Phase transition-induced initial decomposition of nitrogen-rich binary CN compound 2,2′-azobis(5-azidotetrazole) and its precursor 2-amino-5-azidotetrazole via tetrazole ring opening under external electric fields: a comparative DFT-D study

Abstract

A comparative DFT-D study was performed to investigate the external electric field-induced crystal structures, electronic features, Hirshfeld surfaces, vibrational properties and initial decomposition mechanisms of nitrogen-rich binary CN compound 2,2′-azobis(5-azidotetrazole) (C₂N₁₆) and its precursor 2-amino-5-azidotetrazole (CH₂N₈). The results show that there exist phase transitions at the critical points of 0.006 a.u. and 0.008 a.u. for CH₂N₈ and C₂N₁₆, respectively, which are embodied in various properties of these compounds and induce their initial decomposition of the tetrazole ring opening via the breaking of N-N single bonds. The analysis of band gaps and density of states suggests the external electric field-induced enhancing ability for electron transition from the occupied orbitals to empty ones and N–N bond breaking may be the initial decomposition pathway for them. The variations in Hirshfeld surfaces indicate the spatial change and adjustment of non-bonding interactions in the two crystals. The discussions on vibrational properties indicate that IR characteristic peaks of all vibrational modes in the two crystals show a gradual red shift toward a low frequency region. The external electric field-induced initial decomposition pathways of both crystals are tetrazole ring opening via the breaking of a N–N single bond. Our findings provide insights for a comprehensive understanding of external electric field-induced phase transition and initial decomposition mechanisms of nitrogen-rich binary CN energetic compounds.