Molecular Association and Reactivity of the Pyridine Dimer Cation

Abstract

A recent experimental report has identified the formation of the C−N hemibonded 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 were investigated employing Born− Oppenheimer molecular dynamics (BOMD) simulations. An antiparallel π-stacked pyridine dimer in the neutral ground state is transformed into a noncovalently interacting C−H•••N hydrogen-bonded structure which can lead to proton transfer in the cationic state. Additionally, C−N-and N−N-bonded adducts were formed in the cationic state. Further, metastable C−H•••H−C-bonded cationic species was observed, which rearranged to an N−N bonded adduct. In contrast to the experimental observation, migration of the proton to the α position was not observed in the C−N bonded adduct owing to a high barrier of about 2 eV. The observed trends in the molecular association, proton transfer, and the formation of C−N and N−N bonded adducts are a consequence of the roaming dynamics of one pyridine moiety over the other in the cationic state.