Oxidative ortho-C-N fusion of aniline by OsO4. Isolation, characterization of oxo-amido Osmium(VI) complexes, and their catalytic activities for oxidative C-C bond cleavage of unsaturated hydrocarbons

In an unusual reaction of osmium(VIII) oxide with p-substituted aromatic amines (X-C(6)H(4)-NH(2), where X = Me, H, Cl) in heptane afforded the brown osmium(VI)-oxo complexes [OsO(L)(2)] (1a-c, L = N-aryl-1,2-arylenediamide) in moderate yields. The ligand L is formed in situ via oxidative ortho-C-N fusion of arylamines. The reaction occurs in an inert atmosphere, and a part of Os(VIII) is used up for the oxidation of aromatic amine. Single crystal X-ray structure of a representative complex 1a is solved. The structural analysis has authenticated the ortho-C-N fusion of ArNH(2) resulting in formation of the diamide ligand, L. The complex as a whole is penta-coordinated, and the coordination sphere has a distorted square pyramidal geometry (tau = 0.26). A similar reaction of osmium(VIII) oxide with the preformed N-phenyl-1,2-phenelene diamine produced the complex 1a in nearly quantitative yield. The substituted phenazine, 5-phenyl-3-phenylimino-3,5-dihydro-phenazine-2-ylamine, is obtained as a byproduct of the latter reaction. The complexes, 1a-c, can be reduced in a reversible one-electron step, as probed by cyclic voltammetry. The one electron reduced paramagnetic Os(V) intermediate is, however, Electron Paramagnetic Resonance (EPR) silent. Solution spectra of the osmium complexes show several multiple transitions in the UV-vis region. Density functional theory calculations were employed to confirm the structural features and to support the spectroscopic assignments. The complex 1a catalyzes oxidation of a wide variety of unsaturated hydrocarbons like alkenes, alkynes, and aldehydes to the corresponding carboxylic acids in the presence of tert-butylhydroperoxide (TBHP) efficiently at room temperature.     

Colossal Stability of SiB11(BO)12−: An Implication as Potential Electrolyte in High-Voltage Alkali-ion Battery

High-voltage alkali metal-ion batteries (AMIBs) require a non-hazardous, low-cost, and highly stable electrolyte with a large operating potential and rapid ion conductivity. Here, we have reported a halogen-free high-voltage electrolyte based on SiB₁₁(BO)₁₂⁻. Because of the weak π-orbital interaction of −BO as well as the mixed covalent and ionic interaction between SiB₁₁-cage and −BO ligand, SiB₁₁(BO)₁₂⁻ has colossal stability. SiB₁₁(BO)₁₂⁻ possesses extremely high vertical detachment energy (9.95 eV), anodic voltage limit (∼10.05 V), and electrochemical stability window (∼9.95 V). Furthermore, SiB₁₁(BO)₁₂⁻ is thermodynamically stable at high temperatures, and its large size allows for faster cation movement. The alkali salts MSiB₁₁(BO)₁₂ (M=Li, Na, and K) are easily dissociated into ionic components. Electrolytes based on SiB₁₁(BO)₁₂⁻ greatly outperform commercial electrolytes. In short, SiB₁₁(BO)₁₂⁻-based compound is demonstrated to be a high-voltage electrolyte for AMIBs.     

A noble interaction: An assessment of noble gas binding ability of metal oxides (metal = Cu,Ag, Au)

An in silico study is performed on the structure and the stability of noble gas (Ng) bound MO complexes (M = Cu, Ag, Au). To understand the stability of these Ng bound complexes, dissociation energies, dissociation enthalpy, and dissociation free energy change are computed. The stability of NgMO is also compared with that of the experimentally detected NgMX (X= F, Cl, Br). It is found that MO has lower Ng binding ability than that of MX. All the dissociation processes producing Ng and MO are endothermic in nature and for the Kr‐Rn bound MO (M = Cu, Au), and Xe and Rn bound AgO cases, the corresponding dissociation processes are turned out to be endergonic in nature at standard state. The Wiberg bond indices of Ng? M bonds and Ng→M electron transfer gradually increase from Ar to Rn and for the same Ng they follow the order of NgAuO > NgCuO > NgAgO. Energy decomposition analysis shows that the Ng? M bonds in NgMO are partly covalent and partly electrostatic in nature. Electron density analysis further highlights the partial covalent character in Ng? M bonds. © 2016 Wiley Periodicals, Inc.     

Stability, reactivity, and aromaticity of compounds of a multivalent superatom

In this article, we analyze the stability, reactivity, and possible aromatic behavior of two recently reported clusters (Reveles, J. U.; Khanna, S. N.; Roach, P. J.; Castleman, A. W., Jr. Proc. Natl. Acad. Sci. 2006, 103, 18405), viz., Al(7)C(-) and Al(7)O(-) in the light of the principles of the maximum hardness and minimum electrophilicity as well as the nucleus-independent chemical shift values. Stability of these clusters in the context of addition/removal of an electron or an Al atom is now clearly understood.     

Direct observation of nanoparticle embedding into the surface of a polymer melt

Direct embedding of metal nanoparticles (NPs) into the surface of a polymer melt is observed by TEM and a new embedding mechanism proposed. Upon annealing above the glass transition temperature of polystyrene (PS), NPs (20 nm gold) are rapidly covered by a thin PS wetting layer, h* approximately 1.3-1.8 nm (i.e., about two or three monomers). Because it creates capillary pressure on a NP, this "universal" wetting layer is proposed to be responsible for NP embedding. The value of h* is independent of the molecular weight of PS and constant during the embedding process. The value of h* is found to be similar to the equilibrium wetting layer thickness of a polymer melt spreading on a metal substrate. Using a model that includes the spreading coefficient, long-range van der Waals interactions, and a chain-stretching penalty, h* is shown to be independent of the molecular weight of the polymer. Using this model and the measured value of h*, the interfacial energy between Au NP and PS is estimated to be 8.7 J/m2.     

Vibronic interaction and triplet state photophysics of phenylisatin and oxindole

Photophysical study of phenylisatin and oxindole triplet states have been made at room temperature and in different glasses at 77K. Qualitatively, in all respects the compounds have identical spectroscopic characteristics. Phosphorescence emission, excitation along with their polarization and lifetime suggest that a perturbation of the zero-point level of emitting state (³ππ*) by a close-lying triplet state (³nπ*) leads to a number of new spectral features. The experimental observations have been interpreted satisfactorily in terms of a switch (³ππ* state to ³nπ*) in the character of the lowest triplet states (T₁ and T₂) and also a similar switch in the character of the excited singlet states S₁ and S₂ for a change of glass matrix from MCH to ethanol. Invoking of first order and second order spin-orbit coupling explains the phosphorescence emission unambiguously.     

Wave induced sliding at the interface between a layered elastic medium and a half-space

The sliding interface between an unrestrained elastic half-space and a grounded layered half-space excited by an incident harmonic wave is investigated. The problem is formulated considering various possible boundary conditions and boundary inequalities at the sliding interface. The Coulomb friction model without distinction between the static and kinetic coefficients of friction is considered to govern the sliding condition. Three possible bands at the interface, namely slip, stick, and separation, are considered. The interface is assumed to be preloaded under normal and shear stresses. The solution is developed by modifying the problem of welded interface, which then is reduced to a set of algebraic equations. The effects of the incident angle, layer thickness, friction coefficient and externally applied stresses on the drift velocity of the unrestrained half-space are studied numerically for a pair of materials. It is shown that the sliding interface, and hence the drift velocity of unrestrained half-space is noticeably influenced by the layered medium. These results are expected to be useful for the development of a new kind of ultrasonic drive in future.     

Turbulent Flame Speeds of Premixed Supersonic Flame Kernels

It is unclear whether turbulent flame speed scalings established in low speed regimes are applicable to supersonic flames. To investigate this question, the canonical flame kernel is investigated in a scramjet-like channel having a one degree wall divergence. The growth, shape and internal kernel dynamics are investigated. Results are presented for three Mach numbers, four equivalence ratios, and three turbulence generators. Schlieren photography provides flame images for growth rate statistics and particle image velocimetry (PIV) provides turbulence statistics and investigation of internal kernel dynamics. Supersonic flame kernels are self-propagating and respond to the equivalence ratio in a fashion that is similar to low speed flames. However, supersonic flame kernels have features that are not present in subsonic flame kernels. Baroclinicity, resulting from pressure-density misalignment, creates a reacting vortex ring structure. Further, the mean kernel shape has a Mach number dependence and the vortex ring enhances the turbulent flame speed through entrainment of reactants and augmented flame surface growth. Hence, the previously established (low speed) flame speed scalings are inappropriate for supersonic flame kernels. Drawing motivation from vortex ring literature, the ring propagation velocity is used as the characteristic velocity and a new flame speed scaling is proposed.     

Simulation of Transverse Combustion Instability in a Multi-Injector Combustor using the Time-Domain Impedance Boundary Conditions

The time-domain impedance boundary condition (TDIBC) is used as a reduced-order model (ROM) in large-eddy simulation (LES) to study self-sustained transverse oscillations in an experimentally studied high-pressure, shear coaxial multi-injector combustor. This work is an extension of the recent study using ROM-LES to simulate a single-element combustor that exhibited longitudinal instability. Here, we focus on transverse instability in a seven-injector combustor. The fuel and oxidizer inlets are truncated and the conventional inflow boundary conditions at the original inlet are replaced by an impedance describing function (IDF) in the form of a reflection coefficient that couples with LES through characteristic based boundary conditions at the truncated inlet. The impedance model is also generalized to include the effects of entropy fluctuations at the inflow. The hybrid ROM-LES simulations are compared with LES simulations with the full combustor geometry. Results show very good agreement and confirm that the use of TDIBC within LES is a viable tool to account for complex acoustic/boundary interaction in a physical way without explicitly solving the full geometry at LES level. Some simplifications and approximations have to be invoked and these constraints are also discussed.