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 π-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, π-stacking networks can even be realized with molecules possessing electron rich π-clouds. In this work, the N₂ molecule as a possible π-bonding partner is explored for the first time in which hetero π-stacking was achieved between pyrrole and N₂ precursors. The matrix isolation experiments performed by seeding pyrrole and N₂ mixtures in an Ar matrix at low temperatures with subsequent infrared spectral characterization revealed the generation of adducts stabilized through a π(pyrrole)···π(N₂) interaction. Under identical conditions with the likelihood of two competing π-stacking and hydrogen-bonding interactions in pyrrole-N₂ associates, π-stacking dominates energetically over hydrogen-bonding interaction.