Syntheses, crystal structures, and energetic properties of four cyclo-pentazolate salts [NHn(CH3)4-n]+N5− (n = 0∼3)

Abstract

The formation of non-metallic pentazolate salts from the combination of simple nitrogen-rich cations with cyclo-N5− is expected to be applied in propellants and explosives. In this work, a series of structurally similar cations ([NH3CH3]+, [NH2(CH3)2]+, [NH(CH3)3]+, and [N(CH3)4]+) were used to synthesize four cyclo-N5− containing energetic salts, and the contribution of crystal stacking mode, hydrogen bonding, C–H···π and π-stacking interactions in the stabilization of cyclo-N5− salts has been investigated by geometrical and Hirshfeld surface analyses as well as theoretical calculations. All salts have been thoroughly characterized by single-crystal X-ray diffraction, infrared (IR), multinuclear NMR (1H and 13C) spectroscopy, and elemental analysis. The decomposition temperatures of all salts are higher than 75 °C, as measured by thermogravimetric (TG). These compounds all show low sensitivities (IS ≥ 35 J, FS > 360 N) measured by standard BAM methods. Their heats of formation and detonation performances were calculated using the Born–Haber energy cycle and K-J method (“Pilem” program), respectively. This study has great significance for future design and synthesis of cyclo-N5− containing energetic materials.