RESUMO
The polymorphism and the dynamics of a simple rigid molecule (1-fluoro-adamantane) have been studied by means of X-ray powder diffraction and broadband dielectric spectroscopy. At temperatures below the melting point, the molecule forms an orientationally disordered Phase I with a cubic-centered structure (Phase I, Fm3¯m, Z = 4). This phase possesses eight equilibrium positions for the fluorine atom, with equal occupancy factors of 1/8. A solid-solid phase transition to a low-temperature tetragonal phase (Phase II, P4¯2(1)c, Z = 2) reduces the statistical disorder to only four possible equivalent sites for the fluorine atom, with fractional occupancies of 1/4. The dynamics has been rationalized under the constraints imposed by the space group of the crystal structure determined by powder X-ray diffraction. The dielectric spectroscopy study reveals that the statistical disorder in Phase II is dynamic in character and is associated with reorientational jumps along the two- and three-fold axes. In the dielectric loss spectra, the cooperative (α) relaxation exhibits a shoulder on the high-frequency side. This remarkable finding clearly reveals the existence of two intrinsic reorientational processes associated with the exchange of the F atom along the four sites. In addition to such "bimodal" relaxation, a secondary Johari-Goldstein relaxation is detected at lower temperatures.
RESUMO
Convenient access to new aryl(dihydro)naphthothiophenes is described using a common ß-chloroacrolein derivative. Our strategy is based on the construction of a condensed thiophene ring prior to a Suzuki-Miyaura coupling and allowed installing various substituents at the molecular platform. The overall shapes of these architectures were confirmed by X-ray analyses and were in good agreement with theoretical calculations. It has been established that the relative orientation between all fragments that composed molecules within this series is strongly related to both steric and electronic factors. Contribution of these key parameters revealed to be crucial to rationalize attempts to prepare fluorenone and fluorene derivatives from aryl(dihydro)naphthothiophene platforms.
