Intermolecular interaction characteristics of the all-carboatomic ring, cyclo[18]carbon: Focusing on molecular adsorption and stacking

Recently, an intriguing all-carboatomic ring, cyclo[18]carbon, was observed in the condensed phase for the first time, and it quickly attracted widespread attention. In this article, we first investigated the interaction of the cyclo[18]carbon with external environment through electrostatic potential and our recently proposed van der Waals potential, and then examined the strength and nature of the intermolecular interactions between cyclo[18]carbon and various small molecules in detail by state-of-art quantum chemistry calculations and elaborate wavefunction analyses. Finally, we studied the cyclo[18]carbon dimer, which is closely related to actual status of the cyclo[18]carbon in condensed phase. These researches show that the cyclo[18]carbon has a strong tendency to adsorb small molecules to or near its ring center, and the dispersion attraction is found to play a leading role in the binding interaction, while the electrostatic effect has a nonnegligible influence on the configuration of the molecular complexes. Two cyclo[18]carbon molecules can form a relatively stable dimer through prominent π-π stacking effect. Its ideal configuration is found to have a face-to-face D9d symmetry, but this geometry can be easily broken by relative sliding between the two rings due to thermal motion, as revealed by ab initio molecular dynamic simulation.