A study of out-of-plane cation dynamics in a bis-thiourea pyridinium chlorideinclusion compound

Abstract

The out-of-plane motion of the pyridinium cation in the bis-thiourea pyridinium chloride inclusion compound has been studied in a wide temperature range using ¹H NMR, dielectric spectroscopy and quasielastic neutron scattering. The geometry of this motion is obtained from the Q-dependence of the elastic incoherent structure factor determined from the quasielastic neutron scattering measurements. We find that the pyridinium cation performs out-of-plane reorientations around the axis passing through two opposite atoms of the ring. The correlation times as a function of temperature were measured in the three known crystallographic phases, finding a good agreement between the three techniques employed. The activation energy for this motion changes from 5 ± 1 kJ mol⁻¹ in the low-temperature phase to 1.2 ± 0.2 kJ mol⁻¹ in the intermediate and high-temperature phases.