The successful synthesis of the pentazolate salt (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl has received considerable attention, as it ends the long search for a method for the bulk preparation of cyclo-N 5 - , a molecular ring with high energy density (Zhang, C.; et al. Science 2017, 355, 374.). A debate has recently arisen on the possible existence of a neutral HN 5 species in the pentazolate salt (Huang, R.-Y.; et al. Science 2018, 359, eaao3672.; Jiang, C.; et al. Science 2018, 359, eaas8953.). Herein, we show that the debate can be reconciled by the temperature effect on the proton transfer. At a low temperature (123 K), the proton transfer from H 3 O + to cyclo-N 5 - is energetically unfavorable; therefore, few neutral HN 5 species exist in the pentazolate salt, which is consistent with the single-crystal X-ray diffraction measurements (Zhang, C.; et al. Science 2017, 355, 374.). As the temperature increases toward room temperature, endothermic proton transfer becomes increasingly feasible, promoting the formation of H 2 O···HN 5 via H 2 O-H-N 5 as an intermediate species. In addition, the confusion over the apparent absence of a peak in the measured infrared spectrum corresponding to the out-of-plane bending of H 3 O + can be resolved by the computationally established ultrafast interconversion among the neutral and anionic species under ambient conditions.
ASJC Scopus subject areas
- Colloid and Surface Chemistry