Molecular Packing Density Coefficient Contradiction of High-Density Energetic Compounds and a Strategy to Achieve High Packing Density
Fucheng Bao, Ying Xiong, Rufang Peng, Chaoyang Zhang
Abstract
High packing density (dc) is of great importance in the field of energetic materials, as it is positively correlated with energy performances, which refer to power, detonation property, or specific kinetic energy of a cylinder. This makes high dc a focus for designing new energetic molecules. This article systematically analyzes the composition, molecular topology, intermolecular interaction, molecule density (dm), and packing coefficient (PC) of the top 36 highest dc (≥1.90 g/cm3) CHNO compounds extracted from CSD. For these compounds, a dm–PC contradiction exists. as the dm increases, the PC decreases. The absence of a planar structure and a strong hydrogen bonding acceptor or donor in high-dm molecules is responsible for the low PC and the contradiction. Two strategies are summarized for achieving a high dc: first, to design caged molecules with high oxygen balance because they generally possess extraordinarily high dm to remedy the shortcoming of a rather low PC, and the other is to design planar molecules with dense and strong hydrogen bonding acceptors and donors to obtain high PCs and further high dc based on moderate dm. The introduction of NH2 needs to be emphasized in the second strategy. This work is expected to guide the design of new high-density energetic compounds.