Quantenmechanische Behandlung von tief liegenden elektronischen Zuständen des Ammonium-Radikals mit der Methode der Einzentrumentwicklung

Zusammenfassung Mit der Methode der Einzentrumentwicklung (OCE) werden der Grundzustand und einige tief liegende angeregte Zustände des NH₄-Radikals unter Verwendung einer minimalen Basis von wasserstoffartigen bzw. Slaterschen Funktionen berechnet. Zur Kontrolle der Brauchbarkeit der Modellrechnungen bei der Interpretation experimenteller Ergebnisse werden zusätzlich die Alkaliatome Lithium und Natrium behandelt. Es ergibt sich eine deutliche Uberlegenheit der Funktionen vom Slater-Typ. Das Ammoniumradikal erweist sich gegenüber Autoionisation als stabil, während der Grundzustand bezüglich des Zerfalls in NH₃+H in der Nähe der Stabilitätsgrenze liegt. Einige Eigenschaften von metallammoniakalischen Lösungen werden mit den hier vorgelegten Ergebnissen in Zusammenhang gebracht.

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OCE-calculations of the ground state and some low lying excited states of NH₄

The ground state and some low lying excited states of NH₄ are calculated using the one-center expansion method (OCE) with a minimum basis set of hydrogen- resp. Slater-type functions. To check the validity of the method calculations are done for the alkali atoms lithium and sodium; comparison with experimental results shows that Slater-type functions are much more suitable. NH₄ comes out to be stable against autoionization. Concerning the dissociation into NH₃+H the ground state of NH₄ is very close to the limit of stability. Some properties of solutions of metals in liquid ammonia are correlated with the presented results.

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Résumé Calcul de l'état fondamental et d'états excités inférieurs de NH₄ avec emploi d'une base minimale de fonctions hydrogénoïdes (ou de Slater) dans une méthode avec développement par rapport à un centre (OCE). Des calculs sont effectués sur les atomes de lithium et de sodium afin de tester la valeur de la méthode; la comparaison avec les résultats expérimentaux montre que les fonctions de Slater donnent de meilleurs résultats. NH₄ apparait comme stable par rapport à l'autoionisation. L'état fondamental de NH₄ est trés prés de la limite de stabilité en ce qui concerne la dissociation selon NH₃+H. Les résultats obtenus sont mis en rapport avec certaines propriétés des solutions métalliques dans l'ammoniac liquide.

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Für die Mlichkeit, die numerischen Rechnungen mit der elektronischen Rechenanlage CD 6600 im Regionalen Rechenzentrum der Universität Stuttgart ausführen zu dürfen, sind wir Herrn Prof. Dr. J. H. Argyris und der Deutschen Forschungsgemeinschaft zu Dank verpflichtet. Herrn Dr. H. Dorada von der Firma Control Data GmbH danken wir für tatkräftige Hilfe bei der Ausführung der numerischen Rechnungen. Einer von uns (W. Sarholz) dankt der Deutschen Forschungsgemeinschaft für finanzielle Unterstützung.     

Polyamide synthesis from 6-aminocapronitrile, part 2: heterogeneously catalyzed nitrile hydrolysis with consecutive amine amidation

To test the potential of heterogeneous catalysts for the nylon-6 synthesis from 6-aminocapronitrile, a number of zeolites, aluminum silicate, and metal oxides were tested as catalysts for the model reaction of pentanenitrile with water and hexylamine to N-hexylpentanamide. All zeolitic and aluminum silicate systems showed an insufficient performance, while the metal oxides (TiO(2), ZrO(2), Nb(2)O(5)) showed very promising results. The kinetic behavior of the metal oxides was further investigated. First the nitrile was catalytically hydrolyzed to the terminal amide and subsequently the amidation of the hexylamine occurred. To polymerize 6-aminocapronitrile into nylon-6, more than 99 % nitrile conversion was required to obtain a high-molecular-weight polymer. Pentanenitrile conversions larger than 99 % can be obtained within six hours, at 230 degrees C, by using ZrO(2) as the catalyst. A kinetic study (by using IR spectroscopy) on the behavior of the metal oxides demonstrated that the adsorbed nitrile was catalytically hydrolyzed at the surface, but remained tightly bound to the surface. Zirconia-catalyzed polymerizations of 6-amino-capronitrile demonstrated that high-molecular-weight nylon-6 is feasible by using this route.     

Tetrakis(3,5‐di­methyl­pyridine)­dihydrido­silicon dibromide bis(aceto­nitrile) solvate and 3,5‐dimethylpyridinium bromide

In the course of an attempt to synthesize tetrakis(3,5‐di­methyl­pyridine)­dihydridosilicon dibromide, crystals of its aceto­nitrile disolvate, C₂₈H₃₈N₄Si²⁺·2Br^?·2C₂H₃N, (I), and of 3,5‐di­methyl­pyridinium bromide, C₇H₁₀N⁺·Br^?, (II), were obtained in the same reaction flask. They have both been structurally characterized.     

Complexes of germanium bromides with 4‐picoline and 3,4‐lutidine

The reactions of GeBr₄ with 4‐methyl­pyridine and 3,4‐di­methyl­pyridine lead to tetra­bromo­bis(4‐methyl­pyridine)­germanium, [GeBr₄(C₆H₇N)₂], and tetra­bromo­bis(3,4‐di­methyl­pyridine)­germanium, [GeBr₄(C₇H₉N)₂], respectively. These structures show the same features as the corresponding silicon complexes.     

trans‐Tetra­chloro­bis(4‐methyl­pyridine)­germanium(IV)

The structure of the title compound, [GeCl₄(C₆H₇N)₂], (I), is the first example of an addition compound of GeCl₄ with two aromatic nitro­gen bases. The mol­ecule, with essential D_2h symmetry, has crystallographic C_2h symmetry. The environment around the Ge atom can be described as a slightly distorted octahedron with the 4‐methyl­pyridine ligands occupying axial positions and the four chloro ligands in the equatorial plane. The structure of (I) is isomorphous with the corresponding silicon halides.     

Identifying the Role of Brønsted and Lewis Acid Sites in the Diels-Alder Cycloaddition of 2,5-DMF and Ethylene

The role of Lewis and Brønsted acid sites in the Diels-Alder cycloaddition (DAC) of ethylene to 2,5-dimethylfuran (2,5-DMF) to p-xylene was investigated. Amorphous silica catalysts containing Al³⁺ (ASA), Ga³⁺ (ASG), and In³⁺ (ASI) were prepared via homogeneous deposition-precipitation. Silica modified with Zr⁴⁺ (ASZ) was prepared by impregnation. Their acidic properties were characterized by various IR and NMR spectroscopic techniques. Measurements using pyridine as a probe molecule highlighted the presence of mostly Lewis acid sites (LAS) in all materials. Using CO as a probe, in contrast, demonstrated the existence of Brønsted acid sites (BAS) in ASA and ASG, which were nearly absent in ASI and ASZ. Differences in basic strength can explain the contrast in results observed between the two probe molecules. The highest p-xylene yield (~20 %) in the DAC reaction, could be achieved with ASA and ASG. The lack of BAS in ASI and ASZ resulted in inferior performance in the DAC, with p-xylene yields below 5 %. These results indicate the importance of BAS for the DAC reaction. Several other heterogeneous and homogeneous catalysts were explored for the DAC reaction to show the generality of our conclusion that BAS play a critical role in obtaining p-xylene from 2,5-DMF and ethylene.     

Confined Carbon Mediating Dehydroaromatization of Methane over Mo/ZSM‐5

Non‐oxidative dehydroaromatization of methane (MDA) is a promising catalytic process for direct valorization of natural gas to liquid hydrocarbons. The application of this reaction in practical technology is hindered by a lack of understanding about the mechanism and nature of the active sites in benchmark zeolite‐based Mo/ZSM‐5 catalysts, which precludes the solution of problems such as rapid catalyst deactivation. By applying spectroscopy and microscopy, it is shown that the active centers in Mo/ZSM‐5 are partially reduced single‐atom Mo sites stabilized by the zeolite framework. By combining a pulse reaction technique with isotope labeling of methane, MDA is shown to be governed by a hydrocarbon pool mechanism in which benzene is derived from secondary reactions of confined polyaromatic carbon species with the initial products of methane activation.     

Size dependence of photocatalytic oxidation reactions of Rh nanoparticles dispersed on (Ga1-xZnx)(N1-xOx) support

Mixed Ga–Zn oxynitrides were synthesized using coprecipitation, wet‐precipitation, and sol‐id‐solution methods. The oxynitrides were used as supports for Rh nanoparticle catalysts in photo‐catalytic wa...