Ultraslow motion of domain wall in channel inclusion compound studied by means of NMR cross-relaxation

We report temperature dependent 1H NMR relaxation measurements of the powder thiourea-hexachloroethane inclusion compound, [2.95(NH2)2CS]·C2Cl6, at different resonance frequencies, from 23 to 55.5 MHz. Significant reduction of spin–lattice relaxation time at 38–47 MHz is caused by the cross-relaxation of protons via the quadrupole chlorine nuclei. We conclude that the effective 1H–35Cl cross-relaxation observed in powder sample is due to a slow mode process, when the molecules of the domain wall exhibit a correlated translational and rotational motion over the channel. Such a propagation of the domain wall was predicted by atom-atomic potential calculation. We show that the NMR cross-relaxation effect is an effective tool in studying ultraslow motions, in particular in incommensurate structures.