Nonmetallic Pentazole Salts Based on Furazan or 4-Nitropyrazole for Enhancing Density and Stability
Wei Hu, Hongwei Yang, Jieyi Chen, Chong Zhang, Chengguo Sun, Bingcheng Hu, Guangbin Cheng
Abstract
In this work, three novel nonmetallic pentazole salts (6–8) based on furazan or 4-nitropyrazole were synthesized. Some coplanar groups were introduced into the compounds to improve the planarity of the crystal packing. 4-Amino-1,2,5-oxadiazole-3-carbohydrazonamide pentazolate (6), 5-(4-amino-1,2,5-oxadiazol-3-yl)-4H-1,2,4-triazole-3,4-diamine pentazolate (7), and 5,5′-(4-nitro-1H-pyrazole-3,5-diyl)-bis(4H-1,2,4-triazole-3,4-diamine) pentazolate (8) all show more stable π–π stacking and exhibit superior thermal stability (110.5–116.4 °C) than most other reported nonmetallic pentazole salts (Tonset: 80–110 °C), and compound 8 has the highest crystal density (1.722 g·cm–3/173 K) of nonmetallic pentazole salts to date. All salts have been thoroughly characterized by NMR (1H and 13C) spectroscopy, infrared (IR), Roman (RA), and elemental analysis. The decomposition temperature of all salts displays more than 110 °C, which is measured by differential scanning calorimetry (DSC). These compounds all shows low sensitivity (IS > 35 J, FS > 360 N) measured by standard BAM methods. Glycidyl azide polymer (GAP) based propellant formula with the addition of salt 6 or 7 shows a higher specific impulse (6, Isp = 262.1 s; 7, Isp = 263.9 s) than that of RDX (Isp = 259.0 s). This study can provide a new crystal engineering way for the synthesis of pentazole salt to solve the problem of low density and poor stability.