Design,Synthesis,and Performance Studies On High-nitrogen Azoles And All-nitrogen Energetic Compounds

With the development of the international situation and the needs of the national defense industry,energetic materials are playing an increasingly important role in national strategic layout and national defense security.In recent decades,nitrogen-rich heterocyclic energetic compounds have become a research hotspot because of the high nitrogen contents,high heats of formation,and good thermal stability,meanwhile,the development of all-nitrogen compounds such as pentazole anions has also attracted much attention.In this paper,we focus on high nitrogen skeletons such as triazole and tetrazole,all-nitrogen groups（-N₃）,and all-nitrogen compounds.The synthetic routes,crystal structures and energetic properties of several series of high-nitrogen heterocyclic compounds were explored,and theoretical studies of ionic and covalent all-nitrogen compounds were also conducted.The full text mainly divides into following five parts:Firstly,by introducing four nitroamino groups into 1,2,4-biotriazole with 61.74%nitrogen contents,one neutral compound and ten energetic salts were prepared.The structural differences between the molecule,divalent anion and tetravalent anion were investigated by single crystal XRD,in order to explore the potential structure-property relationships.These compounds all have excellent physicochemical properties with densities ranging from 1.75 to2.13 g·cm^-3,excellent detonation velocities ranging from 8667 to 9609 m·s^-1,and detonation pressures ranging from 35.62 to 42.42 GPa.In particular,compound 2-4 has a high density(1.91 g·cm^-3)and outstanding detonation properties(D:9421 m·s^-1;P:40.34 GPa),as well as divalent hydrazine 2-11 and hydroxylamine salts 2-12 which exhibit properties comparable to CL-20(D:9597,9609 m·s^-1;P:40.35,42.42 GPa).In addition,the thermal and mechanical stability（T_d:164～248℃;IS:9～15 J;FS:80～180 N）of energetic salts were enhanced due to the extensive hydrogen bonding interactions between the anions and cations.The excellent energetic performance and good stability suggest that the tetranitramonium-1,2,4-bistriazole compounds can be used as candidates for novel high-energy-density materials.Secondly,a new high-nitrogen ligand 3-4 and the corresponding two silver energetic coordination polymers（3-5 and 3-6）were synthesized by using 1H-tetrazole containing79.98%nitrogen as the main framework and linking furazan via C-C bond.Their structures were determined by single-crystal XRD.Polymer 3-5 and 3-6 have high crystal density(2.451/2.675 g·cm^-3)and high heats of detonation(0.91/0.88 kcal·g^-1).Their detonation properties are 7286 m·s^-1/27.89 GPa and 8085 m·s^-1/40.08 GPa,respectively,which are at advanced level among the reported silver complexes.In addition,laser detonation experiments showed that two polymers have low detonation delay times（<20μs）at a detonation energy of 70 m J,confirming their potential as novel laser-initiating energetic materials.Thirdly,to overcome the problem of negative oxygen balance and limited performance of azide-based compounds,the strategy of combining oxygen-rich nitro group with azide group was carried out,and N,N’-methylenebis-4-azido-3-Nitroamm-onium-1,2,5-oxadiazole（4-4）was synthesized.The crystal structures and energetic properties of it and its precursor（4-3）were fully investigated.In contrast to its precursor,compound 4-4 exhibits a U-shaped crystal structure and compact face-to-face and wave-like crystal stacking.The influence of the molecular structure on the properties was specifically analyzed by Hirsheld surface and bond dissociation energy（BDE）.The introduction of nitro groups makes compound 4-4 a zero oxygen balance and high density(1.78 g·cm^-3),as well as the good detonation properties(D:9018 m·s^-1;P:34.5 GPa),superior to 4-3 and several reported azide materials.Standard BAM tests and initiation tests showed that compound 4-4 has high sensitivity（IS:2 J;FS:10 N）and good initiation ability.Therefore,4-4 is a promising primary explosive.Fourthly,in order to increase the energy level of the pentazolate materials,the cyclo-N₅^-ring was combined with nitroxide coordinate bonds to form a novel cyclo-N₅O^-with higher oxygen contents.The structures and energetic properties of nine cyclo-N₅O^-salts（A1-A9）and three covalent compounds（B1-B3）were investigated by quantum chemical methods and density functional theory（DFT）.The results show that A1-A9 have higher density and better detonation performance than the conventional cyclo-N₅^-salts.Among them,compounds A1,A9 and B1 have outstanding detonation properties(D:10138,9911,9950 m·s^-1;P:43.9,40.9,41.4 GPa),which are much higher than those of CL-20.All these N-oxide pentazole anion derivatives have good impact stability(h₅₀:11～55 cm).In addition,surface electrostatic potential,infrared spectra,frontier molecular orbitals and natural bond orbitals were fully investigated.Finally,a variety of cyclic isomers of all-nitrogen molecules N₄,N₆,N₈,N₁₀,N₁₂ have been investigated theoretically and computationally using quantum chemical simulations and the B3LYP method of density functional theory,mainly including theoretical IR,surface electrostatic potential,molecular orbitals,natural bond orbitals,non-covalent interactions,and energy properties.These all-nitrogen isomers all exhibit excellent heats of formation(7.92～16.60 k J·g^-1),high detonation performance(D:9714～12293 m·s^-1;P:36.8～72.3 GPa),high specific impulse（325.0～436.2 s）,which are higher than those of CL-20.Molecules of different conformations exhibit different energy levels,and all-nitrogen conformations suitable for development are screened by comparison.Meanwhile,the impact sensitivities of all-nitrogen isomers were predicted using h₅₀ values.