New synthetic and structural aspects in the chemistry of alkylaluminum fluorides. The mutual influence of hard and soft ligands and the hybridization as rigorous structural criterion

A general synthetic strategy starting from metal alkyls is reported based on the hydrogen difluoride anion as a suitable reagent for obtaining organometallic fluorides. The newly prepared compounds are [Me(4)N][(i-Bu)(2)AlF(2)] (1), [Ph(4)P][(i-Bu)(2)AlF(2)] (2), and [Ph(4)P][AlF(4)] (3), containing the tetrahedral anions [(i-Bu)(2)AlF(2)](-) and [AlF(4)](-). The actual structures are prototypes that allowed a comparison of inorganic and organometallic fluorides in the frame of the hard and soft acid and base principle, by means of ab initio calculations. A new theoretical model is designed to put in equation form the qualitative statements of the Bent rule. The model allows the rationalization of the tendencies of bond angle variation in [R(2)MX(2)] systems containing a main group metal (M), in terms of hybridization of the central atom and the reciprocal influence of hard and soft ligands.     

Calculation of cross sections for positron-Ar collisions

The three-body classical trajectory Monte-Carlo (CTMC) method is used to investigate positron-argon atom collisions. The total ionization cross sections are presented along with singly and doubly differential cross sections. The existence of the cusp-like peak in the triply differential electron and positron spectra at positron impact is predicted.     

Cluster aggregation: a new method for producing atomic and molecular clusters

A new method for the production of cold free clusters is presented. A beam of large rare gas clusters is passed through a low pressure atomic gas. The gas atoms are picked up by the rare gas clusters whereby they condense. A complete evaporation of rare gas atoms from the newly formed clusters then follows once the number of captured particles becomes sufficiently large. The method is demonstrated for Xe clusters with size up to 500 atoms per cluster but it should work for most materials, including the refractory materials.     

Selective mixed coupling of carboxylic acids (II). — photolysis of unsymmetrical diacylperoxides with alkenyl-, halo-, keto-, carboxyl-groups and a chiral α-carbon. Comparison with the mixed kolbe electrolysis

Alkenoyl and functionalized alkanoyl dodecanoyl peroxides are prepared in 70 to 97 % yield and photolyzed at ?78° C. Thereby 4- to 10-alkenoyl and 4-alkanoyl peroxides afford good yields (56 – 68 %) of unsymmetrical coupling products. Similarly α- to σ-haloalkanoyl, cholanoyl or 3- and 4-carboxyalkanoyl peroxides can be coupled (40 – 70 %). The α-chiral diacyl peroxide ls undergoes the photochemical coupling reaction with 80 % retention of its configuration. The photolysis of diacyl peroxides at ?78° C proves to be a favorable supplement of the Kolbe-electrolysis in cases, where the electrolysis fails or produces low yields.     

Intramolecular multiple scattering in electron diffraction from fluoro-methyl halides

Relative elastic differential cross sections for scattering of 1 keV electrons from CF₃H, CF₄, CF₃Cl, CH₃F and CH₃Cl molecules were measured for momentum transfer from 3 Å^?1 to 29 Å^?1. The oscillatory residuals remaining after substraction of the atomic scattering and the molecular interference contributions calculated in the independent atom model are ascribed to the influence of intramolecular multiple scattering. The data reflect the dominant contributions of the CF₃-group and show larger oscillations than obtained from triple scattering calculations according to the method of Liu and Bonham using the second Born approximation.     

Oxidation of micro or trace amounts of bromide to bromate by peroxodisulphate before their iodometric determination by titration or spectrophotometry

The optimum conditions for the oxidation of bromide to bromate by peroxodisulphate at 120 degrees as well as for the decomposition of the excess of oxidant have been determined. The predicted advantages of this oxidizing agent, viz. minimal blanks and destruction of small amounts of interfering organic matter and reducing substances, were confirmed. The bromate was determined iodometrically either by titration with thiosulphate or by spectrophotometry in absence of oxygen at 355 nm. The titrimetric finish applied to 0.8-8 micromole of bromide gave a mean yield of 100.0%, s = 6 nmole. The spectrophotometric finish applied to 0.05-0.25 micromole of bromide gave a mean yield of 98.9%, s = 1.1 nmole. Interfering amounts of iodide present in the sample and oxidized to iodate can be corrected for by making use of the pH-dependence of the reaction of iodide with bromate and iodate.