. Experiments and theoretical calculations indicate that both RMOFs have similar nitrogen fixation pathways. The enhanced catalytic efficiency of Gd-IHEP-8 versus Gd-IHEP-7 is attributed to intermediates stabilized by enhanced hydrogen bonding.

Relativistic Effects Stabilize the Planar Wheel-like Structure of Actinide-Doped Gold Clusters: An@Au7 (An = Th to Cm).

Despite the chemistry of actinide-ligand bonding is continuing and of burgeoning interest, investigations of the chemical bonding of bimetallic complexes involving transuranics remain relatively less, and there are rarely studies on the bonding features between actinide and coinage metals (CM). We present a systematic research on the series of An@Au7 (An = Th to Cm), UCM7 (CM = Cu, Ag, Au), and WAu7 clusters to investigate the unique geometries, electronic structures, and chemical bonding between An 5f6d orbitals and CM ns orbitals, and to find their periodicity across the actinides and within the group of transition metals. A unique planar wheel-like structure for An@Au7 clusters with the help of actinide metals encapsulation via spin-orbit coupling, resulting in An(III). Instead, the transition-metal (TM) element W retains its usual six-gold-coordination structure in WAu7, thus forcing the seventh Au out of plane. The An-CM interactions, depending on the ion radii, become stronger with the increase of the atomic number of the actinide metals, as well as the CM. These results show that the presence of actinides in clusters can lead to unique electronic and geometrical structures.

New theoretical insights into high-coordination-number complexes in actinides-centered borane.

The coordination number of a given element affects its behavior, and consequently, there is great interest in understanding the related chemistry, which could greatly promote the extension and development of new materials, but remains challenging. Herein, we report a new record high coordination number (CN) for actinides established in the cage-like An(BH)24 (An = Th to Cm) via using relativistic quantum chemistry methods. Analysis of U(BH)n (n = 1 to 24) confirmed these series of systems as being geometric minima, with the BH acting as a ligand located in the first shell around the uranium. In contrast, global searches revealed a low CN half-cage structure for UB24, which could be extended to the series of AnB24 materials and which prevails over the competing structural isomers, such as cages. The intrinsic geometric difference for AnB24 and An(BH)24 mainly arise from the B sp3 hybridization in borane inducing strong interactions between An 5f6d7s hybrid orbitals and B 2pz orbitals in An(BH)24 compared to that of AnB24. This fundamental trend presents a valuable insight for future experimental endeavors searching for isolable complexes with high-coordination actinide and provides details of a new structural motif of boron clusters and nanostructures.