Kristallstrukturbestimmung von N-Trimethylsily-N′-methylimidazoliumbromid

Crystal Structure Determination of N-Trimethylsilyl-N′-Methylimidazolium Bromide The reaction of Trimethylbromosilane and N-Methylimidazole (NMI) led to a 1:1 compound stable at room temperature. The reaction was carried out at room temperature and colorless single crystals were obtained by sublimation. The addition compound crystallizes in the orthorhombic space group Pbnb (No. 56) with lattice constants a = 1218.3(2)pm, b = 1333.6(1)pm, c = 1360.2(2)pm, Z = 8, D_calc = 1.414 g/cm³. For 1506 independent reflections, measured at 21°C the structure could be refined to R = 0.067 and R_w = 0.062.     

Zur Kristallstruktur des Ammonium- und Natriumfluorids

Zusammenfassung Im Rahmen einer Modellrechnung wird eine Bestimmung der Gitterstruktur und der Gitterkonstanten von Ammoniumfluorid und dem isoelektronischen Natriumfluorid durchgeführt. Unter den zur Konkurrenz zugelassenen Gittertypen Kochsalz- und Wurtzitstruktur wählt die Rechnung jeweils den in der Natur realisierten Typ als stabilsten aus. Für die Gitterkonstanten ergeben sich gute Werte.

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On the crystal structure of ammonium- and sodiumfluoride

By means of a model calculation a determination of the lattice structure and the lattice constants of ammoniumfluoride and the isoelectronic sodiumfluoride has been carried out. Of the lattice types discussed (sodiumchloride- and wurtzite structure) the calculation predicts in each case the correct type as the most stable one, as it is realized in nature. The calculated lattice constants agree very well with the experimental results.

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Résumé Par un calcul de modèle on a déterminé la structure de réseau et les constantes correspondantes du fluorure d'ammonium et fluorure de sodium isoélectronique. Le calcul prédit dans chaque cas le type de réseau le plus stable (entre les structures de type chlorure de sodium ou wurtzite) et c'est bien celui réalisé dans la nature. Les constantes de réseau calculées sont en bon accord avec celles obtenues expérimentalement.

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Der Deutschen Forschungsgemeinschaft danke ich für die finanzielle Unterstützung.     

Complexes of mixed silicon halides with 4‐picoline

The reaction products of an addition reaction of five different silicon tetrahalides with the aromatic nitro­gen base 4‐methyl­pyridine are presented. The following five structures are isomorphous: (I) tetra­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Cl₄­N₂Si, (II) bromo­tri­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Br­Cl₃N₂Si, (III) di­bromo­di­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Br₂­Cl₂N₂Si, (IV) tri­bromo­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄Br₃­Cl­N₂Si, and (V) tetra­bromo­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄Br₄N₂Si. The mol­ecules of (I) and (V), with D_2h symmetry, have crystallographic C_2h symmetry, while the molecules of (II), (III) and (IV) have a lower molecular symmetry, but as a result of the disorder of the halogen ligands, they appear to be of the same crystallographic symmetry. The environment around the Si atom can be described as a slightly distorted octahedron with the methyl­pyridine ligands occupying axial positions and the four halogen ligands in the equatorial plane. In spite of the different substitution pattern of the silicon centre, there are only insignificant differences between these five structures.     

Coordination properties of ionic liquid-mediated chromium(II) and copper(II) chlorides and their complexes with glucose

The structural and coordination properties of complexes formed upon the interaction of copper(II) and chromium(II) chlorides with dialkylimidazolium chloride (RMIm(+)Cl(-)) ionic liquids and glucose are studied by a combination of density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS). In the absence of the carbohydrate substrate, isolated mononuclear four-coordinated MeCl(4)(2-) species (Me = Cu, Cr) dominate in the ionic liquid solution. The organic part of the ionic liquid does not directly interact with the metal centers. The interactions between the RMIm(+) cations and the anionic metal chloride complexes are limited to hydrogen bonding with the basic Cl(-) ligands and the overall electrostatic stabilization of the anionic metal complexes. Exchange of Cl(-) ligands by a hydroxyl group of glucose is only favorable for CrCl(4)(2-). For Cu(2+) complexes, the formation of hydrogen bonded complexes between CuCl(4)(2-) and glucose is preferred. No preference for the coordination of metal chloride species to specific hydroxyl group of the carbohydrate is found. The formation of binuclear metal chloride complexes is also considered. The reactivity and selectivity patterns of the Lewis acid catalyzed reactions of glucose are discussed in the framework of the obtained results.     

Non-Pincer-Type Manganese Complexes as Efficient Catalysts for the Hydrogenation of Esters

Catalytic hydrogenation of carboxylic acid esters is essential for the green production of pharmaceuticals, fragrances, and fine chemicals. Herein, we report the efficient hydrogenation of esters with manganese catalysts based on simple bidentate aminophosphine ligands. Monoligated Mn PN complexes are particularly active for the conversion of esters into the corresponding alcohols at Mn concentrations as low as 0.2 mol % in the presence of sub-stoichiometric amounts of KO^tBu base.     

Understanding the Anomalous Alkane Selectivity of ZIF-7 in the Separation of Light Alkane/Alkene Mixtures

C2 and C3 alkanes are selectively adsorbed from mixtures over the corresponding alkenes on the zeolite imidazolate framework ZIF-7 through a gate-opening mechanism. As a result, the direct production of the pure alkene upon adsorption and the pure alkane upon desorption in packed columns is possible. Herein, a detailed investigation of the step-wise adsorption and separation of alkanes and alkenes is presented, together with a rigorous performance assessment. A molecular picture of the gate-opening mechanism underlying the unprecedented selectivity towards alkane adsorption is proposed based on DFT calculations and a thermodynamic analysis of the adsorption-desorption isotherms.     

Synthese und Kristallstrukturbestimmung von Dimethyldi-(N-Methylimidazolium)siliciumbromid

Synthesis and Crystal Structure Determination of Dimethyldi-(N-Methylimidazolium)silicon Bromide The reaction of dibromodimethylsilane with n-methylimidazole (NMI) leads to a 1:2 compound stable at room temperature. The reaction was carried out at room temperature and colorless, moisture sensitive crystals were obtained by sublimation. The addition compound crystallizes in the orthorhombic space group Pcam (No. 57) with lattice constants a = 1 110 96(8) pm, b = 1 142.3(2) pm and c = 1 238.9(3) pm. For 1 317 independent reflections, measured at 21°C, the structure could be refined to R = 0.040 and R_w = 0.041.