Graphite-like Packing Modes Facilitating High Thermal Stability: A Comparative Study in the Polymorphs of Planar Energetic Molecules

Hygroscopicity can cause undesirable chemical reactions, affect the stability and compatibility, and also the reduce strength and detonation performance of energetic materials; therefore, it should be avoided for civil and military applications. The existence of acidic protons in the molecule is the main causes of hygroscopicity, and the most common strategy to eliminate acidic hydrogen includes the formation of salts, introduction of N-CH 3 or N-NH 2 groups, etc. In this work, we present the preparation of tricyclic fused-ring energetic compounds derived from bi(1,2,3-triazole) by introducing an N,N′alkylidene bridge which could act as a "buffer" to reduce the external stimuli, therefore resulting in compounds with enhanced thermal stability and reduced sensitivity as well as elimination of the hygroscopicity and acidity in the meantime. Their physical and chemical properties were determined and interpreted by both experimental and theoretical methods. The nonhygroscopicity, good thermal stability (C1, T d = 277 °C; C2, T d = 290 °C), low sensitivity (C1, IS = 30 J, FS > 360 N; C2, IS = 50 J, FS > 360 N), and detonation properties (C1, D = 8287 m s −1 ; P = 29.4 GPa; C2, D = 8027 m s −1 ; P = 25.4 GPa) comparable to those of TATB (D = 8114 m s −1 ; P = 31.2 GPa) make them desirable candidates as high-energy insensitive energetic materials.

Section: Resultsmentioning

confidence: 99%

New Role for an N,N′-Alkylidene Bridge: Taming the Hygroscopicity of Acidic Energetic Materials with Enhanced Stability

Teng

Lai

Cai

et al. 2022

“…Layered packing structures of energetic materials (EMs) can effectively buffer against externally mechanical stimuli by interlayer slipping, leading to a better energy and safety (E&S) balance than other packing modes. − However, the rational design of layered energetic crystals is still a challenge due to the complicated intermolecular interactions and the difficulties of accurate prediction of crystal structure, − limiting the design of EMs mainly at the molecular level, such as the permutation and combination between various parent rings (i.e., benzene and oxadiazole) with functional groups (i.e., nitro, amino, and azide groups). − Furthermore, a minor modification of molecules changes the crystal structures and performances (especially for impact sensitivity) greatly in most cases, which increases the difficulty of constructing layered energetic crystals. , As a result, only a handful of advanced layered EMs exist are present, most of which were accidentally discovered in experiments …”

Section: Introductionmentioning

confidence: 99%

Multi-Level Structural Design Strategy toward Low-Sensitivity Energetic Materials: From Planar Molecule to Layered Packing Crystal

Cao¹,

Zhang²,

Lai³

et al. 2022

Self Cite

Layered packing structures have been of great interest in the field of energetic materials (EMs) due to their excellent balances between energy and safety. Nevertheless, the present advanced layered EMs and rational design approaches are still lacking. In this work, we proposed a multi-level structural design strategy for layered EMs, from molecular to crystal level. Inspired by the experimentally known energetic crystals with the specific NH2···NO2 intermolecular motifs, we established a set of guidelines for designing and screening potential target molecules based on the H2N–C–C–NO2 moiety via a systematic analysis of structure/composition–performance relationships. Subsequently, the possible crystal packing structures were searched accurately by the evolutionary algorithm USPEX coupled with a recently developed energetic molecule-specific polarizable force field. The theoretical results show that B1 (4,4′-diamino-3,3′-dinitro-[5,5′-biisoxazole] 2,2′-dioxide) and C2 [(E)-3,3′-(diazene-1,2-diyl) bis (4-amino-5-nitroisoxazole 2-oxide)] are promising candidates of advanced layered EMs with good mechanical sensitivities (better than TNT) and detonation performances (superior to FOX-7). Hopefully, our multi-level design procedure can accelerate the discovery of novel layered EMs with advanced properties.

“…14−16 Very recently, reactive molecular dynamics simulations have suggested that a layered packing fashion always exhibits the highest apparent activation energies of the initial decomposition reactions than other packing modes in the same energetic compounds with polymorphs. 17 Therefore, layered energetic crystals attract much attention currently due to their well-balanced detonation performance and mechanical sensitivity. 10,12 Compared with the existing molecular design method of EMs, layered packing modes involve complex intermolecular interactions, making it difficult to design layered energetic crystals.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Crystal engineering aims to clarify the relationships between molecules, crystals, and properties and further utilize these relationships to design and prepare novel materials with desired physical and chemical properties, − which are widely used in many solid materials, such as drugs, , organic semiconductors, , and metal–organic frameworks. , In the field of energetic materials (EMs), crystal engineering has been regarded as an effective approach in recent years to alleviate the contradiction between energy and safety performances since special packing modes can possess both high energy and low sensitivity, especially the layered packing structures. − On the one hand, statistical analysis shows that layered energetic crystals have relatively high packing coefficients, which benefit in increasing crystal densities and detonation performances. On the other hand, the layered packing structures can buffer against external stimuli by interlayer slipping, contributing to low mechanical sensitivities. − Very recently, reactive molecular dynamics simulations have suggested that a layered packing fashion always exhibits the highest apparent activation energies of the initial decomposition reactions than other packing modes in the same energetic compounds with polymorphs . Therefore, layered energetic crystals attract much attention currently due to their well-balanced detonation performance and mechanical sensitivity. , …”

Section: Introductionmentioning

confidence: 99%

Distinguishing the Packing Modes of Planar Energetic Molecules with Two “H₂N–C–C–NO₂” Groups Based on π-Holes

Cao¹,

Zhang²,

Lai³

et al. 2022

Self Cite

Energetic materials (EMs) with layered packing structures exhibit good balances between high energy and low sensitivity, while it is a challenge to create them due to unclear correlations between planar molecules and packing modes. In this work, a systematic investigation on 10 geometrically similar planar EMs was performed with the help of computational methods, aiming to dig out the dominant factors responsible for layered and non-layered packing modes. After a comprehensive analysis, including packing structures, Hirshfeld surfaces, energy frameworks, the "Atoms in Molecules" theory, molecular electrostatic potential, and so on, we found that π-holes around C−NO 2 bonds can act as indicators to distinguish layered and non-layered packing modes. The π-holes with a positive electrostatic potential and a large region can form directional interactions with electron-rich nitro groups, resulting in non-layered packing structures. Thus, it is reasonable that no obvious π-holes are observed in the layered energetic crystals. The present contribution is hopefully to accelerate the development of advanced layered EMs.