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

Area of Science:

• Physical Chemistry
• Spectroscopy
• Supramolecular Chemistry

Background:

• Weak interactions, particularly π-stacking, are crucial for stabilizing molecular aggregates.
• Experimental evidence for unconventional π-stacking, especially involving non-aromatic molecules, remains limited.
• Nitrogen (N2) molecules, with their electron-rich π-clouds, were investigated as potential π-bonding partners.

Purpose of the Study:

• To investigate the potential of the N2 molecule in forming π-stacking interactions.
• To characterize hetero π-stacking between pyrrole and N2 using spectroscopic methods.
• To compare the energetic favorability of π-stacking versus hydrogen bonding in pyrrole-N2 adducts.

Main Methods:

• Matrix isolation spectroscopy at low temperatures.
• Infrared spectral characterization of molecular adducts.
• Computational analysis of competing interaction energies.

Main Results:

• Hetero π-stacking was successfully achieved between pyrrole and N2 molecules.
• Adducts stabilized by a π(pyrrole)···π(N2) interaction were identified.
• π-stacking interaction was found to be energetically dominant over hydrogen bonding in pyrrole-N2 associates.

Conclusions:

• The N2 molecule can act as a π-bonding partner in hetero π-stacking interactions.
• Matrix isolation spectroscopy is effective for studying weak interactions at low temperatures.
• Energetic preference for π-stacking over hydrogen bonding was confirmed for the pyrrole-N2 system.