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Multi negative differential resistance (NDR) with large peak to valley ratio (PVR) and rectifying actions were observed for a CNT|C–(B–C)2–C|CNT molecular device.

International audience; Reaction of [(XA2)U(CH2SiMe3)2] (1; XA2 = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9- dimethylxanthene) with 1 equivalent of [Ph3C][B(C6F5)4] in arene solvents afforded the arene-coordinated uranium alkyl cations, [(XA2)U(CH2SiMe3)(hn-arene)][B(C6F5)4] {arene = benzene (2), toluene (3), bromobenzene (4) and fluorobenzene (5)}. Compounds 2, 3, and 5 were crystallographically characterized, and in all cases the arene is π-coordinated. Solution NMR studies of 2-5 suggest that the binding preferences of the [(XA2)U(CH2SiMe3)]+ cation follow the order: toluene ≈ benzene > bromobenzene > fluorobenzene. Compounds 2-4 generated in C6H5R (R = H, Me or Br, respectively) showed no polymerization activity under 1 atm of ethylene. By contrast, 5 and 5-Th (the thorium analogue of 5) in fluorobenzene at 20 and 70 °C achieved ethylene polymerization activities between 16 800 and 139 200 g mol-1 h-1 atm-1, highlighting the extent to which common arene solvents such as toluene can suppress ethylene polymerization activity in sterically open f-element complexes. However, activation of [(XA2) An(CH2SiMe3)2] {M = U (1) or Th (1-Th)} with [Ph3C][B(C6F5)4] in n-alkane solvents did not afford an active polymerization catalyst due to catalyst decomposition, illustrating the critical role of PhX (X = H, Me, Br or F) coordination for alkyl cation stabilization. Gas phase DFT calculations, including fragment interaction calculations with energy decomposition and ETS-NOCV analysis, were carried out on the cationic portion of 2'-Th, 2', 3' and 5' (analogues of 2-Th, 2, 3 and 5 with hydrogen atoms in place of ligand backbone methyl and tert-butyl groups), providing insight into the nature of actinide–arene bonding, which decreases in strength in the order 2'-Th > 2' ≈ 3' > 5'.

The 1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) aqueous complexes of AcIII with H2O, dimethyl sulfoxide (DMSO), OH-, and F- as axial ligands were studied using density functional theory. Formation of the [AcIII(DOTA)(OH)]2- and [AcIII(DOTA)(F)]2- complexes is predicted to be significantly more favorable than that of [AcIII(DOTA)(H2O)]- and [AcIII(DOTA)(DMSO)]- because of the enhanced relative Gibbs free energies. Further electronic structure analyses demonstrate that the type and nature of the bond between Ac and the ligand donor atom is the main driving force that determines the thermodynamic stability of the complexes. Specifically, the [AcIII(DOTA)]- complex strongly binds to OH- and F- via covalent bonds, while the bonding to H2O and DMSO is ionic and relatively weaker.

Advancing the field of chemical separations is important for nearly every area of science and technology. Some of the most challenging separations are associated with the americium ion Am(III) for its extraction in the nuclear fuel cycle

High-valence americyl to californyl complexation with the dipyriamethyrin ligand.

225Ac-based radiopharmaceuticals have the potential to become invaluable in designated cancer therapy. However, the limited understanding of the solution chemistry and bonding properties of actinium has hindered the development of existing and emerging targeted radiotherapeutics, which also poses a significant challenge in the discovery of new agents. Herein, we report the geometric and electronic structural properties of hydrated AcIII cations in the [AcIII(H2O)n]3+ (n = 4–11) complexes in aqueous solution and gas-phase using density functional theory. We found that nine water molecules coordinated to the AcIII cation is the most stable complex due to an enhanced hydration Gibbs free energy. This complex adopts a closed-shell 18-electron configuration (1S21P61D10) of a superatom state, which indicates a non-negligible covalent character and involves H2O → AcIII σ donation interaction between s-/p-/d-type atomic orbitals of the Ac atom and 2p atomic orbitals of the O atoms. Furthermore, potentially existing 10-coordinated complexes need to overcome an energy barrier (>0.10 eV) caused by hydrogen bonding to convert to 9-coordination. These results imply the importance of superatom states in actinide chemistry generally, and specifically in AcIII solution chemistry, and highlight the conversion mechanism between different coordination numbers., The stable 9-coordinated complex adopts a closed-shell 18-electron configuration of a 1S21P61D10 jellium state, while potential 10-coordinated complexes need to overcome an energy barrier (>0.10 eV) caused by hydrogen bonding to convert to 9-coordination.

Evolutionary searches using the USPEX method (Universal Structure Predictor: Evolutionary Xtallography) combined with density functional theory (DFT) calculations were performed to obtain the global minimum structures of beryllium (Ben, n = 3–25) clusters. The thermodynamic stability, optoelectronic and photocatalytic properties as well as the nature of bonding are considered for the most stable clusters. It is found that the cluster with n = 15 is the transition point at which the configurations change from 3D hollow cages to filled cage structures (with an interior atom appearing in the structure). All the ground state structures are energetically favorable with negative binding energies, suggesting good synthetic feasibility for these structures. The calculated relative stabilities and electronic structure show that the Be4, Be10 and, Be17 clusters are the most stable structures and can be considered as superatoms. The electron configurations of Be4, Be10 and Be17 clusters with 8, 20 and 34 electrons are identified as 1S2 1P6, 1S2 1P6 1D10 2S2, 1S2 1P6 1D10 2S2 1F14, respectively. Theoretical simulations determined that all the ground state structures exhibit excellent thermal stability, where the upper-limit temperature that the structures can tolerate is 900 K. During AIMD simulation of O2 adsorption onto the Be17 cluster an interesting phenomenon was happening in which the pristine Be17 cluster becomes a new stable Be17O16 cluster. Based on ELF (electron localization function) analysis, it can be concluded that the Be–Be bonds in the small clusters are primarily of van der Waals type, while for the larger clusters, the bonds are of metallic nature. The Ben clusters show very strong absorption in the UV and visible regions with absorption coefficients larger than 105 cm−1, which suggests a wide range of potential advanced optoelectronics applications. The Be17 cluster has a suitable band alignment in the visible-light excitation region which will produce enhanced photocatalytic activities (making it a promising material for water splitting).

Density functional theory (DFT) calculations were carried out to investigate the tunable nature of band gaps of polythiophene (PTh)- and polypyrrole (PPy)-based conjugated polymers. Two series of c...

Decreases in Arctic Sea ice extent and thickness have led to more open ice conditions, encouraging both shipping traffic and oil exploration within the northern Arctic. As a result, the increased potential for accidental releases of crude oil or fuel into the Arctic environment threatens the pristine marine environment, its ecosystem, and local inhabitants. Thus, there is a need to develop a better understanding of oil behavior in a sea ice environment on a microscopic level. Computational quantum chemistry was used to simulate the effects of evaporation, dissolution, and partitioning within sea ice. Vapor pressures, solubilities, octanol-water partition coefficients, and molecular volumes were calculated using quantum chemistry and thermodynamics for pure liquid solutes (oil constituents) of interest. These calculations incorporated experimentally measured temperatures and salinities taken throughout an oil-in-ice mesocosm experiment conducted at the University of Manitoba in 2017. Their potential for interpreting the relative movements of oil constituents was assessed. Our results suggest that the relative movement of oil constituents is influenced by differences in physical properties. Lighter molecules showed a greater tendency to be controlled by brine advection processes due to their greater solubility. Molecules which are more hydrophobic were found to concentrate in areas of lower salt concentration.

Electronic transport properties of a pristine C

Evolutionary searches using the USPEX method (Universal Structure Predictor: Evolutionary Xtallography) combined with density functional theory (DFT) calculations were performed to obtain the global minimum structures of beryllium (Be

Adsorption of actinide (Ac = U, Np, Pu) complexes with environmentally relevant ligands on silicene and germanene surfaces has been investigated using density functional theory to determine the geometrical, energetic, and electronic properties. Three types of ligands for each central metal atom are considered: OH

In this work, we report the potential energy surface between superatoms (SPES) based on first-principles theory. The calculations show that superatoms have SPES crossing behavior between different electronic states similar to an atomic potential energy surface (PES). However, unlike atoms, the relative rotation between superatoms results in new dimensions for the SPES. The rotation is divided into two types, around the direction of the line between two superatoms and perpendicular to it. At the equilibrium distance, the former rotation results in maximum energy and charge changes of 0.03 eV and 10-2 e respectively. However, the latter rotation yields changes that are 17 times and 7 times those of the former. These findings help promote the understanding of intermolecular interactions, and will contribute to the bottom-up superatomic-based assembly of novel materials.

The anions pertechnetate, TcO4-, and perrhenate, ReO4-, exhibit very similar chemical and physical properties. Revealing and understanding disparities between them enhances fundamental understanding of both. Electrospray ionization generated the gas-phase proton bound dimer (TcO4-)(H+)(ReO4-). Collision induced dissociation of the dimer yielded predominantly HTcO4 and ReO4-, which according to Cooks' kinetic method indicates that the proton affinity (PA) of TcO4- is greater than that of ReO4-. Density functional theory computations agree with the experimental observation, providing PA[TcO4-] = 300.1 kcal mol-1 and PA[ReO4-] = 297.2 kcal mol-1. Attempts to rationalize these relative PAs based on elementary molecular parameters such as atomic charges indicate that the entirety of bond formation and concomitant bond disruption needs to be considered to understand the energies associated with such protonation processes. Although in both the gas and solution phases, TcO4- is a stronger base than ReO4-, it is noted that the significance of even such qualitative accordance is tempered by the very different natures of the underlying phenomena.

The 1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) aqueous complexes of Ac

Relativistic density functional theory has been employed to characterize [AnO2(L)]0/-1 complexes, where An = U, Np, Pu, and Am, and L is the recently reported hexa-aza porphyrin analogue, termed dipyriamethyrin, which contains six nitrogen donor atoms (four pyrrolic and two pyridine rings). Shorter axial (An═O) and longer equatorial (An-N) bond lengths are observed when going from AnVI to AnV. The actinide to pyrrole nitrogen bonds are shorter as compared to the bonds to the pyridine nitrogens; the former also play a dominant role in the formation of the actinyl (VI and V) complexes. Natural population analysis shows that the pyrrole nitrogen atoms in all the complexes carry higher negative charges than the pyridine nitrogens. Upon binding actinyl ions with the ligand a significant ligand-to-metal charge transfer takes place in all the actinyl (VI and V) complexes. The formation energy of the actinyl(VI,V) complexes in the gas-phase is found to decrease in the order of UO2L > PuO2L > NpO2L > AmO2L. This trend is consistent with results for the formation of complexes in dichloromethane solution. The calculated ΔG and ΔH values are negative for all the complexes. Energy decomposition analysis (EDA) indicates that the interactions between actinyl(V/VI) and ligand are mainly controlled by electrostatic components over covalent orbital interactions, and the covalent character gradually decreases from U to Am for both pentavalent and hexavalent actinyl complexes.

Diels-Alder reaction of tetraarylcyclopentadienones with benzo[b]thiophene dioxides in xylenes at reflux led to the formation of tetra aryl-substituted dibenzothiophene as well as penta aryl-substituted benzene analogues depending on the influence of aryl substituents present on cyclopentadienones. The intermediate dihydrodibenzothiophene-dioxides underwent aromatization either through de-oxygenation or extrusion of sulfur dioxide to furnish substituted dibenzothiophenes or benzenes.

The anions pertechnetate, TcO4-, and perrhenate, ReO4-, exhibit very similar chemical and physical properties. Revealing and understanding disparities between them enhances fundamental understanding of both. Electrospray ionization generated the gas-phase proton bound dimer (TcO4-)(H+)(ReO4-). Collision induced dissociation of the dimer yielded predominantly HTcO4 and ReO4-, which according to Cooks' kinetic method indicates that the proton affinity (PA) of TcO4- is greater than that of ReO4-. Density functional theory computations agree with the experimental observation, providing PA[TcO4-] = 300.1 kcal mol-1 and PA[ReO4-] = 297.2 kcal mol-1. Attempts to rationalize these relative PAs based on elementary molecular parameters such as atomic charges indicate that the entirety of bond formation and concomitant bond disruption needs to be considered to understand the energies associated with such protonation processes. Although in both the gas and solution phases, TcO4- is a stronger base than ReO4-, it is noted that the significance of even such qualitative accordance is tempered by the very different natures of the underlying phenomena.

Commonly accepted uranium oxidation states in molecular complexes are III+ to VI+. Recently, this has been extended experimentally by the synthesis of seminal U(II) complexes, Y·[U(Cp′)3] and Y·[URE] (Y = K+(2.2.2-cryptand), Cp′ = C5H4SiMe3, H3RE = (Ad,MeArOH)3mesitylene and Ad = adamantyl). Relativistic density functional theory has been applied to explore whether the uranium oxidation state (+I) is possibly accessible. Calculations show that the U(I) complex of a heterocalix[4]arene (H2L) is energetically stable. It features a 5f5-dominated electronic configuration, four δ(U–Ar)-bond orbitals and a moderate UII/UI reduction potential. Its stability and structural/bonding/energetic properties were corroborated by comparisons with theoretically designed complexes [UI(Cp′)3]2− and [UIRE]2−.

The field of organic electronics has been heavily impacted by the discovery and development of π-conjugated conducting polymers. These polymers show great potential for integration into future optical and electronic devices due to their capacity to transition between semiconducting and conducting states as well as the ability to alter mechanical properties by controlled doping, chemical modification, and stacking or creating composites with other materials. Among π-conjugated polymers, polythiophene and its derivatives has been one of the most extensively studied and is widely investigated computationally and experimentally for use in electronic devices such as light-emitting diodes, water purification devices, hydrogen storage, and biosensors. Various theoretical modeling studies of polythiophene ranging from an oligothiophene approach to infinite chain lengths (periodic boundary conditions) have been undertaken to study a variety of electronic and structural properties of these polymers. In this review,...

3,4–Dimethyl diphenyldithiophosphate of cobalt(II) with N-donor ligands [{(ArO)2PS2}2CoL2] [Ar = 3,4–(CH3)2C6H3 (1–3); L = C5H5N (1), 3,4–(CH3)2C5H3N (2) and 4–(C2H5)C5H4N (3)] have been synthesized and characterized by elemental analyses, infrared spectroscopy (IR), powder X-ray diffraction (PXRD) and single crystal X–ray analysis. Complex 1 crystallizes in the monoclinic space group P21/n whereas complexes 2 and 3 crystallize in the triclinic space group P¯1. The crystal structures of complexes 1–3 reveal mononuclear units with the Co(II) center chelated in bidentate fashion by four S atoms of the two diphenyldithiophosphate ligands. The N atoms from two donor ligands are axially coordinated, leading to distorted octahedral geometry around Co(II). The complexes have been optimized using density functional theory (DFT), structural parameters have been calculated, and the energy gaps of the frontier orbitals (HOMO–LUMO) have been predicted. Mayer bond orders have also been calculated. Structural parameters from the crystallographic and DFT studies are in good agreement with each other. To explore the biological potential, complexes were evaluated for their antibacterial activity against three bacterial strains. The bacterial growth inhibition capacity of the ligand and complexes followed the order of 3 > 2 > 1 > L1.

To understand interfacial behavior of actinides adsorbed onto mineral surfaces and unravel their structure–property relationship, the structures, electronic properties, and energetics of various ligated uranyl species adsorbed onto TiO2 surface nanoparticle clusters (SNCs) were examined using relativistic density functional theory. Rutile (110) and anatase (101) titania surfaces, experimentally known to be stable, were fully optimized. For the former, models studied include clean and water-free Ti27O64H20 (dry), partially hydrated (Ti27O64H20)(H2O)8 (sol) and proton-saturated [(Ti27O64H20)(H2O)8(H)2]2+ (sat), while defect-free and defected anatase SNCs involving more than 38 TiO2 units were considered. The aquouranyl sorption onto rutile SNCs is energetically preferred, with interaction energies of −8.54, −10.36, and −2.39 eV, respectively. Energy decomposition demonstrates that the sorption is dominated by orbital attractive interactions and modified by steric effects. Greater hydrogen-bonding involvemen...

Solvation effects influence reaction equilibria by preferentially stabilizing reactants or products (differential solvation). We propose using simple electrostatic concepts to qualitatively interpret and understand these effects, applying the Born and Kirkwood-Onsager equations. Scenarios include, for charged species, redox potentials, different total absolute charges between reactants and products, and size differences between reactants and products. In addition, for neutral species, they are differences in total dipole moment and size differences. These scenarios are illustrated with several examples from different areas of chemistry.

In this article, an implementation of the newest iteration of the Minnesota solvation model, SM12, into the Amsterdam density functional (ADF) computational package is presented. ADF makes exclusive use of Slater-type orbitals (STO), which correctly represent the true atomic orbitals for atoms, whereas SM12 and the underlying charge model 5 (CM5) have previously only been tested on Gaussian-type orbitals (GTO). This new implementation is used to prove the basis set independence of both CM5 and SM12. A detailed comparison of the SM12 and COSMO solvation models, as implemented in ADF, is also presented. We show that this new implementation of SM12 has a mean unsigned error (MUE) of 0.68 kcal/mol for 272 molecules in water solvent, 4.10 kcal/mol MUE for 112 charged ions in water, and 0.92 kcal/mol MUE for 197 solvent calculations of various molecules. SM12 outperforms COSMO for all neutral molecules and performs as well as COSMO for cationic molecules, only falling short when anionic molecules are taken into consideration, likely due to CM5's use of Hirshfeld charges and their poor description of anionic molecules, though CM5 seems to improve upon this discrepancy.

Ab initio calculations based on plane wave methods show that the band gap of PdS2 is strongly dependent upon the thickness of layers including van der Waals (vdW) interactions. The valence band maximum (VBM) is sensitive to the out-of-plane, and the conduction band minimum (CBM) to the in-plane lattice constants. The out of plane bonding is enhanced by the vdW force, which in turn affects the in-plane bonding. On application of biaxial compressive and tensile strain, the band gap decreases from 1.03 eV to 0.27 eV & 0.14 eV and 0.04 eV & 0.32 eV in case of bilayers with different stackings (AA & AB) respectively. The band gap is found to decrease from 1.03 eV to 0.0 eV (0.03 eV) and 0.0 eV (0.05 eV) on applying an electric field in the z direction on AA (AB) bilayers of PdS2. The effects of strain on the thermoelectric properties of PdS2 monolayer and bilayer were also studied. The electrical conductivity increases with the increase in tensile strain while it decreases with compressive strain in bilayers. As expected for thermoelectric application, the trend in the variation of the Seebeck coefficient is of opposite nature. The present work demonstrates the flexibility available for modulating the electronic and thermoelectric properties of this material for a variety of different applications.

Mercury (Hg) is a global environmental contaminant. Major anthropogenic sources of Hg emission include gold mining and the burning of fossil fuels. Once deposited in aquatic environments, Hg can undergo redox reactions, form complexes with ligands, and adsorb onto particles. It can also be methylated by microorganisms. Mercury, especially its methylated form methylmercury, can be taken up by organisms, where it bioaccumulates and biomagnifies in the food chain, leading to detrimental effects on ecosystem and human health. In support of the recently enforced Minamata Convention on Mercury, a legally binding international convention aimed at reducing the anthropogenic emission of-and human exposure to-Hg, its global biogeochemical cycle must be understood. Thus, a detailed understanding of the molecular-level interactions of Hg is crucial. The ongoing rapid development of hardware and methods has brought computational chemistry to a point that it can usefully inform environmental science. This is particularly true for Hg, which is difficult to handle experimentally due to its ultratrace concentrations in the environment and its toxicity. The current account provides a synopsis of the application of computational chemistry to filling several major knowledge gaps in environmental Hg chemistry that have not been adequately addressed experimentally. Environmental Hg chemistry requires defining the factors that determine the relative affinities of different ligands for Hg species, as they are critical for understanding its speciation, transformation and bioaccumulation in the environment. Formation constants and the nature of bonding have been determined computationally for environmentally relevant Hg(II) complexes such as chlorides, hydroxides, sulfides and selenides, in various physical phases. Quantum chemistry has been used to determine the driving forces behind the speciation of Hg with hydrochalcogenide and halide ligands. Of particular importance is the detailed characterization of solvation effects. Indeed, the aqueous phase reverses trends in affinities found computationally in the gas phase. Computation has also been used to investigate complexes of methylmercury with (seleno)amino acids, providing a molecular-level understanding of the toxicological antagonism between Hg and selenium (Se). Furthermore, evidence is emerging that ice surfaces play an important role in Hg transport and transformation in polar and alpine regions. Therefore, the diffusion of Hg and its ions through an idealized ice surface has been characterized. Microorganisms are major players in environmental mercury cycling. Some methylate inorganic Hg species, whereas others demethylate methylmercury. Quantum chemistry has been used to investigate catalytic mechanisms of enzymatic Hg methylation and demethylation. The complex interplay between the myriad chemical reactions and transport properties both in and outside microbial cells determines net biogeochemical cycling. Prospects for scaling up molecular work to obtain a mechanistic understanding of Hg cycling with comprehensive multiscale biogeochemical modeling are also discussed.

A comprehensive molecular analysis of a simple aqueous complexing system. U(VI) acetate. selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods was achieved by an international round-robin test (RRT). Twenty laboratories from six different countries with a focus on actinide or geochemical research participated and contributed to this scientific endeavor. The outcomes of this RRT were considered on two levels of complexity: first, within each technical discipline, conformities as well as discrepancies of the results and their sources were evaluated. The raw data from the different experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was high. By contrast, luminescence spectroscopic data turned out to be strongly related to the chosen acquisition parameters. Second, the potentials and limitations of coupling various spectroscopic and theoretical approaches for the comprehensive study of actinide molecular complexes were assessed. Previous spectroscopic data from the literature were revised and the benchmark data on the U(VI) acetate system provided an unambiguous molecular interpretation based on the correlation of spectroscopic and theoretical results. The multimethodologic approach and the conclusions drawn address not only important aspects of actinide spectroscopy but particularly general aspects of modern molecular analytical chemistry.

During the last half a century, great achievements have been made in molecular recognition in parallel with the invention of numerous synthetic receptors. However, the selective recognition of hydrophilic molecules in water remains a generally accepted challenge in supramolecular chemistry but is commonplace in nature. In an earlier Communication [ Huang et al. J. Am. Chem. Soc. 2016 , 138 , 14550 ], we reported a pair of endo-functionalized molecular tubes that surprisingly prefer highly hydrophilic molecules over hydrophobic molecules of a similar size and shape. The hydrophobic effect and hydrogen bonding were proposed to be responsible, but their exact roles were not fully elucidated. In this Article, we present a thorough study on the binding behavior of these molecular tubes toward 44 hydrophilic molecules in water. Principal component analysis reveals that the binding strength is weakly correlated to the hydrophobicity, volume, surface area, and dipole moment of guests. Furthermore, molecular dynamics simulations show the hydrophobic effect through releasing the poorly hydrogen-bonded cavity water contributes to the binding of all the hydrophilic molecules, while hydrogen bonding differentiates these molecules and is thus the key to achieve a high selectivity toward certain hydrophilic molecules over other molecules with a similar size and shape. Therefore, a good guest for these molecular tubes should meet the following criteria: the hydrogen-bonding sites should be complementary, and the molecular volume should be large enough to expel all the cavity water but not too large to cause steric hindrance. This rule of thumb may also be used to design a selective receptor for certain hydrophilic molecules. Following these guidelines, a "best-fit" guest was found for the syn-configured molecular tube with a binding constant as high as 10

Singlet fission (SF) is a particularly interesting process that can ultimately excite two electrons using a single photon and has strong potential for increasing the efficiency of photovoltaic devices (solar cells). One limitation of SF research is the relatively small number of known materials that undergo efficient SF. With this limitation in mind, we have used simple computational criteria (TD-DFT excitation energies) to screen various chromophores. Starting from known SF molecules (pentacene, tetracene, pyrene, isobenzofuran, among others), the influence of peripheral substituents was investigated. Depending on the starting molecule and the type of substitution (e.g., symmetric vs. asymmetric, electron donating vs. withdrawing), the influence of chemical modifications is often modest but sometimes large enough to significantly influence the energetics of SF. Specifically, we look at systematic trends of excitation energies among pentacene derivatives and calculated the energy change for SF to estimate the degree of spontaneity, compared to pentacene. The most significant changes are generally caused by substituent groups containing either nitrogen or oxygen, when they are placed opposite each other in the middle of the pentacene molecule. Of all other molecules tested in addition to pentacene and tetracene, only isobenzofuran derivatives were predicted to satisfy all required energetic conditions for efficient SF.

A Schiff-base polypyrrolic ligand (H4L) can accommodate two U3+ ions and form a Pacman-like complex [U2(L)]2+ according to relativistic density functional theory. Sixteen species, featuring four structural models in four electronic states, are energetically stable. Ligand flexibility, lack of axial restriction, and suitable U–N interactions allow the two U3+ ions to stretch freely over a wide range, in contrast to U2@Cn (n = 60, 74, 80) studied previously. Diverse U3+–U3+ interactions are found. The quintet state of the Out–In model, which is calculated to be the global ground state both including and excluding the spin–orbit coupling energy, likely shows a weak single U2 bond. In both vertical and tilt In–In species, a triple bond is found. It is composed of two two-electron–two-center bonds and two one-electron–two-center bonds; moreover, the tilt conformer is almost isoenergetic with Out–In. The Out–Out species shows no U···U bonding. Comparison with explicitly THF-solvated diuranium complexes is also ...

To understand the sensing behaviors of molecular fluorescent probes, lumazine (Lm) and 6-thienyllumazine (TLm) and their complexation with metal(II) ions ([(L)nM(H2O)m](2+), M = Cd(2+) and Hg(2+)) were examined by scalar relativistic density functional theory (DFT). A red shifting from L to [(L)nM(H2O)m](2+) was found. This is due to the metal affinity that stabilizes the LUMOs of [(L)nM(H2O)m](2+) greater than the HOMOs. Singlet excited-state structures of L and [(L)nM(H2O)m](2+) (M = Cd(2+) and Hg(2+)) were fully optimized using time-dependent DFT (TDDFT). Their fluorescent emissions in aqueous solution were calculated to be 371 nm (Lm), 439 nm (cis-TLm), and 441 nm (trans-TLm), agreeing with experimental values of 380 nm for Lm and 452 nm for TLm. Theoretical support is presented for a sensing mechanism of photoinduced charge transfer of the L probe. The mechanism of the chelation-enhanced fluorescence (CHEF) and the chelating quenched fluorescence (CHQF) is explained. Fluorescence amplification (for Cd(2+)) is due to blocking of the nitrogen lone pair orbital due to the stabilizing interaction with the vacant s-orbital of the metal ion, while fluorescence quenching (Hg(2+)) results from the energy of the LUMO of the metal ion being between HOMO and LUMO of the sensor. Effects of structure rearrangements on the fluorescence spectra of the sensors are insignificant. This proposed mechanism of metal orbital controlled fluorescence enhancement/quenching suggests a development concept in the future design of fluorescent turn-on/off sensors.

Tuning the building blocks of pyrrole and arene/pyridine in hybrid heterocalix[4]arene allows for the possible accessibility of several intriguing divalent uranium complexes, which are energetically stabilized by enhanced δ(U–Ar) bonds and further corroborated by computed UIII/II reduction potentials.

Quantum chemistry has been used to investigate the oxidation of water by a family of seven catalysts based on [Ru(tpy)(bpy)(OH2)]2+ (tpy = 2,2′:6′,2′′-terpyridine, bpy = 2,2′-bipyridine). The electron-donating −OMe and −NH2 groups (EDG) and electron-withdrawing −COOH and −NO2 groups (EWG) are installed in the catalyst by replacing hydrogen atoms on the bpy and tpy ligands. The EDG induces an increase in the electron density at the Ru center, whereas the EWG does the opposite. Reduced electron density at the metal center facilitates Ru(N+1)/Ru(N) reduction and thus a higher reduction potential. Catalytic evolution of one oxygen molecule from two water molecules using all catalysts is an exothermic process if driven by CeIV. The exothermicity increases from EDG to EWG via parents. Regarding intermediates, the singlet states of 7-coordinated catalysts are slightly more stable than the triplet states of 6-coordinated catalysts for most catalysts. Only for a strong EWG (−NO2) containing catalyst, the triplet 6...

Density functional theory [B3LYP/6-311+G(d,p)] was used in combination with the conductor-like polarizable continuum model (CPCM) solvation model to investigate the relative stability and site-specific pKaij values of neutral and ionized tautomers of lumazine (LM) and 6-thienylLM (TLM). Two types of populations should be taken into consideration when calculating the pKaij, tautomers, and conformers. The major tautomer of neutral LM in aqueous solution is 13-LM (the 13 notation refers to the acidic protons being in positions 1 and 3 of LM) TLM has decreased acidity at N8 relative to LM. Further, the trans conformer of TLM is more acidic than cis. Similar to the case of LM, for TLM, N1 is more acidic than N3 in the uracil part. However, N8 is predicted to be a stronger acid than N1 for TLM. This acidity enhancement is essentially because of a specific stabilization of the anion when the thienyl group replaces H. Two factors are responsible for the acidity strength of N8: The thienyl ring upon deprotonation acts inductively as an electron-withdrawing group, and the excess electron density is dispersed better when the system is trans and contains second-row atoms. Accurate pKa calculation requires that all conformers/tautomers be included into the calculation. Copyright © 2014 John Wiley & Sons, Ltd.

The structures and bonding of gas-phase [(UO2)2(OH)n](4-n) (n = 2-6) complexes have been studied using density functional theory (DFT), MP2, and CCSD(T) methods with particular emphasis on ground state structures featuring cation-cation interactions (CCIs) between the uranyl groups. An interesting trend is observed in the stabilities of members of this series of complexes. The structures of [(UO2)2(OH)2](2+), [(UO2)2(OH)4], and [(UO2)2(OH)6](2-) featuring CCIs are found at higher energies (by 3-27 kcal/mol) in comparison to their conventional μ2-dihydroxo structures. In contrast, the CCI structures of [(UO2)2(OH)3](+) and [(UO2)2(OH)5](-) are respectively degenerate with and lower in energy than the structures with the μ2-dihydroxo format. The origin of this trend lies in the symmetry-based need to balance the coordination numbers and effective atomic charges of each uranium center. The calculated IR vibrational frequencies provide signature probes that can be used in differentiating the low-energy structures and in experimentally confirming the existence of the structures featuring CCIs.

To advance the understanding of the chemical behavior of actinides, a series of trans-bis(imido) uranium(VI) complexes, U(NR)2(THF)2(cis-I2) (2R; R = H, Me, (t)Bu, Cy, and Ph), U(NR)2(THF)3(trans-I2) (3R; R = H, Me, (t)Bu, Cy, and Ph) and U(N(t)Bu)2(THF)3(cis-I2) (3(t)Bu'), were investigated using relativistic density functional theory. The axial U═N bonds in these complexes have partial triple bonding character. The calculated bond lengths, bond orders, and stretching vibrational frequencies reveal that the U═N bonds of the bis-imido complexes can be tuned by the variation of their axial substituents. This has been evidenced by the analysis of electronic structures. 2H, for instance, was calculated to show iodine-based high-lying occupied orbitals and U(f)-type low-lying unoccupied orbitals. Its U═N bonding orbitals, formed by U(f) and N(p), occur in a region of the relatively low energy. Upon varying the axial substituent from H to (t)Bu and Ph, the U═N bonding orbitals of 2(t)Bu and 2Ph are greatly destabilized. We further compared the U═E (E = N and O) bonds of 2H with 3H and their uranyl analogues, to address effects of the equatorial tetrahydrofuran (THF) ligand and the E group. It is found that the U═N bonds are slightly weaker than the U═O bonds of their uranyl analogues. This is in line with the finding that cis-UNR2 isomers, although energetically unfavorable, are more accessible than cis-UO2 would be. It is also evident that 2H and 3H display lower U═(NH) stretching vibrations at 740 cm(-1) than the U═O at 820 cm(-1) of uranyl complexes. With the inclusion of both solvation and spin-orbit coupling, the free energies of the formation reactions of the bis-imido uranium complexes were calculated. The formation of the experimentally synthesized 3Me, 3Ph, and 2(t)Bu are found to be thermodynamically favorable. Finally, the absorption bands previously obtained from experimental studies were well reproduced by time-dependent density functional theory calculations.

In this paper, the structural and electronic properties of polythiophene and polyprrrole-based systems have been investigated using first-principles calculations both in periodic and oligomer forms. Of particular interest is the band gap modulation through substitutions and bilayer formation. Specifically, S has been substituted by Se and Te in polythiophene, leading to polyseleophene and polytellurophene, respectively, and N has been substituted by P and As in polypyrrole. The values obtained of the binding energy suggest that all the systems studied can be realized experimentally. Stacking (bilayer formation) of pure polythiophene, polypyrrole and their derivatives leads to linear suppression of the band gap or HOMO-LUMO gap as a function of the stacking. Mixed bilayers, including one formed from polythiophene on top of polypyrrole, have also been considered. Overall, a wide range of band gaps can be achieved through substitutions and stacking. Hybrid (B3LYP) calculations also suggest the same trend in the band gap as PBE calculations. Trends in the binding energy are similar for both periodic and molecular calculations. In addition, the $\Gamma$-point phonon calculation are performed in order to check the stability of selected systems., Comment: 22 pages, 13 figures, and 4 Tables

Eighteen actinyl complexes of a Schiff-base polypyrrolic macrocycle (H4L), [(Sol)(AnmO2)(H2L)]n− (Sol = Vacant, pyridine (py) and tetrahydrofuran (THF); An=U, Np and Pu; m = VI and n = 0, m = V and n = 1) were investigated using relativistic density functional theory. Comparison of complexes with and without the explicit solvent coordination to the metal center, and changes in actinide element and metal oxidation state provide insight into their effects on structural and energetic properties of the complexes. Compared with those of the solvent-free complexes, the An=O bond lengths of the solvated complexes differ within 0.01 A, and the deviation of the O=An=O angles is less than 1°. The H···Oendo bonds are relatively sensitive to the explicit solvent coordination, showing the largest discrepancy of 0.05 A. Charges and electron-spin densities of actinides are only slightly affected by the inclusion of the explicit solvent. Reduction potentials of actinyl complexes have been addressed, and their dependence on the bulk solvent polarity is being discussed, using a simple model based on the Born equation.

A dramatic difference in the ability of the reducing An(III) center in AnCp3 (An=U, Np, Pu; Cp=C5 H5 ) to oxo-bind and reduce the uranyl(VI) dication in the complex [(UO2 )(THF)(H2 L)] (L="Pacman" Schiff-base polypyrrolic macrocycle), is found and explained. These are the first selective functionalizations of the uranyl oxo by another actinide cation. At-first contradictory electronic structural data are explained by combining theory and experiment. Complete one-electron transfer from Cp3 U forms the U(IV) -uranyl(V) compound that behaves as a U(V) -localized single molecule magnet below 4 K. The extent of reduction by the Cp3 Np group upon oxo-coordination is much less, with a Np(III) -uranyl(VI) dative bond assigned. Solution NMR and NIR spectroscopy suggest Np(IV) U(V) but single-crystal X-ray diffraction and SQUID magnetometry suggest a Np(III) -U(VI) assignment. DFT-calculated Hirshfeld charge and spin density analyses suggest half an electron has transferred, and these explain the strongly shifted NMR spectra by spin density contributions at the hydrogen nuclei. The Pu(III) -U(VI) interaction is too weak to be observed in THF solvent, in agreement with calculated predictions.