Abstract:To investigate the effect of micro-defects on the shock response， chemical decomposition， and damage evolution of pentazolate salts， ab initio molecular dynamics method is employed to simulate the dynamics evolution and initial chemical reaction mechanisms for perfect Mn（N₅）₂ crystal and the crystal with 3% vacancy defects under different shock velocities （8， 9， 10， 11 km·s^-1 and 12 km·s^-1）. The calculated Hugoniot curves indicate that the vacancy-containing system exhibits a slightly higher compression ratio under high-pressure conditions than the perfect system. The molecular dynamics results indicate that when shock velocity v_shock<10 km·s^-1， perfect and vacancy-containing system only show a slight （<10%） volume compression and neither of them exhibit chemical reactions within 5000 fs. When v_shock=10 km·s^-1， N─N starts to uniformly rupture within the space of perfect crystal at 512.8 fs， whereas the reaction of vacancy-containing system is advanced to 281.6 fs and the N─N is ruptured near the vacancy. When v_shock continually increases to 11 and 12 km·s^-1， the starting time of reaction for two systems is further advanced and the reaction process is further speeded up. The positive effects of the vacancy on shock sensitivity and chemical reaction process are weakened with the increase of v_shock. The simulated results at the atomistic scale reveal that vacancy defect is one of the early nucleation structures of hot spots. The stress near the vacancy promotes the cascade decomposition of the surrounding pentazolate anion， thereby causing the growth and propagation of damage and ignition of energetic materials.

Abstract:In order to study the formation rule of hydrogen bonds in pentazole non-metal salts and its influence on stability, the Reduced Density Gradient (RDG) theoretical analysis method was used. The hydrogen bonding interactions of a single N₅^- anion and its surrounding cations in the structure were investigated. The hydrogen bond length was read from the single crystal structure of each compound, and the strength was obtained from the RDG analysis. Results show that N₅^- anion can form two types of hydrogen bonds, N—H…N and O—H…N, with N—H and O—H proton donors with electro positivity. O—H…N hydrogen bonds are stronger, while N—H…N hydrogen bonds are weaker. There are two factors influencing the stability of N₅^- anion, one is the structure symmetry of N₅^- anion, and the other is the graphene-like structure that forms a crystal plane layer. Under the interaction of hydrogen bonding, N₅^- anion maintain good structural symmetry (biguanidinium pentazolate salt, 10) and graphene-like structure (3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b] [1,2,4]triazol-2-ium pentazolate salt, 12), which can significantly improve the stability and bring the decomposition temperature up to 124.8 and 120.9 ℃. On the contrary, if the hydrogen bonding causes serious deformation of N₅^- anion structure, which leads to the loss of symmetry and fails to provide planar stacking (oxalohydrazinium pentazolate salt, 3 and 4,4’,5,5′-tetraamino-3,3′-bi-1,2,4-triazol-2-ium pentazolate salt, 4), the stability of the N₅^- anion will decrease significantly, and the decomposition temperature is only 95 ^oC.

Abstract:In order to compare the densities, heats of formation, detonation velocities, and detonation pressures of the energetic pentazolate salts at the same level, density functional theory (DFT) method was used to study the sixteen N₅ˉ based nonmetallic energetic salts synthesized in the past two years. According to the Born-Haber energy cycle, the calculated heats of formation of the pentazolate salts are between 95.2 kJ·mol^-1 and 1362.0 kJ·mol^-1 at the MP2/6-311++G(d,p) level. The average heat of formation of the salts formed by the triazole-containing cation and N₅ˉ is the highest among the five types of N₅ˉ salts. The densities(at 298.15 K) of these pentazolate salts range from 1.395 g·cm^-3 to 1.650 g·cm^-3, which are much lower than the theoretical densities of all-nitrogen compounds. The detonation velocities and detonation pressures calculated by the Kamlet-Jacobs formula agree well with the calculation results from EXPLO5. Most of the N₅ˉ-containing ionic salts have detonation velocities between 6500 m·s^-1 and 8000 m·s^-1 and detonation pressures between 15 GPa and 26 GPa, which are lower than RDX. The theoretical detonation performance of biguanidinium, hydroxylammonium, and hydrazinium pentazolates are outstanding. Their detonation velocities (8622-9032 m·s^-1) are equal or slightly higher than that of RDX, and their detonation pressures (29.5-32.3 GPa) are lower than that of RDX. Thus, their predicted performance are not revolutionary. They do not exhibit the distinct advantages of all-nitrogen anion derivatives, and are far from the expectation of their ultra-high energy.

Abstract:In the early stage, studies on pentazole chemistry are mainly focused on the substituent effect and stability of aryl pentazole compounds, but the successful preparation of room-temperature stable pentazole ionic compounds has not been achieved. Until to 2017, for the first time, the Chinese scientists reported their successful preparation of isolated and stable cyclo-N₅^- compounds through an oxidative cleavage strategy at low temperature. Subsequently, a variety of cyclo-N₅^- based salts with different structures were synthesized, attracting a wide of attention in the fields of energetic materials. Up to now, full-nitrogen pentazole materials have achieved a series of breakthroughs and various full-nitrogen pentazole salts have also been prepared with the de composition temperatures mostly higher than 100 ℃. The ionic salts based on cyclo-N₅^- anion and nitrogen-rich cations will open a new avenue to develop cyclo-N₅^- based energetic materials. This work reviews the theoretical calculations, organic syntheses, structural characterization, and the perspectives on pentazole compounds, which aims to provide guidance for the researchers working in the field of polynitrogen materials.

Abstract:Sodium pentazole salt was prepared by treating 2, 6-dimethyl-4-(2H-pentazol-2-yl) phenolate with m-chloroperbenzoic acid (m-CPBA) and ferrous bisglycinate [Fe(Gly)₂] under low-temperature conditions, thereinto, m-CPBA and Fe(Gly)₂ were oxidizer and catalyst, respectively. The synthetic conditions were optimized, as following:the molar ratio between arylpentazole, Fe(Gly)₂ and m-CPBA was 1:3:4.5, the reaction time was 24 h and the reaction temperature was-45 ℃(crude yield of 28%). The effect of different oxidizing cleavage reagents on the yield of sodium pentazole salt was studied and the reason for the low yield of sodium pentazole salt was analyzed. In addition, sodium pentazole salt and the reaction by-product (2, 6-dimethylcyclohexa-2, 5-diene-1, 4-dione) were characterized by X-ray single crystal diffractometer (XRD), NMR (¹⁵NMR and ¹H NMR), FT-IR, mass spectrometry and elemental analysis. Based on these results, the mechanism of oxidizing cleavage of the C─N bond in arylpentazole by m-CPBA and Fe(Gly)₂ was speculated.