Theoretical prediction of pressure-stabilized all-nitrogen N12 molecular crystal with π-π stacking

Abstract

All-nitrogen compounds are ideal high-energy-density materials, as they decompose environmentally friendly into nitrogen gas (N2). However, achieving structural stability often conflicts with high-energy performance. In this study, we demonstrate that two aromatic pentazole rings can be linked by an -N=N- bond with sp² orbital hybridization, resulting in a planar π-conjugated compound known as N12. Computational analyses, including the electron localization function and isochemical shielding surface, demonstrate that the pentazole anion in N12 maintains electron delocalization and exhibits aromaticity. Interestingly, under high pressure, the N12 molecule can form a super π-π stacking crystalline structure. The thermodynamic and dynamic stabilities of crystalline N12 are verified using phonon spectrum and ab initio molecular dynamics calculations. Electronic structure calculations reveal that N12 crystal exhibits semiconducting properties with a large bandgap and is comparable to stable CHON energetic materials. Unlike other all-nitrogen compounds, the π-π stacking in the N12 crystalline structure contributes to a high mass density and a large decomposition barrier, which is crucial to both achieving high energy performance and high structural stability. Therefore, further evaluations of detonation performance reveal that N12 crystalline possesses excellent detonation velocity and pressure among the known all-nitrogen molecular crystals. This work enhances the understanding of nitrogen chemistry and provides new insights into the stabilization of all-nitrogen compounds through π-π stacking.