Synthesis mechanism of four metallic Cyclo-N5− energetic materials: A theoretical Perspective

In the past five years, over 20 types of cyclo-N5− energetic materials (EMs) have been successfully synthesized. Metallic cyclo-N5− EMs exhibit higher density and performance compared to non-metallic cyclo-N5− EMs. However, the mechanisms for such metallic cyclo-N5− EMs remain unexplored. Herein, we performed a thorough quantum chemistry study on the mechanistic pathway for the cyclo-N5− trapped by metal cations in four cyclo-N5− EMs: [Na(H2O) (N5)] · 2H2O, [M(H2O)4(N5)2] · 4H2O (M = Mn, Fe, and Co), by density functional theory methods and transition state theory. During the synthesis process, the cyclo-N5− in the precursor hybrid aromatic compound is susceptible to electrophilic attack by metal cations. This attack disrupts the hydrogen bond interaction surrounding the cyclo-N5−, ultimately leading to the formation of either an ionic bond or a coordination bond between the metal cation and the cyclo-N5−, resulting in an electrophilic substitution reaction. In addition, solvent effects reduce the energy of the ionic bond, thereby promoting the reaction. Our findings will provide valuable insights for future route design and contribute to enhancing the synthesis yield of cyclo-N5− EMs in both theoretical and experimental aspects.