ABSTRACT
After an introductory overview of all currently known tris(dialkylamido)alanes with the formula [Al(NR2)3]n (n = 1, 2), a simplified synthetic method based on the usage of is presented. The simplification results from the fact that the ether adduct can already be obtained during the necessary synthesis of the alane moiety and that the use of trimethylamine is no longer required. Current conflicts regarding the experimental data of tris(diethylamido)alane and their interpretation have been resolved by means of single crystal structure analysis. The N-methylpiperazine derivative was described for the first time and characterised by various analytical methods. In temperature-dependent NMR measurements ranging from -35 °C to 90 °C coalescence phenomena of 13C and 1H NMR signals of tris(N-methylpiperazino)alane as well as thermal migration of 1H NMR signals of tris(diethylamido)alane were observed.
ABSTRACT
AlH3 (PPh3 )2 was synthesized as a stable solid being the first known 1 : 2 alane arylphosphane adduct. Although only weakly intra-molecularly coordinated, it displays as a molecular crystal significant inertness against atmospheric humidity and oxygen due to strong steric screening of the alane unit. The compound readily dissociates PPh3 in solution allowing for its use as a Lewis acidic reducing agent. These features lead to an easy to store, easy to use reducing agent that may enable the quantitative investigation of aluminum hydride chemistry including reduction, complexation and hydroalumination reactions. The structure contains two non-equivalent penta-coordinated aluminum centers that despite long Al-P distances of ca. 2.7â Å display unusually high quadrupolar coupling constants CQ of 25.1 and 26.5 in 27 Al solid state NMR measurements. The product was also tested as a reducing agent on a small set of selected compounds with various functional groups.
ABSTRACT
Three-dimensional nanocomposite networks consisting of percolated Si nanowires in a SiO2 matrix, Si:SiO2, were studied. The structures were obtained by reactive ion beam sputter deposition of SiOx (x ≈ 0.6) thin films at 450 ∘C and subsequent crystallization using conventional oven, as well as millisecond line focus laser treatment. Rutherford backscattering spectrometry, Raman spectroscopy, X-ray diffraction, cross-sectional and energy-filtered transmission electron microscopy were applied for sample characterization. While oven treatment resulted in a mean Si wire diameter of 10 nm and a crystallinity of 72% within the Si volume, almost single-domain Si structures of 30 nm in diameter and almost free of amorphous Si were obtained by millisecond laser application. The structural differences are attributed to the different crystallization processes: conventional oven tempering proceeds via solid state and millisecond laser application via liquid phase crystallization of Si. The five orders of magnitude larger diffusion constant in the liquid phase is responsible for the three-times larger Si nanostructure diameter. In conclusion, laser treatment offers not only significantly shorter process times, but moreover, a superior structural order of nano-Si compared to conventional heating.
ABSTRACT
In two experiments using a radial-arm maze, pairs of rats made choices among eight maze locations, each containing a large quantity of one of two food types. The choices made by 1 rat affected the choices made by the other rat. Under most conditions, visits by 1 rat increased the tendency of the other rat to subsequently choose that maze location. However, the effect depended on the quality of the food available in a particular location. When it was possible for the rats to observe each other on the maze arms and a rat had experienced that a location contained the less preferred food type, a previous visit to that location by the foraging partner decreased the tendency to visit that location. These effects are attributed to working memory for the spatial choices of another rat, and they indicate that memory produced by a rat's own visit to a maze location is integrated with memory for the behavior of another rat to determine spatial choice.
