Comparative theoretical studies of energetic azo s-triazines

Design and selection of high energy materials based on 4,8-dihydrodifurazano[3,4-b,e]pyrazine

In order to search for high energy density materials, various 4,8-dihydrodifurazano[3,4-b,e]pyrazine based energetic materials were designed. Density functional theory was employed to investigate the relationships between the structures and properties. The calculated results indicated that the properties of these designed compounds were influenced by the energetic groups and heterocyclic substituents. The -N3 energetic group was found to be the most effective substituent to improve the heats of formation of the designed compounds while the tetrazole ring/-C(NO2)3 group contributed much to the values of detonation properties. The analysis of bond orders and bond dissociation energies showed that the addition of -NHNH2, -NHNO2, -CH(NO2)3 and -C(NO2)3 groups would decrease the bond dissociation energies remarkably. Compounds A8, B8, C8, D8, E8, and F8 were finally screened as the potential candidates for high energy density materials since these compounds possess excellent detonation properties and acceptable thermal stabilities. Additionally, the electronic structures of the screened compounds were calculated.

Computational Design of High Energy RDX-Based Derivatives: Property Prediction, Intermolecular Interactions, and Decomposition Mechanisms

A series of new high-energy insensitive compounds were designed based on 1,3,5-trinitro-1,3,5-triazinane (RDX) skeleton through incorporating -N(NO₂)-CH₂-N(NO₂)-, -N(NH₂)-, -N(NO₂)-, and -O- linkages. Then, their electronic structures, heats of formation, detonation properties, and impact sensitivities were analyzed and predicted using DFT. The types of intermolecular interactions between their bimolecular assemble were analyzed. The thermal decomposition of one compound with excellent performance was studied through ab initio molecular dynamics simulations. All the designed compounds exhibit excellent detonation properties superior to 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), and lower impact sensitivity than CL-20. Thus, they may be viewed as promising candidates for high energy density compounds. Overall, our design strategy that the construction of bicyclic or cage compounds based on the RDX framework through incorporating the intermolecular linkages is very beneficial for developing novel energetic compounds with excellent detonation performance and low sensitivity.

Cis-Trans Isomerization and Thermal Decomposition Mechanisms of a Series of Nx (x = 4, 8, 10, 11) Chain-Catenated Energetic Crystals

Nitrogen-rich compounds based on heteroaromatic rings with different lengths of nitrogen chains are at the forefront of the energetic materials field. We studied the decomposition processes and reaction kinetics of a series of N_x (x = 4, 8, 10, 11) chain-catenated energetic crystals at various temperatures (2400-3000 K) based on a combinational strategy based on density functional tight binding molecular dynamics (DFTB-MD) simulations and density functional theory (DFT). The results show that the thermal decomposition and reaction kinetics are dependent on both the temperature and nitrogen chain's length. There are two sequential stages in the initial decomposition process for the crystals N₈ and N₁₀: (i) competition between cis-trans isomerization and initial unimolecular decomposition and (ii) subsequent complicated global decomposition reactions. Increasing either the temperature or nitrogen chain's length will accelerate the competition and make initial decomposition dominate. However, cis-trans isomerization does not occur in the crystals N₄ and N₁₁. The dominant initiation paths for N₄, N₈, and N₁₀ occur in the heterocycle and in the bond between the heterocycle and azo group, while that for N₁₁ is ring elimination. The decomposition reactions exhibit a clear first-order kinetics character. The energy paths based on DFT calculations are determined as an addition to the DFTB-MD results. Our findings provide insights into the comprehensive understanding of thermal decomposition behaviors of nitrogen chain-catenated and even all-nitrogen energetic materials.

Theoretical determination of the effects of various linkages between trinitrobenzenes on energetic properties and sensitivity

Density functional theory (DFT) has been applied to understand the influence of various linkages on the energetic properties and stability of the polynitro-biphenyl compounds. Structures were optimized using the B3PW91/6-31G(d,p) level, and the heats of formation (HOFs) were computed by employing the selected isodesmic reactions. The results reveal that the -N=N- linkage helps to gain high HOF while the -O-, -NH-C(O)NH-, and -NH-C(O)-C(O)-NH- show a negative impact on energy content. Kamlet-Jacobs (K-J) equations were used to determine detonation properties based on the computed densities and HOFs, while stability and sensitivity were investigated by correlating with the bond dissociation energy (BDE), charge on the nitro group, and the balance parameter on surface potentials. Comparing the effect of different linkages on performance and stability of selected polynitro-biphenyl derivatives reveals that -NH-NH- and -N=N- are suitable for a connection between energetic moieties and these results are expected to demonstrate primary information for designing new energetic materials. Graphical abstract.

Molecular design on a new family of azaoxaadamantane cage compounds as potential high-energy density compounds

A new family of azaoxaadamantane cage compounds were firstly designed by introducing the oxygen atom into hexanitrohexaazaoxaadmantane (HNHAA) to replace the N–NO2 group. Their properties including heats of formation (HOFs), detonation properties, strain energies, thermal stability, and sensitivity were extensively studied by using density functional theory. All of the title compounds exhibit surprisingly high density (ρ > 2.01 g/cm3) and excellent detonation properties (detonation velocity (D) > 9.29 km/s and detonation pressure (P) > 40.80 GPa). In particular, B (4,8,9,10-tetraazadioxaadamantane) and C (6,8,9,10-tetraazadioxaadamantane) have a remarkably high D and P values (9.70 km/s and 44.45 GPa, respectively), which are higher than that of HNHAA or CL-20. All of the title compound have higher thermal stability and lower sensitivity (h50 > 19.58 cm) compared with the parent compound HNHAA. Three triazatrioxaadamantane cage compounds, D (6,8,9-triazatrioxaadamantane), E (6,8,10-triazatrioxaadamantane), and F (8,9,10-triazatrioxaadamantane), are expected to be relatively insensitive explosives. All of the title compounds exhibit a combination of high denotation properties, good thermal stability, and low insensitivity.

Molecular design and selection of 1,2,5-oxadiazole derivatives as high-energy-density materials

A family of 1,2,5-oxadiazole-based energetic compounds were designed and their properties were investigated fully by density functional theory.

Designing and looking for novel cage compounds based on bicyclo-HMX as high energy density compounds

We designed four cage compounds by introducing intramolecular linkages into the bicyclo-HMX framework. Their molecular and electronic structures, energetic properties, thermal stability, and impact sensitivity were evaluated using DFT.

Theoretical design and prediction of properties for dinitromethyl, fluorodinitromethyl, and (difluoroamino)dinitromethyl derivatives of triazole and tetrazole

Twelve series of –CH(NO₂)₂, –CF(NO₂)₂and –C(NF₂)(NO₂)₂substituted derivatives of triazole and tetrazole were designed, some physicochemical or detonation properties of them were calculated.

Theoretical investigations on azole-fused tricyclic 1,2,3,4-tetrazine-2-oxides

Fused compounds, a unique class of large conjugate structures, have emerged as prime candidates over traditional nitrogen-rich mono-ring or poly-ring materials. Meanwhile, compounds containing catenated nitrogen chains have also attracted attention from scientists due to their high heats of formation. On the other hand, the azoxy [–N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N(O)–] moiety has been found to increase density effectively in the molecular structure of compounds. Therefore, combining fused heterocyclic organic skeletons with the azoxy moiety can be regarded as an effective method for increasing the density and heat of formation, which results in substantial increase in detonation properties. Based on the above-mentioned considerations, in this study, a series of new non-hydrogen-containing 5/6/5 fused ring molecules with azoxy moiety structures are designed. Furthermore, their properties as potential high-energy-density materials, including their density, heats of formation, detonation properties, and impact sensitivity, have been extensively evaluated using thermodynamic calculations and density functional theory. Among the investigated compounds, 1,3,8,10-tetranitrodiimidazo[1,5-d:5′,1′-f][1,2,3,4]tetrazine 5-oxide (B), 1,10-dinitrobis([1,2,3]triazolo)[1,5-d:5′,1′-f][1,2,3,4]tetrazine 5-oxide (C) and 2,9-dinitrobis([1,2,4]triazolo)[1,5-d:5′,1′-f][1,2,3,4]tetrazine 5-oxide (D) display remarkable stabilities and are predicted to be high-performance energetic materials due to their high density (>1.94 g cm⁻³), detonation velocity (>9616 m s⁻¹), and detonation pressure (>41.1 GPa). In addition, our design strategy, which combines the azoxy moiety and fused tricyclic skeleton to construct nitrogen-rich molecular structures with high density and positive heat of formation, is a valuable approach for developing novel high-energy-density materials with excellent performance and stability.

In this work, a series of novel non-hydrogen-containing 5/6/5 fused ring molecules with azoxy moiety were designed, some physicochemical or detonation properties of them were calculated.

N-Fluoro functionalization of heterocyclic azoles: a new strategy towards insensitive high energy density materials

The finding of this study shows the introduction of a highly dense –F group instead of hydrogen atoms by N-functionalization, which is a very effective method for increasing the densities and detonation properties and decreasing the sensitivities of energetic molecules.

Theoretical Design on a Series of Novel Bicyclic and Cage Nitramines as High Energy Density Compounds

We designed four bicyclic nitramines and three cage nitramines by incorporating -N(NO₂)-CH₂-N(NO₂)-, -N(NO₂)-, and -O- linkages based on the HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) framework. Then, their electronic structure, heats of formation, energetic properties, strain energy, thermal stability, and impact sensitivity were systematically studied using density functional theory (DFT). Compared to the parent compound HMX, all the title compounds have much higher density, better detonation properties, and better oxygen balance. Among them, four compounds have extraordinary high detonation properties (D > 9.70 km/s and P > 44.30 GPa). Moreover, most of the title compounds exhibit better thermal stability and lower impact sensitivity than CL-20 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) or HNHAA (hexanitrohexaazaadamantane). Thus, all of the seven new nitramine compounds are promising candidates for high energy density compounds. In particular, five compounds exhibit a best combination of better oxygen balance, good thermal stability, excellent detonation properties superior to or comparable to CL-20 or HNHAA, and lower impact sensitivity than CL-20 or HNHAA. The results indicate that our unusual design strategy that constructing bicyclic or cage nitramines based on the HMX framework by incorporating the intramolecular linkages is very useful for developing novel energetic compounds with excellent detonation performance and low sensitivity.

QSPR modeling of detonation parameters and sensitivity of some energetic materials: DFT vs. PM3 calculations

The quantitative structure-property relationship (QSPR) methodology was applied to describe and seek the relationship between the structures and energetic properties (and sensitivity) for some common energy compounds. An extended series of structural and energetic descriptors was obtained with density functional theory (DFT) B3LYP and semi-empirical PM3 approaches. Results indicate that QSPR model constructed using quantum descriptors can be applied to verify the confidence of calculation results compared with experimental data. It can be extended to predict the properties of similar compounds.

Novel trinitroethanol derivatives: high energetic 2-(2,2,2-trinitroethoxy)-1,3,5-triazines

The multicomponent reaction of 2,4,6-trichloro-1,3,5-triazine with potassium trinitromethane and trinitroethanol was exploited for the first synthesis of the hetaryl trinitroethyl ethers.

Computational investigations into the substituent effects of -N₃, -NF₂, -NO₂, and -NH₂ on the structure, sensitivity and detonation properties of N, N'-azobis(1,2,4-triazole)

A series of derivatives of N, N'-azobis(1,2,4-triazole) substituted by -N₃, -NF₂, -NO₂, and -NH₂ groups was studied using the density functional theory method. To reveal the orbital interactions clearly and interpret the stability of the title compounds, natural bonding orbital (NBO) analysis was carried out. Strong p-π and π-π conjugation interactions exist in molecules. Substituent effects on the geometrical and electronic structures, aromaticity of the triazole ring, electronic sensitivity, impact sensitivity, thermal stability, density, solid state heat of formation [ΔH(f)(s)], detonation velocity (D), detonation pressure (P), and specific impulse (I(s)) were investigated. Substituent groups have significant and differing effects on performance. -N₃, -NF₂, and -NO₂ groups are very helpful for enhancing D and P, but the case is different for the -NH₂ group. The order of the contribution of various groups to P and D is -NF₂> -NO₂ > -N₃ > -NH₂. -NF₂ brings the highest D and P, but the lowest I(s). -NO₂ results in the secondary highest D and P and the best electronic stability.-N₃ gives relatively low D, P and stability, but the highest ΔH(f)(s) and I(s). -NH₂ leads to the lowest D and P, while giving the best impact and thermal stabilities. Therefore, it is necessary to consider various aspects comprehensively according to the practical requirements for each compound designed. Taking both detonation performance and sensitivity into consideration, introducing -NH₂ and -N₃ into N, N'-azobis(1, 2, 4-triazole) may be a good choice for designing high-energy density materials.

Exploring highly energetic aliphatic azido nitramines for plasticizers

A set of energetic aliphatic azido nitramines was designed and studied theoretically to find new promising azido nitramine plasticizers for propellants and to investigate the effect of the –CH₂NNO₂– group on performance.

Comparative theoretical studies of dinitromethyl- or trinitromethyl-modified derivatives of CL-20

The heats of formation (HOFs), energetic properties, strain energies, thermal stability, and impact sensitivity for a series of trinitromethyl- or dinitromethyl-modified CL-20 derivatives were studied by using density functional theory. It is found that the trinitromethyl group is an effective structural unit for improving the gas-phase HOFs and energetic properties of the derivatives. However, incorporating the dinitromethyl group into the parent compound is not favorable for increasing its HOFs and detonation properties. The effects of the dinitromethyl or trinitromethyl groups on the stability of the parent compound are discussed. The studies on strain energies show that the introduction of the trinitromethyl group intensifies the strain of the cage skeleton for the title compounds, whereas for the dinitromethyl groups, the case is quite the contrary. An analysis of the bond dissociation energies for several relatively weak bonds suggests that the substitution of the dinitromethyl or trinitromethyl group decreases the thermal stability of the derivatives. The C−NO2 bond in the dinitromethyl or trinitromethyl group is the weakest one and the homolysis of the C−NO2 bond may be the initial step in thermal decomposition. In addition, according to the calculated free space per molecule, the introduction of the dinitromethyl or trinitromethyl group increases the impact sensitivities of the derivatives. Considering the detonation performance, thermal stability, and impact sensitivity, six compounds can be regarded as the target high-energetic compounds.

Computational studies on polynitropurines as potential high energy density materials

As part of a search for high energy density materials (HEDMs), a series of purine derivatives with nitro groups were designed computationally. The relationship between the structures and the performances of these polynitropurines was studied. Density functional theory (DFT) at the B3LYP/6-311G** level was employed to evaluate the heats of formation (HOFs) of the polynitropurines by designing an isodesmic reaction method. Results indicated that the HOFs were influenced by the number and positions of substituent groups. Detonation properties were evaluated using the Kamlet-Jacobs equations, based on the theoretical densities and heats of formation of the polynitropurines. The relative stabilities of the polynitropurines were studied via the pyrolysis mechanism and the UB3LYP/6-311G** method. Homolysis of the ring-NO2 bond is predicted to be the initial step in the thermal decomposition of these purine derivatives. Considering their detonation properties and relative stabilities, the tetranitropurine (D1) derivatives may be regarded as potential candidates for practical HEDCs. These results may provide useful information for further investigations.

Density functional calculations for a high energy density compound of formula C6H 6-n (NO 2) n

A series of polynitroprismanes, C(6)H(6-n )(NO(2))(n) (n = 1-6) intended for use as high energy density compounds (HEDCs) were designed computationally. Their electronic structures, heats of formation, interactions between nitro groups, specific enthalpies of combustion, bond dissociation energies, and explosive performances (detonation velocities and detonation pressures) were calculated using density functional theory (DFT) with the 6-311 G** basis set. The results showed that all of the polynitroprismanes had high positive heats of formation that increased with the number of substitutions for the prismane derivatives, while the specific enthalpy of combustion decreased as the number of nitro groups increased. In addition, the range of enthalpy of combustion reducing is getting smaller. Interactions between ortho (vicinal) groups deviate from the group additivity rule and decrease as the number of nitro groups increases. In terms of thermodynamic stability, all of the polynitroprismanes had higher bond dissociation energies (BDEs) than RDX and HMX. Detonation velocities and detonation pressures were estimated using modified Kamlet-Jacobs equations based on the heat of detonation (Q) and the theoretical density of the molecule (ρ). It was found that ρ, D, and P are strongly linearly related to the number of nitro groups. Taking both their energetic properties and thermal stabilities into account, pentanitroprismane and hexanitroprismane are potential candidate HEDCs.