Hexanitrogen (N6): A Synthetic Leap Towards Neutral Nitrogen Allotropes

The pursuit of nitrogen allotropes is considered a Holy Grail in high-energy-density materials research because they lend themselves as the cleanest envisionable energy storage materials by producing only benign N2 upon energy release. Here, we present the room temperature preparation of N6 (hexanitrogen) in the gas-phase through the reaction of Cl2 or Br2 with AgN3, followed by trapping in argon matrices at 10 K. We also prepared neat N6 as a film at liquid nitrogen temperature (77 K), indicating its unexpectedly high stability. Infrared and UV/Vis spectroscopy, 15N-isotope labelling experiments, and ab initio computations at the CCSD(T)/cc-pVTZ level of theory support our findings. The preparation of a metastable nitrogen allotrope beyond N2 opens new vistas for making long sought after, high-energy materials.