Theoretical insight into different energetic groups on the performance of energetic materials 2,5,7,9-tetranitro-2,5,7,9-tetraazabicyclo[4,3,0]nonane-8-one.

Context: Energetic materials are a class of materials containing explosive groups or containing oxidants and combustibles. The optimization of energetic materials has a significant impact on the development of industry and national defense. For high-energy density compounds (HEDC) that have not been synthesized or are dangerous to experimental operation, it is of guiding significance to predict its energy level, physicochemical properties, and safety through molecular design and theoretical calculation. Cyclic urea nitramine series compounds are a type of energetic compounds with high density and excellent detonation performance. In this study, 2,5,7,9-tetranitro-2,5,7,9-tetraazabicyclo[4,3,0]nonane-8-one (K-56) was used as the parent structure, and 36 energetic derivatives were designed. The effects of introducing single and multiple substituents on the electronic structure, energy gap, heat of formation, detonation performance, thermal stability, thermodynamic parameters, and surface electrostatic potential of K-56 and its derivatives were discussed in detail. The results exhibit the following: (1) the single substitution of -C(NO) (A6) can reduce the detonation velocity of K-56 by 11.9 % and the detonation pressure by 19.8 %, while the double substitution of -C(NO) (B6) can increase the density of K-56 by 11.6 %, the detonation velocity by 10.9 %, and the detonation pressure by 31 %. (2) The heat of formation of K-56 (-110.0 kJ mol) increased by 324.18 % and 628.81 %, respectively, proving that -N is an extremely effective group to improve HOF. (3) The thermal stability of the derivatives generated by the monosubstitution of the target group on the six-membered ring is better than that of the parent compound.

Methods: Gaussian16 and Multiwfn 3.8 packages are the software for calculation. In this study, the parent structure K-56 and its derivatives were optimized at the B3LYP/6-311G (d,p) level to obtain the zero point energy and thermal correction data of all compounds. Then the vibration analysis of the optimized structure is carried out to confirm that its configuration is stable. Then the M06-2X-D3/def2-TZVPP basis set is used to calculate the single point energy.