Theoretical Study Of Hydrogen Bonds And Their Influences On Structures And Properties Of Typical Energetic Ionic Salts

Energetic ionic salts(EISs)possess many excellent properties,such as high energy,low sensitivity and good environmental compatibility,making them promising candidates to replace the conventional CHON explosives.Nevertheless,the structure-property relationships of EISs have not clearly been understood yet.In this thesis,we employed hydrogen bonds(HBs)as a breakthrough point to study the mechanism of the effects of HBs on structures and properties,using the quantum chemistry methods,ab initio molecular dynamic(AIMD)simulations and crystal structure analysis tools.Firstly,dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate(TKX-50)is a recently synthesized EIS with some excellent properties including high energy content,high density,low impact sensitivity and low toxicity,and therefore becomes a promising alternative energetic material.In contrast to commonly applied energetic CHON materials,TKX-50 features strong intermolecular HBs.However,the effects of these strong HBs on its important properties remain unclear.We report herein the two-sided effects of the strong HBs on the stability of TKX-50,through ab initio simulations on shear deformation and thermal decomposition experiments.That is,on the one hand,the strong HBs in TKX-50 lead to layer-like arrangement of the cations and dianions along(010)planes,while adjacent layers are connected only by two types of weakest HBs,which facilitates the conversion of external kinetic energy into interlayer sliding,and contributes to low impact sensitivity;on the other han d,the extensive HBs in TKX-50 serve as a potential source to facilitate H-transfer(including proton transfer),which accelerates subsequent thermal decomposition,and thus deteriorates the thermal stability of TKX-50 relative to its notably low impact sensitivity.In addition,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 EISs.Structural analyses and theoretical calculations of the observed EISs indicate that the strong intermolecular HBs between HA+ and anions are primarily responsible for the high EIS density.Such strong HBs usually exist in HA+-based energetic salts and rarely in other EISs,and are absent in energetic crystals with neutral molecules.Such HBs induce high PCs and relatively high crystal packing densities by compensating 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.Strong HBs are universal in EISs.We studied the two-sided effects of the strong HBs in the TKX-50 crystal.And,on the basis of the research results of the TKX-50 crystal,we analyzed the HBs and packing mode in the HA+-based EISs to study the mechanism of structures and properties.Hopefully,it will promote understanding the mechanism of structures and properties of other EISs,and enrich the knowledge of sensitivity mechanism of energetic materials.These results provide a theoretical base for designing molecules and crystals of high-energy and low-sensitivity explosives.