DFT study on gem-diazidocarbonimidoyl (-NCN6): Azido-cyclization mechanism, solvent effects, and high-nitrogen...

The conjugated system formed by two azido groups and an imine results in a high-energy structural unit (-NCN6) containing 89.1% nitrogen, serving as a promising candidate for the design of novel high-energy density materials (HEDMs). This study investigates the geometric and electronic structures, molecular electrostatic potential, and the isomerization-cyclization reaction pathway of this unit. The findings reveal that the cyclization reaction predominantly occurs during the transformation from azido to tetrazole, accompanied by significant alterations in molecular and electronic configurations. While the reaction is non-spontaneous in the gas phase, the presence of polar solvents, specifically water and dimethyl sulfoxide (DMSO), effectively stabilizes the reaction intermediates and products. Furthermore, an analysis of detonation performance demonstrates that the azido-to-tetrazole isomerization markedly enhances the compound's density, thereby significantly improving its detonation velocity and pressure.

Electronic structure calculations and geometric optimizations were performed using the Gaussian 09 and Multiwfn 3.8 software packages at the B3LYP/6-311G(d,p) level of density functional theory (DFT). To enhance computational accuracy, reaction barriers and molecular enthalpies of formation were determined using the CBS-4 M method. Intrinsic reaction coordinate (IRC) calculations were utilized to confirm transition state structures, and zero-point energy corrections were applied to all total energy calculations. Molecular electrostatic potentials were visualized and rendered using the VMD program. Detonation performance parameters were predicted and evaluated using the EXPLO5 software.