M.-C. Dhamelincourt

The infrared and Raman spectra of ethylammonium hexafluorosilicate [C2H5NH3]2SiF6

The X-rays powder diffraction pattern of [C2H5NH3]2SiF6 was obtained and indexed on the basis of a hexagonal unit cell. The vibrational spectra (IR and Raman) of this compound were recorded and discussed in relation to the above-mentioned crystal structure. The vibrational spectra of the cations indicate that they are disordered and hydrogen bonded to the anions. On the opposite, the Raman spectrum of the anions could be interpreted in terms of ordered groups. The combination bands observed in the 2300-1800 cm(-1) spectral region in the IR spectrum indicate that this compound may contain C-NH3 groups.

Polysulphides in dimethylformamide: a micro‐Raman spectroelectrochemical study

The reduction of sulphur and the redox properties of polysulphide anions in dimethylformamide (DMF) were studied by time-resolved spectroelectrochemistry, coupling cyclic voltammetry with micro-Raman spectrometry. The measurement system allows one to record several spectra in real time during the potential scan of the working electrode. The data obtained under thin-layer conditions, at room temperature, were compared with those obtained by cyclic voltammetry and by visible time-resolved spectrophotometry. The variations of the Raman (535 cm-1) and visible (610 nm) characteristics of the radical anion S3- during the potential scan for S8–DMF and Li2S6–DMF solutions are presented and these results are discussed.

Infrared and Dielectric Studies of [(C2H5)4N]2SiF6

The infrared spectrum of [(C2H5)4N]2SiF6 was recorded and discussed in relation to its crystal structure. This spectrum indicates that cations and anions are distorted and are not hydrogen bonded. Two structural phase transitions were observed in the tetraethylammonium compound [(C2H5)4N]2SiF6 by means of dielectric measurements. High-frequency dielectric dispersion phenomena in this compound were also analysed. The evolution of the dielectric constant with the temperature indicates the presence of two phase transitions, at high temperatures, which are of order-disorder character.

Structure and vibrational study of the trimethylammonium hexafluorosilicate [(CH3)3NH]2SiF6 compound

The X-ray powder diffraction pattern of [(CH(3))(3)NH](2)SiF(6) was obtained and indexed on the basis of a centred cubic unit cell with the P4(1)32 as the likely space group. The Infrared and Raman spectra of this compound have been recorded at room temperature and discussed in relation to the crystal structure. In this salt, the bands corresponding to the cation vibrational modes show that the symmetry of these cations is distorted from the free C(3v) one and that they are strongly hydrogen-bonded to the respective anions. However, the spectra of the anions can be interpreted in term of ordered groups as indicated by the splitting of the bands corresponding to some degenerate vibrational modes. The harmonic frequencies, corresponding to the (CH(3))(3)NH-SiF(6)-NH(CH(3))(3) optimised geometry, were calculated using the SCF semi-empirical MNDO-PM3 method.