Syntheses, Structures, and Properties of Polynitro-Substituted 5,6-Dihydrodiimidazo[1,2-a:2 ',1 '-c]pyrazine Energetic Compounds

A series of polynitro-substituted 5,6-dihydrodiimidazo[1,2-a:2',1'-c]pyrazine energetic compounds were synthesized by cyclization and nitration of biimidazole. All newly synthesized compounds were fully characterized by infrared spectroscopy, H-1 and C-13 nuclear magnetic resonance spectroscopy, and elemental analysis. Single-crystal X-ray diffraction, iso-chemical shielding surfaces, localized orbital locator-pi, Hirshfeld surface analysis, and noncovalent interactions were employed to investigate the structures of 1-6. It is worth mentioning that compounds 3-6 are all thermally stable, with onset decomposition temperatures of 200-330 degrees C (DSC). Moreover, impact and friction sensitivity test results show that they are insensitive. Energy-related parameters, including densities, heats of formation, and detonation properties, were predicted according to the classical methods. In addition, the influence of the number and position of substituted nitro groups on density, heat of formation, and detonation performance was theoretically established. The superior detonation performances and good stabilities make compounds 4 and 5 useful as replacements for TNT.