Orbitals Of Anions Research Articles

Low-valent Main-group Catalysis under Ambient Conditions using a Germylene Cation.

Catalysis using low-valent main-group compounds is usually done under inert conditions; no example of such catalysis has been doable entirely in ambient conditions until now. This aspect is addressed in this work through an air- and water-stable germylene cation [DPMGe][(OH)B(C6F5)3] (2) (DPM=dipyrromethene); it efficiently catalyzes aldehyde and ketone hydrosilylations under ambient conditions. Detailed theoretical studies reveal that compound 2's stability is bolstered by the interaction between the anion and germanium's frontier orbitals. However, the detachment of the anion (in the solution) alters the capability of compound 2 to render exceptional catalytic efficiency. Compound 2 was synthesized under ambient conditions by the equimolar reaction of DPMGeOH (1) with B(C6F5)3.

Realizing Ultrahigh Conversion Efficiency of ≈9.0% in YbCd2Sb2/Mg3Sb2 Zintl Module for Thermoelectric Power Generation.

Recently, YbCd2Sb2-based Zintl compounds have been widely investigated owing to their extraordinary thermoelectric (TE) performance. However, its p orbitals of anions that determined the valence band structure are split due to crystal field splitting that provides a good platform for band manipulation by doping/alloying and, more importantly, the YbCd2Sb2-based device has yet to be reported. In this work, single-phase YbCd1.5Zn0.5Sb2 is successfully obtained through precise chemical composition control. Then, YbMg2Sb2-alloying increases the cationic vacancy defect formation energy and further optimizes carrier concentration. Moreover, the band structure of YbCd1.5Zn0.5Sb2 is subtly manipulated, and the underlying mechanism is experimentally explored. Combined with the reduced lattice thermal conductivity, a high peak ZT value of ∼1.43 at 700K is obtained for YbCd1.425Zn0.475Mg0.1Sb2. Subsequently, choosing Fe90Sb10 as the diffusion barrier layer and adopting the transient liquid phase bonding technique, for the first time, it is demonstrated that YbCd2Sb2/Mg3(Sb, Bi)2 TE module with an ultrahigh conversion efficiency of ≈9.0% at a heat difference of 430K. More importantly, this module displays good thermal stability. This work paves the way for YbCd2Sb2 materials and devices in mid-temperature heat recovery.

An Electronic Structure Investigation of PEDOT with AlCl4- Anions-A Promising Redox Combination for Energy Storage Applications.

In this work, we use density functional theory to investigate the electronic structure of poly(3,4-ethylenedioxythiophene) (PEDOT) oligomers with co-located AlCl4- anions, a promising combination for energy storage. The 1980s bipolaron model remains the dominant interpretation of the electronic structure of PEDOT despite recent theoretical progress that has provided new definitions of bipolarons and polarons. By considering the influence of oligomer length, oxidation or anion concentration and spin state, we find no evidence for many of the assertions of the 1980s bipolaron model and so further contribute to a new understanding. No self-localisation of positive charges in PEDOT is found, as predicted by the bipolaron model at the hybrid functional level. Instead, our results show distortions that exhibit a single or a double peak in bond length alternations and charge density. Either can occur at different oxidation or anion concentrations. Rather than representing bipolarons or polaron pairs in the original model, these are electron distributions driven by a range of factors. Distortions can span an arbitrary number of nearby anions. We also contribute a novel conductivity hypothesis. Conductivity in conducting polymers has been observed to reduce at anion concentrations above 0.5. We show that at high anion concentrations, the energy of the localised, non-bonding anionic orbitals approaches that of the system HOMO due to Coulombic repulsion between anions. We hypothesize that with nucleic motion in the macropolymer, these orbitals will interfere with the hopping of charge carriers between sites of similar energy, lowering conductivity.

First-principles definition of ionicity and covalency in molecules and solids.

The notions of ionicity and covalency of chemical bonds, effective atomic charges, and decomposition of the cohesive energy into ionic and covalent terms are fundamental yet elusive. For example, different approaches give different values of atomic charges. Pursuing the goal of formulating a universal approach based on firm physical grounds (first-principles or non-empirical), we develop a formalism based on Wannier functions with atomic orbital symmetry and capable of defining these notions and giving numerically robust results that are in excellent agreement with traditional chemical thinking. Unexpectedly, in diamond-like boron phosphide (BP), we find charges of +0.68 on phosphorus and -0.68 on boron atoms, and this anomaly is explained by the Zintl-Klemm nature of this compound. We present a simple model that includes energies of the highest occupied cationic and lowest unoccupied anionic atomic orbitals, coordination numbers, and strength of interatomic orbital overlap. This model captures the essential physics of bonding and accurately reproduces all our results, including anomalous BP.

(Invited) Stable Layered Oxyhalide Photocatalysts for Visible-Light-Induced Water Splitting

Water splitting using photocatalysts has attracted considerable attention for producing H2 as a clean energy carrier, while the effective utilization of visible light is imperative to achieve the desired efficiency for practical applications. Recently, mixed-anion compounds such as oxynitrides have been intensively studied as promising candidates since one can expect that higher energy p orbitals of non-oxide anions (e.g., N-2p) elevate their VBM values. Unfortunately, most of them are subject to facile self-oxidation by photogenerated holes, while highly dispersed cocatalyst particles certainly improve the stability of some oxynitrides.Recently, we have revealed that some layered perovskite oxyhalides fulfil the necessary conditions for visible-light-induced water splitting due to their unique VBMs. For example, Bi4NbO8Cl belongs to the n = 1 members of the Sillén–Aurivillius perovskite family [(Bi2O2)2X]3+[A n -1BnO3n+1]3, which is composed of fluorite [Bi2O2], perovskite [NbO4], and halogen [Cl] layers as depicted in Figure 1. DFT calculations show that the VBM mainly consists of O-2p orbitals instead of Cl-3p, but its position determined by electrochemical measurement is much more negative (ca. 2.2 V vs. SHE) than those of conventional metal oxides (ca. 3.0 V). The significantly elevated VBMs of Bi4NbO8Cl can be understood by the strong hybridization between electron-filled Bi-6s and O-2p with the help of empty Bi-6p orbitals. In addition, Madelung site potential analysis for Bi4NbO8Cl indicated that the oxygen sites in the fluorite layer were electrostatically destabilized, which also certainly contributed to the elevation of the VBM that mainly consists of O-2p. Consequently, Bi4NbO8Cl possesses both a narrow band gap (2.4 eV) for visible light absorption up to ca. 500 nm and a more negative CBM (ca.–0.2 V vs. SHE) than the water reduction potential, which were testified by the substantial generation of H2 or O2 in the presence of an electron donor or acceptor, respectively. The substantially high durability against self-oxidative deactivation was also confirmed by the long-term water splitting in a Z-scheme system in which Bi4NbO8Cl was employed as the OEP. Since O– anions are known to be relatively stable, photogenerated holes populated at the O-2p orbitals will not lead to self-oxidative decomposition but rather to the oxidation of water.More oxyhalides with various perovskite layers (n) have been explored. However, reports on the synthesis of multiple-layered (n ≥ 2) perovskites were limited, probably due to the severe conditions required for their synthesis in the conventional solid state reaction. To solve this problem, a new two-step synthesis method including polymerized complex synthesis and a “bricklaying” synthesis were developed; providing a wide variety of new oxyhalides applicable to visible-light-induced water splitting. We also demonstrate that a oxyiodides such as Ba2Bi3Nb2O11I not only has access to a wider range of visible light than its chloride and bromide counterparts, but also exhibit much higher activity due to longer lifetime of photogenerated carriers.These studies on new oxyhalide materials provide new strategies for developing stable photocatalysts for visible-light-induced water splitting by manipulating the interaction between the s orbitals of post-transition metals (e.g., Bi-6s) and O-2p orbitals in the specific crystal structure.

Prediction of bipolar VSi2As4 and VGe2As4 monolayers with high Curie temperature and strong magnetocrystalline anisotropy

Recent studies have demonstrated that two-dimensional intrinsic magnetic materials with high Curie temperature $({T}_{\text{c}})$ and large magnetic anisotropy energy (MAE) are highly desirable for future spintronics. After careful investigations through density functional theory, bipolar ${\mathrm{VSi}}_{2}{\mathrm{As}}_{4}$ and ${\mathrm{VGe}}_{2}{\mathrm{As}}_{4}$ monolayers, with semiconductor valence and conduction band edges fully spin polarized in different spin directions, are demonstrated to be highly stable and have in-plane ferromagnetism (FM) with large MAE of $\ensuremath{\sim}5.5$ meV. The FM interaction is found to be dominated by the superexchange between d orbitals of V atoms through p orbitals of anions. More interestingly, ${T}_{\text{c}}$ is estimated to be $\ensuremath{\sim}900$ K through Monte Carlo simulation, which is significantly higher than room temperature. In addition, both MAE and ${T}_{\text{c}}$ can be substantially regulated and increased under biaxial strain and the transition from FM semiconductors to metals will occur. Our calculations and analyses indicate that ${\mathrm{VSi}}_{2}{\mathrm{As}}_{4}$ and ${\mathrm{VGe}}_{2}{\mathrm{As}}_{4}$ monolayers are ideal systems for the fundamental understanding of magnetic physics as well as building blocks for magnetoelastic applications, high-temperature, or/and gate-tunable spintronic nanodevices.

Formation of CuIn(1-x)GaxS2 Thin Films through a Solution Approach: Nonlinear Variation of Fermi Energy and Band Gap Bowing.

We report the formation of CuIn(1-x)GaxS2 (CIGS) thin films through a solution approach, namely, successive ionic layer adsorption and reaction (SILAR) technique. The obtained films possessed a high degree of crystallinity indicating the efficacy of the deposition process in forming CIGS films. A series of alloys have evidenced band gap bowing, that is, the optical band gap does not follow a linear relationship with the composition; the band gap of an intermediate compound is higher than that is interpolated from a linear relationship or Vegard's law. The composition-dependent band gap followed a quadratic relationship evidencing reverse band gap bowing, manifesting an upward convex behavior. With scanning tunneling spectroscopy (STS) and thereby the density of states of the disordered semiconductors, we have observed a bowing behavior in the transport gap as well and identified the roles of the conduction and valence bands in yielding the bowing phenomenon. The results are explained in terms of the anionic and cationic orbitals involved in forming the two bands. The STS studies have been analyzed further to derive the Urbach energy of the disordered semiconductors. When STS studies are combined with Kelvin probe force microscopy, which in effect provides the Fermi energy of the alloyed semiconductors, we could derive the band edges and the Fermi energy of the whole series in an absolute energy scale during the manifestation of the bowing phenomenon.

The effect of anion exchange on the electronic and optical properties of vacancy ordered double perovskites K2PdX6 (X = Cl, Br, I) using first principle calculations

ABSTRACT Recent studies are confirmed that lead-free perovskite is a possible alternative solution for conventional hybrid lead-based perovskites to achieve better photovoltaic efficiency. This work investigates the structural, mechanical, electronic, and optical properties of vacancy ordered double perovskite of K2PdX6 (X = Cl, Br, I) for photovoltaic applications through the density functional theory at the HSE06 level of theory. The bond length of Pd-X is linearly increased while exchanging the anions from Cl to I. The mechanical study reveals that the vacancy-ordered double perovskites K2PdCl6, K2PdBr6, and K2PdI6 are elastically classified as ductile materials. The K2PdBr6 hold a favourable bandgap of 1.62 eV for single junctions solar cell applications. The studied perovskite bandgaps depend on the Pd-4d, s and p orbitals of anions. The optical study uncover that the studied perovskites are higher optical absorption in the visible regions. Based on calculated results, we conclude that these K2PdBr6 vacancy ordered double perovskites might be suitable material for photovoltaic applications.

Electronic structures, effective masses and optical properties of B6Ch (Ch=O, S, Se, Te) based on DFT study

In this paper, crystal structures, effective masses, electronic and optical properties of B6Ch (Ch = O, S, Se, Te) are studied within density functional theory (DFT). The band structures show that B6O, B6S and B6Se are semiconductors, while the zero-bandgap B6Te displays metallic properties. Moreover, the optical properties involving absorption coefficients, refractive index and extinction coefficients of B6Ch are shown and analyzed. The obtained results lead to a conclusion that B6Ch results in heavier effective masses and poor transparency. This is explained by the fact that the s orbitals of anion will cause lower dispersion of band edge and influence its positions.

Orbital Design of Two-Dimensional Transition-Metal Peroxide Kagome Crystals with Anionogenic Dirac Half-Metallicity.

Assembling p orbital ferromagnetic half-metallicity and a topological element, such as a Dirac point at the Fermi level, in a single nanomaterial is of particular interest for long-distance, high-speed, and spin-coherent transportation in nanoscale spintronic devices. On the basis of the tight-binding model, we present an orbital design of a two-dimensional (2D) anionogenic Dirac half-metal (ADHM) by patterning cations with empty d orbitals and anions with partially filled p-type orbitals into a kagome lattice. Our first-principles calculations show that 2D transition-metal peroxides h-TM2(O2)3 (TMO3, TM = Ti, Zr, Hf), containing group IVB transition-metal cations [TM]4+ bridged with dioxygen anions [O2]8/3- in a kagome structure, are stable ADHMs with a Curie temperature over 103 K. The 2/3 filled π* orbitals of dioxygen anions are ferromagnetically coupled, leading to p orbital ferromagnetism and a half-metallic Dirac point right at the Fermi level with a Fermi velocity reaching 2.84 × 105 m/s. We proposed that 2D h-TM2(O2)3 crystals may be extracted from ABO3 bulk materials containing 2D TMO3 layers.

Recent Progress in Mixed‐Anion Materials for Solar Fuel Production

Mixed‐anion materials, consisting of metal cation(s) and more than two anionic species in a single phase, are promising as photocatalysts for water splitting and CO2 fixation using visible light. Oxynitrides, oxysulfides, and oxyhalides that contain d0 transition‐metal or d10 typical‐metal cations have absorption bands in the visible‐light region and band‐edge potentials suitable for these reactions. In general, visible‐light absorption by these materials arises from the p orbitals of anions that are less electronegative than oxygen, forming a valence band above the level of oxygen 2p orbitals. Less electronegative anions in mixed‐anion compounds are essential for visible‐light absorption but are inherently less stable than oxygen, potentially causing oxidative decomposition of the materials during photoreaction. More importantly, mixed‐anion compounds are more difficult to synthesize than single‐anion compounds like oxides, and reducing the density of defects that act as recombination centers for photogenerated charge carriers in the material remains challenging. There is therefore much room for improving the activities of mixed‐anion photocatalysts. Herein, the development of mixed‐anion materials for solar‐to‐fuel conversion over the past 10 years is highlighted with a focus on key milestones in research developments.

Origin of p‐Type Conduction in Amorphous CuI: A First‐Principles Investigation

Recently, Jun et al. (Adv. Mater. 2018, 30, 1706573) reported Sn‐doped amorphous phases of CuI (a‐CuI) as a new class of transparent p‐type semiconductors. It is surprising that high mobilities are found despite amorphous structures tend to localize carriers, particularly the directional p orbitals of anions. To reveal the microscopic origin of the new p‐type amorphous semiconductors, density functional theory calculations are performed, and structural and electrical properties of a‐CuI are investigated. Amorphous models from melt‐quench simulations consist of structural motifs that resemble local orders in crystalline polymorphs of CuI. Despite the absence of translational symmetry, states at valence band maximum (VBM) are substantially extended in linear ways due to the hybridization between I‐5p states, explaining the high hole mobilities in the experiment. Sn‐doped a‐CuI is also investigated and it is found that Sn atoms stabilize the amorphous structure without disturbing the hole transport. Furthermore, results on nonstoichiometric models show that Cu‐deficiency increases the hole concentration in a‐CuI and also enhances the delocalization of VBM states, which is consistent with the experimental observation that the hole mobility increases with doping concentrations. Herein, the origin of hole conduction in amorphous CuI is enlightened, which is believed to contribute in the development of high‐performance p‐type amorphous materials.

High-resolution photoelectron spectroscopy of the pyridinide isomers

Isomer-specific, high-resolution photoelectron spectra of cryogenically cooled pyridinide anions obtained using slow photoelectron velocity-map imaging are presented. New vibrational structure in the detachment spectrum of para-pyridinide is resolved, and the spectra of meta- and ortho-pyridinide are reported for the first time. These spectra yield electron affinities of 1.4797(5), 1.4473(5), and 0.8669(7) eV for the para-, meta-, and ortho-pyridyl radicals, respectively, as well as a number of vibrational frequencies for each neutral isomer. While most of the resolved structure in all three spectra is readily assigned by comparison to B3LYP/6-311+G* Franck-Condon simulations, the para-pyridinide spectrum shows newly resolved fine structure attributed to anharmonic coupling within the vibrational manifold of the corresponding neutral radical. Isomeric trends in the photoelectron angular distributions are rationalized by approximating the detached anion orbitals as superpositions of s-, p-, and d-like hydrogenic orbitals, based on an application of Sanov’s generalized mixing model [D. Khuseynov et al., J. Chem. Phys. 141, 124312 (2014)]. The presented experimental and theoretical results are used to address the relative energies of the anion and neutral isomers, as well as the site-specific bond dissociation energies of pyridine.

(Keynote) Stable Mixed-Anion Photocatalysts for Visible-Light-Induced Water Splitting

Photo-induced water splitting using semiconductor photocatalysts has attracted considerable attention for producing H2 as a clean energy carrier, while the effective utilization of visible light is imperative to achieve the desired efficiency for practical applications.[1, 2] Recently, mixed-anion compounds such as oxynitrides have been intensively studied as promising candidates since one can expect that higher energy p orbitals of non-oxide anions (e.g., N-2p) elevate their valence band maximum (VBM) values. Unfortunately, most of them are subject to facile self-oxidation by photogenerated holes, while highly dispersed cocatalyst particles certainly improve the stability of some oxynitrides.[3] We have recently demonstrated that Sillén–Aurivillius type perovskite oxyhalides such as Bi4NbO8Cl can stably and efficiently oxidize water to O2 under visible light without any surface modifications, and also exhibits a stable Z-scheme water splitting when coupled with a H2-evolving photocatalyst.[4] It was revealed that the VBMs of these materials consist mainly of O-2p orbitals, instead of Cl-3p (or Br-4p), but their positions are much more negative than those of conventional oxides. [5, 6] Thus, they possess narrow bandgaps for visible light absorption as well as sufficiently negative CBMs for water reduction. DFT calculation visualized a fairly strong hybridization between the Bi-6s and O-2p orbitals, which can explain why the O-2p orbitals are elevated in energy, combined with the result on Madelung site potential analysis that can rationalize the origin of high energy of O-2p orbital in these materials. Since O– anions are known to be relatively stable, photogenerated holes populated at the O-2p orbitals will not lead to self-decomposition but to oxidize water. These results could provide new strategies for developing durable photocatalytic materials for water splitting under visible light, by manipulating the interaction between post-transition metal s orbitals and O-2p orbitals. [1] R. Abe, J. Photochem. Photobiol. C: Photochemistry Reviews, 11 (2011) 179. [2] R. Abe, J. Tang et al., Chem. Rev. 118 (2018) 5201. [3] R. Abe, M. Higashi, K. Domen, J. Am. Chem. Soc., 132, (2010) 11828. [4] H. Fujito, H. Kunioku, H. Kageyama, R. Abe et al., J. Am. Chem. Soc., 38 (2016) 2082. [5] D. Kato, H. Kunioku, R. Abe, H. Kageyama et al. J. Am. Chem. Soc., 139 (2017) 18725. [6] H. Kunioku, H. Kageyama, R. Abe et al., J. Mater. Chem. A, 6 (2018) 3100. Key Words: Photocatalyst, Semiconductor, Water splitting, Solar energy

Hydrocarbon-soluble, hexaanionic fulleride complexes of magnesium.

The reaction of the magnesium(i) complexes [{(Arnacnac)Mg}2], (Arnacnac = HC(MeCNAr)2, Ar = Dip (2,6-iPr2C6H3), Dep (2,6-Et2C6H3), Mes (2,4,6-Me3C6H2), Xyl (2,6-Me2C6H3)) with fullerene C60 afforded a series of hydrocarbon-soluble fulleride complexes [{(Arnacnac)Mg} n C60], predominantly with n = 6, 4 and 2. 13C{1H} NMR spectroscopic studies show both similarities (n = 6) and differences (n = 4, 2) to previously characterised examples of fulleride complexes and materials with electropositive metal ions. The molecular structures of [{(Arnacnac)Mg} n C60] with n = 6, 4 and 2 can be described as inverse coordination complexes of n [(Arnacnac)Mg]+ ions with C60 n- anions showing predominantly ionic metal-ligand interactions, and include the first well-defined and soluble complexes of the C60 6- ion. Experimental studies show the flexible ionic nature of the {(Arnacnac)Mg}+···C60 6- coordination bonds. DFT calculations on the model complex [{(Menacnac)Mg}6C60] (Menacnac = HC(MeCNMe)2) support the formulation as an ionic complex with a central C60 6- anion and comparable frontier orbitals to C60 6- with a small HOMO-LUMO gap. The reduction of C60 to its hexaanion gives an indication about the reducing strength of dimagnesium(i) complexes.

Orbital Alignment for High Performance Thermoelectric YbCd2Sb2 Alloys

As a typical class of Zintl thermoelectrics, AB2C2 (A = Eu, Yb, Ba, Ca, Mg; B = Zn, Cd, Mg, and C = Sb, Bi) compounds have shown a superior thermoelectric performance, largely stemming from the existence of multiple transporting bands in both conduction types. Being similar to many III–V and elemental semiconductors, the transport of holes in AB2C2 Zintls usually involves multiple valence bands with extrema at the Brillouin zone center Γ. However, these valence bands, originating from different orbitals, are unnecessarily aligned in energy due to the crystal field splitting. Formation of solid solutions between constituent compounds having opposite arrangements in energy of band orbitals is believed to be particularly helpful for thermoelectric enhancements, because orbital alignment increases band degeneracy while alloy defects scatter phonons. These effects are simultaneously realized in this work, where the p orbitals of anions in YbCd2–xZnxSb2 alloys are well-aligned for maximizing the electronic performance, and meanwhile high-concentration Cd/Zn substitutions are introduced for minimizing the lattice thermal conductivity. As a result, a significantly enhanced thermoelectric figure of merit, zT ∼ 1.3, is achieved, being a record among AB2C2 Zintls in p-type. This work demonstrates not only YbCd2–xZnxSb2 alloys as efficient thermoelectrics but also orbital alignment as an effective strategy for advancing thermoelectrics.

Rapid debromination of polybrominated diphenyl ethers (PBDEs) by zero valent metal and bimetals: Mechanisms and pathways assisted by density function theory calculation

Polybrominated diphenyl ethers (PBDEs) undergo debromination when they were exposed in zerovalent metal or bimetallic systems. Yet their debromination pathways and mechanisms in these systems were not well understood. Here we reported the debromination pathways of three BDE congeners (BDE-21, 25 and 29) by nano-zerovalent iron (n-ZVI). All these BDE congeners have three bromine substituents that were located in ortho-, meta- and para-positions. Results demonstrated that BDE-21, 25 and 29 preferentially debrominate meta-, ortho- and para-bromines, respectively, suggesting that bromine substituent at each position (i.e. ortho-, meta- or para-) of PBDEs can be preferentially removed. Singly occupied molecular orbitals of BDE anions are well correlated with their actual debromination pathways, which successfully explain why these BDE congeners exhibit certain debromination pathways in n-ZVI system. In addition, microscale zerovalent zinc (m-ZVZ), iron-based bimetals (Fe/Ag and Fe/Pd) were also used to debrominate PBDEs, with BDE-21 as target pollutant. We found that the debromination pathways of BDE-21 in m-ZVZ and Fe/Ag systems are the same to those in n-ZVI system, but were partially different from those in Fe/Pd systems. The debromination of BDE-21 in Pd-H2 system as well as the solvent kinetic isotope effect in single metal and bimetallic systems suggests that H atom transfer is the dominant mechanism in Fe/Pd system, while e-transfer is still the dominant mechanism in Fe/Ag system.

Covalent interactions in oxides

The covalent character of ionic metal compounds, in particular oxides, may lead to substantial departures from nominal oxidation states. Since this covalent character changes the effective charge of the cation, it contributes to the chemical and physical properties of these compounds. A novel method of determining the degree of the covalent mixing by projection is presented. In this method, cation and ligand orbitals determined for the isolated species are projected on the total wavefunctions for clusters used to model the electronic structure of these compounds. An important advantage of this method is that it can be used to obtain estimates of the uncertainties in the assignments of effective charges to the cations and anions. Such estimates of the uncertainty directly reflect the overlap of cation and anion orbitals and, hence, their potential for chemical bonding. These kinds of estimates are not generally given when assignments of charge are made. The core-hole states created in X-ray photoemission spectroscopy, XPS, have a very different covalent character than the initial states where the core shells are filled. It is shown that the increase of the covalent character in the core-hole configurations provides insight into a major aspect of the core-hole screening.

Design and synthesis of new family of ionic liquids based on 2-iminium-1,3-dithiolanes: A combined theoretical and experimental effort

An efficient method for synthesis of 2-iminium-1,3-dithiolane as a new family of ionic liquids with reaction of dithiocarbamates with methyl triflouromethanesulfonate was described. Theoretical study on the synthesized ionic liquids was also performed by quantum chemistry calculation. Geometry optimization on the ion pairs was carried out with the B3LYP/6-311++G(d,p) level of theory. The interaction energies were calculated, and corrected by the basis set superposition error (BSSE) calculated by the counterpoise method. The results of natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) analyses indicate that the interactions occur via hydrogen bonding between oxygen atom lone pairs (lp(O)) of triflouromethanesulfonate anion and antibonding orbitals of σ*C–H of 2-iminium-1,3-dithiolane cations. Also, the results of QTAIM analysis show that the hydrogen bonds are closed shell (electrostatic) in the nature. Finally, the 1H and 13C calculated chemical shifts at the B3LYP/6-311++G** level were in agreement with experimental chemical shifts for synthesized ionic liquids.

Electronic Control of the Tip-Induced Hopping of an Hexaphenyl-Benzene Molecule Physisorbed on a Bare Si(100) Surface at 9 K

In this work, we show that the hopping directivity of individual hexaphenyl-benzene (HPB) molecules physisorbed along the SA step edge of a bare Si(100)-2×1 surface can be reversibly controlled with a periodic hopping length. This is achieved by using the tunnel electrons of a low temperature (9 K) scanning tunneling microscope (STM). A statistical analysis of the electronic excitations applied at various positions on the HPB molecule reveals that the hopping process is related to a strong decrease of the tunnel junction conductance. This process is associated with a charge transfer from the silicon surface to the HPB molecule leading to a hopping mechanism that occurs in two sequential steps. The first step of the hopping process involves the formation of an HPB– anion that triggers the molecular motion into a metastable state. The second step is related to the neutralization of the HPB– anion which provokes the manipulation of the molecule to its final steady position. Our experimental data are supported by the calculations of the relaxed molecule using the density functional theory on the Si(100) surface that takes the van der Waals forces interactions into account. Additional calculations of the HPB– anion orbitals depict the spatial localization of the extra charge inside the HPB molecule and the relative energies of the HPB– molecular orbitals. Finally, our study shows that the hopping direction can be optimized by positioning the STM tip at specific locations along the hopping pathway.