Molecular dynamics simulation of cation dynamics in bis-thiourea pyridinium nitrate inclusion compound

Molecular dynamics simulations have been performed on the high temperature phase of the bis-thiourea pyridinium nitrate inclusion compound. Three different potential models have been tested. In the three cases, the analysis of the centre of mass motion of pyridium cations indicates that they do not diffuse along the channels. However, only the potential including a specific hydrogen bonding interaction provides a description of the in-plane cation reorientation in reasonable agreement with the experimental results deduced from quasielastic neutron scattering (QENS) measurements. This model shows that the pyridinium cation reorients among three non-equivalent positions and gives reorientational correlation times comparable to those extracted from the QENS data. We conclude that the particular geometry of this reorientation is due to the formation of hydrogen bonds of different strength between the pyridinium cation of the guest sublattice and the host sublattice.