Cholesteric helix inversion: Novel nitro compounds showing unusual changes of the cholesteric helical pitch

We present a homologeous series of liquid crystalline trioxadecalin compounds having a terminal alkoxy chain and a nitro group. The (1S, 3R, 6R,8R)-3-(4'-nitrophenyl)-8-(4'-octoxyphenyl)-2,4, 7-trioxabicyclo [4.4.0]decane 2 c shows a temperature-dependent inversion of the cholesteric helix at lower temperatures. For higher temperatures, the reciprocal helical pitch reaches a minimum, then it increases, tending to a second inversion point just above the clearing point. An additional chiral centre in the side chain leads for nitro compounds 3 to non-mesomorphic behaviour. For the cyano compounds 4, the change in the cholesteric helix is suppressed, for the R configuration, but for the S configuration helical inversion occurs at high temperatures and selective reflection above the transition to the TGB_A phase.     

Multiple Zeolite Structures from One Ionic Liquid Template

This study reports the use of 1‐butyl‐3‐methyl imidazolium methanesulfonate ionic liquid as a template in the synthesis of zeolites. It is found that the silicon source determines the formation of beta (BEA), mordenite framework inverted (MFI), or analcime (ANA) zeolites. Depending on this source, different preorganized complexes are obtained that drive the formation of the different zeolite structures. In the presence of ethanol, the ionic liquid form preorganized complexes that drive the formation of MFI. In its absence, BEA is obtained. Whereas, the large amount of sodium present when using sodium metasilicate leads to ANA formation. A molecular simulation study of the relative stability of the template‐framework system and location of the template provides further insight into the mechanism of synthesis.     

DFT Simulations of Water Adsorption and Activation on Low‐Index α‐Ga2O3 Surfaces

Density functional theory (DFT) calculations are used to explore water adsorption and activation on different α‐Ga₂O₃ surfaces, namely (001), (100), (110), and (012). The geometries and binding energies of molecular and dissociative adsorption are studied as a function of coverage. The simulations reveal that dissociative water adsorption on all the studied low‐index surfaces are thermodynamically favorable. Analysis of surface energies suggests that the most preferentially exposed surface is (012). The contribution of surface relaxation to the respective surface energies is significant. Calculations of electron local density of states indicate that the electron‐energy band gaps for the four investigated surfaces appears to be less related to the difference in coordinative unsaturation of the surface atoms, but rather to changes in the ionicity of the surface chemical bonds. The electrochemical computation is used to investigate the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) on α‐Ga₂O₃ surfaces. Our results indicate that the (100) and (110) surfaces, which have low stability, are the most favorable ones for HER and OER, respectively.     

cis‐Bis(2,2′‐bipyridyl‐N,N′)dichlorosilicon diiodide

The crystal and molecular structure of the title compound, C₂₀H₁₆Cl₂N₄Si²⁺·2I^?, has been determined at 173 K. To our knowledge, this is the first crystal structure of a silicon tetrahalide complex with a bidentate base as a ligand. The two chloro ligands are cis relative to each other. The Si—N bonds trans to a chloro ligand are longer than the Si—N bonds trans to an Si—N bond. This feature is observed for the majority of M(bipy)₂Cl₂ (M = metal and bipy = 2,2′‐bipyridyl) complexes, but it does not hold for all structures retrieved from the Cambridge Structural Database. The two pyridyl rings of each bipyridyl unit are nearly coplanar, whereas the bipyridyl units are almost perpendicular to each other. The two I^? ions are more than 5 Å from the silicon centre. As a result, the compound can definitely be described as ionic. The crystal packing is stabilized by short C—H?I contacts.     

Influence of preparation procedure on the surface chemistry and catalytic characteristics of FeZSM-5 zeolite in selective oxidation of benzene to phenol

The influence of preparation procedure on the nature of active centers, surface chemistry, and catalytic characteristics of FeZSM-5 zeolite in selective oxidation of benzene to phenol using N₂O as an oxidizing agent was studied.     

Untersuchung der UV-Absorptionsspektren einiger Pyridin-Additionsverbindungen

Zusammenfassung Von den Pyridinaddukten PyHCl, BF₃ · Py, BCl₃ · Py, BBr₃ · Py, AlCl₃ · Py, AlBr₃ · Py, SiF₄ · 2Py, SiCl₄ · 2Py, SiHCl₃ · 2Py, SiBr₄ · 2Py, GeCl₄ · 2Py, und PCl₅ · Py wurden UV-Absorptionsspektren aufgenommen. Mit Hilfe einfacher Hückelrechnungen gelang es, die Verschiebung der längstwelligen -^*-Bande gegenüber der des freien Pyridins qualitativ zu deuten, und zwar sowohl für ein positives als auch für ein negatives h _N im freien Pyridin. Die für den zweiten Fall erhaltenen -Ladungsdichten stehen in Einklang mit den Ergebnissen einer ab initio-Rechnung für HCN von McLean [7] und denen einer LCAO-Rechnung unter Einschluß von - und -Elektronen für Pyridin von Veillard und Berthier [8]. Die Additionspartner des freien Pyridins konnten auf Grund der durchgeführten Rechnungen nach wachsender Akzeptorstärke angeordnet werden.

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Investigations on the UV-absorption spectra of some pyridine addition compounds

UV-absorption spectra of the pyridine addition compounds PyHCl, BF₃ · py, BCl₃ · py, BBr₃ · py, AlCl₃ · py, AlBr₃ · py, SiF₄ · 2py, SiCl₄ · 2py, SiHCl₃ · 2py, SiBr₄ · 2py, GeCl₄ · 2py, and PCl₅ · py were measured. The shift of the long-wave - ^*-pyridine band could be explained by a simple Hückel calculation, using either a positive or a negative h _N for the pyridine molecule. The charge distribution, resulting from calculation with negative h _N agrees with those obtained by an ab-initio-calculation of McLean for HCN [7] and by a LCAO-calculation, including - and -electrons, for pyridine of Veillard and Berthier [8]. The Lewis acids, forming addition compounds with pyridine, are arranged according to increasing acceptor strength using the results of the Hückel-calculations.

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Résumé Mesure des spectres d'absorption U.V. des composés de la pyridine: PyHCl, BF₃ · py, BCl₃ · py, BBr₃ · py, AlCl₃ · py, AlBr₃ · py, SiF₄ · 2py, SiCl₄ · 2py, SiHCl₃ · 2py, SiBr₄ · 2py, GeCl₄ · 2py, et PCl₅ · py. Le déplacement de la bande ^* de la pyridine, a été interprété à l'aide d'un simple calcul Hückel, utilisant une valeur h _N positive ou négative pour la molécule de pyridine. La distribution de charge résultant de calculs avec h _N négatif est en accord avec celle obtenue par calcul ab initio pour HCN [7] (Mac Lean) et par un calcul LCAO à électrons et pour la pyridine (Veillard et Berthier [8]). Les acides de Lewis qui forment un composé d'addition avec la pyridine sont classés selon le pouvoir accepteur croissant d'après les résultats du calcul Hückel.

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Herrn Prof. Dr. Hermann Hartmann danken wir herzlich für die freundliche Unterstützung, die er uns bei dieser Arbeit gewährte. Der Deutschen Forschungsgemeinschaft gilt unser Dank für die Bereitstellung finanzieller Mittel.