Molecular Association and Reactivity of the Pyridine Dimer Cation

A recent experimental report has identified the formation of C–N hemi-bonded pyridine dimer cation following vacuum ultraviolet near-threshold photoionization [J. Phys. Chem. Lett. 2021, 12, 4936–4943]. Herein, the dynamics and consequent reactivity of the pyridine dimer cation was investigated employing Born-Oppenheimer Molecular Dynamics (BOMD) simulations. The neutral anti-parallel π-stacked pyridine dimer is transformed to non-covalently interacting C–H∙∙∙N hydrogen-bonded and C–H∙∙∙H–C bonded complex in the cationic state. Further, the C–H∙∙∙N hydrogen-bonded structure leads to proton transfer. Additionally, C–N and N–N hemi-bonded pyridyl-pyridinium cations are also formed. The observed trends in the molecular association, proton transfer and formation of pyridinium cations are a consequence of roaming dynamics of one pyridine moiety over the other in the cationic state.