Hydrogen Bond and π-π Stacking Interaction: Stabilization Mechanism of Two Metal Cyclo -N 5 - -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(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.