A series of energetic cyclo-pentazolate salts: rapid synthesis, characterization, and promising performance

Abstract

Pentazolate anion (cyclo-N₅⁻)-containing compounds represent a unique class of energetic materials, which have attracted significant research attention. Since the bulk synthesis of cyclo-N₅⁻ has been achieved, significant progress has been made in pairing cyclo-N₅⁻ with different cations to synthesize nitrogen-rich energetic salts. However, to date, no rapid and efficient synthetic route has been developed. Herein, we investigated cyclo-N₅⁻ in detail as a potential all-nitrogen, room-temperature stable anion for the rapid and efficient synthesis of energetic ionic derivatives (2–10) for use as environmentally benign explosives. High yields (>90%) of potassium (2), ammonium (3), hydroxylammonium (4), hydrazinium (5), aminoguanidinium (6), diaminoguanidinium (7), biguanidinium (8), 3,4-diamino-1,2,4-triazolium (9), and 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazol-2-ium (10) pentazolates were obtained by metathesis reactions of AgN₅ (1) and the respective chloride salts driven by the precipitation of AgCl. All the compounds were thoroughly characterized via infrared (IR) and multinuclear NMR (¹H and ¹³C) spectroscopy and elemental analysis. The solid-state structural features of the synthesized compounds were also investigated via single-crystal X-ray diffraction and several theoretical techniques. Moreover, their thermal stabilities were investigated by thermogravimetric (TG) and differential scanning calorimetry (DSC). Their heats of formation and detonation performance were calculated using the Born–Haber energy cycle and EXPLO5 v6.01 program, respectively. The data based on impact and friction tests show that these compounds range from being sensitive to insensitive. Based on the experimental and theoretical data, the biguanidinium pentazolate 8 (N = 81.36%, T_d = 124.8 °C, ΔH_f = 1362.0 kJ mol⁻¹, D = 9.257 km s⁻¹, P = 33.0 GPa, IS = 35 J, and FS = 300 N) shows potential as a high-performance energetic material.