Hydrogen Bond and π-π Stacking Interaction: Stabilization Mechanism of Two Metal Cyclo-N(5)(–)-Containing Energetic Materials

[Image: see text] 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(H(2)O)(N(5))]·2H(2)O (Na-cyclo-N(5)(–)) and [Mg(H(2)O)(6)(N(5))(2)]·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···O and O–H···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.