Enhanced Intermolecular Hydrogen Bonds Facilitating the Highly Dense Packing of Energetic Hydroxylammonium Salts

The energy and performance of energetic materials can be improved by increasing their crystal packing density. Thus, we propose a strategy involving salification with hydroxylammonium cations (HA(+)) to increase the packing coefficients (PCs) and packing densities of energetic ionic salts (EISs). Structural analyses and theoretical calculations of the observed EISs indicate that the strong intermolecular hydrogen bonds (HBs) between HA+ and anions are primarily responsible for the increase in EIS density. Such strong HBs usually exist in HA(+)-based energetic salts and rarely in other EISs but are absent in energetic crystals with neutral molecules. Such HBs induce high PCs and relatively high crystal packing densities by compensating for the relatively lower molecular density of HA(+) compared with other cations. Moreover, in combination with HBs in common explosives, we find a simple dependence showing that the shorter the strongest HB corresponds to the higher PC, suggesting that the strongest HB can be regarded as a simple indicator of PC. This study proposes that enhancing intermolecular HBs is the main strategy to increase compactness because H atoms usually exist in currently available energetic materials.