Theoretical Prediction and Comprehensive Characterization of an All-Nitrogenatomic Ring, Cyclo[18]Nitrogen (N₁₈)

The cyclic molecule cyclo[18]carbon composed of 18 carbon atoms has been observed in condensed phase experiment in recent years and has attracted great attention. Through state-of-art quantum chemistry calculation, this study found that 18 nitrogen atoms can also form a macrocyclic system, cyclo[18]nitrogen (N₁₈), though its lifetime is very short at room temperature and can only exist for a relatively long time at very low temperatures. We comprehensively theoretically studied properties of N₁₈, including geometric configurations, thermal decomposition mechanism and rate, molecular dynamics behavior, energetic properties, vibrational and electronic spectra. We also discussed in depth the electronic structure of N₁₈, including nature of the N-N bonds, lone-pairs, charge distribution characteristics, electronic delocalization, and aromaticity. This work is not only the first exploration of the macrocyclic N₁₈ molecule, but also the first time to systematically examine a very long-chain substance fully composed of nitrogen atoms in isolated state.