Ligand-assisted reduction of osmium tetroxide with molecular hydrogen via a [3+2] mechanism

Osmium tetroxide is reduced by molecular hydrogen in the presence of ligands in both polar and nonpolar solvents. In CHCl3 containing pyridine (py) or 1,10-phenanthroline (phen), OsO4 is reduced by H2 to the known Os(VI) dimers L2Os(O)2(mu-O)2Os(O)2L2 (L2 = py2, phen). However, in the absence of ligands in CHCl3 and other nonpolar solvents, OsO4 is unreactive toward H2 over a week at ambient temperatures. In basic aqueous media, H2 reduces OsO4(OH)n(n-) (n = 0, 1, 2) to the isolable Os(VI) complex, OsO2(OH)4(2-), at rates close to that found in py/CHCl3. Depending on the pH, the aqueous reactions are exergonic by deltaG = -20 to -27 kcal mol(-1), based on electrochemical data. The second-order rate constants for the aqueous reactions are larger as the number of coordinated hydroxide ligands increases, k(OsO4) = 1.6(2) x 10(-2) M(-1) s(-1) < k(OsO4(OH)-) = 3.8(4) x 10(-2) M(-1) s(-1) < k(OsO4(OH)2(2-)) = 3.8(4) x 10(-1) M(-1) s(-1). The observation of primary deuterium kinetic isotope effects, k(H2)/k(D2) = 3.1(3) for OsO4 and 3.6(4) for OsO4(OH)-, indicates that the rate-determining step in each case involves H-H bond cleavage. Density functional calculations and thermochemical arguments favor a concerted [3+2] addition of H2 across two oxo groups of OsO4(L)n and argue against H* or H- abstraction from H2 or [2+2] addition of H2 across one Os=O bond. The [3+2] mechanism is analogous to that of alkene addition to OsO4(L)n to form diolates, for which acceleration by added ligands has been extensively documented. The observation that ligands also accelerate H2 addition to OsO4(L)n highlights the analogy between these two reactions.     

The Effects of an Oscillating External Field on the Damping Behavior of the Single-Mode Cavity in the Thermal Bath

International Journal of Theoretical Physics - By using the solution of the equation for density operator of the single-mode cavity driven by an oscillating external field in the thermal bath...     

A New Expression for Multidimensional Franck-Condon Integrals

A new closed form expression for the Franck-Condon integrals for overlap between arbitrary multidimensional harmonic oscillators has been exactly derived by employing the generating functions method. The calculations lead to the deduction of some general rules whereby an arbitrary multidimensional Franck-Condon integral can be expressed as sums of products of the Hermite polynomials. Copyright 1999 Academic Press.     

Investigation of critical influential speed for moving mass problems on beams

A traveling mass due to its mass inertia has significant effects on the dynamic response of the structures. According to recent developments in structural materials and constructional technologies, the structures are likely to be affected by sudden changes of masses and substructure elements, in which the inertia effect of a moving mass is not negligible. The transverse inertia effects have been a topic of interest in bridge dynamics, design of railway tracks, guide way systems and other engineering applications such as modern high-speed precision machinery process. In this study an analytical–numerical method is presented which can be used to determine the dynamic response of beams carrying a moving mass, with various boundary conditions. It has been shown that the Coriolis acceleration, associated with the moving mass as it traverses along the vibrating beam shall be considered as well. Influences regarding the speed of the moving mass on the dynamic response of beams with various boundary conditions were also investigated. Results illustrated that the speed of a moving mass has direct influence on the entire structural dynamic response, depending on its boundary conditions. Critical influential speeds in the moving mass problems were introduced and obtained in numerical examples for various BC’s.     

On the chemical bonding features in palladium containing compounds: A combined QTAIM/DFT topological analysis

Topological analyses of the electron density on N-benzoyl-L-pheylalanine and its palladium(II) complexes are carried out using the quantum theory of atoms in molecules (QTAIM) at the M06/6-31G(d) theoretical level. The topological parameters derived from the Bader theory are also analyzed; these are characteristics of Pd bond critical points and ring critical points. The calculated structural parameters are the highest occupied molecular orbital energy (E _HOMO), the lowest unoccupied molecular orbital energy (E _LUMO), the hardness (η), the softness (S), the absolute electronegativity (χ), the electrophilicity index (ω), and the fractions of electrons transferred (ΔN) from ethylenediamine, 2,2′-bipyridine and 1,10-phenanthroline complexes to N-benzoyl-L-pheylalanine. The numerous correlations and dependences between the energy terms of the symmetry adapted perturbation theory approach, geometrical, topological, and energy parameters are detected and described.     

Absorption and resonance Raman spectroscopy of the 1Bu state of trans‐1,3,5‐hexatriene including vibronic coupling

The vibronic coupling between the first excited S₁ (2¹A_g) and the second excited S₂ (1¹B_u) singlet electronic states in spectroscopy of trans‐1,3,5‐hexatriene molecule is investigated on the basis of a model consisting of two electronic states coupled by two vibrational modes. Employing a perturbation theory that treats the intramolecular couplings in a perturbative manner, the absorption and resonance Raman cross sections and excitation profiles of this molecule are calculated using the time‐correlation function formalism. The non‐Condon corrections are included in evaluation of cross sections. The multidimensional time‐domain integrals that arise in these calculations have been evaluated for the case in which S₀ (1¹A_g) S₂ (1¹B_u) electronic transition takes place between displaced and distorted harmonic potential energy surfaces. The calculated spectra are in good agreement with the experimental ones. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of the Photoelectron Spectra of Selenium Difluoride and Selenium Dichloride Based on Franck-Condon Factors

The vibrational structure of the photoelectron spectra of selenium difluoride and selenium dichloride have been simulated using the computed Franck-Condon factors in the harmonic oscillator approximation. Spectral simulations have been carried out employing the coupled-cluster singles, doubles, and triples (CCSD(T)) and the Becke three-parameter Lee, Yang, and Parr (B3LYP) values for the ground electronic states of the neutral molecules and the cations selenium difluoride and selenium dichloride, respectively. The Duschinsky rotations among the normal modes of two ground electronic states of species involved in the transition are fully taken into account. The ionization energies obtained for selenium difluoride and selenium dichloride are in reasonable agreement with the experimentally determined values. The spectral simulations of vibrational structures including frequency changes and Duschinsky rotation upon the electronic excitation are in agreement with the experimental results.     

Solving the nonlinear equations for one-dimensional nano-sized model including Rydberg and Varshni potentials and Casimir force using the decomposition method

The Adomian decomposition method has been applied to solve the nonlinear equations from the one-dimensional model for a nano-sized-oscillator. The model includes Rydberg and Varshni potentials as well as Casimir force with fractional damping. New approximate solution of the equations of motion for anharmonic vibrations of a nano-sized oscillator with the elastic force deriving from the Rydberg and Varshni potentials has been obtained.     

Alkane oxidation by osmium tetroxide

Aqueous alkaline OsO4 at 85 degrees C oxidizes saturated alkanes, including primary, secondary, and tertiary C-H bonds. Isobutane affords tert-butanol in quantitative yield based on consumed OsO4. Cyclohexane is oxidized to a mixture of adipate and succinate. Ethane and propane are oxidized to acetate, which itself is further oxidized under the reaction conditions. A few turnovers of isobutane oxidation have been accomplished using NaIO4 as the terminal oxidant. The alkane oxidation is an example of ligand accelerated catalysis, as hydroxide binding to OsO4 is required for reaction. A concerted mechanism involving [3+2] addition of a C-H bond to two oxo groups of OsO4(OH)- is suggested, analogous to the pathways for dihydroxylation of alkenes by OsO4(L) and for addition of H2 to OsO4(L).