Ruthenium(II) complexes bearing pyridine‐based tridentate and bidentate ligands: catalytic activity for transfer hydrogenation of aryl ketones

Ru(II) complexes of the general formula [RuCl₂(′′)(L)] (1: ′N = N_b, L = MeOH; 2: ′N = N_b, L = CH₃CN; 3: ′N = N_d, L = CH₃CN; 4: ′N = N_p, L = CH₃CN), [Ru(p‐cymene)(_a–b)Cl]Cl (5a: N N_a = 2,2′‐bipyridine; 5b: N N_b = 4,4′‐dimethyl–2,2′‐bipyridine), [Ru(′′)(_a–b)Cl]Cl (6a: ′N = N_b, _a = 2,2′‐bipyridine; 6b: ′N = N_b, _b = 4,4′‐dimethyl‐2,2′‐bipyridine; 7a: ′N = N_d, _a = 2,2′‐bipyridine; 7b: ′N = N_d, _b = 4,4′‐dimethyl‐2,2′‐bipyridine; 8a: ′N = N_p, _a = 2,2′‐bipyridine; 8b: ′N = N_p, _b = 4,4′‐dimethyl‐2,2′‐bipyridine) and [Ru(′′)(_a)Cl]BF₄ (9a: ′N = N_b; _a = 2,2′‐bipyridine) were synthesized from the corresponding [RuCl₂(p‐cymene)]₂ dimer, ′′ and _a–b ligands. The compounds were characterized by elemental analysis, IR and NMR. Complex 9a was studied by X‐ray diffraction, confirming its cationic‐mononuclear [RuCl(_bb)(_a)]⁺ nature. The synthesized Ru(II) complexes (1–8) were employed as catalysts for the transfer hydrogenation of ketones to secondary alcohols in the presence of KOH using 2‐propanol as a hydrogen source at 82°C. The rates of the transfer hydrogenation reactions strongly depended on the type of and ancillary ligands. Copyright © 2012 John Wiley & Sons, Ltd.     

Rate Constants for the Gas‐Phase Reactions of Ozone and Nitrate Radicals with the Sesquiterpenes: Valencene and Farnesol

Sesquiterpenes are constituents of a variety of essential oils that are used in flavorings, perfumes, personal care, and cleaning products. Two sesquiterpenes that are commonly used as indoor fragrances are valencene and farnesol. Knowing the reaction rate constants of these chemicals with ozone (O₃) and nitrate radical () is an important factor in determining their fate indoors. In this study, the bimolecular rate constants of , , , and were measured using the relative rate technique at 297 ± 3 K and 1 atm total pressure. Using the rate constants reported here and measured/modeled indoor concentrations of O₃ and (20 ppb and 1 ppt, respectively), pseudo–first‐order‐rate lifetimes , , , and were determined.     

Computational study of basis set and electron correlation effects on anapole magnetizabilities of chiral molecules

In the presence of a static, nonhomogeneous magnetic field, represented by the axial vector at the origin of the coordinate system and by the polar vector , assumed to be spatially uniform, the chiral molecules investigated in this paper carry an orbital electronic anapole, described by the polar vector . The electronic interaction energy of these molecules in nonordered media is a cross term, coupling and via , one third of the trace of the anapole magnetizability a_αβ tensor, that is, . Both and W^BC have opposite sign in the two enantiomeric forms, a fact quite remarkable from the conceptual point of view. The magnitude of predicted in the present computational investigation for five chiral molecules is very small and significantly biased by electron correlation contributions, estimated at the density functional level via three different functionals. © 2016 Wiley Periodicals, Inc.     

Influence of surface properties on the interfacial adhesion in carbon fiber/epoxy composites

A polyacrylonitrile‐based carbon fiber was electrochemically oxidized in an aqueous ammonium bicarbonate solution with current density of up to 2.76 A/m² at room temperature. X‐ray photoelectron spectroscopy revealed that the oxygen content increased with increasing current density before approaching saturation. The increase can be divided into two regions, the rapid increase region (0–1.78 A/m²) and a plateau region (1.78–2.76 A/m²). The surface chemistry analysis showed that the interlaminar shear strength (ILSS) value of the carbon fiber/epoxy composite could be improved by 24.7%. The carbon structure was examined using Raman spectroscopy in terms of order/disorder in the graphite structure and the results indicated that the relative percentage of graphite carbon in the form of sp² hybridization increased above a current density of 1.39 A/m². The increasing non‐polar graphite carbon on the carbon fiber surface decreased the surface energy. As a result, both the surface free energy () and its polar component () decreased when current density increased above 1.78 A/m². The ILSS value had no direct relationship with the nature and surface density of the oxygen‐containing functional groups nor with the carbon structure. It is the surface free energy (), especially the polar component (), which played a critical role in affecting the interfacial adhesion of carbon fiber/epoxy composites. The ILSS value changed with increasing current density and could be divided into three distinct regions, as chemical interaction region (I), anchor force region (II) and matrix damage region (III). Copyright © 2013 John Wiley & Sons, Ltd.     

Theoretical prediction of the optical rotation of chiral molecules in ordered media: A computational study of (Ra)‐1,3‐dimethylallene, (2R)‐2‐methyloxirane,and (2R)‐N‐methyloxaziridine

A theoretical procedure has been developed and implemented to calculate the optical rotation of chiral molecules in ordered phase via origin‐independent diagonal components , of the optical activity tensor and origin‐independent components , for , of the mixed electric dipole‐electric quadrupole polarizability. Origin independence was achieved by referring these tensors to the principal axis system of the electric dipole dynamic polarizability at the same laser frequency ω. The approach has been applied, allowing for alternative quantum mechanical methods based on different gauges, to estimate near Hartree–Fock values for three chiral molecules, (2R)‐N‐methyloxaziridine C₂NOH₅, (2R)‐2‐methyloxirane (also referred to as propylene oxide) C₃OH₆, and ( )‐1,3‐dimethylallene C₅H₈, at two frequencies. The theoretical predictions can be useful for an attempt at measuring correspondent experimental values in crystal phase. © 2015 Wiley Periodicals, Inc.     

Electronic Spectroscopy of Methylcyanodiacetylene (CH3C5N)

The results of a study devoted to the electronic spectroscopy of gaseous, solid, and cryogenic matrix‐isolated methylcyanodiacetylene (CH₃C₅N) are reported. UV absorption and optical phosphorescence spectra of the compound are described here for the first time, and the corresponding vibronic assignments are proposed. UV absorption, studied directly or through the excitation of phosphorescence, revealed the ¹E‐‐ ¹A₁ system, very weak ¹A₂– ¹A₁ bands, and a strong, broad absorption feature, tentatively identified as ¹E– ¹A₁. Spectral measurements were assisted by quantum chemical calculations at the DFT and ab initio (coupled cluster) levels of theory.     

Size of a polymer chain in an environment of quenched chains

We perform high‐coordination three‐dimensional (3D) lattice simulations of a single chain of N monomers embedded in matrices of quenched chains, at different concentrations ρ, using pruned‐enriched Rosenbluth sampling. The partition function is well‐described by the expression, , where is a universal constant, and is the concentration dependent lattice connectivity constant. For sufficiently long chains, , we find that the radius of gyration R varies nonmonotonically with ρ; R decreases gradually from its unperturbed dimensions R₀ until , after which it increases relatively rapidly due to repulsion between monomers. Motivated by the similarity in the shape of the curves, and results on Gaussian chains, we successfully superpose all the simulation data onto a single master curve. Finally, we test the relationship , suggested by a Flory‐type scaling model, where ρ_c is the critical percolation threshold, and is a universal constant. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1611–1619     

Additivity in kramers pairs symmetry: Multiplets with up to four unpaired electrons

Many fermions Kramers pairs formalism is considered from the prospective of the sum of individual single fermion time‐reversal operators. The obtained many fermions “pseudo Kramers pairs operator” ( ), as well as its square ( ), have formally the same structure as the many fermion spin operators and . Nevertheless, the shape of eigenfunctions with respect to and is different. Herein all Kramers adapted eigenfunctions of for cases of up to four unpaired fermions are compiled, and their properties with respect to further advocated. It will be shown that degeneracy of the multiplets recovers the proper behavior with respect to Pascal's triangle. A projection operator for obtaining the “high spin” Kramers adapted eigenfunctions is suggested. Noncommutation of with spin and angular momentum operators and degeneracy is discussed at last. © 2016 Wiley Periodicals, Inc.     

Dealing with the shifted and inverted Tietz–Hua oscillator potential using the J‐matrix method

The tridiagonal J‐matrix approach has been used to calculate the low and moderately high‐lying eigenvalues of the rotating shifted Tietz–Hua (RSTH) oscillator potential. The radial Schrödinger equation is solved efficiently by means of the diagonalization of the full Hamiltonian matrix, with the Laguerre or oscillator basis. Ro–vibrational bound state energies for 11 diatomic systems, namely , , , NO, CO, , , , , , and NO⁺, are calculated with high accuracy. Some of the energy states for molecules are reported here for the first time. The results of the last four molecules have been introduced for the first time using the oscillator basis. Higher accuracy is achieved by calculating the energy corresponding to the poles of the S‐matrix in the complex energy plane using the J‐matrix method. Furthermore, the bound states and the resonance energies for the newly proposed inverted Tietz–Hua IRSTH‐potential are calculated for the H₂‐molecule with scaled depth. A detailed analysis of variation of eigenvalues with n, quantum numbers is made. Results are compared with literature data, wherever possible. © 2015 Wiley Periodicals, Inc.     

Synthesis of gradient copolysiloxanes by simultaneous copolymerization of cyclotrisiloxanes and mechanism for kinetics inverse between anionic and cationic ring‐opening polymerization

Trifluoropropylmethylsiloxane–phenylmethylsiloxane gradient copolysiloxanes were synthesized by anionic and cationic ring‐opening polymerization (ROP) of 1,3,5‐tris(trifluoropropylmethyl)cyclotrisiloxane ( ) and phenylmethylcyclotrisiloxane ( ). The analysis of reactivity ratios revealed that the reactivity of toward anionic ROP was higher than that of ; however, exhibited lower reactivity compared with during the cationic ROP. AB and BAB type gradient copolymers were obtained because of a difference in the reactivity of the monomers. The microstructure of copolymers was characterized by ²⁹Si NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. Furthermore, the mechanism for kinetics inverse of copolymerization was proposed based on the results of the optimized molecular configuration. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 835–843     

Quantum control of electron‐proton symmetry breaking in dissociative ionization of H2 by intense laser pulses

Forward and backward electron/proton ionization/dissociation spectra from one‐dimensional non‐Born‐Oppenheimer H₂ molecule exposed to ultrashort intense laser pulses ( W/cm², λ = 800 nm) have been computed by numerically solving the time‐dependent Schrödinger equation. The resulting above‐threshold ionization and above‐threshold dissociation spectra exhibit the characteristic forward‐backward asymmetry and sensitivity to the carrier‐envelope phase (CEP), particularly for high energies. A general framework for understanding CEP effects in the asymmetry of dissociative ionization of H₂ has been established. It is found that the symmetry breaking of electron‐proton distribution with π periodic modulation occurs for all CEPs except for ( integer) and the largest asymmetry coming from the CEP of . At least one of the electron and proton distributions is asymmetric when measured simultaneously. Inspection of the nuclear and electron wave packet dynamics provides further information about the relative contribution of the gerade and ungerade states of to the dissociation channel and the time delay of electrons in asymmetric ionization. © 2014 Wiley Periodicals, Inc.     

Geometry of the canonical Van Vleck transformation

Bloch's transformation from the zeroth‐order space for a perturbation problem to the corresponding space of exact eigenvectors, was found as a geometrically defined alternative to the algebraically constructed Van Vleck transformation. Klein's theorem of uniqueness transferred some of this geometrical interpretation to its canonical form . Quite recently Kvaal has taken a large step further by writing as a product of commuting planar rotations, obtained by describing and in terms of certain principal vectors and canonical angles. Kvaal's approach is now developed further, using a new commutation relation which simplifies algebraic manipulations substantially. It allows for a simple definition of an operator for the angle between and which has Kvaal's vectors and angles as eigenvectors and eigenvalues. Klein's theorem is refined in various ways. The impact of the approach on a number of previous results is considered. © 2015 Wiley Periodicals, Inc.     

Low‐energy structures of benzene clusters with a novel accurate potential surface

The benzene‐benzene (Bz‐Bz) interaction is present in several chemical systems and it is known to be crucial in understanding the specificity of important biological phenomena. In this work, we propose a novel Bz‐Bz analytical potential energy surface which is fine‐tuned on accurate ab initio calculations in order to improve its reliability. Once the Bz‐Bz interaction is modeled, an analytical function for the energy of the clusters may be obtained by summing up over all pair potentials. We apply an evolutionary algorithm (EA) to discover the lowest‐energy structures of clusters (for ), and the results are compared with previous global optimization studies where different potential functions were employed. Besides the global minimum, the EA also gives the structures of other low‐lying isomers ranked by the corresponding energy. Additional ab initio calculations are carried out for the low‐lying isomers of and clusters, and the global minimum is confirmed as the most stable structure for both sizes. Finally, a detailed analysis of the low‐energy isomers of the n = 13 and 19 magic‐number clusters is performed. The two lowest‐energy isomers show S₆ and C₃ symmetry, respectively, which is compatible with the experimental results available in the literature. The structures reported here are all non‐symmetric, showing two central Bz molecules surrounded by 12 nearest‐neighbor monomers in the case of the five lowest‐energy structures. © 2015 Wiley Periodicals, Inc.     

Photodetachment of hydrogen negative ion near inelastic surfaces: Arbitrary laser polarization direction

The photodetachment of hydrogen negative ion near different inelastic surfaces is investigated by the semiclassical closed orbit theory for arbitrary laser polarization direction . A two‐term formula of photodetachment cross section consisting of a smooth background term and an oscillatory term is derived. The oscillatory term contains an extra angular factor that describes the dependence of oscillations in total cross section on the laser polarization direction. It is observed that the amplitude of oscillations in cross section reaches maximum at when laser polarization is parallel to the z‐axis and it approaches zero as the laser polarization direction becomes perpendicular to the z‐axis. It is also observed that as the reflection coefficient , which accounts for the inelastic behavior of the surfaces, increases the amplitude of oscillation also increases. © 2015 Wiley Periodicals, Inc.     

Experimental and Kinetic Modeling Study of Methanol Ignition and Oxidation at High Pressure

A detailed chemical kinetic model for oxidation of CH₃OH at high pressure and intermediate temperatures has been developed and validated experimentally. Ab initio calculations and Rice–Ramsperger–Kassel–Marcus/transition state theory (RRKM/TST) analysis were used to obtain rate coefficients for , , , and . The experiments, involving CH₃OH/O₂ mixtures diluted in N₂, were carried out in a high‐pressure flow reactor at 600–900 K and 20–100 bar, varying the reaction stoichiometry from very lean to fuel‐rich conditions. Under the conditions studied, the onset temperature for methanol oxidation was not dependent on the stoichiometry, whereas increasing pressure shifted the ignition temperature toward lower values. Model predictions of the present experimental results, as well as rapid compression machine data from the literature, were generally satisfactory. The governing reaction pathways have been outlined based on calculations with the kinetic model. Unlike what has been observed for unsaturated hydrocarbons, the oxidation pathways for CH₃OH under the investigated conditions were very similar to those prevailing at higher temperatures and lower pressures. At the high pressures, the modeling predictions for onset of reaction were particularly sensitive to the reaction.     

A Visible‐Light‐Triggered Conformational Diastereomer Photoswitch in a Bridged Azobenzene

Ketal‐substituted bridged azobenzenes have been synthesized; these display a symmetrical boat conformation with the ketal in pseudo‐equatorial positions. These bridged Z‐azobenzenes (Z₁) readily photoisomerize to the E‐isomer as well as another Z‐conformer (Z₂) with ketal function on the pseudo‐axial position upon irradiation at 406 nm. The two diastereomeric conformers display distinct physicochemical characteristics. Spectroscopic and NMR investigations supported that interconversion of two conformers occurs via the E‐isomer, with good photochemical quantum yield (Φ =0.45±0.03, Φ =0.33±0.05, Φ =0.37±0.06 and Φ =0.36±0.04). The system shows high photostability and no thermal equilibrium between the two stable Z₁ and Z₂ conformers.     

DFT characterization of nanostructured germanium surfaces induced by cobalt atoms

By deposition in ultra‐high vacuum of cobalt on a Ge(111)–c(2 × 8) surface, Mocking et al. obtained a surface reconstruction. In the present paper, we analyse the related atomic structure, proposed by these authors, by means of density functional theory calculations. The surface presents ordered clusters that consist of six Ge atoms arranged in a triangle, lying above three Co atoms. The latter are located at substitutional positions within the top plane of the Ge(111) first bilayer. These clusters are similar to what is obtained on part of the Co‐induced Si(111) surface. For this surface, the clusters are terminated either by six Si atoms or by one, two or three adatoms above the six Si atoms. As the Co–Ge clusters systematically display six protrusions in the scanning tunnelling microscopy measurements by Mocking et al., we investigated why Ge adatoms are not present. Comparison of the Gibbs energy, interatomic distances, as well as charge density indicates that Ge adatoms on top of Co‐Ge clusters are less stable than Si adatoms in the Co‐Si system. Copyright © 2013 John Wiley & Sons, Ltd.     

Variation of the strain rate during CSM nanoindentation of glassy polymers and its implication on indentation size effect

The indentation strain rate is currently assumed to remain unvaried during continuous stiffness measurement (CSM) nanoindentation where is imposed to remain constant. To probe the validity of this assumption for the nanoindentation of glassy polymers, a series of experiments have been performed at different set values on poly(methyl methacrylate) and polycarbonate using CSM technique. It is firstly shown that the actual value changes drastically at shallow indentation depths and it takes a considerable depth, which is material independent, for this parameter to attain a stabilized value. Furthermore, the strain rate is measured directly as the descent rate of the indenter divided by its instantaneous depth ( ), and indirectly via considering the variations of the load and hardness during the test. Both of these approaches reveal that the strain rate is considerably larger at shallow depths, and the depth beyond which it becomes constant is material and ratio dependent. Finally, by considering the relationship between the hardness and strain rate, it is observed that although the strain rate variation alters the hardness, its contribution is not able to justify the observed indentation size effect; hence, other contributing factors for this phenomenon are discussed for their possible effects. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2179–2187     

Energy decomposition analysis of cation–π, metal ion–lone pair,hydrogen bonded,charge‐assisted hydrogen bonded,and π–π interactions

This study probes the nature of noncovalent interactions, such as cation–π, metal ion–lone pair (M–LP), hydrogen bonding (HB), charge‐assisted hydrogen bonding (CAHB), and π–π interactions, using energy decomposition schemes—density functional theory (DFT)–symmetry‐adapted perturbation theory and reduced variational space. Among cation–π complexes, the polarization and electrostatic components are the major contributors to the interaction energy (IE) for metal ion–π complexes, while for onium ion–π complexes ( , , , and ) the dispersion component is prominent. For M–LP complexes, the electrostatic component contributes more to the IE except the dicationic metal ion complexes with H₂S and PH₃ where the polarization component dominates. Although electrostatic component dominates for the HB and CAHB complexes, dispersion is predominant in π–π complexes.Copyright © 2015 Wiley Periodicals, Inc.     

Hollow Gold Cages and Their Topological Relationship to Dual Fullerenes

Golden fullerenes have recently been identified by photoelectron spectra by Bulusu et al. [S. Bulusu, X. Li, L.‐S. Wang, X. C. Zeng, PNAS 2006 , 103, 8326–8330]. These unique triangulations of a sphere are related to fullerene duals having exactly 12 vertices of degree five, and the icosahedral hollow gold cages previously postulated are related to the Goldberg–Coxeter transforms of C₂₀ starting from a triangulated surface (hexagonal lattice, dual of a graphene sheet). This also relates topologically the (chiral) gold nanowires observed to the (chiral) carbon nanotubes. In fact, the Mackay icosahedra well known in gold cluster chemistry are related topologically to the dual halma transforms of the smallest possible fullerene C₂₀. The basic building block here is the (111) fcc sheet of bulk gold which is dual to graphene. Because of this interesting one‐to‐one relationship through Euler's polyhedral formula, there are as many golden fullerene isomers as there are fullerene isomers, with the number of isomers N_iso increasing polynomially as ). For the recently observed , , and we present simulated photoelectron spectra including all isomers. We also predict the photoelectron spectrum of . The stability of the golden fullerenes is discussed in relation with the more compact structures for the neutral and negatively charged Au₁₂ to Au₂₀ and Au₃₂ clusters. As for the compact gold clusters we observe a clear trend in stability of the hollow gold cages towards the (111) fcc sheet. The high stability of the (111) fcc sheet of gold compared to the bulk 3D structure explains the unusual stability of these hollow gold cages.