Antoine Potier

Vibrational spectroscopy and normal coordinate analysis of μ halo hexahalodialuminates ions Al2X−7 (X = Cl, Br, I) in some salts and in Friedel-Crafts solutions

Infrared and Raman spectra are reported for (Me4N)Al2Cl7, (Et4N)Al2Cl7, KAl2Br7 and CsAl2I7 in the solid state at ordinary temperature. An assignment for practically all the vibrational modes is proposed for the three ions Al2C−7, Al2Br−7 and Al2I−7. To elucidate the species occurring in the Friedel-Crafts liquids [the Ar:2AlX3: HX liquid mixture (X = Cl, Br)], the spectra of these solutions were also recorded. The quasi identity of the halogenide part of the spectra with the previous one leads to the unique formulation ArH+2Al2X−7 for these solutions, in these cases the Al2X−7 ion appears at a higher local symmetry of the AlX3 groups than in the solid state. An approximate valence force field calculation confirms the assignments. It also shows the transferability of force constants for a X-AlX3 model. Spectroscopic particularities are explained in terms of different coupling between bridged and terminal stretching modes.

Calcul du champ de force de l'anhydride perchlorique a partir de l'approximation des vibrations de groupe

Abstract The study of a valence force field for Cl 2 O 7 is made in correlation with known fields for HClO 4 and Cl 2 O. It supports our preceding assignments of experimental frequencies in the approximation of ‘group’ vibrations. Vibration frequencies ν s , ν as and δ for the bridge Cl-O-Cl at 700, 775 and 165 cm −1 exhibit high coupling with end group movements as is shown by the potential energy distribution. This explains the failure of previous calculations based on simplified models to yield the characteristic frequencies of the bridge. Standard mean square vibration amplitudes as deduced from the calculated field agree with those deduced by Beagley from electron diffraction measurements.

ANHYDROUS IRON PERCHLORATES

Durch Umsetzen von flussigem Cl2O6 mit FeCl3 werden entsprechend Gleichung A vier wasserfreie Perchlorate dargestellt.