Nachweis der Mehrfachemission von Sekundärelektronen mittels Proportionalzählrohr

A proportional counter is used as analyser for electron energies (in the range 10 to 20 keV). The resolving power for 20 keV is 21%. The multiple emission of secondary electrons is investigated with this counter.     

NMR-spektroskopische Untersuchungen zur Solvatation von Tetraphenylimidodiphosphatokomplexen der Lanthanoiden

NMR-spectroscopic Investigations on Solvation of Lanthanoide Complexes of Tetraphenylimidodiphosphate The additional coordination of solvent molecules to chelate complexes LnA₃ of rare earth ions (Ln³⁺) and tetraphenylimidodiphosphate ions (A^?) has been studied by ¹H-NMR spectroscopy. The nature of the solvent has a great influence on the spectra observed especially in the case of paramagnetic Ln³⁺ ions. In acetone as solvent TmA₃ forms a disolvate preferably. The brutto stability constants for the additional coordination of acetone as ligands by TmA₃ are β₁ = (0.013 ± 0.003) mol^?1 · l and β₂ = (0.016 ± 0.001) mol^?1 · l².     

Activation of alkynes by the dinitrogen complex [CoH(N2)(PPh 3)3] towards catalytic oligomerization and cyclization reactions

The complex [CoH(N₂)(PPh ₃)₃] catalyses oligomerization and cyclization reactions of alkynes under mild conditions. Hence, alkyne cocyclotrimerization to benzene derivatives was mainly observed for ethyl propiolate, affording the three possible isomers of tricarbethoxybenzene; phenylacetylene undergoes mainly linear dimerization totrans-PhCCCH=CHPh and trimerization; linear dimers are also the predominant products from 3-hexyne, but 1-octyne (with a long chain) undergoes mainly isomerization to 2-octyne; higher oligomers are also usually formed. Except for ethyl propiolate, hydrogenated dimers are detected in low yields (e.g.trans,trans-PhCH=CHCH=CHPh from phenylacetylene), whereas 3-hexene is formed in considerable yield from 3-hexyne. A novel type of cocyclization reaction with a nitrile (NCMe) appears to occur with phenylacetylene to give (although in low yield) 4,6-dimethyl-5-phenyl-pyrimidine. Alkynols are unreactive under the chosen conditions.

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Die Aktivierung von Alkinen mit dem Distickstoffkomplex [CoH(N₂)(PPh ₃)₃] gegenüber katalytischer Oligomerisierung und Cyclisierungsreaktionen

Zusammenfassung Der Komplex [CoH(N₂)(PPh ₃)₃] katalysiert Oligomerisations- und Cyclisierungsreaktionen von Alkinen unter milden Bedingungen. Die Cyclotrimerisierung von Propinsäureethylester ergibt die drei möglichen Isomeren von Tricarbethoxybenzol; Phenylacetylen reagiert hauptsächlich zu linearen Dimeren (vor allemtrans-PhCCCH=CHPh) und Trimeren; lineare Dimere herrschen auch bei 3-Hexin vor, während 1-Octin (mit langer Alkylkette) vorwiegend zu 2-Octin isomerisiert wird. In allen Fällen werden ebenfalls höhere Oligomere gebildet. Außer bei Propinsäureethylester entstehen ebenfalls in geringer Menge hydrierte Dimere (z. B.trans,trans-PhCH=CHCH=CHPh aus Phenylacetylen). Eine neue Art von Cocyclisierungsreaktion mit einem Nitril (NCMe) scheint bei der Bildung (in geringer Ausbeute) von 4,6-Dimethyl-5-phenyl-pyrimidin aus Phenylacetylen vorzuliegen. Alkinole reagieren unter den Versuchsbedingungen nicht.

     

Monte Carlo simulation of the three-dimensional Potts model

The phase transition of the three-dimensional 3-state Potts model at zero field is investigated by a careful Monte Carlo analysis. The transition is found to be of first order. Fluctuations appear to be very strong and critical exponents can be defined with reasonable accuracy. The results are compared with those of the 4-state Potts model.     

Komplexchemie reaktiver organischer Verbindungen,XX

A new convinient route to [Ta(η-C₅H₅)₂Cl₂] is described. The compound [Ta(η-C₅H₅)₂(SCH₃)₂] and hence {[Ta(η-C₅H₅)₂(SCH₃)₂Pt(SCH₃)₂ Ta(η-C₅H₅)₂](PFδ)₂} are derived from it. Monocyclopentadienylniobium halides are shown to be precursors of the new derivative given in the title.