Ferroelectricity of Inclusion Compounds of Thiourea with Pyridinium Iodide and Nitrate

International audienceThe character of phase transitions in the inclusion compounds of thiourea with pyridinium iodide and nitrate has been analyzed, and a model of ferroelectricity of these compounds has been proposed. Analysis of the temperature dependence of specific heat and intensity of the Bragg peaks has shown that the ferro-paraelectric phase transitions are continuous, in contrast to the nonferroelectric phase transitions. The ferroelectricity of the inclusion systems studied is of the mixed type and has a displacement component and an order−disorder component

Discovery of an intermediate phase in bis-thiourea pyridinium chloride inclusion compound.

International audienceThis paper reports the occurrence of a new phase for bis-thiourea pyridinium chloride inclusion compound, which is intermediate to the high- and low-temperature ones already reported. The structure of the intermediate phase was determined by the x-ray diffraction and the following sequence of space groups was obtained: Cmcm-->(237 K)Cmc2(1)-->(206 K)Pbca. The triplication of the lattice a parameter in the intermediate phase was observed. Detailed investigations of its phase transitions were performed by differential scanning calorimetry, x-ray diffraction, and dielectric spectroscopy methods. The phase transition at T(1)=237 K is continuous while at T(2)=206 K is discontinuous. Both phase transitions have been classified as of order-disorder type. The high- and low-temperature phases are nonpolar in contrast to the intermediate phase, for which we could not found ferroelectric ordering

New ferroelectric: Bis-thiourea pyridinium bromide inclusion compound

International audienceDielectric measurements (permittivity and hysteresis loop) of monocrystals of bis-thiourea pyridinium bromide inclusion compound have revealed for the first time ferroelectric properties of the studied samples. In the present article, a model of ferroelectric ordering on the basis of single-crystal x-ray diffraction data is described. In the low-temperature phase, the spontaneous polarization is directed along the a axis and ferroelectricity is of the mixed type (displacement and order-disorder component), whereas in the intermediate phase the spontaneous polarization is directed along the c axis and ferroelectricity is of the order-disorder type

Structural Refinement of Carbimazole by NMR Crystallography

: The characterization of the three-dimensional structure of solids is of major importance, especially in the pharmaceutical field. In the present work, NMR crystallography methods are applied with the aim to refine the crystal structure of carbimazole, an active pharmaceutical ingredient used for the treatment of hyperthyroidism and Grave's disease. Starting from previously reported X-ray diffraction data, two refined structures were obtained by geometry optimization methods. Experimental 1H and 13C isotropic chemical shift measured by the suitable 1H and 13C high-resolution solid state NMR techniques were compared with DFT-GIPAW calculated values, allowing the quality of the obtained structure to be experimentally checked. The refined structure was further validated through the analysis of 1H-1H and 1H-13C 2D NMR correlation experiments. The final structure differs from that previously obtained from X-ray diffraction data mostly for the position of hydrogen atoms

Structural and dynamical aspects of the phase transition in the new thiourea thiazolium bromide inclusion compound.

International audienceA new thiourea thiazolium bromide inclusion compound is presented here. Detailed investigations of its phase transition were performed by differential scanning calorimetry, x-ray diffraction, and dielectric and nuclear magnetic resonance spectroscopy methods, completed by calculation of the steric hindrances for molecular reorientations and simulations of the second moment of the nuclear magnetic resonance line by the Monte Carlo method. A second order ferrielectric structural phase transition has been detected at 190.5 K as thiazolium cations collectively reorient inside channels. The dynamics is discussed in terms of inequivalent energy barriers associated with cation rotation as the symmetry breaking occurs. Oscillations of thiourea molecules and NH(2) groups have been also observed

QENS and NMR Study of Water Dynamics in SBA-15 with a Low Water Content

In this study, motions performed by water molecules adsorbed on the silica surface of SBA-15 material with 6.1% of water content (15% of pore filling) were investigated using NMR and Quasielastic Neutron Scattering (QENS) techniques. The results show no sign of translational diffusion of water, but two types of stochastic localized motions were identified, and both described using a model of proton jumps between two sites. For both motions, the characteristic jump distances and correlation times, as well as activation energies, have been extracted and found to differ significantly. On this basis, the faster motion was ascribed to jumps of water molecules between neighboring positions (<i>d</i> = 2.5 Å, τ = 4 ps at 300 K, and <i>E</i>_a = 5.2 ± 0.2 kJ/mol from NMR data, and 5.6 ± 1.1 kJ/mol from QENS), while the slower one exhibits a temperature dependent jump distance and was ascribed to jumps of water molecules between more spatially separated positions (<i>d</i> = 2.9–4.3 Å, τ = 25 ps at 300 K, and <i>E</i>_a = 16.1 ± 0.3 kJ/mol from NMR, and 17.3 ± 0.3 kJ/mol from QENS data)

Computationally Assisted (Solid-State Density Functional Theory) Structural (X-ray) and Vibrational Spectroscopy (FT-IR, FT-RS, TDs-THz) Characterization of the Cardiovascular Drug Lacidipine

The structural properties of a second-generation dihydropyridine calcium antagonist, lacidipine, were explored by combining low-temperature X-ray diffraction with optical vibrational spectroscopy and periodic density functional theory (PBC DFT) calculations. Crystallographic analysis cannot discriminate between two possible molecular symmetries in crystals made of pure lacipidine: the space group <i>Ama</i>2, where the lacipidine molecule lies on mirror symmetry, or a <i>Cc</i> space group with distorted lacipidine molecules. Intermolecular interactions analysis reveals an infinite net of moderate-strength N–H···O hydrogen-bonds, which link the molecular units toward the crystallographic <i>b</i>-axis. Weak interactions were identified, revealing their role in stabilization of the crystal structure. The vibrational dynamics of lacidipine was thoroughly explored by combining infrared and Raman spectroscopy in the middle- and low-wavenumber range. The given interpretation was fully supported by state-of-the-art solid-state density functional theory calculations (plane-wave DFT), giving deep insight into the vibrational response and providing a complex assignment of spectral features. The vibrational analysis was extended onto the lattice-phonon range by employing time-domain terahertz spectroscopy. Analysis of the anisotropic displacement parameters suggests noticeable dynamics of the terminal (<i>tert</i>-butoxycarbonyl)­vinyl moiety. The terahertz study provides direct experimental evidence of “crankshaft” type motions in the terminal chain. By combining low-wavenumber vibrational spectroscopy with the first-principles calculations, we were able to prove that the quoted thermodynamically stable phase corresponds to the monoclinic <i>Cc</i> space group