Investigate Of N-? Stacking Structure And Organic Azide Crystals Stacking Of Energetic Crystals

Energetic materials(EMs),as a class of promising energy materials,are widely used in military,civil,industrial and other fields.However,the inherent contradiction between its energy and safety has greatly restricted its practical development.The intrinsic structure(molecular structure and crystal structure)of EMs determines its energy and safety to a certain extent.Therefore,the study of its structure-activity relationship is particularly important.In this paper,Hirshfeld surface analysis,electrostatic potential and other methods were used to study the intermolecular interactions,crystal packing structures and their effects on the properties of EMs in two types of Energetic crystals(ECs).The main research contents are as follows:(1)The Hirshfeld surface analysis method is a method that can directly reveal the intermolecular interactions.The common intermolecular interactions and crystal packing structures in ECs can be quickly determined by using the Hirshfeld surface analysis method.At the same time,we found that the intermolecular interactions of the same molecule in different crystal environments are different,and the Hirshfeld surface and two-dimensional fingerprints are unique.We also combined Hirshfeld surface analysis and intermolecular friction symbol to predict the shear-sliding properties of ECs,and studied the relationship between intermolecular interactions and impact sensitivity,which further expanded the application range of Hirshfeld surface analysis.But at the same time,we also found that the roughness of quantitative analysis of intermolecular interaction strength by this method is its main disadvantage.(2)By analyzing the intermolecular interactions in ECs,we found a special kind of intermolecular interactions: n-? stacking.The characteristic of this interaction is that the group containing lone-pair electrons will form a "T-shaped" stacking pattern with the ? system.Since most molecules in EMs contain nitro groups and ? systems,and the lone-pair of electrons on the nitro groups are more active,this interaction is prevalent in large number of EMs.Through electrostatic potential analysis,intermolecular relative distance measurement and dimerization energy calculation,and the energy range of this interaction is 6.3?20.0 k J/mol,which is weaker than the common hydrogen bonding and ?-? stacking,so it is difficult to occur alone in planar molecules of stronger hydrogen bond acceptors and donors.Although n-? stacking is an electrostatic interaction in principle,van der Waals interactions are also involved because the molecules in an n-? pair are usually neutral and rarely polarize.We think that in the case of relatively close intermolecular distance,more lone-pair electrons acting on the more stable ?-system will form stronger n-? stacking.(3)By analyzing a series of energetic molecules containing azide radicals,we found that most of them are planar.From the analysis of the packing patterns of the crystals,most of these planar molecules form face-to-face and wave-like packings.However,the introduction of azide group can effectively increase the energy of EMs,but at the same time,it greatly increases the sensitivity.Therefore,how to introduce azide group in the design of energetic molecules needs to be carefully considered.In addition,by analysis of lattice energy,density and packing coefficient,we found that the structural characteristics of azide itself make the intermolecular distance in the crystal longer and the packing coefficient larger,which can effectively maintain the planarity of the molecules,especially for those with face-to-face stacking,the molecular planarity is even better than that of TATB molecules.In addition,through IRI calculation analysis,we found that these molecules are mainly related by van der Waals interactions,and azide group hardly participate in the intermolecular interactions.In this paper,the application of Hirshfeld surface analysis method in EMs and the intermolecular interactions and crystal packing patterns in two types of ECs are investigated.We hope to provide more ideas and references for the design and theoretical research of EMs in the future.