Origin of the considerably high thermal stability of cyclo-N₅⁻ containing salts at ambient conditions

Abstract

Ionization, conjugation, hydrogen bonding, coordination bonding and π–π stacking consolidate the cyclo-N5− caged in salt crystals.

Formation mechanism of insensitive tellurium hexanitride with armchair-like cyclo-N6 anions

“…5, which accounts for most of the tellurium mixing energy barriers (129.80 kJ/mol), and plays an important role in improving the chemical barrier and insensitivity property. Moreover, the study of the stability of arylpentazoles indicates that the potential barriers of their various compounds are 78-100 kJ/mol, which are lower than the predicted potential barriers of cyclo-N 6 in our report 37 . As is known, a large pressure is required to overcome the energy barrier (~82.98 kJ/mol) of dinitrogen N 2 to shape the polynitrogen phase during synthesis.…”

Symmetrical cyclo-N5− hydrogen bonds: stabilization mechanism of four non-metallic cyclo-pentazolate energetic salts

“…Zhang mentioned that in the crystal structure of cyclo -N 5 − -containing salts, ionization and conjugation are the two important factors for the stability of the cyclo -N 5 − ring. 2 Ionization is efficient at strengthening the N-rich molecules, which naturally attract electrons. The negative ionization stabilizes cyclo -N 5 − as an independent fragment.…”

“…This is a necessary condition for the stable existence of the cyclo -N 5 − ring itself. In these successfully synthesized cyclo -N 5 − -containing non-metallic salts, 2,29,30 each cation group is shared by several cyclo -N 5 − rings through SCHBs and is in an intermediate equilibrium position so that the conjugation of cyclo -N 5 − can be maintained without being broken. Therefore, the SCHB is fundamentally the main reason why the conjugation of cyclo -N 5 − is not broken in the crystal.…”

“…In recent decades, the cyclo-pentazolate anion ( cyclo -N 5 − ) has become a hot spot with a broad interest in the development of high-energy-density materials (HEDMs). 1,2 Its high-energy release and environmentally friendly products are the main reasons for many years of pursuit. 3–10 However, cyclo -N 5 − obtained from the experimentally synthesized scheme is extremely short-lived, unstable under common conditions, and extremely susceptible to decomposition into N 2 and N 3 − .…”

“…14,22–29 In theoretical calculations, Zhang et al has counted the hydrogen bonds in 19 successfully prepared cyclo -N 5 − -containing species, as well as pointed out that hydrogen bonds stabilize these crystals. 2 In 2019, M. Lu et al reported that the hydrogen-bonding network played a crucial role in the stabilization of cyclo -N 5 − in two non-metallic cyclo-pentazolate salts: [C 4 H 9 N 10 N 5 ]·3H 2 O and [(C 5 H 9 N 10 ) 2 ClN 5 ]·3.5H 2 O. 30 The role of hydrogen bonds is analyzed from a qualitative point of view.…”