Electronic energy levels of weakly coupled nanostructures: C60-metal interfaces

A new approach based on density functional theory and the Anderson impurity model is developed to calculate charging energies and quasiparticle energy gaps of molecular systems weakly coupled to an environment. The approach is applied to C60 adsorbed on Au(111) and Ag(100) surfaces, resulting in electronic structures that are in excellent agreement with recent experiments. Image-charge screening effects on molecular orbital energies are found to be of similar magnitude for the two surfaces, but charge-transfer screening and spin fluctuations also affect the Ag case due to a partially occupied C60 orbital.     

Comparison of mechanistic models for correlation of activation energies of liquid‐phase addition of carbon‐centered radicals to terminal olefins

The performance of different models for the influence of enthalpy and polar effects on radical additions is compared for the extensive data set from the Fischer group, supplemented by additional data. The best correlations result from the Fischer–Radom (FR) model, but it also contains the largest number of adjustable radical‐dependent parameters not based on physical observables. Updating the literature values of , IP, and EA that are inputs to the FR model led to some deterioration in the quality of the correlations; this is symptomatic of remaining deficiencies in the thermochemical databases. In contrast, the Lalevee–Allonas–Fouassier (LAF) model gives poorer correlation but this is in part compensated because it uses the same inputs but with no adjustable parameters. Hammett‐type models based on polar and radical substituent constants rather than on molecular properties of the reactants perform even more poorly. In all cases, poorer correlation, as judged by increasing sd(ΔE), is accompanied by a systematic bias to over‐predict the lower E values and under‐predict the higher ones. The enthalpy contribution in the FR and LAF models is expressed as a linear Evans–Polanyi dependence of E on ΔH. Replacement by nonlinear Marcus dependences does not significantly improve performance. An attempt to significantly reduce the number of adjustable parameters in the FR model by anchoring them to a base set applicable to all radicals, which is then modulated for spin delocalization based on observable ESR hyperfine constants in the initial and adduct radicals, showed modest success. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of Rhodomyrtone Analogs Modified at C7

We developed a route to rhodomyrtone analogs that feature different acyl groups at C7. Since electrophilic substitution reactions on the aryl part of the rhodomyrtone core led to C5 derivatives, the C5 position was blocked by a chlorine. Subsequent Duff type formylation followed by Grignard addition to the aldehyde group and oxidation gave various phenones. The benzyl protecting groups were removed by hydrogenation or boron tribromide. Some derivatives turned out to be quite active against multiple resistant Staphylococcus aureus strains and a rhodomyrtone resistant mutant (Rom^R). The chlorine at C5 seems to have a beneficial effect on the antibacterial activity.     

Photodegradation of CuBi2O4 Films Evidenced by Fast Formation of Metallic Bi using Operando Surface-sensitive X-ray Scattering**

CuBi₂O₄ has recently emerged as a promising photocathode for photo-electrochemical (PEC) water splitting. However, its fast degradation under operation currently poses a limit to its application. Here, we report a novel method to study operando the semiconductor-electrolyte interface during PEC operation by surface-sensitive high-energy X-ray scattering. We find that a fast decrease in the generated photocurrents correlates directly with the formation of a metallic Bi phase. We further show that the slower formation of metallic Cu, as well as the dissolution of the electrode in contact with the electrolyte, further affect the CuBi₂O₄ activity and morphology. Our study provides a comprehensive picture of the degradation mechanisms affecting CuBi₂O₄ electrodes under operation and poses the methodological basis to investigate the photocorrosion processes affecting a wide range of PEC materials.     

A Complete Triad of Zero-Valent 17-Electron Monoradicals of Group 7 Elements Stabilized by m-Terphenyl Isocyanides

The first consistent series of mononuclear 17-electron complexes of three Group 7 elements has been isolated in crystalline form and studied by X-ray diffraction and spectroscopic methods. The paramagnetic compounds have a composition of [M⁰(CO)(CNp-F-Ar^DArF2)₄] (M=Mn, Tc, Re; Ar^DArF2=2,6-(3,5-(CF₃)₂C₆H₃)₂C₆H₂F) and are stabilized by four sterically encumbering isocyanides, which prevent the metalloradicals from dimerization. They have a square pyramidal structure with the carbonyl ligands as apexes. The frozen-solution EPR spectra of the rhenium and technetium compounds are clearly anisotropic with large ⁹⁹Tc and ^185,187Re hyperfine interactions for one component. High-field EPR (Q band and W band) has been applied for the elucidation of the EPR parameters of the manganese(0) complex.     

The behavior of the structure function at large wavevectors for polymers in different regimes

Off‐lattice Monte Carlo simulations employing the pivot algorithm are used to generate ideal and excluded volume linear polymers in three dimensions. The structure function at large wavevectors is calculated from the resulting configurations. This is compared to the exact equation for ideal chains and to experimental data and both scaling and renormalization group predictions for excluded volume chains. It is found that using the des Cloizeaux form for the distance distribution function in an analytic calculation of the structure function leads to close agreement with the experimental and Monte Carlo data.