Berechnung der Bandstruktur vom Vanadiumcarbid VC

Zusammenfassung Die Bandstruktur von stöchiometrischem Vanadiumcarbid VC wird mit Hilfe der quasi-selbstkonsistenten APW-Methode ermittelt. Als Austauschpotential wird ein parametrisiertes Slatersches Austauschpotential verwendet. Die Energie-Eigenwerte werden für 256k-Punkte in der 1. Brillouin-Zone berechnet. Zur Berechnung der Zustandsdichte werden weitere Energiewerte (für insgesamt 16384k-Punkte) nach der LCAO-Interpolationsmethode von Slater und Koster bestimmt und mit diesen die Zustandsdichte ermittelt. Die partiellen LCAO-Zustandsdichten zeigen weitgehende Übereinstimmung mit den APW-Charakterdichten und geben Aufschluß über denl-Charakter der Energiebänder. Die Ladungsverteilung im Kristall weist auf eine Ladungsüberführung vom Vanadium zum Kohlenstoff und damit auf eine gewisse Ionizität der Verbindung VC hin.

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Calculation of the band structure of vanadium carbide VC

The energy band structure of stoichiometric VC has been calculated by the quasi-self-consistent APW method. For the exchange potential a parametrized Slater-free-electron approximation has been used. The energy eigenvalues have been calculated for 256k-points in the first Brillouin zone. Further energy values (for a total number of 16384k-points) have been obtained by the LCAO interpolation method of Slater and Koster. From these energy values the density-of-states histogram has been calculated. The partial LCAO-densities-of-states are largely in agreement with the APW-character-densities. Both quantities give information about thel-character of the energy bands. The charges in the APW-spheres indicate a charge transfer from vanadium to carbon.

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Résumé La structure des bandes énergétiques du VC de composition stoichiométrique a été calculée par la méthode APW quasiautoconsistante. On s'est servi d'un potentiel d'échange paramétrisé selon Slater. Les eigen-valeurs d'énergie sont déterminées pour 256 pointsk dans la premiere zone de Brillouin. Pour dériver la densité d'états énergétiques ainsi que les densités d'états partielles (densités d'états du caractère 2s, 2p et3d) des valeurs d'énergie pour d'autres pointsk (en somme 16384) sont trouvées avec l'aide de la méthode d'interpolation LCAO de Slater et Koster. Il n'y a pas des différences significantes entre ces quantités et les densités des caractèresl calculées directement par la méthode APW. Des densités d'états partielles on peut dériver le caractèrel des bandes énergétiques.De la distribution des charges dans le cristal résulte un transfer de charge du vanadium au carbon ce qui signifie que le VC possède une certaine ionicité.

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Dem Gedenken an Herrn Prof. Dr. K. H. Hansen gewidmet.

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Dem Jubiläumsfonds der österreichischen Nationalbank sind wir für die gewährte finanzielle Unterstützung zu großem Dank verpflichtet. Herrn Prof. Dr. H. Nowotny danken wir für die Förderung, die er dieser Arbeitsrichtung angedeihen läßt. Die große Hilfe von Herrn Dr. K. Schwarz, University of Florida, Gainesville, wird dankbar anerkannt.     

Darstellung und Kristallstruktur von (n-Bu4N)3[Ir(NCS)(SCN)5]

Preparation and Crystal Structure of (n-Bu₄N)₃[Ir(NCS)(SCN)₅] The evaporated ethanolic extrakt of the reaction product of K₃[IrCl₆] and HNO₃, refluxed with an aqueous KSCN solution yields a mixture of the linkage isomers [Ir(NCS)_n(SCN)_6?-n]^3?, n = 0? 2, and small amounts of linkage isomeric chloropentarhodanoiridates(III), from which [Ir(NCS)(SCN)₅]^3? has been isolated by ion exchange chromatography on DEAE-cellulose. The X-Ray structure determination on a single crystal of (n-Bu₄N)₃[Ir(NCS)(SCN)₅] (monoclinic, space group P 2₁/a, a = 17.513(5), b = 32.607(5), c = 23.661(5) Å, β = 94.757(5)°, Z = 8) confirms the existance of a heteroleptic hexakis(thiocyanato(N)-thiocyanato(S))iridate(III) with an Ir? N distance of 2.03 Å and Ir? S bond lengths between 2.29 and 2.38 Å. The SCN groups with angles between 166 and 175° are nearly linear with Ir? S? C angles from 99.9 to 109.4°. The Ir? N? C angles of the two crystallographic independent anions are 166 and 174°.     

A convenient synthesis of phenols

Abstract

Anilines are rapidly, often within 60?minutes, converted into the corresponding phenols in up to 87% isolated yield. The presented experimentally simple protocol display broad compatibility with a variety of functional groups, and in particular, well suited for the preparation of methyl-substituted phenols. Such phenols are not easily available by other synthetic approaches. The formation of phenolic radical coupling products was not observed even for activated anilines using this open flask method.     

Advanced Bifunctional Oxygen Reduction and Evolution Electrocatalyst Derived from Surface‐Mounted Metal–Organic Frameworks

Metal–organic frameworks (MOFs) and their derivatives are considered as promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are important for many energy provision technologies, such as electrolyzers, fuel cells and some types of advanced batteries. In this work, a “strain modulation” approach has been applied through the use of surface‐mounted NiFe‐MOFs in order to design an advanced bifunctional ORR/OER electrocatalyst. The material exhibits an excellent OER activity in alkaline media, reaching an industrially relevant current density of 200 mA cm^?2 at an overpotential of only ≈210 mV. It demonstrates operational long‐term stability even at a high current density of 500 mA cm^?2 and exhibits the so far narrowest “overpotential window” ΔE_ORR‐OER of 0.69 V in 0.1 m KOH with a mass loading being two orders of magnitude lower than that of benchmark electrocatalysts.     

A practical synthesis of gramicidin s and sugar amino Acid containing analogues

A practical gram-scale and high-yielding synthesis of the antimicrobial peptide gramicidin S is presented. An Fmoc-based solid-phase peptide synthesis protocol is employed for the generation of the linear decapeptide precursor, which is cyclized in solution to afford the target compound. The versatility of our method is demonstrated by the construction of eight gramicidin S analogues (15a-h) having nonproteinogenic sugar amino acid residues (4-7) incorporated in the turn regions.     

Active site structure and redox processes of cytochrome c oxidase immobilised in a novel biomimetic lipid membrane on an electrode

Membrane-bound cytochrome c oxidase was attached to an electrode via a His-tag linker and studied by surface enhanced resonance Raman spectroscopy, demonstrating intact redox site structures and electron transfer between the electrode and the immobilized enzyme.     

Synthesis of bridged sugar amino acids: a new entry into conformationally locked δ- and ε-amino acids

The synthesis of three methylene bridged sugar amino acids is described. Key transformations in the synthetic strategy are a CO-insertion on fully protected ribose, an aldol condensation with formaldehyde and an oxetane forming cyclisation step. A novel Leu-enkephalin analogue containing the δ-SAA 1 was prepared using standard solution phase peptide chemistry.