Nitrogen: A New Class of π-Bonding Partner in Hetero π-Stacking Interaction

Spectroscopy under isolated conditions at low temperatures is an excellent tool to characterize the aggregates stabilized through weak interactions. Within the framework of weak interactions, the pi-stacking interactions are considered unconventional with the limited experimental proofs, wherein the bonding associates are either aromatic and heterocyclic compounds or their combinations. Besides aromatic compounds, pi-stacking networks can even be realized with molecules possessing electron rich pi-clouds. In this work, the N-2 molecule as a possible pi-bonding partner is explored for the first time in which hetero pi-stacking was achieved between pyrrole and N-2 precursors. The matrix isolation experiments performed by seeding pyrrole and N-2 mixtures in an Ar matrix at low temperatures with subsequent infrared spectral characterization revealed the generation of adducts stabilized through a pi(pyrrole)center dot center dot center dot pi(N-2) interaction. Under identical conditions with the likelihood of two competing pi-stacking and hydrogen bonding interactions in pyrrole-N-2 associates, pi-stacking dominates energetically over hydrogen-bonding interaction.