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21.
Oscar E. Piro Eduardo E. Castellano Roberto C. V. Piatti Agustín E. Bolzn Alejandro J. Arvia 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(4):m252-m255
The crystal structures of two salts of bis(thiourea)gold(I) complexes, namely bis(thiourea‐κS)gold(I) chloride, [Au(CH4N2S)2]Cl, (I), and bis[bis(thiourea‐κS)gold(I)] sulfate, [Au(CH4N2S)2]2SO4, (II), have been determined. The chloride salt, (I), is isomorphous with the corresponding bromide salt, although there are differences in the bonding. The AuI ion is located on an inversion centre and coordinated by two symmetry‐related thiourea ligands through the lone pairs on their S atoms [Au—S 2.278 (2) Å and Au—S—C 105.3 (2)°]. The sulfate salt, (II), crystallizes with four independent [Au(CH4N2S)2]+ cations per asymmetric unit, all with nearly linear S—Au—S bonding. The cations in (II) have similar conformations to that found for (I). The Au—S distances range from 2.276 (3) to 2.287 (3) Å and the Au—S—C angles from 173.5 (1) to 177.7 (1)°. These data are relevant in interpreting different electrochemical processes where gold–thiourea species are formed. 相似文献
22.
On the basis of Altona's empirical generalization of the Karplus equation, an expression of 3JH,H as function of pseudorotation parameters for five-membered rings, was deduced. The resulting equation was parametrized by means of molecular mechanics calculations for tetrahydrofuran and tetrahydrothiophene. Estimation of 3JH,H for the full pseudorotational itinerary was made. From the best fit between calculated and measured 3JH,H values the preferred conformation of those rings may be established. The procedure was applied for the conformational analysis of 4-thiohexofuranose derivatives, having and β,
-galacto and D- manno, and -
-talo configurations. 相似文献
23.
Tutusaus O Viñas C Núñez R Teixidor F Demonceau A Delfosse S Noels AF Mata I Molins E 《Journal of the American Chemical Society》2003,125(39):11830-11831
exo-Cluster dicarbollides substitution has allowed tuning of the E degrees (Ru(II)/Ru(III)) potential to obtain the best-performing Kharasch catalyst. We postulate that this is possible through the to-and-fro electron movement between the boron cluster and the sulfonium moieties. 相似文献
24.
A method based on headspace solid-phase microextraction-gas chromatography-mass spectrometry is proposed for the quality control of multilayer packaging and its manufacturing process. Volatile organic compounds (VOCs) are produced in the manufacturing process of the packaging. They can cause organoleptic problems or modify the properties of the packaging depending on the nature and the amount of the VOCs formed. The quantification using packaging samples with a known VOC concentration for the calibration is proposed in order to reduce the analysis time, and the method is validated using a statistical test. Finally, the method is applied to the determination of odour-responsible compounds in multilayer packaging samples obtained under different extrusion-coating conditions, i.e. type of extruder, type of polymer and extrusion speed. 相似文献
25.
The properties of isolated neutral oxygen vacancies and divacancies of metal oxides of increasing complexity (MgO, CaO, alpha-Al2O3, and ZnO) have been studied by means of density-functional theory within a supercell periodic approach. Vacancy formation energies, vacancy-vacancy interactions, and geometry rearrangements around these point defects have been investigated in detail. The characterization of the electronic structure of these point defects has been established by analysis of the density of states and of the topology of the electron density and of electron localization function. It is found that the chemical character of the oxide determines the properties of the oxygen vacancies. For the covalent ZnO oxide, a more complex scheme arises in which the relaxation around the oxygen vacancy is much larger leading to the formation of Zn4-like almost metallic particles in the crystal. The relationship of these structures with the crystal shear planes is discussed. The present study shows that supercells containing approximately 200-300 atoms provide converged values for the geometric and electronic structure of oxygen vacancies of these metal oxides in the point defect low concentration limit. 相似文献
26.
Borasio M Rodríguez de la Fuente O Rupprechter G Freund HJ 《The journal of physical chemistry. B》2005,109(38):17791-17794
Methanol decomposition and oxidation on Pd(111) at millibar pressure were studied by in situ polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS), on-line gas chromatography and pre- and postreaction X-ray photoelectron spectroscopy (XPS). Various dehydrogenation products such as methoxy CH3O, formaldehyde CH2O, formyl CHO, and CO could be spectroscopically identified. Methanol oxidation proceeds via dehydrogenation to formaldehyde CH2O, which either desorbs or is further dehydrogenated to CO, which is subsequently oxidized to CO2. Carbonaceous overlayers that are present during the reaction may favorably affect the selectivity toward CH2O. The reaction takes place on metallic Pd, and no indications of an involvement of Pd surface oxide were observed. 相似文献
27.
On the basis of a detailed study of the pilocarpine-induced nickel(II) pre-wave using various polarographic techniques, an electrode process mechanism is proposed in which the formation of a catalytic complex between aquo-nickel(II) and veronalate-nickel(II) on the one hand and unprotonated pilocarpine adsorbed on the electrode surface on the other is followed by the reduction of nickel(II) in the complex and the release of the catalytic ligand. The pre-peak recorded by differential-pulse polarography in the system 1 × 10?3 M Ni(II)-1 × 10?2 M sodium veronal, nitric acid (pH 8.5) (with ionic strength maintained at 0.2 with sodium nitrate) can be used for quantitative determination of pilocarpine at concentrations in the range 2.5 × 10?7-8 × 10?6 M. 相似文献
28.
A tungsten neopentylidene complex has been found to decompose to yield a heterochiral dimer that contains a W=W double bond and no bridging ligands. Decompositions of related bisalkoxide complexes also yield compounds that contain an "unsupported" W=W double bond, while a sample of [Mo(NAr)(CH2-t-Bu)(OC6F5)]2 has been found to be a homochiral species related to [W(NAr)(CH2-t-Bu)(OC6F5)]2. 相似文献
29.
Studies about the development of a new effective aromatization process for converting gasoline rich in light saturated hydrocarbons, using modified molecular shapeselective zeolites, have been carried out. Naphthas with olefins and naphthenes are potential feedstocks. The yield of aromatic hydrocarbons increases with decreasing hydrogen content of the feed. Zn-SABO and Zn-ZSM type zeolites have been shown to be excellent catalysts for the process. 相似文献
30.
X. Assfeld M. F. Ruizlopez J. Gonzalez R. Lopez J. A. Sordo T. L. Sordo 《Journal of computational chemistry》1994,15(5):479-487
The effect of correlation energy, basis set size, zero-point energy (ZPE) correction, and solvation on the reaction mechanism of the ketene–imine cycloaddition reaction has been investigated. The electrostatic solvent effect was studied with a self-consistent reaction field method in which the solvation energy is obtained using a multipole expansion of the molecular charge distribution. The ab initio results have been analyzed by means of a theoretical method based on the expansion of the MOs of the supermolecule in terms of those of the reactants and the performance of the configuration analysis. In gas phase, due to the correlation energy and/or the ZPE corrections, the reaction is predicted to be a one-step process. In solution, the stabilization of the charge-transferred configurations results in the occurrence of a very stable, Zwitterionic intermediate giving a two-step mechanism. © 1994 by John Wiley & Sons, Inc. 相似文献