Quantum-chemical simulation of the elementary step of the oxidation reactions of styrene and its derivatives involving <Superscript>1</Superscript>О<Subscript>2</Subscript> (<Superscript>1</Superscript>Δg)

The results of simulation of the oxidation reaction of styrene and its methyl (two isomers) and phenyl derivatives with molecular oxygen in the excited singlet state (¹Δg) have enabled the conclusion that the reaction can proceed through several mechanisms. For styrene and its phenyl derivative, three reaction channels are possible, and for the methyl derivative, there are four possible channels. For the first two substrates, the major channel is 1,2-addition to form dioxetane; for the methyl derivatives, an extra channel to give a hydroperoxide species is possible in addition to the above channel. The multichannel reaction character revealed by calculations makes it possible to qualitatively understand the reason behind the moderate selectivity (no more than 70%) of such reactions in the case of styrene and its derivatives.     

Intermetallic Pd<Subscript>1</Subscript>–Zn<Subscript>1</Subscript> nanoparticles in the selective liquid-phase hydrogenation of substituted alkynes

A comparative study of the catalytic characteristics of monometallic Pd/α-Al₂O₃ and bimetallic Pd–Zn/α-Al₂O₃catalysts in the liquid-phase hydrogenation of structurally different substituted alkynes (terminal and internal, symmetrical and asymmetrical) was carried out. It was established that an increase in the reduction temperature from 200 to 400 and 600°C led to a primary decrease in the activity of Pd–Zn/α-Al₂O₃ due to the formation and agglomeration of Pd1–Zn1 intermetallic nanoparticles. The Pd–Zn/α-Al₂O₃ catalyst containing Pd1–Zn1 nanoparticles exhibited increased selectivity to the target alkene formation, as compared with that of Pd/α-Al₂O₃. Furthermore, the use of the Pd–Zn/α-Al₂O₃ catalyst made it possible to more effectively perform the kinetic process control of hydrogenation because the rate of an undesirable complete hydrogenation stage decreased on this catalyst.     

Enthalpies of formation of 3,4- and 3,5-dinitro-1-trimethyl-1<Emphasis Type="Italic">Н</Emphasis>-pyrazoles

The standard enthalpies of combustion and formation for isomeric polynitropyrazoles, viz., 3,4- and 3,5-dinitro-1-trinitromethyl-1Н-pyrazoles, were measured by combustion calorimetry in an oxygen atmosphere. The enthalpies of formation for the 3,4-dinitro isomer by 19.7 kJ mol^–1 exceeds the corresponding parameter for the 3,5-isomer.     

Phase Diagram of the NaNO<Subscript>2</Subscript>—KNO<Subscript>3</Subscript> System in the 0 to 1 Molar Fraction Range of Concentrations of KNO<Subscript>3</Subscript>

The temperature dependence of the phase composition of KNO₃—NaNO₂ mixtures in the 0 to 1 molar fraction range of concentrations of KNO₃ is investigated. A phase diagram of the KNO₃—NaNO₂ binary system in the range of concentrations from 0 to 1 molar fractions of KNO₃ is drawn on the basis of DTA results. The composition of the eutectic mixture and its melting temperature is determined experimentally.     

Quantum-chemical simulation of unit process for the oxidation reactions of ethylene and its derivatives invoving <Superscript>1</Superscript>O<Subscript>2</Subscript> (<Superscript>1</Superscript>Δg)

The results of simulation of oxidation reactions of ethylene derivatives with different substituents (F atoms, CH₃O and CH₃ groups) and butadiene molecule with participation of ¹O₂ (¹Δg) have shown the possibility to realize different routes for the majority of the considered reactions. The largest product variety is obtained for butadiene and CH₃ derivatives of ethylene. For butadiene, along with 1,2-cycloaddition reactions resulting in four-membered dioxetane (which is realized in all cases), the possibility to form six-membered cyclic epidioxides (1,4-addition) and diepoxide products with two three-membered rings (epoxidation) has been found. The formation of hydroperoxide forms along with 1,2-addition reactions is also possible for all CH₃ derivatives of ethylene. Formation conditions and relative stability of the noted products have been analyzed for each case and certain features of the revealed reaction pathways with the transfer of two oxygen atoms have been discussed.     

Enantioselective Palladium‐Catalyzed Insertion of α‐Aryl‐α‐diazoacetates into the O?H Bonds of Phenols

A palladium‐catalyzed asymmetric O H insertion reaction was developed. Palladium complexes with chiral spiro bisoxazoline ligands promoted the insertion of α‐aryl‐α‐diazoacetates into the O H bond of phenols with high yield and excellent enantioselectivity under mild reaction conditions. This palladium‐catalyzed asymmetric O H insertion reaction provided an efficient and highly enantioselective method for the preparation of synthetically useful optically active α‐aryl‐α‐aryloxyacetates.     

Reactive epitaxy of beryllium on Si(1 1 1)-(7×7)

Scanning tunneling microscopy (STM) and photoelectron spectroscopy (PES) have been used to investigate the nucleation, growth, and structure of beryllium on Si(1 1 1)-(7×7). STM indicates that a chemical reaction occurs at temperatures as low as 120 K, resulting in a nano-clustered morphology, presumed to be composed of a beryllium silicide compound. Upon annealing to higher temperatures, PES data indicate that beryllium diffuses into the selvage region. High temperature annealing (∼1175 K) results in the formation of a universal ring cluster structure suggesting a Be–Si bond length less than 2.5 Å, in agreement with previous calculations regarding hypothetical Be₂Si.     

Use of integrated intensities of X-ray powder diffraction patterns of Mg<Subscript>1 − x</Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O solid solutions for the quantitative determination of their composition

X-ray diffraction spectra were obtained for polycrystalline samples of Mg_{1 ? x} Zn _x O solid solutions (x = 0.3, 0.5, 0.6, and 0.7) by X-ray powder diffraction. The theoretical integrated intensity ratio between the 111 and 002 reflections was plotted versus the percentage of zinc in the solid solutions. The possibility of extracting information on polycrystalline samples (the composition and the presence of microstructural features) from comparison of the theoretical and experimental integrated intensity ratios between the 111 and 002 reflections was investigated. The Le Bail procedure for the extraction of integrated intensities from X-ray powder diffraction patterns, followed by the use of these intensities in calculations with the SHELX-97 program package, was tested for the determination of the zinc fraction in polycrystalline samples of Mg_{1 ? x} Zn _x O solid solutions.     

Possibility of Mo<Subscript>2</Subscript>O<Subscript>6</Subscript> formation at high temperatures in the range of pressures from 1 to 1 × 10<Superscript>−5</Superscript> bar

Gibbs free energy minimization was used to consider the formation of complex molybdenum oxide (Mo₂O₆) at 2400 K in the range of pressures from 1 to 1 to 1 × 10⁻⁵ bar for the basic component ratio Mo: O₂ = 1: 1. Several ways are shown to lead to Mo₂O₆ formation: when P = 1 bar, a synthesis reaction involving simple molybdenum oxides (MoO, MoO₂, MoO₃) is the main way; when P = 1 × 10⁻³ bar or lower, reactions of (MoO₃) _n (n = 3−5) complex oxides with metallic molybdenum and molybdenum monoxide (MoO) are.     

Synthesis and photophysical properties of semiconductor molecules of D<Subscript>1</Subscript>–A–D<Subscript>2</Subscript>–A–D<Subscript>1</Subscript> structure on the basis of quinoxaline and dithienosilole derivatives for organic solar cells

new DTS(FCT₂)₂ organic semiconductor of the D₁–A–D₂–A–D₁ structure containing dithienosilole and quinoxaline chromophores as electron-donating and electron-accepting moieties, respectively, has been synthesized. The study of optical and electrochemical properties shows that the material absorbs light in a wide range of the solar spectrum through 700 nm and has an appropriate arrangement of energy levels for the efficient dissociation of excitons. The obtained results demonstrate that this approach to the design of semiconductor molecules of the D₁–A–D₂–A–D₁ structure is promising for high-performance organic solar cells.     

Mechanism of the zinc-catalyzed addition of azide ion to unsaturated compounds: Synthesis of 5-substituted 1<Emphasis Type="Italic">Н</Emphasis>-tetrazoles from nitriles and of 1-substituted 1<Emphasis Type="Italic">Н</Emphasis>-tetrazole-5-thiols from isothiocyanates

The mechanism of the formation of 5-substituted 1H-tetrazoles from organic nitriles and thiocyanates in the presence of NaN₃ and ZnCl₂ in aliphatic alcohols was studied. The results of this study allowed efficient methods of synthesis of substituted tetrazoles from nitriles, thiocyanates, and isothiocyanates to be proposed.     

Fragments of the coherent phase diagram and the kinetics of growth of elastically strained layers of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te solid solutions

The influence of the elastic component of the Gibbs energy of mixing on phase formation in the Cd-Hg-Te system was studied by a comparison of calculated dependences of layer parameters on growth conditions performed with and without the inclusion of mechanical strains in the growth system. The appearance of elastic strains between a layer and a substrate of the initial binary compounds insignificantly decreased the growth rate and almost did not influence the composition of the growing layer. The approximation of coherent conjugation of phases in the presence of elastic strain in the system and the assumption of the existence of chemical phase equilibrium at the interphase boundary give similar results for material growth. Both approaches quite satisfactorily describe the experimental data on layer growth under various temperature-time conditions.     

Theoretical evaluation of the radiative lifetimes of LiCs and NaCs in the A<Superscript>1</Superscript>Σ<Superscript>+</Superscript> state

Calculations of the adiabatic potential energy curves and the transition dipole moments between the ground (A¹Σ⁺) and the first excited (A¹Σ⁺) states have been determined for the LiCs and NaCs molecules. The calculations are performed using an ab initio approach based on non-empirical pseudopotentials for Cs⁺, Li⁺ and Na⁺ cores, parameterized l-dependent polarization potentials and full configuration interaction calculations. The potential energy curves and the transition dipole moment are used to estimate the radiative lifetimes of the vibrational levels of the A⁺Σ⁺ state using the Franck–Condon (FC) approximation and the approximate sum rule method. The radiative lifetimes associated with the A⁺Σ⁺ state are presented here for the first time. These data can help experimentalists to optimize photoassociative formation of ultracold molecules and their longevity in a trap or in an optical lattice.     

Electrochemical characterization of polypyrrole–LiNi<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>O<Subscript>2</Subscript> composite cathode material for aqueous rechargeable lithium batteries

A series of polypyrrole (PPy)–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrodes are formed by physical mixing of polypyrrole with LiNi_1/3Mn_1/3Co_1/3O₂ cathode material. LiNi_1/3Mn_1/3Co_1/3O₂ is synthesized by reaction under autogenic pressure at elevated temperature method. Highly resolved splitting of 006/102 and 108/110 peaks in the XRD pattern provide an evidence to well-ordered layered structure of the compound. The ratios of the intensities of 003 and 104 peaks are found to be >1, which indicate no pronounced mixing of the cation. Cyclic voltammetry and AC impedance studies revealed that the addition of polypyrrole significantly decreases the charge-transfer resistance of LiNi_1/3Mn_1/3Co_1/3O₂ electrodes. The electrochemical reactivity of PPy–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrode is examined during lithium ion insertion and de-insertion by galvanostatic charge–discharge testing; 10 wt.% PPy–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrode exhibits better electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiNi_1/3Mn_1/3Co_1/3O₂ electrode. The cell with 10 wt.% PPy added cathode shows significant improvement in the electrochemical performance compared with that having pristine cathode. The capacity remains about 70% of the initial value after 50 cycles while for cell with pristine cathode only about 28% of initial capacity remains after 40 cycles.     

Thermodynamic analysis of the structure of aqueous solutions of C<Subscript>12</Subscript>–C<Subscript>18</Subscript> hydrocarbons

Thermodynamic cycles including the increments \(\Delta G_{CH_2 }^0 , \Delta H_{CH_2 }^0 \), and \(T\Delta S_{CH_2 }^0 \) were constructed for dissolution, evaporation, hydrophobic hydration of C₅–C₉ hydrocarbons, and transfer from vapor (\(\Delta G_{CH_2 }^0 \) = ?0.7 kJ·mol^?1, \(\Delta H_{CH_2 }^0 \) = 2.9 kJ·mol^?1, \(T\Delta S_{CH_2 }^0 \) = 3.6 kJ·mol^?1) and water (\(\Delta G_{CH_2 }^0 \) = ?1.4 kJ·mol^?1, \(\Delta H_{CH_2 }^0 \) = 5.8 kJ·mol^?1, \(T\Delta S_{CH_2 }^0 \) = 7.2 kJ·mol^?1) to micelles of C₁₂–C₁₈ hydrocarbons. The formation of bistable hydrated micelles of C₁₂–C₁₈ is explained by a transition between the order-disorder states in an assembly of small (nano) systems of water. The extensive parameters of small systems and critical phenomena predicted by fluctuation theory are discussed.     

<Superscript>1</Superscript>H NMR study of complexation of α- and β-cyclodextrins with some biologically active acids

Reactions of - and -cyclodextrins with some biologically active acids were studied by ¹H NMR spectroscopy. Inclusion complexes are found to be formed only with aromatic amino acids (phenylalanine and tryptophan) and ascorbic acid. The complexes of cyclodextrin with citric acid are obtained through interactions between the polar groups of the guest molecule and the OH groups of the host molecule located on the outside.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 234–236.Original Russian Text Copyright © 2005 by Terekhova, Kulikov, Kumeev, Nikiforov, Alper.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Kinetics of the outer-sphere oxidation of thiourea by heteropoly-α<Subscript>2</Subscript>-17-tungsto-1-vanadodiphosphate anion

Kinetics of the oxidation of thiourea (tu) by heteropoly-α₂-17-tungsto-1-vanadodiphosphate anion, α₂-[P₂V^VW₁₇O₆₂]^7?, have been studied spectrophotometrically in aqueous acidic medium at 25 °C. At low pH (2.4–3.0), the neutral form of tu is the only reactive species. At higher pH (4.2–4.9), both neutral and deprotonated forms of tu participate in the reaction. The observed mixed-order kinetics suggest two parallel reactions: one in which the order in [tu] is unity, and a second in which it is two. In both cases, the order in [α₂-[P₂V^VW₁₇O₆₂]^7?] is unity. Based on the kinetic studies, a mechanism is proposed, in which a second-order proton-coupled electron transfer involving NH₂CSNH₂ and α₂-[P₂V^VW₁₇O₆₂]^7? proceeds through a sequential electron transfer, followed by proton transfer such that the reaction is an “activation-controlled” outer-sphere electron transfer process. By applying the Marcus equation, the self-exchange rate constants for the couples \({\text{NH}}_{2} {\text{CSNH}}_{2}^{ \cdot + }\)/NH₂CSNH₂ and α₂-[P₂V^VW₁₇O₆₂]^7?/α₂-[P₂V^IVW₁₇O₆₂]^8? were evaluated.     

The Synthesis of Lead-Free Ferroelectric Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>TiO<Subscript>3</Subscript> Thin Film by Solution-Sol–Gel Method

Bi_1/2Na_1/2TiO₃ (described as BNT) is considered as a promising lead-free ferroelectric material. In this study, BNT sol was synthesized by mixing bismuth oxide and sodium carbonate dissolved in nitric acid and titanium tetraisopropoxide in ethylene glycol, which was called a solution-sol–gel method and very cost-effective synthesis method, while very high-cost metal alkoxides are used as precursors in conventional sol–gel method. FT-IR and Raman analyses indicated that the chemical modification of titanium tetraisopropoxide by glycolic acid or oxalic acid occurred and the synthesis of stable BNT sol was possible. In the results of high temperature X-ray analysis and DTA/TG analyses, the crystallization of BNT was thought to occur at between 500 and 700C following the evaporation of solvent and organics and poly-condensation processes. The main crystal phase of the film was identified as rhombohedral crystal phase of Bi_1/2Na_1/2TiO₃ by XRD and Raman spectroscopy analyses, although a small amount of Bi₄Ti₃O₁₂ existed as a second phase.     

Kinetics of surface pyrolysis of a silane–germane gas mixture under conditions of epitaxial film deposition of Si<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solutions

Specific features of the pyrolysis of hydride molecules on the surface of a Si_1–x Ge _x film under conditions of epitaxial film deposition of a mixture of silicon and germanium hydrides have been studied. Temperature dependences of the kinetic coefficients responsible for the rate of hydrogen desorption from the Si_1–x Ge _x film surface and the rate of dissociation of gas molecule radicals adsorbed by the surface of the growing film have been obtained for the first time, using the developed kinetic models of surface pyrolysis and the results of engineering experiments in the temperature range 450–800°C. A correlation between the dissociation frequencies of silane and germane molecules, as well as a correlation of the dissociation frequencies with other kinetic parameters of the system were revealed.     

Chemical stability of Ba(Ce<Subscript>1−x</Subscript>Ti<Subscript>x</Subscript>)<Subscript>1−y</Subscript>Y<Subscript>y</Subscript>O<Subscript>3</Subscript> proton-conducting solid electrolytes

The purpose of this work was to investigate the influence of titanium and yttrium dopants on chemical stability of selected Ba(Ce_1−xTi_x)_1−yY_yO₃ compounds. The presented results are the part of wider research concerning the crystallographic structure, microstructure, electrical and transport properties of these groups of materials. Samples of Ba(Ce_1−xTi_x)_1−yY_yO₃ with x=0.05, 0.07, 0.10, 0.15, 0.20, 0.30 and y=0.05, 0.10, 0.20 (for x=0.05) were prepared by solid-state reaction method. Initially, differential thermal analysis (DTA) and thermogravimetry (TG) were used for optimization of preparation conditions. Subsequently, DTA-TG-MS (mass spectrometry) techniques were applied for evaluation of the stability of prepared materials in the presence of CO₂. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results were used to determine the phase composition, structure and microstructure of materials and to assist the interpretation of DTA-TG-MS results. The strong influence of Ti and Y dopants contents (x and y) on the properties was found. The introduction of Ti dopant led to the improvement of chemical stability against CO₂. The lower Ti concentration the better resistance against CO₂ corrosion was observed. Doping by Y had the opposite effect; the decrease of chemical stability was determined. In this case the higher Y dopant concentration the better resistance was observed. The attempt to correlate the influence of dopant on structure and chemical stability was also presented.