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We report the synthesis, single-crystal structure, solid-state ultraviolet-visible-near-infrared spectroscopy, and theoretical calculations on the first trivalent plutonium crown ether inclusion complex, [(H3O)(18-crown-6)][Pu(H2O)4(18-crown-6)](ClO4)4·2(H2O) (denoted as PuIII-18C6). Single-crystal X-ray diffraction reveals that PuIII-18C6 crystallizes in the orthorhombic space group of Pccn, which is assembled by independent ionic pairs including [Pu(H2O)4(18-crown-6)]3+, [(H3O)(18-crown-6)]+, and perchlorate anions. The plutonium atom is fully encapsulated within the cavity of the 18-crown-6, generating a distorted bicapped square antiprism geometry. The theoretical evaluation confirms that weak Pu-O dative bond is involved between PuIII ions with 18-crown-6. This work may deepen the understanding of the host-guest interactions between trivalent transuranic and macrocyclic ligands.

Electrocatalytic hydrogen production in alkaline media is extensively adopted in industry. Unfortunately, further performance improvement is severely impeded by the retarded kinetics, which requires the fine regulation of water dissociation, hydrogen recombination, and hydroxyl desorption. Herein, we develop a multi-interface engineering strategy to make an elaborate balance for the alkaline hydrogen evolution reaction (HER) kinetics. The graphene cross-linked three-phase nickel sulfide (NiS-NiS2-Ni3S4) polymorph foam (G-NNNF) was constructed through hydrothermal sulfidation of graphene wrapped nickel foam as a three-dimensional (3D) scaffold template. The G-NNNF exhibits superior catalytic activity toward HER in alkaline electrolyte, which only requires an overpotential of 68 mV to drive 10 mA·cm−2 and is better than most of the recently reported metal sulfides catalysts. Density functional theory (DFT) calculations verify the interfaces between nickel sulfides (NiS/NiS2/Ni3S4) and cross-linked graphene can endow the electrocatalyst with preferable hydrogen adsorption as well as metallic nature. In addition, the electron transfer from Ni3S4/NiS2 to NiS results in the electron accumulation on NiS and the hole accumulation on Ni3S4/NiS2, respectively. The electron accumulation on NiS favors the optimization of the H* adsorption, whereas the hole accumulation on Ni3S4 is beneficial for the adsorption of H2O. The work about multi-interface collaboration pushes forward the frontier of excellent polymorph catalysts design.

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.

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.

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.

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.

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.

Crystalline coordination complexes of actinides, especially in atypical oxidation states, are not only fundamentally important for expanding the notably limited knowledge on the bonding nature of a...

Despite continuing and burgeoning interest in americium (Am) coordination chemistry in recent years, investigations of the electronic structures and bonding chemistry of high oxidation state americium complexes and their implications for minor actinide separation remain relatively less explored to date. Here, we used density functional theory (DFT) to create high oxidation states of americium but experimentally feasible models of Am(V) and Am(VI) complexes of phenanthroline ligand (DAPhen) as [AmO

Designing and constructing bifunctional electrocatalysts with high efficiency, high stability and low cost for overall water splitting to produce clean hydrogen fuel is attractive but highly challenging. Here we constructed puffed quaternary FexCoyNi1-x-yP nanoarrays as bifunctional electrodes for robust overall water splitting. The iron was used as the modulator to manipulate the electron density of NiCoP nanoarray, which could increase the positive charges of metal (Ni and Co) and P sites. The resultant electronic structure of FexCoyNi1-x-yP was supposed to balance the adsorption and desorption of H and accelerate the oxygen evolution reaction (OER) kinetics. Moreover, the morphological structure of FexCoyNi1-x-yP was modulated through the kinetically controlled alkaline etching by using the amphoteric features of initial FeCoNi hydroxide nanowires. The resultant puffed structure has rich porosity, cavity and defects, which benefit the exposure of more active sites and the transport of mass/ charge. As a result, the cell integrated with the puffed quaternary FexCoyNi1-x-yP nanoarrays as both the cathode and anode only requires the overpotentials of 25 and 230 mV for hydrogen evolution reaction (HER) and OER at the current density of 10 mA cm-2 in alkaline media and a cell voltage of 1.48 V to drive the overall water splitting. Moreover, the puffed FexCoyNi1-x-yP demonstrates remarkable durability for continuous electrolysis even at a large current density of 240 mA cm-2.

Inspired by natural lives, materials with switchable mechanical properties have been constructed by virtue of the development of dynamic chemistry. However, the limited dynamic reactions are hampering their further development. The progress in organotellurium chemistry brings opportunity to open new frontiers of dynamic reactions for fabrication of mechanically responsive materials. Herein, a bioinspired mechanically responsive hydrogel upon redox mediated by dynamic coordination between telluroether and platinum ions is reported. The low electronegativity and superior σ electron-donating capability of telluroether facilitate its coordination with Pt ions. Remarkably, the coordination interaction is highly redox-active. Telluroether can dissociate from Pt ions upon oxidation (e.g., H2O2) because the effect of the polar solvent dramatically reduces the thermodynamic activity of oxidized telluroether. In turn, the coordination interaction is easily regenerated via reduction (e.g., vitamin C) of oxidized tel...

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.

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.

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.

Uranium(III) compounds are very reactive and exhibit a broad range of chemical-bonding tendencies owing to the spatially diffused valence orbitals of uranium. A systematic study on the geometries, electronic structures, and chemical bonding of NU-XO (X = C, N, O) is performed using relativistic quantum chemistry approaches. The NU-CO and NU-NO complexes have an end-on structure, that is, (NU) (η

As a group 12 element, mercury locating at the sixth row with a valent electronic configuration of 5 d 10 6 s 2 has been treated as a main group element featuring +I and +II oxidation states for a long time. C. K. Jorgensen conjectured the existences of HgF4 and HgF6 molecules in early 1960s, where HgF4 was first synthesized in 2007, but HgF6 as the Hg(+VI) compound was less known. In this paper we explored the electronic structure and decomposition paths of HgF6 by scalar (X1C) and 2-component relativistic (X2C) density functional calculations and more accurate multi-reference NEVPT2 calculations. It is found that the HgF6 molecule, where the mercury atom presents an extraordinary high oxidation state of +VI, is protected by a considerable barrier height of about 22 kcal/mol for the decomposition into HgF4 and two isolated fluorine atoms. The results propose that HgF6 is kinetically stable and may exist under exorbitant conditions.

Oxidation state is a key chemical quantity that allows the understanding and prediction of the majority of chemical reactions; however, the main deficiency using the formal oxidation state comes from the materials containing multivalent metals. Among them, the most complicated element plutonium (Pu) is an outstanding instance. Here, we calculate the orbital occupation numbers under the frameworks of first-principles density functional theory (DFT) + U methods to quantitatively determine the Pu-oxidation state of the recently reported complex molecular solids: [K(crypt)]Pu[C5H3(SiMe3)2]3, Pu3(DPA)5(H2O)2, and Pu3(DPA)6H. The results show that the oxidation state of Pu is an extremely low Pu2+ in the former and a mixed Pu3+/Pu4+ in the latter two compounds, which is consistent with the experimental identifications. The steric effects and the environmentally sensitive localization → delocalization transition of Pu 5f electrons can rationally elucidate the formation of the unusual oxidation states. Such atomi...

It is known that few Co-based superconducting compounds have been found compared with their Fe- or Ni-based counterparts. In this study, we have found superconductivity of 4 K in the LaCoSi compound for the first time. The combined analysis of neutron and synchrotron X-ray powder diffractions reveals that LaCoSi exhibits an isostructure with the known Fe-based LiFeAs superconductor, which is the first "111" Co-based superconductor. First-principles calculation shows that LaCoSi presents a quasi-two-dimensional band structure that is also similar to that of LiFeAs. The small structural distortion may be more conducive to the emergence of superconductivity in the LaCoSi compound, which provides a direction for finding new Co-based superconducting compounds.

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 .

Defects in metal oxides can significantly improve their physical and chemical properties. However, the conventional methods to generate defects often require complex procedures and harsh conditions. In this study, we design a simple and room-temperature preparation route to prepare defective metal oxide nanoparticles with high yield. The formation of defects is attributed to the generation of oxygen vacancies (VO) and hydrogenation caused by charge transfer at a Mg-metal oxide junction structure. Defective TiO2 exhibits excellent performance toward wastewater cleaning and water splitting. The proposed route is promising in terms of convenience, low cost, and large-scale production.

Systematic americyl-hydration cations were investigated theoretically to understand the electronic structures and bonding in [(AmO2)(H2O)n]2+/1+ (n = 1–6). We obtained the binding energy using density functional theory methods with scalar relativistic and spin–orbit coupling effects. The geometric structures of these species have been investigated in aqueous solution via an implicit solvation model. Computational results reveal that the complexes of five equatorial water molecules coordinated to americyl ions are the most stable due to the enhanced ionic interactions between the AmO22+/1+ cation and multiple oxygen atoms as electron donors. As expected, Am–Owater bonds in such series are electrostatic in nature and contain a generally decreasing covalent character when hydration number increases.

The structural and electronic properties of Pu2On (n = 1–8) molecules have been systematically studied within the screened hybrid density functional theory. On the basis of the calculations, pluton...

Water dissociation, hydroxyl desorption, and hydrogen recombination are three major prerequisites for all-pH hydrogen evolution reaction (HER). Herein, a multi-interfacial engineering in hierarchical CoNi2S4/WS2/Co9S8 (NiCoWS) hybrid frameworks was developed. The NiCoWS is composed of highly exposed active sites and abundant heterogeneous interfaces. The NiCoWS exhibits small overpotentials of 70 mV, 61 mV, and 146 mV at 10 mA cm−2 in alkaline, acid, and neutral medium, respectively, for HER. The robust performance of NiCoWS should originate from the collective synergy of special morphological, electronic, and interfacial structures. The hierarchical nanosheet framework can facilitate the transport of charge/mass as well as the exposure of more active interface sites. Density functional theory (DFT) calculations verify that the multi-interfacial engineering in NiCoWS can endow the electrocatalyst with enhanced electrical conductivity and favorable adsorption energies of H*, H2O* and H…OH*.

The following gas-phase uranyl/12-crown-4 (12C4) complexes were synthesized by electrospray ionization: [UO2(12C4)2]2+ and [UO2(12C4)2(OH)]+. Collision-induced dissociation (CID) of the dication resulted in [UO2(12C4-H)]+ (12C4-H is a 12C4 that has lost one H), which spontaneously adds water to yield [UO2(12C4-H)(H2O)]+. The latter has the same composition as complex [UO2(12C4)(OH)]+ produced by CID of [UO2(12C4)2(OH)]+ but exhibits different reactivity with water. The postulated structures as isomeric [UO2(12C4-H)(H2O)]+ and [UO2(12C4)(OH)]+ were confirmed by comparison of infrared multiphoton dissociation (IRMPD) spectra with computed spectra. The structure of [UO2(12C4-H)]+ corresponds to cleavage of a C–O bond in the 12C4 ring, with formation of a discrete U–Oeq bond and equatorial coordination by three intact ether moieties. Comparison of IRMPD and computed IR spectra furthermore enabled assignment of the structures of the other complexes. Theoretical studies of the chemical bonding features of the complexes provide an understanding of their stabilities and reactivities. The results reveal bonding and structures of the uranyl/12C4 complexes and demonstrate the synthesis and identification of two different isomers of gas-phase uranyl coordination complexes.

Bismuth oxyhalides (BiOX, X = Cl, Br, and I) are a new family of promising photocatalysts. BiOCl and BiOBr possess large band gaps and weak absorption in visible light regions, which limit their applications. Although the band gap of BiOI is suitable to absorb most of the visible light, its redox capability is very weak. In this work, the doping and strain effects on the electronic structures and optical properties of BiOCl are explored using first principle calculations. The results show that doping in BiOCl, especially co-doping of Sb and I atoms, can obviously decrease the band gaps along with enhancing the optical absorption coefficients of pristine BiOCl because of the electronegativity difference between Sb/I atoms and Bi/Cl atoms. Meanwhile the band gap of BiOCl can be tuned under strain. This work offers potential strategies to enhance BiOCl absorption coefficients in the visible light region and its photocatalyst activity.

© The Royal Society of Chemistry 2016. Understanding of the nature and extent of chemical bonding in uranyl coordination complexes is crucial for the design of new ligands for nuclear waste separation, uranium extraction from seawater, and other applications. We report here the synthesis, infrared spectroscopic characterization, and quantum chemical studies of a molecular uranyl-di-15-crown-5 complex. The structure and bonding of this unique complex featuring a distinctive 6-fold coplanar coordination staggered sandwich structure and an unusual non-perpendicular orientation of the uranyl moiety are evaluated using density functional theory and chemical bonding analyses. The results provide fundamental understanding of the coordination interaction of uranyl with oxygen-donor ligands.

The chemistry of lanthanides (Ln=La-Lu) is dominated by the low-valent +3 or +2 oxidation state because of the chemical inertness of the valence 4f electrons. The highest known oxidation state of the whole lanthanide series is +4 for Ce, Pr, Nd, Tb, and Dy. We report the formation of the lanthanide oxide species PrO4 and PrO2 (+) complexes in the gas phase and in a solid noble-gas matrix. Combined infrared spectroscopic and advanced quantum chemistry studies show that these species have the unprecedented Pr(V) oxidation state, thus demonstrating that the pentavalent state is viable for lanthanide elements in a suitable coordination environment.

Relativistic quantum chemistry investigations are carried out to tackle the puzzling oxidation state problem in a series of MO 3 - trioxide anions of all d-and f-block elements with five valence electrons. We have shown here that while the oxidation states of V, Nb, Ta, Db, Pa are, as usual, all +V with divalent oxygen O(-Ⅱ) in MO 3 - anions, the lanthanide elements Pr and Gd cannot adopt such high +V oxidation state in similar trioxide anions. Instead, lanthanide element Gd retains its usual +Ⅲ oxidation state, while Pr retains a +IV oxidation state, thus forcing oxygen into a non-innocent ligand with an uncommon monovalent radical (O · ) of oxidation state -Ⅰ. A unique Pr · - · (O) 3 biradical with highly delocalized unpairing electron density on Pr(IV) and three O atoms is found to be responsible for stabilizing the monovalent-oxygen species in PrO 3 - ion, while GdO 3 - ion is in fact an OGd + (O 2 2- ) complex with Gd(Ⅲ). These results show that a naive assignment of oxidation state of a chemical element without electronic structure analysis can lead to erroneous conclusions.

Despite growing interest in actinide (An) complexes and their bonding chemistry in recent years, the characteristics of the chemical bonding of actinides in solid-state compounds remain to be relatively unclear compared with those of molecular complexes. Herein, we systematically characterized the structural and electronic properties of trisodium actinates [Na3AnO4 (An = Th to Cm)] using first-principles theoretical methods. In general, the band structures exhibit a transition from charge-transfer insulator with the p-d band gap type to Mott-insulator with the f-f band gap type at Na3PuO4. The conjugation effects of actinide contraction and the decreased energy of the 5f bands in these compounds are responsible for the transition. Consistently, the pentavalent An ions can be achieved from Pa to Pu, and then upon the reduction of the 5f atomic orbitals, strong spin polarization leads to tetravalent Am(f5)IV and Cm(f6)IV. These results improve our knowledge of the OS of actinides in solid-state compounds and establish the connection among local structure, chemical composition, and properties for understanding the underlying mechanism of An chemical state in actinide materials for specific applications.

The nature and extent of the highest oxidation state (HOS) in solid-state actinide compounds are still unexplored compared with those of small molecules, and there is burgeoning interest in studying the actinide–ligand bonding nature in the condensed state. A comprehensive understanding of the electronic structure and unraveling the possibility of a HOS are of paramount importance in solid-state actinide chemistry. Here, we report the physical OS of the early to middle actinides (Th → Cm) in solid-state compounds via a more rigorous quantum mechanical definition of OS under the DFT+U theoretical frameworks for the first time. This work implies that the highest physical OS of the Pu solid ion is PuV in PuO2F and PuOF4, which can be achieved via tuning the ligand, thus improving our knowledge of oxidation states and chemical bonding in high OS solid-state compounds. We highlight the importance of ligand design in terms of the actinide HOS, employing a highly electronegative ligand and showing the capacity to form multiple bonds.

Recently an all-metal aromatic sandwich compound of a [Sb3Au3Sb3](3-) ion has been synthesized and characterized experimentally, which indicates that there might exist a variety of stable all-metal sandwich complexes. The intralayer and interlayer chemical bonding interaction in this system plays significant roles in their stability, chemical properties and functionalities. Here we report a systematic theoretical study on the geometries, electronic structures, and chemical bonding of the [Sb3Au3Sb3](3-) ion and its congeners of [X3Au3X3](3-) (X = N, P, As, Sb, Bi, Uup) as well as [X3M3X3](3-) (M, X = Cu, As; Ag, Bi; Au, Sb; Rg, Uup) to understand the special stabilities of these species. Additional studies are also performed on the oligomers [Sb3(Au3Sb3)n](3-) (n = 1-4) to explore whether the sandwich compound can form stable extended systems. Through extensive theoretical analyses, we have shown that among the [Au3X6](3-) (X = N, P, As, Sb, Bi, Uup) species, [Sb3Au3Sb3](3-) is most stable due to superb matching of Sb3 and Au3 in both geometric size and fragment orbital energies. The significant stability of the [Au3Sb6](3-) ion is determined by the interlayer (p-d-p)σ interactions between the vertical Au 5d6s hybrid orbitals of Au3 and Sb 5pπ orbitals of the Sb3 rings. Each Sb3 ring demonstrates unique σ aromaticity, which remains when the complex is extended to oligomers. The results suggest that it is likely that there might exist other stable [ApMpAp](x-) (M = transition metals, A = main group elements, p = 3, 4, 5, …) sandwich ions and oligomers.

The concept of oxidation state (OS) is based on the concept of Lewis electron pairs, in which the bonding electrons are assigned to the more electronegative element. This approach is useful for keeping track of the electrons, predicting chemical trends, and guiding syntheses. Experimental and quantum-chemical results reveal a limit near +8 for the highest OS in stable neutral chemical substances under ambient conditions. OS=+9 was observed for the isolated [IrO4 ]+ cation in vacuum. The prediction of OS=+10 for isolated [PtO4 ]2+ cations is confirmed computationally for low temperatures only, but hasn't yet been experimentally verified. For high OS species, oxidation of the ligands, for example, of O-2 with formation of . O-1 and O-O bonds, and partial reduction of the metal center may be favorable, possibly leading to non-Lewis type structures.

The chemistry of lanthanides (Ln=La-Lu) is dominated by the low-valent +3 or +2 oxidation state because of the chemical inertness of the valence 4f electrons. The highest known oxidation state of the whole lanthanide series is +4 for Ce, Pr, Nd, Tb, and Dy. We report the formation of the lanthanide oxide species PrO4 and PrO2 (+) complexes in the gas phase and in a solid noble-gas matrix. Combined infrared spectroscopic and advanced quantum chemistry studies show that these species have the unprecedented Pr(V) oxidation state, thus demonstrating that the pentavalent state is viable for lanthanide elements in a suitable coordination environment.

Calculations using density functional theory were performed to explore the mechanisms for atmospheric degradation of isopropyl methyl methylphosphonate (IMMP). The potential energy surface profiles for OH-initiated reaction of IMMP were constructed, and all possible degradation channels were considered. Rate constants were further calculated using transition state theory. It was established from these calculations that H-abstractions from alkyl groups have much lower energy barriers than substitutions of alkoxyl groups, and four possible H-abstraction channels are competitive. Investigations into the secondary reactions under the presence of O2/NO were also performed. It is shown that O2 addition, reaction of peroxide radicals with NO to form RO radicals, and removal of ·RO are the major degradation pathways for alkyl radicals. Four selected products, CH3OP(O)(CH3)OC(O)CH3, CH3OP(O)(O)CH3, (CH3)2CHOP(O)(CH3)OH, and (CH3)2CHOP(O)(CH3)OCHO, are predicted to be the major products in this study. © 2013 Wiley Periodicals, Inc.

Xylenes are important constituents of many liquid fuels, as well as precursors of secondary organic aerosols (SOAs). To examine the mechanisms for formation of SOAs in the atmosphere, the abstraction reaction of p-xylene with OH and the secondary degradation channels of its intermediates were first and extensively investigated with density functional theory at the B3LYP/6-31+G (d, p) level. The result indicates that H-abstraction from methyl groups is a barrier-less path while that from phenyl groups require a free energy barrier of approximately 2.8 kcal mol−1. Upon formation of p-xylyl, further addition by O2 readily occurs to form peroxy radical. Subsequently, possible degradation channels for the formation of main products (p-tolualdehyde and p-quinone methide) have been determined in presence of NO. The free energy profile constructed shows that the entire reaction process is exothermic. In addition, the dipole moment of p-tolualdehyde is higher than that of p-xylene, consistent with their relative hygroscopic values. This indicates that the degradation products of p-xylene can readily immerse into the SOA phase, while p-xylene may be subject to further atmospheric degradation to form non-volatile compounds.

Sesquiterpenes, one of the most important classes of biogenic volatile organic compounds, are potentially significant precursors to secondary organic aerosols (SOAs) in nature. The electronic structure of sesquiterpenes and their reactivity in the ozonolysis reaction were investigated by density functional theory. Results from the CIS calculations combined with an analysis of transition intensities show that the first peaks in the ultraviolet (UV) spectra for saturated and unsaturated isomers are σ–σ* and π–π* transitions, respectively. The UV absorption wavelength and absorbency are dictated by the electronic structures of these compounds. An increase in the number of double bonds and formation of a conjugated system expand the range of absorption in the UV region. An isomer with an endocyclic C = C bond presents weaker UV transition intensity than its corresponding exocyclic isomer. Results from conceptual DFT chemical reactivity indices of isomers suggest that no quantitative linear relationships between the structural changes and their reactivity, such as different degrees of unsaturated C = C double bonds, or the number of substituents attached to the C = C bond were discovered. In the ozonolysis reaction of sesquiterpenes, isomers with larger steric hindrance of substituents or endocyclic C = C bond possess higher chemical reactivity compared to isomers with smaller steric hindrandce or with an exocyclic C = C bond. These results are imperative to a better understanding of SOAs production mechanisms in the troposphere.

By use of density functional theory, a systemic theoretical study was conducted on the structural and electronic properties of ground-state silicon monoxide clusters ((SiO)(n), where n = 1-26). In our calculations, the most energetically favorable geometry for each cluster size was found to undergo a structural change from one dimension (linear) to three dimensions at cluster size n = 4, with the buckled structure as the favorable one. The sp(3) silicon containing structures are favorable for n = 5-13, and the Si-cored structures are energetically favorable at n = 14 and larger. Furthermore, for the lowest-energy structures obtained, the energy gaps between the highest occupied and lowest unoccupied molecular orbital, binding energies, ionization potentials, and electron affinities were calculated and analyzed to understand the evolutions in geometries and to identify any particularly stable species.