Tetramethyldisilan-1,2-diyl-verbrückte Dicyclopentadienyl-und Diindenylmetalldichloride der 4. Gruppe – Kristallstruktur von

Tetramethyldisilane-1,2-diyl bridged Dicyclopentadienyl and Diindenyl Metal Dichlorides of the Group 4 Metals – Crystal Structure of Dicyclopentadienyl and diindenyl metal dichlorides of the type Cp′? SiMe₂SiMe₂? Cp′MCl₂ (Cp′ = C₅H₄, M = Ti ( 1 ), Zr ( 2 ), Hf ( 3 ); Cp′ = C₉H₇, M = Zr ( 4 ), Hf ( 5 )) were synthesized and characterized by means of their ¹H, ¹³C, ²⁹Si-n.m.r., MS, and IR spectra. The crystal structure of 2 was determined.     

Preparation d'alcools acetyleniques et propargyliques F-alkyles

A number of α-β acetylenic carbinols R_FCCC(OH)RR′, in which the acetylenic proton was substituted by a F-alkyl group, were first prepared, from a classical reaction of (F-alkynyl)- lithium derivatives R_FCCLi upon various carbonyl compounds.On another hand, the reaction of propargyl bromide metallic complexes (organoaluminic, or ultrasonic irradiation activated organozinc) upon some polyfluorinated ketones R_FCOR led to the formation, in convenient yields, of the propargylic carbinols HCCCH₂C(OH)RR_F.The synthesis and properties of these series of new (F-alkyl) substituted acetylenic and propargylic alcohols are described and discussed.     

Darstellung und Charakterisierung der Trisilylphosphane (Ph 3Si) n P(SiMe 3)3−n,n=1,2,3

A simple preparation of the title compounds is achieved by reacting Na₃P/K₃P with stoichiometric mixtures of chlorotriphenylsilane and chlorotrimethylsilane.³¹P- and²⁹Si-NMR-Data as well as Ir and Raman spectra of the compounds are reported.

     

The vibrational spectra of linear and branched perchlorosilanes Si n Cl2n+2 and their simulation using a local symmetry force field

Infrared andRaman vibrational spectra ofn-Si₄Cl₁₀,n-Si₅Cl₁₂,neo-Si₅Cl₁₂ and [(SiCl₃)₃Si]₂ have been measured and assigned. A local symmetry force field has been developed to simulate vibrational spectra of all (noncyclic) perchlorosilanes Si _n Cl_2n+2 known today (n=2, 3, 4, 5, 8). The observed spectra are reproduced satisfactorily

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Die Vibrationsspektren linearer und verzweigter PerchlorsilaneSi _n Cl _2n+2 und deren Simulierung mittels eines lokalen Symmetrie-Kraftfeldes

Zusammenfassung Infrarot- undRaman-Spektren vonn-Si₄Cl₁₀,n-Si₅Cl₁₂,neo-Si₅Cl₁₂ und [(SiCl₃)₃Si]₂ wurden aufgenommen und zugeordnet. Ein lokales Symmetrie-Kraftfeld zur Simulation der Spektren aller bisher bekannten (nicht cyclischen) Perchlorsilane Si _n Cl_2n+2 (n=2, 3, 4, 5, 8) wird angegeben. Die beobachteten Spektren werden zufriedenstellend reproduziert

     

Determination of trace impurities in boron nitride by graphite furnace atomic absorption spectrometry and electrothermal vaporization inductively coupled plasma optical emission spectrometry using solid sampling

Two digestion-free methods for trace analysis of boron nitride based on graphite furnace atomic absorption spectrometry (GFAAS) and electrothermal vaporization inductively coupled plasma spectrometry optical emission (ETV-ICP-OES) using direct solid sampling have been developed and applied to the determination of Al, Ca, Cr, Cu, Fe, Mg, Mn, Si, Ti and Zr in four boron nitride materials in concentration intervals of 1–23, 54–735, 0.05–21, 0.005–1.3, 1.6–112, 4.5–20, 0.03–1.8, 6–46, 38–170 and 0.4–2.3 μg g^− 1, respectively. At optimized experimental conditions, with both methods, effective in-situ analyte/matrix separation was achieved and calibration could be performed using calibration curves measured with aqueous standard solutions. In solid sampling GFAAS, before sampling, the platform was covered with graphite powder and, for determination of Si, also the Pd/Mg(NO₃)₂ modifier was used. In the determination of all analyte elements by solid sampling ETV-ICP-OES, Freon R12 was added to argon carrier gas. For solid sampling GFAAS and ETV-ICP-OES, the achievable limits of detection were within 5 (Cu)–130 (Si) ng g^− 1 and 8 (Cu)–200 (Si) ng g^− 1, respectively. The results obtained by these two methods for four boron nitride materials of different purity grades are compared each with the other and with those obtained in analysis of digests by ICP-OES. The performance of the two solid sampling methods is compared and discussed.     

Time dependent neutron transport theory in multigroup-P L-approximation

Summary A method is developed for solving the time dependent neutron transport equation in multigroupP _L approximation for one-dimensional geometries. The partial differential equations in time and space are solved by means of a power series expansion in the spatial variable. The resulting ordinary differential equations are solved up to theNth order, and the last spatial coefficients are used to satisfy the boundary conditions. Integration of the purely time dependent differential equations is carried out by means of Lie series.Numerical oscillations, appearing for high ordersN, are avoided by subdividing each zone into smaller subzones. Even and odd spatial moments must be developed in opposite directions in each subzone, and the stationary solution representing the initial condition for the time dependent calculation must be developed in the same manner.Results of two calculations in spherical geometry are presented. One is the start-up of a small experimental reactor usingP ₃ theory, the other is a demonstration of neutron waves inP ₁ theory.

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Zusammenfassung Es wird eine Methode zur Lösung der zeitabhängigen Neutronentransportgleichung in der Multigruppen-P _L-Näherung für eindimensionale Geometrien entwickelt. Für die Lösung der partiellen Differentialgleichungen in Ort und Zeit wird eine Potenzreihe im Ort angesetzt. Das sich ergebende gewöhnliche Differentialgleichungssystem wird bis zu einer gewählten OrdnungN erfüllt, und die letzten Koeffizienten der Ortsentwicklungen dienen zur Befriedigung der Randbedingungen. Die Integration in der Zeit erfolgt dann mit der Lie-Reihen-Methode.Zur Vermeidung der Oszillationen, die bei hohen OrdnungenN auftreten, werden die einzelnen Zonen in kleinere Abschnitte unterteilt. Die geraden und ungeraden Momente müssen in den Abschnitten in entgegengesetzter Richtung entwickelt werden. Die stationäre Lösung, die als Anfangsbedingung für die zeitabhängige Rechnung dient, muss mit demselben Entwicklungsschema ermittelt werden.Die Methode wird angewendet zur Lösung derP ₁- undP ₃-Gleichungen in sphärischen Reaktoren. Zwei Beispiele werden damit berechnet: Das Anfahren eines kleinen Versuchsreaktors inP ₃-Näherung und die Nachweisung von Neutronenwellen inP ₁-Theorie.

     

Comparison of various calibration techniques for the direct spectroscopical analysis of SiC powders

Techniques for the direct analysis of powdered advanced ceramics provide an advantageous alternative to methods using wet digestion in sample preparation. The direct spectrochemical methods based on electrothermal vaporization (ETV-ICP-OES, solid-ETV-AAS, etc.) show a great similarity to the classical method of d. c. arc excitation. The calibration procedure is the major difficulty of all techniques applied for direct solid sample analysis, as there is a lack of suitable reference materials of ceramics. Consequently, it was necessary to verify various possibilities of preparation and application of model calibration samples. The results of such a calibration are compared with those using within-laboratory standards.     

1,1,2,2-tetrabromodisilane: gas-phase molecular structure and conformational composition as determined by electron diffraction

The molecular structure of 1,1,2,2-tetrabromodisilane has been investigated using gas-phase electron diffraction data obtained at 110°C. At this temperature the molecules exist as a mixture of about equal parts (X = 0.5 ±0.2) of the two conformers with the H---Si---Si---H torsion angle equal to 180° (anti) or 60° (gauche). Assuming that the two conformers differ in their geometries only in the torsion angle φ, some of the important distance (r_a) and angle () parameters are: r(Si---Si) = 2.349(19) Å, r(Si---Br) = 2.205(5) Å, r(Si---H) = 1.485 Å (assumed), Br---Si---Br = 110.1(1.6)°, Si---Si---Br = 107.1(1.2)° Si---Si---H = 108.6° (assumed). The error limits are 2σ. The observed conformational composition (X_anti = 0.5(0.2)) corresponds to an energy difference between the conformers of ΔE = E(gauche) — E(anti) = 0.5 ± 0.6 kcal mol⁻¹, assuming ΔS = Rln2.     

The Cyclohexasilanes Si6H11X and Si6Me11X with X=F,Cl, Br and I: A Quantum Chemical and Raman Spectroscopic Investigation of a Multiple Conformer Problem

The conformers of the monohalocyclohexasilanes, Si₆H₁₁X (X=F, Cl, Br or I) and the haloundecamethylcyclohexasilanes, Si₆Me₁₁X (X=F, Cl, Br or I) are investigated by DFT calculations employing the B3LYP density functional and 6‐31+G* basis sets for elements up to the third row, and SDD basis sets for heavier elements. Five minima are found for Si₆H₁₁X—the axial and equatorial chair conformers, with the substituent X either in an axial or equatorial position—and another three twisted structures. The equatorial chair conformer is the global minimum for the X=Cl, Br and I, the axial chair for X=F. The barrier for the ring inversion is ～13 kJ mol^?1 for all four compounds. Five minima closely related to those of Si₆H₁₁X are found for Si₆Me₁₁X. Again, the equatorial chair is the global minimum for X=Cl, Br and I, and the axial chair for X=F. Additionally, two symmetrical boat conformers are found as local minima on the potential energy surfaces for X=F, Cl and Br, but not for X=I. The barrier for the ring inversion is ～14–16 kJ mol^?1 for all compounds. The conformational equilibria for Si₆Me₁₁X in toluene solution are investigated using temperature dependent Raman spectroscopy. The wavenumber range of the stretching vibrations of the heavy atoms X and Si from 270–370 cm^?1 is analyzed. Using the van′t Hoff relationship, the enthalpy differences between axial and equatorial chair conformers (H_ax?H_eq.) are 1.1 kJ mol^?1 for X=F, and 1.8 to 2.8 kJ mol^?1 for X=Cl, Br and I. Due to rapid interconversion, only a single Raman band originating from the “averaged” twist and boat conformers could be observed. Generally, reasonable agreement between the calculated relative energies and the experimentally determined values is found.     

Synthese et reactivite d'organomagnesiens perfluores. V.[1] Synthese et identification de nouveaux composes perfluoroalkyles du mercure a chaine longue.

The reaction of mercuric salts HgY₂ or organic mercuric compounds R_HHgX with long chain perfluorinated Grignard reagents R_FMgBr leads to a series of new perfluoroalkyl mercury derivatives with the general formula R_FHgZ (R_F=C₄F₉, C₆F₁₃, C₈F₁₇ ; Z=R_F,R_H,Y with Y = I,Br,Cl, NO₃,OCOCH₃,OCOCF₃).The synthesis of these organomercuric compounds is described, and their spectroscopic properties are reported.