Abstract:The crystal data of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50), dihydroxylammonium azotetrazole-1,1′-diolate (ATZO-1), and sodium 5,5′-azotetrazole-5-oxide pentahydrate (ATO-Na) were analyzed and compared. The effects of the introduction of ─N􀰗N─ and ─N􀰗N(O)─ into the structure of bis-tetrazolium molecules was summarized from the micro-level. Results show that the bistetrazole linked from two tetrazolium rings directly has the densest structure among three compounds, the symmetrical and compact structure further make it own the highest crystal density. Based on the Born-Haber cycle and the Hess law, the heat of formation for TKX-50, ATZO-1 and dihydroxylammonium 5,5′-azotetrazole-5-axide (ATO-1) were calculated. According to the Kamlet Jacobs formula (K-J equation), detonation parameters of these three compounds were also obtained. By comparison, it could be found that both the introduction of ─N􀰗N─ and ─N􀰗N(O)─ bonds can increase the enthalpy of formation for compounds to a certain extent. However, due to the apparent density difference in three crystals, TKX-50 still holds the highest detonation value.

Abstract:The calculations of the crystal structures, in-crystal intermolecular interactions, physicochemical properties, crystal stability and detonation performance for 16 reported cocrystal explosives were carried out to explore their effect on crystal stability and detonation performance of cocrystal explosives. We show that the crystal stability of the cocrystal explosives is mainly determined by the hydrogen bonding (HB) amount when the HB strength is less than 21 kJ·mol^-1. When the HB strength is more than 21 kJ·mol^-1, the crystal stability of the cocrystal explosives is mainly determined by the HB strength. Compared to traditional single-component explosives, the reported 16 cocrystals exhibit better nitrogen content and oxygen balance, but their material densities and detonation performance are less competitive. Through the analysis of CL-20 cocrystal explosives, it is theoretically suggested that enhancing HB strength, instead of introducing more hydrogen atoms to increase HB amount, could be useful to improve crystal stability of cocrystal explosives. This strategy can simultaneously meet the requirement of oxygen balance and nitrogen content in resulting satisfactory detonation performance of cocrystal explosives.

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:The synthesis of novel high energy low sensitivity materials is important for improving of energy level and safety performance of weapons. 5,6-Diaminofurazano[3,4-b]pyrazine-4,7-dioxide (DAFPO) was firstly synthesized by oxidation reaction using 5,6-diaminofurazano[3,4-b]pyrazine as raw material. Its structure was characterized by nuclear magnetic resonance (¹H, ¹³C and ¹⁴N spectrum), infrared spectroscopy and element analysis. The single crystal of DAFPO·2H₂O was cultivated from ethyl acetate. Its crystal structure was determined by X-ray single-crystal diffraction, and the intermolecular interactions were investigated by Hirshfeld surface analysis. DAFPO·2H₂O belongs to orthorhombic system, space group Pna2₁, the crystal density is 1.806 g·cm^-3 at 296 K. The crystal is stabilized by strong O…H and N…H hydrogen bonds interactions existed in different molecules. The thermal behavior of DAFPO was studied by DSC and TG/DTG method, giving decomposition temperature at 131.8 ℃. Based on atomization reaction and Gaussian 09 software, the calculated solid heats of formation of DAFPO is 753.5 kJ·mol^-1. Its density is 1.86 g·cm^-3 by gas expansion replacement method. The calculated detonation velocity and detonation pressure predicted by EXPLO5 code are 8836 m·s^-1 and 36.0 GPa, respectively. According to standard BAM method, the impact sensitivity is above 40 J, and the friction sensitivity is above 360 N. It is found that DAFPO is a novel low sensitivity energetic material with high energy level and good safety performance.

Abstract:6-((2H-tetrazol-5-yl)-amino)-1,2,4,5-tetrazin-3(2H)-one (TATzO) was synthesized and characterized by FT-IR, elemental analysis, ¹H NMR and ¹³C NMR and single crystal X-ray diffraction. The single crystal structure solution indicates that a hydrate forms (TATzO·H₂O) and it crystallizes in the orthorhombic Pnma space group with a density of 1.730 g·cm^-3 at 296 K. The thermal behavior and thermal decomposition kinetic of TATzO·H₂O were studied by differential scanning calorimetry (DSC) and thermogravimetry-derivative thermogravimetry (TG-DTG) methods. The thermal decomposition peak temperature is determined to be 230.46°C, indicating a similar thermal stability to cyclotrimethylenetrinitramine (RDX). The apparent activation energies (E) and pre-exponential constant (A) of the compound are 169.03 kJ·mol^-1 and 15.65 s^-1, respectively. The thermal ignition temperature (T_be) and the critical temperature of thermal explosion (T_bp) is 213.75℃ and 223.03℃，respectively. The enthalpy of formation was theoretically calculated by Gaussian 03, and the detonation velocity (D) and detonation pressure (p) were calculated by the Kamlet-Jacobs (K-J) equation. The obtained D and p are 7757m·s^-1 and 25.74 GPa, respectively. The impact sensitivity is larger than 24 J.

Abstract:1²,5²-difluoro-1⁴,1⁶,3⁴,3⁶,5⁴,5⁶,7⁴,7⁶-octanitro-2,4,6,8-tetraoxa-1,3,5,7(1,3)-tetrabenzenacyclooctaphane (ZXC-20) was synthesized from 2,3,4-trifluoro-nitrobenzene by nitration, cyclization and nitration. The single crystal of ZXC-20·EtOH was obtained by solvent evaporation method, and its single crystal structure was characterized by X-ray single crystal diffraction. The density of the compound was determined by automatic densitometer. The thermal decomposition temperature of ZXC-20 were recorded on a differential scanning calorimeter (DSC). The detonation parameters such as detonation velocity and detonation pressure of ZXC-20 were calculated by EXPLO5 v6.01. The results show that the crystal belongs to P-1 space group. Its cell parameters are a =10.620(6) Å, b =10.641(6) Å, c=16.549(12) Å, V=1524.5(16) ų, Z=2, F(000)=788.0. The actual density of ZXC-20 is 1.912 g·cm^-3 at 298 K. The thermal decomposition temperature is 333.76 ºC. The crystal belongs to P-1 space group. The theoretical detonation velocity and theoretical detonation pressure of ZXC-20 are 8070 m·s^-1 and 29.5 GPa, respectively, which are better than TATB. ZXC-20 is a potential fluorine-containing heat-resistant explosive.

Abstract:Three new nitrogen-rich energetic complexes Cu(DNABT)(NH₃)_2-x(NH₂NO₂)_x(x=0,1,2) were designed by incorporating N,N′-dinitroamino-bi(1,2,4-triazole) (DNABT) with copper, ammonia and nitramine. Their molecular, electronic and crystal structures, heat of formation, density, detonation performance and sensitivity were studied theoretically. The results show that the Cu and DNABT linked coordination bond is weaker than other bonds which possibly trigger the decomposition. The number of ammonia and nitramine ligands have a significant different effect on the structure and properties of the designed complex. All designed complexes possess high density (2.07-2.13 g·cm^-3), good energetic performance (detonation velocity: 8.44-9.12 km·s^-1, detonation pressure: 34.2-40.0 GPa) and acceptable sensitivity (7-22 cm), especially for the complex with x=1, whose energy is higher than RDXand similar sensitivity to RDX, being a potential high energy density compound.