Structure and Dynamics of the Crystalline Stable Phase of 2-Chlorothiophene

Abstract

The dynamics of a simple and rigid molecule (2-chlorothiophene) has been studied by means of broadband dielectric spectroscopy (BDS) within the low-temperature stable crystalline phase, whose structure has been determined by means of X-ray powder diffraction (XRPD) measurements. The triclinic P1 structure consists of two molecules per asymmetric unit (Z'=2) with site occupancies 80:20 and 60:40 for each molecule of the asymmetric unit. Such a statistical intrinsic disorder is associated with two dynamical relaxation processes corresponding respectively to out-of-plane relaxations around the C-Cl twofold molecular axis and in-plane reorientational motions as proposed previously (Fujiromi and Oguni, J. Phys. Chem. Solids 1993, 54. 437-612). The XRPD and BDS measurements allow rationalizing published nuclear quadrupole resonance data. We show that only the concurrent use of different experimental techniques provides the answer to a complicate case of orientational molecular dynamics in the solid state.