The molybdenum-tungsten phosphate (W2-xMoxO3(PO4)(2)) was synthetised and characterised using several techniques. Its catalytic performances was studied in butan-2-ol conversion. The UV-visible investigations showed that the catalyst contains Mo(V) ions. This results was confirmed by the EPR spectra. Additional UN. visible in-situ experimentss, in dynamic conditions revealed that butan-2-ol reduces Mo(VI) into Mo(V) ions. The active sites in the catalytic reaction appearto be built up arround the Mo(VI) ions.

Ln résonance paramagnétique électronique (RPE) de sulfures de molybdène amorphes MoS2+x (1 ⩾ x ⩾ 0) à 9 GHz et 35 GHz montre trois signaux à température ambiante. A 9 GHz, les modifications des spectres sont suivies en fonction de la température de l’échantillon (in situ) et après traitements thermiques. Une simulation par ordinateur de l’ensemble du spectre permet de déterminer les paramètres spectraux et d’identifier les centres : a) un centre de trou d’électron localisé sur un atome de soufre (g1 = 2,0485, g2 = 2,0295, g3 = 2,0031), b) un centre Mo(V) entouré d’atomes de soufre (g┴ = 1,9993, g// = 1,9531), c) un centre Mo(V) entouré d’atomes d’oxygène provenant de traces d’oxydes (g┴ = 1,9398, g// = 1,9013).

Electron paramagnetic resonance (EPR) of amorphous molybdenum sulfides MoS2+x (1 greater-than-or-equal-to x greater-than-or-equal-to 0) at 9 GHz and 35 GHz reveals three signals at room temperature. At 9 GHz, modifications of spectra are observed following the temperature of the sample (in situ) or after thermal treatments. A computer simulation of the total spectrum allows to find spectral parameters and to identify the centers: a) an electron hole center localized on a sulphur atom (g1 = 2.0485, g2 = 2.0295, g3 = 2.0031), b) a Mo(V) center surrounded by sulphur atoms (g perpendicular-to = 1.9993, g parallel-to = 1.9531), c) a Mo(V) center surrounded by oxygen atoms which result from a contamination by oxide traces (g perpendicular-to = 1.9398, g parallel-to = 1.9013).

The angular dependence of the EPR linewidth has been measured for CuSO4·5H2O at X-band and room temperature in the K1K3 principal plane of the magnetic susceptibility, where the copper ions are magnetically equivalent. After having separated the contribution of the two magnetic systems in this compound, by estimating the various spectral densities contained in the EPR linewidth, we interpret experimental data in terms of spin diffusion processes limited by cut-off effects in the antiferromagnetic linear chain system. We finally present a discussion about the nature of these cut-off effects.

AbstractEPR and related MMB powder spectra of Cu(NO3)2 · 2.5 H2O are recorded at X‐band and room temperature. A good agreement is found with computer simulated spectra. An automatic fitting procedure gives accurate principal values of the g‐factors and linewidths.

A computer simulation of the ESR powder spectrum of CuF2.2H2O is carried out, and an automatic fitting procedure permits us to obtain the principal g values and crystallite linewidth. For this compound, microwave Faraday and Cotton- Mouton-Voigt effects related to ESR have been measured at X-band and room temperature. Then, the computer simulations is applied to the magneto-microwave effects by substituting for the ESR lineshape function the various crystallite lineshape functions corresponding to the rotation and ellipticity of elementary Faraday and Cotton-Mouton-Voigt effects. The computer simulations of the magneto-microwave powder effects are in close agreement with experimental data.

Magneto-microwave Faraday and Cotton-Mouton-Voigt effects related to anisotropic ESR powder spectra were studied at X-band and room temperature on polycrystalline samples of CuCl2·2H2O and Cu(NH4SO4)2·6H2O. For both compounds, computer simulations of the powder ESR spectra were carried out with a rather simplified model accounting for a crystallite Lorentzian lineshape and complete anisotropies of the g factor, transition probability, and linewidth. One observes a good agreement between simulated and experimental spectra, and an automatic fitting procedure permits one to obtain for each compound the principal values of the g factor and linewidth, in close agreement with results from previous single-crystal ESR studies. The same model is then transposed to the magnetomicrowave effects, by substituting for the ESR lineshape function the various crystallite lineshape functions corresponding to the rotation and ellipticity of elementary Faraday and Cotton-Mouton-Voigt effects. Computer simulations of the magneto-microwave powder effects are in close agreement with experimental data.