Theoretical studies of energetic nitrogen-rich ionic salts composed of substituted 5-nitroiminotetrazolate anions and various cations

Theoretical Investigation of Energetic Salts with Pentazolate Anion

Energetic salts based on pentazolate anion (cyclo-N₅⁻) have attracted much attention due to their high nitrogen contents. However, it is an enormous challenge to efficiently screen out an appropriate cation that can match well with cyclo-N₅⁻. The vertical electron affinity (VEA) of the cations and vertical ionization potential (VIP) of the anions for 135 energetic salts and some cyclo-N₅⁻ salts were calculated by the density functional theory (DFT). The magnitudes of VEA and VIP, and their matchability were analyzed. The results based on the calculations at the B3LYP/6-311++G(d,p) and B3LYP/aug-cc-pVTZ levels indicate that there is an excellent compatibility between cyclo-N₅⁻ and cation when the difference between the VEA of cation and the VIP of cyclo-N₅⁻ anion is −2.8 to −1.0 eV. The densities of the salts were predicted by the DFT method. Relationship between the calculated density and the experimental density was established as ρ_Expt = 1.111ρ_cal − 0.06067 with a correlation coefficient of 0.905. This regression equation could be in turn used to calibrate the calculated density of the cyclo-N₅⁻ energetic salts accurately. This work provides a favorable way to explore the energetic salts with excellent performance based on cyclo-N₅⁻.

Comparative Theoretical Studies on a Series of Novel Energetic Salts Composed of 4,8-Dihydrodifurazano[3,4-b,e]pyrazine-based Anions and Ammonium-based Cations

4,8-Dihydrodifurazano[3,4-b,e]pyrazine (DFP) is one kind of parent compound for the synthesis of various promising difurazanopyrazine derivatives. In this paper, eleven series of energetic salts composed of 4,8-dihydrodifurazano[3,4-b,e]pyrazine-based anions and ammonium-based cations were designed. Their densities, heats of formation, energetic properties, impact sensitivity, and thermodynamics of formation were studied and compared based on density functional theory and volume-based thermodynamics method. Results show that ammonium and hydroxylammonium salts exhibit higher densities and more excellent detonation performance than guanidinium and triaminoguanidinium salts. Therein, the substitution with electron-withdrawing groups (–NO₂, –CH₂NF₂, –CH₂ONO₂, –C(NO₂)₃, –CH₂N₃) contributes to enhancing the densities, heats of formation, and detonation properties of the title salts, and the substitution of –C(NO₂)₃ features the best performance. Incorporating N–O oxidation bond to difurazano[3,4-b,e]pyrazine anion gives a rise to the detonation performance of the title salts, while increasing their impact sensitivity meanwhile. Importantly, triaminoguanidinium 4,8-dihydrodifurazano[3,4-b,e]pyrazine (J4) has been successfully synthesized. The experimentally determined density and H₅₀ value of J4 are 1.602 g/cm³ and higher than 112 cm, which are consistent with theoretical values, supporting the reliability of calculation methods. J4 proves to be a thermally stable and energetic explosive with decomposition peak temperature of 216.7 °C, detonation velocity 7732 m/s, and detonation pressure 25.42 GPa, respectively. These results confirm that the derivative work in furazanopyrazine compounds is an effective strategy to design and screen out potential candidates for high-performance energetic salts.

Theoretical design of novel energetic salts derived from bicyclo-HMX

We designed three novel cage energetic anions by introducing ionic bridges containing NΘ, N(OΘ) and N(NΘNO₂) into cis-2,4,6,8-tetranitro-1H,5H-2,4,6,8- tetraazabicyclo[3.3.0] octane (bicyclo-HMX or BCMHX). The properties of 21 energetic salts, based on cage anions and ammonium-based cations, were studied by density functional theory (DFT) and volume-based thermodynamics (VBT) calculations. Compared to the parent nonionic BCHMX, most title salts have lower predicted impact sensitivities, higher predicted densities, larger predicted heats of formation (HOFs) and better predicted detonation properties. In particular, 11 energetic salts not only exhibit excellent predicted energetic properties, superior to 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20), but also have lower predicted sensitivity than CL-20. The best salt had a predicted detonation velocity of 10.06 km s^-1, a predicted detonation pressure of 48.54 GPa and a predicted sensitivity (h₅₀) of 23.99 cm. By introducing ionic bridges into highly nitrated rings, or modifying the original bridge with ionic bridges, some highly nitrated cage compounds with both excellent performance and low sensitivity can be developed strategically. Graphical abstract Heats of detonation, detonation velocities, and detonation pressures of salts derived from bicyclo-HMX.

Computational study of azole salts as high-energy materials

The crystal densities, heats of formation (HOFs), detonation properties, and impact sensitivities of a series of azole salts were investigated by the density functional theory and volume-based thermodynamics calculations. The HOFs of cations and anions and lattice energies were obtained based on the Born–Haber energy cycles. The detonation parameters (Q, D, and P) of 18 energetic salts have been calculated by the Kamlet–Jacobs equations with the calculated density and HOFs. The outcomes reflected that the hydroxylammonium cation has greater impact on the density and detonation properties of the azole salts than the hydrazine cation. Among all of the series salts under investigation, 2-amino-3-nitroamino-4,5-dinitropyrazole and 3-nitroamino-4,5-dinitropyrazole anions have greater HOFs and better detonation performances than other anions. In summary, the incorporations of all the cations studied here with the 2-amino-3-nitroamino-4,5-dinitropyrazole or 3-nitroamino-4,5-dinitropyrazole anions can be considered as potential high-energy salts.

Positive and negative linear compressibility and electronic properties of energetic and porous hybrid crystals with nitrate anions

Within the framework of DFT-D calculations, the compressibility anisotropy of UN and DATN energetic nitrates and the Ag(en)N hybrid crystal is established.

A comparative theoretical study of heterocycle-functionalized tetrazolate- and tetrazolate-1-oxide-based dianionic salts

Density functional theory and volume-based thermodynamics calculations have been performed to study the crystal densities, heats of formation, energetic properties, thermodynamics of formation, and impact sensitivity for a series of heterocycle-functionalized tetrazolate- and tetrazolate1-oxide-based dianionic salts. The results show that the hydroxylammonium cation is better than the tetrazolium cation for increasing the densities and detonation performance of the tetrazolate dianionic salts. The salts containing series B (tetrazolate-1-oxide) have larger densities and detonation performance than corresponding ones containing series A (tetrazolate) with the same cation. Incorporating a zwitterionic N-oxide into the nitrogen system is helpful for increasing its density and detonation performance for each salt series, but it is not favorable for improving its heat of formation. The salt including the tetrazine-dioxide conjugated with two tetrazolide exhibits the best energetic performance. The salts containing the tetrazolium cation could be possibly synthesized by the proposed reactions. Some of the salts with the cation hydroxylammonium show lower impact sensitivity than RDX or HMX.