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

A 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 NH2 groups have been also observed. (c) 2008 American Institute of Physics.