Challenging the Limits of Binary CN Compounds: From Azidoformamidinium to Triazidocarbenium Pentazolate Salts

This work ingeniously introduces the azido groups into nonmetallic pentazolate salts, designing a series of pentazolate salts and conducting an in-depth investigation of their properties. Notably, the azidoformamidinium pentazolate tames the azido group and cyclo-N₅⁻ within a nitrogen-rich compound, with the triazidocarbenium pentazolate achieving a CN ratio of 1:14. Initially, the interactions between cations and anions were analyzed in detail. Atomic dipole moment corrected Hirshfeld demonstrated that increasing the number of azido groups further polarizes the ionic systems and enhances the interactions between cations and anions. Symmetric-adapted perturbation theory revealed that electrostatic attractions were the dominant contribution in all 3 systems. Because of the high enthalpies of formation provided by the azido groups, the detonation performance of all 3 systems are remarkable. Even the azidoformamidinium pentazolate outperforms most currently known nonmetallic pentazolate salts. Given their practical applicability and synthetic safety, the azidoformamidinium pentazolate was prioritized for synthesis. Fingerprint plots and independent gradient model based on Hirshfeld analysis indicated that the azidoformamidinium cation forms N–H…N hydrogen bonds with cyclo-N₅⁻ and exhibits pi–pi stacking interactions, which positively contribute to the system’s stability. These findings were strongly supported by localized orbital locator analysis. More importantly, differential scanning calorimetry revealed its onset decomposition temperature, while ab initio molecular dynamics and transition state theory provided a deeper understanding of its decomposition pathways. This research aims to provide valuable insights for improving the performance of pentazolate derivatives and proposes a novel approach to pushing the boundaries of binary CN compounds.