Synthese,Struktur und dynamisches Verhalten von Cyclopentadienylboranen

The cyclopentadienylboranes I–XI have been synthesized by the reaction of halogenoboranes with cyclopentadienyl-trimethylsilanes, -trimethylstannanes and -lithium compounds. Substitution reactions at the boron atom in III and VIII with tetramethylstannane and dimethylamine lead to the cyclopentadienylboranes XII–XV. The structures of I–XV have been investigated by ¹H-, ¹³C- and ¹¹B-n.m.r. measurements. The 5-trimethylsilyl-cyclopentadienylboranes show a dynamic behaviour due to sigmatropic rearrangements. The influence of a boryl ligand on the speed of these rearrangements is discussed.     

Improvement in precision and accuracy of spark source mass spectrometric analysis by sample dissolution and isotope dilution

Summary In order to avoid the influence of sample heterogeneity, matrix effects and the non-availability of well analyzed standard samples on the precision and the accuracy of spark source mass spectrometric analysis, metal and silicate samples are dissolved chemically. For quantitative analysis, isotope dilution and calibration with standard solutions are used, whereby a precision of better than ±3% and ±8%, respectively, is obtained. This development has improved the precision by about a factor of 3 and increased the reliability of the analysis.

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Verbesserung der Genauigkeit und der Richtigkeit der funken-massenspektrometrischen Analyse durch chemisches Auflösen der Probe und Anwendung der Isotopenverdünnungsmethode

Zusammenfassung Um den Einfluß der Probenheterogenität, von Matrixeffekten und des Fehlens von gut analysierten Standardproben auf die Genauigkeit und Richtigkeit der funken-massenspektrometrischen Analyse zu vermeiden, sind metallische und silicatische Proben chemisch gelöst worden. Zur quantitativen Analyse wird die Isotopenverdünnungsmethode und eine Eichung mit Standardlösungen verwendet, wobei eine Genauigkeit von besser als ±3% bzw. ±8% erreicht wird. Diese Entwicklung hat die Genauigkeit gegenüber der direkten Methode um einen Faktor von ungefähr 3 verbessert und die Zuverlässigkeit der Analyse erhöht.

     

Arene-metal complexes: Preparation and reactions of h6-arene-Cr(CO)2(diphos) and analogs

Reaction of 1,2-bis(triphenylphosphino)ethane (diphos) with h⁶-arenetricarbonylchromium(0) complexes results in replacement of one CO by diphos to give h⁶-arene(diphos)dicarbonylchromium(0) (e.g., complex 4) and μ-diphosbis(h⁶-arene)tetracarbonyldichromium(0). Comparison of rate of arene exchange for h⁶-benzenetricarbonylchromium, h⁶-benzene(triphenylphosphine)dicarbonylchromium, and complex 4 showed that: (1) replacement of CO by a phosphine retards arene exchange and (2) the effect of diphos in stabilizing an h⁴-benzene ligand in complex 4 is not sufficient to allow rapid arene exchange. Nucleophilic substitution for hydrogen was observed for the first time in a phosphine-substituted arene-chromium complex.     

Polymerisation von α-Methylstyrol durch Bestrahlung mit Elektronen

Zusammenfassung Es wird die durch Elektronenbestrahlung ausgelöste Substanzpolymerisation von-Methylstyrol beschrieben. Auf Grund der Untersuchungen des Polymerisationsverlaufes und der Taktizitäten der Polymeren mit Hilfe der magnetischen Kernresonanz wird ein kationischer Mechanismus angenommen.

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Summary The polymerization in bulk of-methylstyrene induced by irradiation with electrons is studied. From investigations of the polymerization and polymer tacticities by nuclear magnetic resonance it is concluded that the polymerization takes place by a kationic mechanism.

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Wir danken Herrn cand. phys.Klaus Kolbe für die Taktizitätsbestimmungen.     

Trace element analysis of geological glasses by laser plasma ionization mass spectrometry (LIMS): A comparison with other multielement and microanalytical methods

Laser plasma ionization mass spectrometry (LIMS) is used in our laboratory as an in-situ microanalytical method for the investigation of solids, especially of rocks and minerals. To demonstrate the accuracy of this method we have analyzed homogeneous geological glass samples. The results are compared with data obtained from other analytical techniques. The performance of the LIMS method for geochemical investigations is discussed. Received: 2 December 1996 / Revised: 21 February 1997 / Accepted: 26 February 1997     

DFB laser diodes in the wavelength range from 760 nm to 2.5 μm

We present a novel device technology to produce DFB laser diodes which are suitable for tunable diode laser spectroscopy. The new technological approach employs lateral metal distributed feedback (DFB) gratings in close proximity to the laser ridge which results in single mode emission with high spectral purity and output powers as required for most spectroscopic applications. Over the entire wavelength range from the visible (760 nm) up to the near-infrared (2.5 microm) single mode emission can be obtained for devices based on different semiconductor systems such as GaAs, InP and GaSb. Typical side mode suppression ratios are better than 35 dB for cw-room temperature operation and narrow linewidths ensure high spectroscopic resolution.