Photochemistry with Chlorine Trifluoride: Syntheses and Characterization of Difluorooxychloronium(V) Hexafluorido(non)metallates(V), [ClOF2][MF6] (M=V,Nb, Ta,Ru, Os,Ir, P,Sb)

A photochemical route to salts consisting of difluorooxychloronium(V) cations, [ClOF₂]⁺, and hexafluorido(non)metallate(V) anions, [MF₆]⁻ (M=V, Nb, Ta, Ru, Os, Ir, P, Sb) is presented. As starting materials, either metals, oxygen and ClF₃ or oxides and ClF₃ are used. The prepared compounds were characterized by single-crystal X-ray diffraction and Raman spectroscopy. The crystal structures of [ClOF₂][MF₆] (M=V, Ru, Os, Ir, P, Sb) are layer structures that are isotypic with the previously reported compound [ClOF₂][AsF₆], whereas for M=Nb and Ta, similar crystal structures with a different stacking variant of the layers are observed. Additionally, partial or full O/F disorder within the [ClOF₂]⁺ cations of the Nb and Ta compounds occurs. In all compounds reported here, a trigonal pyramidal [ClOF₂]⁺ cation with three additional Cl⋅⋅⋅F contacts to neighboring [MF₆]⁻ anions is observed, resulting in a pseudo-octahedral coordination sphere around the Cl atom. The Cl−F and Cl−O bond lengths of the [ClOF₂]⁺ cations seem to correlate with the effective ionic radii of the M^V ions. Quantum-chemical, solid-state calculations well reproduce the experimental Raman spectra and show, as do quantum-chemical gas phase calculations, that the secondary Cl⋅⋅⋅F interactions are ionic in nature. However, both solid-state and gas-phase quantum-chemical calculations fail to reproduce the increases in the Cl−O bond lengths with increasing effective ionic radius of M in [MF₆]⁻ and the Cl−O Raman shifts also do not generally follow this trend.     

Deuterium isotope effects on 13C chemical shifts of negatively charged NH…N systems

Deuterium isotope effects on ¹³C chemical shifts are investigated in anions of 1,8‐bis(4‐toluenesulphonamido)naphthalenes together with N,N‐(naphthalene‐1,8‐diyl)bis(2,2,2‐trifluoracetamide) all with bis(1,8‐dimethylamino)napthaleneH⁺ as counter ion. These compounds represent both “static” and equilibrium cases. NMR assignments of the former have been revised. The NH proton is deuteriated. The isotope effects on ¹³C chemical shifts are rather unusual in these strongly hydrogen bonded systems between a NH and a negatively charged nitrogen atom. The formal four‐bond effects are found to be negative indicating transmission via the hydrogen bond. In addition, unusual long range effects are seen. Structures, ¹H and ¹³C NMR chemical shifts and changes in nuclear shieldings upon deuteriation are calculated using density functional theory methods. Copyright © 2013 John Wiley & Sons, Ltd.     

A model for the capacitated,hop-constrained,per-packet wireless mesh network design problem

Three critical factors in wireless mesh network design are the number of hops between supply and demand points, the bandwidth capacity of the transport media, and the technique used to route packets within the network. Most previous research on network design has focused on the issue of hop constraints and/or bandwidth capacity in wired networks while assuming a per-flow routing scheme. However, networks that employ per-packet routing schemes in wireless networks involve different design issues that are unique to this type of problem. We present a methodology for designing wireless mesh networks that consider bandwidth capacity, hop constraints, and profitability for networks employing a per-packet routing system.     

Modeling ammonia oxidation over a Pt (533) surface

We present a new reaction model for ammonia oxidation on a Pt (533) surface and perform numerical simulations using mean field equations. Kinetic parameters were taken from experiments and Density Functional Theory (DFT) calculations. The model is based on an oxygen-activated ammonia decomposition and includes NHx (x = 0, 1, 2) intermediates. Reaction rates and coverages obtained from calculations show semiquantitative agreement with values from kinetic and in-situ XPS measurements up to 0.1 mbar pressures. Pathways for ammonia oxidation were analyzed by varying kinetic parameters in the model, which provides new insights into the relative importance of different reaction steps.     

Kinetics of ammonia oxidation on stepped platinum surfaces. I. Experimental results

The kinetics of ammonia oxidation with oxygen have been investigated in the 10⁻⁵ and 10⁻⁴ mbar range on Pt(5 3 3) and Pt(4 4 3). Only N₂ and NO but no N₂O were detected as reaction products. The dependence of product formation on temperature and on the partial pressures of the reactants has been studied under steady state conditions. The reactive sticking coefficients were determined under reaction conditions with s_reac of ammonia reaching nearly 0.2. The Pt(5 3 3) surface was found to be catalytically more active than Pt(4 4 3) by a factor of 2-4.     

Energetische Eigenschaften eines 100-kW-Kaskaden-Plasmatrons

Energetical properties of two different cascaded 100 kW-H₂-plasma jets are treated. The losses of the heat are tested in dependence of the current. The influence of the geometrical place on the losses of heat in the plasma jet is shown. Questions of the adaption of the plasma jet to the power supply are discussed.     

Catalytic ammonia oxidation on platinum: mechanism and catalyst restructuring at high and low pressure

Catalytic ammonia oxidation over platinum has been studied experimentally from UHV up to atmospheric pressure with polycrystalline Pt and with the Pt single crystal orientations (533), (443), (865), and (100). Density functional theory (DFT) calculations explored the reaction pathways on Pt(111) and Pt(211). It was shown, both in theory and experimentally, that ammonia is activated by adsorbed oxygen, i.e. by O(ad) or by OH(ad). In situ XPS up to 1 mbar showed the existence of NH(x)(x= 0,1,2,3) intermediates on Pt(533). Based on a mechanism of ammonia activation via the interaction with O(ad)/OH(ad) a detailed and a simplified mathematical model were formulated which reproduced the experimental data semiquantitatively. From transient experiments in vacuum performed in a transient analysis of products (TAP) reactor it was concluded that N(2)O is formed by recombination of two NO(ad) species and by a reaction between NO(ad) and NH(x,ad)(x= 0,1,2) fragments. Reaction-induced morphological changes were studied with polycrystalline Pt in the mbar range and with stepped Pt single crystals as model systems in the range 10(-5)-10(-1) mbar.     

Qualitative und quantitative Spektralanalyse

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