Molecular design and properties of bridged energetic pyridines derivatives

A series of bridged pyridine-based energetic derivatives were designed and their geometrical structures, electronic structures, heats of formation, detonation properties, thermal stabilities, thermodynamic properties and electrostatic potential were fully investigated using density functional theory. The results show that the steric hindrance effect is a decisive factor for structural stability, and the formation of intramolecular or intermolecular hydrogen bonds doesn't provide advantages to stabilize molecular structure, which was demonstrated by insertion of 3,4,5-trinitro-1H-pyrazole, 3,4-dinitro-1H-pyrazol-5-amine, 3,5-dinitro-1H-pyrazol-4-amine and 3-nitro-1H-1,2,4-triazol-5-amine. The azide group and azo bridge play an important role in improving the heats of formation of energetic pyridine-based materials. All designed molecules were found to have values of density ranging from 1.70 g cm^-3 (E6, F6) to 2.11 g cm^-3 (D3), values of detonation velocity ranging from 7.1 km s^-1 (F1) to 9.77 km s^-1 (D8), and values of detonation pressure ranging from 21.5 GPa (F1) to 46.0 GPa (D8). When a p-π conjugation formed between the nitrogen atom and pyridine ring, the bond between nitrogen and hydrogen atoms may be broken as the trigger bond.