Molecular dynamics of cyclohexane guest molecules in the cyclohexane/thiourea inclusion compound: an incoherent quasielastic neutron scattering investigation

Abstract

Incoherent quasielastic neutron scattering (IQNS) has been used to investigate the dynamic properties of cyclohexane guest molecules within the tunnel/cage host structure in the cyclohexane/thiourea inclusion compound. These investigations have been carried out on samples containing perdeuterated thiourea to ensure that the incoherent scattering arises from the cyclohexane molecules. IQNS spectra have been recorded for two experimental geometries of semi-oriented polycrystalline samples (with the tunnel axes of all crystals either parallel or perpendicular to the neutron momentum transfer vector), allowing components of the motion parallel to the tunnel axis to be investigated separately from components of the motion perpendicular to the tunnel axis. In the high-temperature phase (above 149 K; phase I), the dynamics of the cyclohexane molecules can be described as 120° jumps of the molecule about the molecular 3-fold symmetry axis, combined with 120° jumps of this axis about the tunnel axis of the thiourea host structure. The angle between the molecular symmetry axis and the tunnel axis is in the range 50–60°. With the instrumental resolution used in the present study, the dynamic properties of the cyclohexane molecules in the phases at lower temperature cannot be investigated in detail. The IQNS results are compared with a previous assignment, based on 2H NMR data, of the dynamic properties of the cyclohexane/thiourea inclusion compound.