Fluorsilyl- und Fluorboryl-substituierte Cyclotetrasilazane Synthese und Kristallstrukturen

Fluorosilyl and Fluoroboryl Substituted Cyclotetrasilazanes. Synthesis and Crystal Structures Mono- and dilithiated octamethylcyclotetrasilazanes ( 1, 6 ) react with fluorosilanes and F₂BN(SiMe₃)₂, respectively, under retention of the cyclotetrasilazane structure yielding the mono- and disubstituted compounds 2–5 and 7–13 . In the reaction of the dilithium compound 6 with a fluorsilane in equivalent amounts, the bicyclic compounds 14 and 15 are obtained. Crystallographic investigations of the compounds 2, 3, 8 , and 9 indicate that the monosilylated eight-membered ring has a cradle conformation while the disilylated ring has a chair conformation. The X-ray structure of the bicyclic system 14 indicates that the nitrogen atoms of the Si₃N-units have a pyramidal environment.     

Bis(Cyclodisilazan-1-yl)dimethylsilane Synthese und Reaktionen

Bis(cyclodisilazane-1-yl) dimethylsilanes — Synthesis and Reactions The monolithium derivate of trisilazan-1-yl-cyclodisilazane 1 reacts with F₃SiN (SiMe₃)₂ with substitution. The silyl-bridged cyclodisilazanes 3–6 are formed in the reaction of the dilithium derivate of 1 with fluoro- and chlorosilanes. Using lithiumamide and lithiummethanolate a controlled exchange of one fluoro atom of 4 occurs ( 7,8 ). 9 and 10 are formed by hydrolysis of 4 . The aminofunctional compounds 11 und 12 are obtained in the reaction of 5 and 6 with NH₃. The dispirocyclus 13 is formed in the reaction of 8 with tert.-butyllithium. The reaction of dilithiated 1 with 4 gives the spirocyclus 14 . The crystal structure of 14 is discussed.     

Synthese funktioneller Carbonsäure-Silylester

Synthesis of Functional Carboxylic Acid Silylester Di-tert-butylsilandiol reacts with organic acid chlorides to chlorosilanoles R₂Si(OH)Cl 1 (R = t-Bu). The phosphoric acid silylester 2 is obtained from 1 and POCl₃. Lithiated halogenosilanoles react with carboxylic acid chlorides to give silylesters ( 3 – 7 ). Lithium (trimethyl-acetoxy)silanolate 8 is obtained in the reaction of the lithiated diol with the chloride of trimethylacetic acid. The analogous reaction with benzoyl chloride lead to the formation of the bis(benzoic acid) silylester 9 . The condensation product 10 is obtained in the reaktion of the lithiated aminosilanol (t-Bu)₂Si(NH₂)OLi with trimethylacetic acid chlorid and condensation of the formed ester with aminosilanol.     

Lattice Location of 12B in Single-Crystal Ni3Al Studied by β-Radiation Detected NMR

β-radiation detected nuclear magnetic resonance was applied to determine the location of ¹²B probe nuclei in a Ni₃Al single crystal. Combining our results with those of channeling experiments it turned out that more than 90% of the ¹²B ions occupy the octahedral interstitial site with six Ni ions as nearest neighbours.     

Photodesorption and photofragmentation of disilane adsorbed on a hydrogen terminated Si(100) surface

The photochemical mechanisms leading to the desorption and fragmentation of Si₂H₆ adsorbed on a hydrogen terminated Si(100) surface have been explored by recording the time-of-flight distributions of products escaping from the surface and by using electron energy loss spectroscopy to probe possible electronic excitations. Photodesorption of intact Si₂H₆ involves hot electrons that lose energy and move to the conduction band edge before initiating desorption. When the wavelength of the incident light is 193 nm, Si₂H₆ fragments give mostly Si, SiH₂, H₂ and SiH₄, but this pathway is quenched at longer wavelengths. This is consistent with direct excitation, but we also show that a negative ion resonance is accessible to substrate electrons that have been excited by 193 nm light.     

Cross relaxation studied by β NMR

The dipole-dipole interaction between polarized β active probes implanted into a metal and the surrounding host nuclei may lead to a transfer of polarization from the probe to the host. As energy must be conserved in this cross-relaxation (CR) process, resonance-like dips show up at certainB values, if the polarization of the probes is measured as a function of magnetic inductionB. The probe isotope¹²B has been studied in several metallic stoppers. For¹²B in the fec crystals Al, Cu the three possible cubic implantation sites could easily be discriminated by means of the CR technique. The temperature dependence of the dips yielded information on the diffusion of the probes. In the case of¹²B, in Cu above 400 K a further CR structure was found due to trapping of the probe at another site. In the bcc metal VCR spectra belonging to two different¹²B trapping sites could be separately registered using a special radiofrequency technique. Both, static and dynamical properties of the CR could be quantitatively explained by theory.