DFT study of the full catalytic cycle for the propene hydroformylation catalyzed by a heterobimetallic HPt(SnCl3)(PH3)2 model catalyst

DFT calculations were carried out to study the full catalytic cycle for the hydroformylation of propene, catalyzed by the heterobimetallic model catalyst trans‐Pt(H)(PH₃)₂(SnCl₃). Before the study of the full catalytic cycle, the performance of six pure GGA, one GGA with inclusion of dispersion corrections, four hybrid‐GGA, and three meta‐GGA exchange correlation functional to describe a model reaction promoted by Pt‐Sn catalyst were assessed. It is shown that the BP86 and GPW91 functionals, using extended basis set, provides reliable energetic results when compared with the CCSD(T) calculations. All intermediates and transition states along the elementary steps of the entire catalytic cycle were located and the energies involved in the catalytic cycle calculated using BP86 functional. The solvent effects along the entire catalytic cycle were evaluated using the polarizable continuum model. In contrast with the rhodium catalysts, the regioselectivity of the hydroformylation is set at the carbonylation step. The hydrogenolysis is the rate determining step of the entire cycle, with the activation energy of ～21 kcal mol^?1 in agreement with the experimental value of ～25 kcal mol^?1. The trans effect of the SnCl ligand seems to be pronounced only in the first step of the catalytic cycle, facilitating the insertion of the olefin into the Pt? H bond trans to it. The analysis of the stationary points obtained along each elementary step of the catalytic cycle is carried out separately and discussed. The BP86/cc‐pVTZ/SBKJC results shows that the pathway leading to the linear aldehyde is preferred, being in agreement with the experimental findings. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Electron localizability indicators ELI–D and ELIA for highly correlated wavefunctions of homonuclear dimers. II. N2, O2, F2, and Ne2

Electron localizability indicators based on the electron pair density ELI–D and ELIA Electron localizability indicators ELI‐D and ELIA based on the electron pair density are studied for the correlated ground‐state wavefunctions of N₂, O₂, F₂, and Ne₂ diatomics. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations to investigate the local effect of electron correlation on the extent of electron localizability in position space determined by the two indicators. The results are complemented by calculations of effective bond order, vibrational frequency, and Laplacian of the electron density at the bond midpoint. It turns out that for O₂ and F₂, the reliable topology of ELI–D is obtained only at the correlated level of theory. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Self-diffusion of rodlike and spherical particles in a matrix of charged colloidal spheres: a comparison between fluorescence recovery after photobleaching and fluorescence correlation spectroscopy

The fluorescence recovery after photobleaching (FRAP) method and the fluorescence correlation spectroscopy (FCS) have been applied on suspensions of highly charged colloidal spheres with a small content of rod-shaped tobacco mosaic virus (TMV) particles. Since these methods only determine the self-diffusion coefficient of the fluorescently labeled species, D(S) of the rods and the spheres could independently be measured. The ionic strength of the dispersion medium has been varied to measure self-diffusion of rods and spheres in dependence on the degree of order of the matrix spheres. In contrast to FRAP, which allows the determination of the long-time self-diffusion coefficient D(S) (L), FCS measures self-diffusion on a shorter time scale. Thus a comparison of the results that were obtained by FCS and FRAP, in combination with Brownian Dynamics simulations, gives insight into the time dependence of the self-diffusion coefficient of an interacting colloidal system. As the mean interparticle distance of the matrix is of the same order of magnitude as the length of a TMV rod, the rotational motion is influenced by the assembly of spheres around a TMV particle. Since FCS is sensitive both to translational and rotational motion, whereas FRAP, which probes the diffusion at much larger length scales, is only sensitive to the translational motion of TMV, the comparison of diffusion coefficients measured employing FRAP and FCS can give some insights in the rotational diffusion: the experimental data indicate a slowing down of the rotational motion of a TMV rod with increasing structural order of the matrix spheres.     

Metal-metal bonding in ScTaN2. A new compound in the system ScN-TaN

Gray microcrystalline powders of ScTaN(2) were prepared from solid-state reactions of delta-ScN with Ta(3)N(5) powders at T = 1770 K. According to thermal analyses the compound is stable against oxidation by O(2) up to temperatures of T = 800 K. In an Ar atmosphere ScTaN(2) decomposes above T = 1250 K and in a N(2) atmosphere above T = 2000 K under release of N(2) to form delta-ScN and beta-Ta(2)N. The crystal structure (space group P6(3)/mmc, No. 194, a = 305.34(3) pm, c = 1056.85(9) pm, Z = 2) was refined on the basis of X-ray and neutron powder diffraction data. It comprises alternating layers of ScN(6/3) octahedra and trigonal TaN(6/3) prisms, which are also observed in the binary nitrides delta-ScN and theta-TaN, respectively. A small degree of anti-site defects (about 5%) was detected. Only a small solubility of ScN in epsilon-TaN was observed, while the solubility of TaN in delta-ScN is >/=10 mol % at T = 1820 K. ScTaN(2) is a diamagnetic small gap semiconductor or a semimetal, as inferred from magnetization and electrical resistivity measurements, consistent with band structure calculations. Chemical bonding analyses with the COHP method yield significant covalent Ta-Ta interactions. Topological analyses of the electron localization function reveal unexpected Ta-Ta three-center bonding basins within seemingly empty trigonal prisms of the TaN(6/3) layers.     

Experimental and theoretical investigation of epoxide quebrachitol derivatives through spectroscopic analysis

Two synthetic epoxide derivatives, important intermediates in organic synthesis, were obtained from L-quebrachitol, and their conformations were proposed based on spectroscopic analysis. Density functional theory (DFT) calculations of infrared and NMR spectra were shown to be reliable enough for organic chemistry applications. The observed structures were determined with the aid of the DFT spectroscopic data, stressing the relevance and utility of combined experimental/theoretical studies and also the usefulness of the (13)C NMR B3LYP/6-31G(d,p) calculations.     

The use of thermoplastic elastomers as polymer processing aids in processing of linear low density polyethylene

Commercially available thermoplastic elastomers based on block copolymers of diisocyanates and polyols and based on silicones have been reported by Kulikov et al. (2004 and 2006) to delay sharkskin in extrusion of Linear Low Density Polyethylene. In this work thermoplastic elastomers have been used as polymer processing additives in blown film extrusion of Linear Low Density Polyethylene. When a thermoplastic elastomer is added in small amounts to Linear Low Density Polyethylene it deposits at the die surface during extrusion and may postpone the onset of sharkskin enabling up to 20 times higher rate of extrusion. Many thermoplastic elastomers are certified for body and food contacts and could be a cost-effective substitution of fluorinated polymers in processing of Linear Low Density Polyethylene by extrusion. Oscillating and capillar rheometry have been used to reveal the mode of action of the additives. Results of capillar rheometry showed a decrease of apparent viscosity of the polymer melt when additive was added. Therefore Mooney method (Mooney, 1931) was applied to prove occurring slip inside of the die. Substantial delay of sharkskin was achieved also in conditions without slip of molten polyethylene inside the die by adding thermoplastic elastomer based on urethanes. Oscillating rheometry has been used to characterize elasticity of the materials. It could be shown that efficiency to delay sharkskin depends on elasticity of the specific thermoplastic elastomer at processing temperature. Surface tension of the solid materials was used to estimate the mutual affinity of the materials. Therefore a theoretical model of Rathod and Hatzikiriakos (2004) was used to evaluate the data. Finally a classification of polymer processing aids into “slip inducers” and “flow enhancers” by their mode of action was done. Ability of novel processing aids to postpone sharkskin was shown in blown film extrusion. Applicability of polymer processing aids in injection moulding could be proved by use of a mould with spiral cavity.     

Laser desorption ionization time‐of‐flight mass spectrometric study of binary As‐Se glasses

Binary chalcogenide As‐Se glasses and their thin films are important for optics, computers, materials science and technological applications. To increase understanding of the properties of thin films fabricated by plasma deposition techniques, more information concerning the physics of plasma plume is needed. In this study the formation of clusters in plasma plume from different As‐Se glasses by laser desorption ionization (LDI) or laser ablation (LA) was studied by time‐of‐flight mass spectrometry (TOF MS) in positive and negative ion modes. Formation of a number of As_pSe_q singly charged clusters As₃Se (q = 1–5), AsSe (q = 1–3), As₂Se (q = 2–4), and As₃Se (q = 2–5) was found from As‐Se glasses with the molar ratio As:Se in the range from 1:2 to 7:3. The stoichiometry of the As_pSe_q clusters was determined via isotopic envelope analysis and computer modeling. The structure of the clusters is proposed and the relationship to the structure of the parent glasses, as also suggested by Raman scattering spectra, is discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigations of hard elastic polypropylene with respect to the coil-strand-transition model

Hard elastic polypropylene was investigated by x-ray scattering using synchrotron radiation and by performing stress strain measurements in different liquids. It was found that the long period increases with elongation up to 1.3–1.4. Beyond this extension a change in the deformation behavior takes place. In the range from 1.1 to 1.3–1.4 the deformation measurements in the different liquids are in good agreement with the coil-strand-transition model. The proposed linear relationship between the deformation work and the elongation could be confirmed. The same holds for the surface energy. Moreover, the calculated ratio between the surface energy and the deformation work agrees with the measurements.