The objective of this work is to study the effect of interlayer cations on the mechanism of adsorption-desorption of water in the case of a montmorillonite exchanged by alkali metals. This is done through thermodynamic measurements, i.e. isotherms of adsorption and desorption of water. The raw material is subjected to purification treatment by using the sedimentation followed by cationic exchange. IR and XRD analysis of the dry state confirm that the treatment used for obtaining homoionic clays does not deteriorate their structure. The value of the interlayer distance d001obtained from XRD depends directly on the cation radius. IR spectra recorded on our montmorillonite reveals that the area ratio νOH/νSiO peaks which corresponds to the amount of adsorbed water under room atmosphere follows the sequence: K >Rb> Cs > Li > Na In accordance the evolution observed for the desorption enthalpies. The adsorption and desorption isotherms show that the nature of the compensating cation considerably changes the adsorbed / desorbed amount for a given water relative pressure. Thus, the total amount of water adsorbed at P/P0 = 0.5 follows the same sequence.

Confined H$_2$O molecules act as local probes for depressurization phenomena during the pressure induced amorphisation of faujasite NaX at which the OH stretching frequency first decreases and then increases almost to its room pressure value upon further compression. Pair distribution function (PDF) analysis provides evidence that amorphisation corresponds to a collapse of the structure around hydrated sodium cations with strong distortion of the secondary building units (double six-membered rings, sodalite cages). Both the use of guest molecules as local probes in far- and mid-infrared spectroscopy, where we correlate intermolecular water H bonding vibrations and internal mode behaviour under confinement, and PDF analysis could be of great use to study the mechanical behaviour of other hydrated materials.

We have investigated the phonon modes of Ag-3[Co(CN)(6)] using first-principles based methods and high-pressure infrared spectroscopy to understand the origin of its colossal thermal expansion. Griineisen parameters of its zone-center vibrational modes were obtained from the calculations and compared to the experimental ones. We found that optical phonon modes below 100 cm(-1) mainly contribute to its negative thermal expansion, and they also have a significant mixing with acoustic branches. These modes have been assigned to translational motion of the Co-CN-Ag-NC-Co linkages. We also identify a pressure-induced softening of zone-center phonon modes that could account for the experimentally observed phase transition in terms of a first-order displacive instability from the trigona1P-3-1m space group to the acentric Cm space group.

The self-assembly of a bis-urea phenylene-bridged silsesquioxane precursor during sol-gel synthesis has been investigated by in situ infrared spectroscopy, optical microscopy and light scattering. In particular, the evolution of the system as a function of processing time was correlated with covalent interactions associated with increasing polycondensation and non-covalent interactions such as hydrogen bonding. A comprehensive mechanism based on the hydrolysis of the phenylene-bridged organosilane precursor prior to the crystallization of the corresponding bridged silsesquioxane via H bonding and subsequent irreversible polycondensation is proposed.

Vibrational dynamics in the corannulene crystal is exhaustively studied through Raman scattering, infrared spectroscopy, and inelastic neutron scattering. Experimental data are coupled to simulations of the phonon modes performed in the framework of first principle calculations. Intermolecular vibrations (libration and translation) are assigned in the low frequency domain (10-200 cm-1). These modes exhibit specific temperature dependence in the far-infrared.

The crystalline structure of ureidopyrimidinone-based silane (UPY) has been determined. The local and long range order structuring of the bridged silsesquioxane (MUPY) resulting from the sol-gel hydrolysis-condensation of the former precursor has been investigated by MFTIR (Mid Fourier Transform InfraRed) combined with DFT (Density Functional Theory) and XRD (X-ray diffraction) studies. These studies showed that a long range structuring exists within the organic fragments with the transcription of the DDAA (Donor-Donor-Acceptor-Acceptor) H-bonding array from UPY to MUPY whereas a disordered siloxane network was revealed in the hybrid material.