M. Fouassier

The vibrational properties and valence force fields of FeS2, RuS2 pyrites and FeS2 marcasite

Abstract From recently published experimental frequencies and new Raman data obtained for FeS 2 marcasite, the complete valence force fields of FeS 2 , RuS 2 pyrite-type and FeS 2 marcasite compounds were computed. Values of the main force constants and of the principal potential energy distributions are discussed and compared with literature data with particular emphasis on the relative M-S and S-S bondings in these MS 2 phases.

Etude par spectroscopie infrarouge de la conformation du groupement CH3 dans les carbures aromatiques méthyles

Abstract Infrared spectra of crystalline 1–5 dimethyl naphthalene oriented with the (001) plane perpendicular to the beam are studied using polarized infrared radiation in order to assign the methyl stretching vibrations. The infrared spectra of the carbon tetrabromide p. xylene complex is re-investigated and discussed in the same region. The results obtained for these two compounds lead to an interpretation of the infrared spectra of various methyl aromatic hydrocarbons. It is shown that an equilibrium exists between two conformations of the methyl group with respect to the plane of the aromatic ring. This equilibrium is modified by variations of temperature when the molecules are in solution. A discussion of the CH force constants is presented.

Etude des spectres de vibration des composés d'addition (CH3)2CO—11BF3, (CH3)2CO—10BF3, (CD3)2CO—11BF3 et (CD3)2CO—10BF3

Abstract Infrared spectra of four co-ordination compounds (CH3)2CO11BF3, (CH3)2CO10BF3, (CD3)2CO11BF3 and (CD3)2CO10BF3 have been recorded. An assignment is made based upon isotopic shifts and comparison with vibrational spectra of free acetone and acetone-d6. A structure is proposed for the complex. The force constant of the co-ordination is estimated and the normal modes of vibration of various XBF3 groups are discussed.

Vibrational spectra of matrix isolated Al2Cl6. Isotopic fine structure and valence force field

High resolution i.r. and Raman spectra have been recorded for the bridged dimeric aluminium chloride molecules isolated in argon and nitrogen matrices at very low temperatures. An accurate valence force field has been calculated from the frequencies of fifteen fundamental modes and some isotopic shifts due to the 35Cl, 37Cl distribution. The calculated isotopic frequencies and the isotopic patterns are shown to be in agreement with the experimental results. From thermodynamic and spectroscopic considerations, the unobserved ring-puckering mode is predicted to occur at very low frequencies (text-decoration:overlineν≃ 10 cm–1). The Al—Cl bond dissociation energies are 270 and 170 kJ mol–1 for terminal and bridging atoms, respectively; the force constants of the same bonds are 226 and 130 N m–1.

Etude des spectres de vibration des composés d'addition [[(CH3)2N]3PO]2ZnCl2, [(CH3)2N]3PO—10BF3 et [(CH3)2N]3PO—11BF3

Abstract Infrared and Raman spectra of (HMPT) 2 -ZnCl 2 , HMPT- 10 BF 3 and HMPT- 11 BF 3 have been recorded from 40 to 4000 cm −1 . (HMPT = hexamethyl phosphotriamide). An assignment is proposed based upon isotopic shifts, comparison with free HMPT and other OBF 3 groups.

Infrared, Raman, resonance Raman spectra and lattice dynamics calculations of the solid potassium(I) nickel(II) thiophosphate compound, KNiPS4

Abstract The UV-visible (350–850 nm), infrared and Raman (20–700 cm−1) spectra of a new KNiPS4 solid compound have been analyzed using powder samples and crystalline platelets. From polarization measurements, the main electronic transition of 1F2←1A1 type due to the PS43− thiophosphate groups are localized in the 360–570 nm range and vibrational assignments for most of the fundamental modes are proposed. These assignments were checked by complete valence force field lattice dynamics calculations in the various symmetry blocks of the tetragonal crystal structure (D4h14). Potential energy distributions as well as mean squared vibrational amplitude calculations have shown strong ν(NiS) and σ(SPS) couplings in the (NiPS4)− structural chains and remarkably high ν(NiS) infrared frequencies. Furthermore, the resonance Raman spectra of single crystals and powder samples were recorded over a wide range (647.1-476.5 nm) of excitatiob wavelengths. This allowed to probe the nature of the broad electronic transition of the complex centered around 510 nm and responsible for KNiPS4 brown color. The Raman excitation profiles of several fundamentals and combination bands were thus established. Under resonance conditions, various crystalline components of A1g, B1g and B2g symmetry for the ν4(F2) or ν2(E) deformation modes of the PS43− groups are enhanced. No overtone progressions involving totally symmetric modes were observed but anomalously intense high-order combination bands were detected. It is thus concluded that adiabatic as well as non-adiabatic interactions must play a great role in the vibronically induced Raman scattering processes. Reasons for this peculiar behavior are discussed in relation to the X-ray crystal structure of the KNiPS4 compound. All the experimental results imply the presence of substantial site and factor group effects on the optical and vibronic properties of the thiophosphate anions.

Étude des dérivés sulfohydroxyles des halogénures de bore et des cycles dérivés du borsulfol: III. Détermination de la structure et du champ de force moléculaire des sulfohydroxodihalogéno-boranes BX2SH à partir des spectres de vibra

Abstract Sulphurhydroxohalogenoborane, BX 2 SH, is shown by vibrational spectra to be planar with the boron atom exhibiting the same sp 2 hydridization as in the BX 3 halides. The force field available for a BX 2 Cl compound can easily be transferred to the BX 2 SD compound since the SD group shows similar behaviour to that of a chlorine atom. Consequently, the spectra of BCl 2 SD, BBr 2 SD and BI 2 SD can be compared to those of BCl 3 , BBr 2 Cl and BI 2 Cl, respectively. However, in the hydrogen derivatives, a strong interaction between the δ(SH), v (BS) and v a (BX 2 ) modes was found, which became more pronounced when passing from chlorine to iodine. A study of the shape of the γ(SH) band in the gaseous phase, revealed the presence of a double minimum in the potential function, and it was possible to evaluate the potential barrier and maximum amplitude of the movement. Finally an interaction between the hydrogen atom and one of the halogen atoms was observed which became more important when passing from chlorine to iodine.

Optical, Raman and resonance Raman spectra and lattice dynamics calculations of the misfit layer compounds, (SnS)1.17NbS2 and (PbS)1.18TiS2

Abstract The UV—visible (340–800 nm), Raman and resonance Raman spectra (10–850 cm−1) of powdered samples of two misfit layer compounds, (SnS)1.17NbS2 and (PbS)1.18TiS2, at 300 K were investigated. In agreement with X-ray data, vibrational assignments are proposed for most of the internal and external modes of the “TS2” and “MS” sublattices and the band wavenumbers at Γ (k=0) are compared to those in the 2H-NbS2 and 1T-TiS2 polytypes in order to appreciate the interactions in which “MS” acts as the donor part of the structure. In addition, owing to their incommensurate modulated structures along the a direction, new intense Raman signals are observed and explained by the k=0, ±q selection rules (q is the modulation vector); such effects are more dominant in the (PbS)1.18TiS2 compound in which a stronger structural distortion is effective and a weak but non-negligible charge-transfer mechanism is occurring. New information about the lattice dynamics properties of the “TS2” sublattices are thus obtained and confirmed by valence force field calculations on the stoichiometric model compounds (SnS)1.0NbS2 and (PbS)1.0TiS2, which reproduce satisfactorily the essential features of experimental data.

Détermination du champ de force de valence et des modes normaux de vibration des composés d'addition de l'acétone avec le trifluorure de bore

Abstract A valence force field for coordination compounds between acetone and boron trifluoride is computed: it is based upon vibrational spectra of six isotopic species and compared with the force field of free acetone and BF − 4 ion. The formation of complex modifies the electronic state of the base and consequently the diagonal force constant of the CCO group and of the CH bonds. The force constant of the coordination bond (OB) is estimated as 2.10 mdyne A −1 . Below 800 cm −1 all modes involve motions of the acid and base; none corresponds to a stretching of the coordination bond.

Raman study and lattice dynamics calculations of misfit layered compounds : (PbS)1.18TiS2 and (PbS)1.12VS2

Abstract The UV-visible (340–800 nm), Raman and resonance Raman spectra (10–900 cm−1) of powered samples or the two title misfit compounds were investigated. In agreement with X-ray data, vibrational assignments are proposed for the internal modes of the “PbS” and “TS2” sublattices (TiS2 or VS2) and the latter ones are compared to those in the 1T-TiS2 polytype in order to appreciate the interactions due to the “PbS” donor part of the structures. Owing to their incommensurate structures, new resonance enhanced Raman signals are observed and explained by the k = ± q ∗ selection rules (q∗ is the modulation vector); these observations are confirmed by VFF lattice calculations which reproduce the essential experimental data.