Hydrogen Bond and π-π Stacking Interaction: Stabilization Mechanism of Two Metal Cyclo-N5--Containing Energetic Materials

In recent years, cyclo-N-5(-) has attracted extensive attention because all-nitrogen high-energy-density materials (HEDMs) have been expected to reach a TNT equivalent of over 3.0. However, for cyclo-N-5(-)-containing HEDMs, the stabilization mechanism has remained enigmatic. In this study, two typical cyclo-N-5(-)-containing metal hydrates, [Na(H2O)(N-5)]center dot 2H(2)O (Na-cyclo-N-5(-)) and [Mg(H2O)(6)(N-5)(2)]center dot 4H(2)O (Mg-cyclo-N-5(-)), are selected to gain insights into the factors affecting their stability by the first-principles method. Both binding/lattice energy calculations and density of states analysis show that Mg-cyclo-N-5(-) is more stable than Na-cyclo-N-5(-). Hydrogen bonding is the main stabilization mechanism for stabilizing crystals and cyclo-N-5(-). Two types of hydrogen bonds, O-H center dot center dot center dot O and O-H center dot center dot center dot N, are clarified, which construct a 3D hydrogen bond network in Mg-cyclo-N-5(-) and an intralayer 2D hydrogen bond network in Na-cyclo-N-5(-). Moreover, nonuniform stress causes distortion of cyclo-N-5(-). Comparing the two samples, the distortion degree of cyclo-N-5(-) is higher in Na cyclo-N-5(-), which indicates that cyclo-N(5)(-)decomposition is easier. These findings will enhance the future prospects for the design and synthesis of cyclo-N-5(-)-containing HEDMs.