Molecular design of all nitrogen pentazole‐based high energy density compounds with oxygen balance equal to zero

We designed a new family of pentazole‐based high energy density compounds with oxygen balance equal to zero by introducing −NH₂, −NO₂, −N₃, −CF₂NF₂, and −C[NO₂]₃, and the properties including density, heats of formation, detonation performances, and impact sensitivity were investigated using density functional theory. The results show that half of these new energetic molecules exhibit higher densities than RDX (1.82 g/cm³), in which H5 gives the highest density of 2.09 g/cm³. Among all the 54 designed molecules, 22 compounds have higher D and P than RDX and eleven compounds have higher D and P than HMX, indicating that designing the pentazole‐based derivatives with oxygen balance equal to zero is a very effective way to obtain potential energetic compounds with outstanding detonation properties. Taking both the detonation performance and stability into consideration, nine compounds may be recognized as potential candidates of high energy density compounds. It is expected that our results will contribute to the theoretical design of new‐generation energetic explosives.     

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.     

New theoretically predicted RDX‐ and β‐HMX‐based high‐energy‐density molecules

Theoretically new high‐energy‐density materials (HEDM) in which the hydrogens on RDX and β‐HMX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine and octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine, respectively) were sequentially replaced by (N NO₂)x functional groups were designed and evaluated using density functional theory calculations in combination with the Kamlet–Jacobs equations and an atoms‐in‐molecules (AIM) analysis. Improved detonation properties and reduced sensitivity compared to RDX and β‐HMX were predicted. Interestingly, the RDX and β‐HMX derivatives having one attached N NO₂ group [RDX‐(NNO₂)1 and HMX‐(NNO₂)1] showed excellent detonation properties (detonation velocities: 9.529 and 9.575 km·s⁻¹, and detonation pressures: 40.818 and 41.570 GPa, respectively), which were superior to the parent compounds. Sensitivity estimations obtained by calculating impact sensitivities and HOMO‐LUMO gaps indicated that RDX‐(NNO₂)1 and HMX‐(NNO₂)1 were less stable than RDX and HMX but more stable than any of the other derivatives. This method of sequential NNO₂ group attachment on conventional HEDMs offers a firm basis for further studies on the design of new explosives. Furthermore, the newly found structures may be promising candidates for better HEDMs.     

Density functional theory studies of effects of boron replacement on the structure and property of RDX and HMX

In this study, based on two model nitramine compounds hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5, 7-tetrazocine (HMX), two series of new energetic molecules were designed by replacing carbon atoms in the ring with different amounts of boron atoms, their structures and performances were investigated theoretically by the density functional theory method. The results showed that the boron replacement could affect the molecular shape and electronic structure of RDX and HMX greatly, and then would do harm to the main performance like the heat of formation, density, and sensitivity. However, the compound RDX-B2 is an exception; it was formed by replacing two boron atoms into the system of RDX and has the symmetric boat-like structure. Its oxygen balance (4.9%), density (1.91 g/cm³), detonation velocity (8.85 km/s), and detonation pressure (36.9 GPa) are all higher than RDX. Furthermore, RDX-B2 has shorter and stronger N NO₂ bonds than RDX, making it possesses lower sensitivity (45 cm) and better thermal stability (the bond dissociation energy for the N NO₂ bond is 204.7 kJ/mol) than RDX. Besides, RDX-B1 and HMX-B4 also have good overall performance; these three new molecules may be regarded as a new potential candidate for high energy density compounds.     

DFT investigation on detonation properties and sensitivities of bridged triazolo[4,5-d]pyridazine based energetic materials

A series of bridged triazolo[4,5-d]pyridazine based energetic materials were optimized at B3LYP/6-311G(d, p) level of density functional theory (DFT), and their detonation properties and sensitivities were calculated. The results show that the  NN bridge/ N₃ group were beneficial to improve values of heats of formation while  NN bridge/ C(NO₂)₃ group can improve detonation properties remarkably. In view of the sensitivities, compound F2 possesses the minimum values of impact sensitivity which reveals that  NHNH bridge/ C(NO₂)₃ group will decrease the stability of the designed compounds. Take both of detonation properties and sensitivities into consideration, compounds C8, E7, E8, F8 were screened as candidates of potential energetic materials since these compounds possess similar detonation properties and sensitivities values to those of RDX. All the calculated results were except to shine lights on the design and synthesis of novel high energy density materials.     

Theoretical predictions on pentaerythritol tetranitrate-based high energy density compounds

A novel family of pentaerythritol tetranitrate (PETN) derivatives based parent PETN skeleton were designed by introducing two energetic groups –NF₂ and –NO₂. Their electronic structure, heats of formation, detonation properties, impact sensitivity, and thermal stability were investigated by using density functional theory. The findings reveal that most of the title compounds have good detonation performance. The –NF₂ group played an important role in improving the densities, heats of detonation, and detonation properties of the designed molecules. The values of h₅₀ for almost all the PETN derivatives are higher than that of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine. An analysis of bond dissociation energy suggests that the N-NO₂ bond tends to be a trigger bond in thermal decomposition. Taking both detonation properties and thermal stabilities into consideration, the three compounds may be selected as potential high-energy-density compounds.     

Theoretical studies on high energetic density nitramine explosives containing pyridine

The insensitive property of explosives containing pyridine is combined with the high energy of nitramine explosives,and the concept of new nitramine explosives containing pyridine is proposed,into which nitramine group with N N bonds is introduced as much as possible.Based on molecular structures of nitramine compounds containing pyridine,density functional theory(DFT) calculation method was applied to study designed molecules at B3LYP/6-31+G(d) level.The geometric and electronic structures,density,heats of formation(HOF),detonation performance and bond dissociation energies(BDE) were investigated and comparable to 1,3,5-trinitro-1,3,5-triazinane(RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX).The simulation results reveal that molecules B and D perform similarly to traditionally used RDX.Molecule E outperform RDX,with performance that approach that of HMX and may be considered as potential candidate of high energy density compound(HEDC).These results provide basic information for molecular design of novel high energetic density compounds.     

Design and properties prediction of modified CL-20 energetic derivatives

We designed a series of energetic compounds based on the CL-20 molecular skeleton, and the properties including molecular geometric structures, electronic structures, density, heat of formation, detonation performances, and impact sensitivity were evaluated using density functional theory (DFT). The results indicate that five molecules have higher density values than that of Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX; 1.91 g/cm³) and A4 has a larger density value (2.07 g/cm³) than that of CL-20 (2.04 g/cm³). In addition, most of the molecules have better detonation performances and stability than those of CL-20, with A4 showing much greater detonation velocity (9.93 km/s) and pressure (47.32 GPa) than those of CL-20 with a h₅₀ value of 14.02 cm. Taking both excellent detonation performance and low sensitivity into consideration, all seven compounds except for A3 and A5 are considered as potential energetic compounds. These theoretically calculated results would be conducive to the design and synthesis of novel nitramine energetic compounds.     

Theoretical investigation on the structures,densities, and detonation properties of polynitrotetraazaoctahydroanthracenes

The polynitrotetraazaoctahydroanthracenes were optimized to obtain their molecular geometries and electronic structures at density functional theory–B3LYP/6‐31+G(d) level. Detonation velocities (D) and detonation pressures (P) were estimated for this nitramine compounds using Kamlet‐Jacobs equations, based on the theoretical densities (ρ) and heats of formation. It is found that there are good linear relationships between volume, density, detonation velocity, detonation pressure and the number of nitro group. Thermal stability of the compounds was investigated by calculating the bond dissociation energies and energy gap (ΔE_LUMO–HOMO). The simulation results reveal that molecule H performs similarly to famous explosive RDX. These results provide basic information for molecular design of novel high energetic density compounds. © 2011 Wiley Periodicals, Inc.     

Comparative theoretical studies of energetic azo s-triazines

In this work, the properties of the synthesized high-nitrogen compounds 4,4',6,6'-tetra(azido)azo-1,3,5-triazine (TAAT) and 4,4',6,6'-tetra(azido)hydrazo-1,3,5-triazine (TAHT), and a set of designed bridged triazines with similar bridges were studied theoretically to facilitate further developments for the molecules of interests. The gas-phase heats of formation were predicted based on the isodesmic reactions by using the DFT-B3LYP/AUG-cc-PVDZ method. The estimates of the condensed-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. Calculation results show that the method gives a good estimation for enthalpies, in comparison with available experimental data for TAAT and TAHT. The crystal density has been computed using molecular packing calculations. The calculated detonation velocities and detonation pressures indicate that -NF(2), -NO(2), -N═N-, and -N═N(O)- groups are effective structural units for improving the detonation performance of the bridged triazines. The synthesized TAAT and TAHT are not preferred energetic materials due to their inferior detonation performance. The p→π conjugation effect between the triazine rings and bridges makes the molecule stable as a whole. The electrostatic behavior of the bridged triazines is characterized by an anomalous surface potential imbalance when incorporating the strongly electron-withdrawing -NF(2) and -NO(2) groups into the molecule. An analysis of the bond dissociation energies shows that all these derivatives have good thermal stability over RDX and HMX, and the -NH-NH- bridge is more helpful for improving the stability than -N═N(O)- and -N═N- bridges. Considering the detonation performance and thermal stability, three bridged triazines may be considered as the potential candidates of high-energy density materials (HEDMs).     

Trinitromethyl-substituted 5-nitro- or 3-azo-1,2,4-triazoles: synthesis, characterization, and energetic properties

Various new polynitro-1,2,4-triazoles containing a trinitromethyl group were synthesized by straightforward routes. These high nitrogen and oxygen-rich compounds were fully characterized using IR and multinuclear NMR spectroscopy, elemental analysis, natural bonding orbital (NBO) analysis, and differential scanning calorimetry (DSC) and, in the case of 12, with single crystal X-ray structuring. The heats of formation for all compounds were calculated with Gaussian 03 (revision D.01) and then combined with experimentally determined densities to determine detonation pressures (P) and velocities (D) of the energetic materials (Cheetah 5.0). They exhibit high density, good thermal stability, acceptable oxygen balance, positive heat of formation, and excellent detonation properties, which, in some cases, are superior to those of TNT, RDX, and HMX.     

Searching for a new family of modified CL-20 cage derivatives with high energy and low sensitivity

A new family of energetic caged compounds was designed by introducing -NH- into the CL-20 skeleton and their energetic properties and impact sensitivity were investigated by using density functional theory. The results indicate that favorable substitution positions of the amine groups in the skeleton is helpful for increasing the heats of formation. Most of the seven compounds have high crystal densities above 1.9 g/cm³. Five compounds have the predominant detonation properties over CL-20. The derivatives with one NH₂ group have lower impact sensitivity than those with two NH₂ groups. Taking the detonation performance and impact sensitivity into consideration, four compounds may be selected as the potential candidates of high energy density compounds.     

Density functional calculation on a high energy density compound having the formula C2OH4?n (NO2) n

A series of ethylene oxide derivations, C₂OH_4?Cn (NO2) _n (x?=?1?C4), has been designed computationally. We calculated the heats of formation (HOFs), bond dissociation energy (BDE), and explosive performances (detonation velocity and detonation pressure) of the title compounds by using density functional theory with 6-311G** basis set. The results show that most of ethylene oxide derivations have positive HOFs values except I. All the calculated BDE and the bond dissociation energies without zero-point energy corrections (BDE⁰) are larger than 200?kJ?mol^?1, which indicate that all the ethylene oxide derivations have good thermal stabilities. The explosive performances of most of ethylene oxide derivations would rank up with cyclotrimethylenetrinitramine (RDX). The results have not only shown that these compounds may be used as high energy density compounds, but also provide some useful information for further syntheses.     

N‐Oxide 1,2,4,5‐Tetrazine‐Based High‐Performance Energetic Materials

One route to high density and high performance energetic materials based on 1,2,4,5‐tetrazine is the introduction of 2,4‐di‐N‐oxide functionalities. Based on several examples and through theoretical analysis, the strategy of regioselective introduction of these moieties into 1,2,4,5‐tetrazines has been developed. Using this methodology, various new tetrazine structures containing the N‐oxide functionality were synthesized and fully characterized using IR, NMR, and mass spectroscopy, elemental analysis, and single‐crystal X‐ray analysis. Hydrogen peroxide (50 %) was used very effectively in lieu of the usual 90 % peroxide in this system to generate N‐oxide tetrazine compounds successfully. Comparison of the experimental densities of N‐oxide 1,2,4,5‐tetrazine compounds with their 1,2,4,5‐tetrazine precursors shows that introducing the N‐oxide functionality is a highly effective and feasible method to enhance the density of these materials. The heats of formation for all compounds were calculated with Gaussian 03 (revision D.01) and these values were combined with measured densities to calculate detonation pressures (P) and velocities (ν_D) of these energetic materials (Explo 5.0 v. 6.01). The new oxygen‐containing tetrazines exhibit high density, good thermal stability, acceptable oxygen balance, positive heat of formation, and excellent detonation properties, which, in some cases, are superior to those of 1,3,5‐tritnitrotoluene (TNT), 1,3,5‐trinitrotriazacyclohexane (RDX), and octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX).     

Computational insight into energetic cage derivatives based on hexahydro-1,3,5-trinitro-1,3,5-triazine

Four novel cage compounds were designed by introducing –N(NO₂)CH₂–, –N(NO₂)O–, –N(NO₂)N(NO₂)–, and –N=N– linkages into the RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) skeleton. Their molecular geometry, electronic structure, heat of formation, and detonation properties were systematically studied using density functional theory (DFT). In addition, the most stable dimers of the four compounds were constructed to further investigate their stability based on intermolecular interactions. It is found that the unconventional CH⋯O interactions would be the dominant driving force when the title compounds form crystals. Compared with the traditional explosives, the compounds with higher detonation properties and lower impact sensitivity will be considered as promising candidates for high energy density compounds. Our results indicate that our innovative design strategy is extremely useful for developing novel energetic compounds.     

Comparative theoretical studies of substituted bridged bipyridines and their N-oxides

In this work, the experimental synthesized bipyridines azo-bis(2-pyridine),4,4′-dimethyl-3,3′-dinitro-2,2′-azobipyridine, and N,N′-bis(3-nitro-2-pyridinyl)-methane-diamine and a set of designed bipyridines that have similar frameworks but different linkages and substituents were studied theoretically at the B3LYP/6-31G* level of density functional theory. The gas-phase heats of formation were predicted based on the isodesmic reactions, and the condensed-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. The crystal densities have been computed from molecular packing and results show that incorporation of –N=N–, –N=N(O)–, –CH=N–, and –NH–NH– into bipyridines is more favorable than –CH=CH– and –NH–CH₂–NH– for increasing the density. The predicted detonation velocities (D) and detonation pressures (P) indicate that –NH₂, –NO₂, and –NF₂ can enhance the detonation performance, and –NO₂ and –NF₂ are more favorable. Introducing –N=N–, –N=N(O)–, and –NH–NH– bridge groups into bipyridines is also favorable for improving their detonation performance. The oxidation of pyridine N always but that of –N=N– bridge does not always improve the detonation properties. E4–O, the derivative with –N=N– bridge and two –NF₂ substituent groups, has the largest D (9.90 km/s) and P (47.47 GPa). An analysis of the bond dissociation energies shows that all derivatives have good thermal stability.     

Computational study on energetic properties of nitro derivatives of furan substituted azoles

Density functional theory has been used to investigate geometries, heats of formation (HOFs), C-NO₂ bond dissociation energies (BDEs), and relative energetic properties of nitro derivatives of azole substituted furan. HOFs for a series of molecules were calculated by using density functional theory (DFT) and Møller–Plesset (MP2) methods. The density is predicted using crystal packing calculations; all the designed compounds show density above 1.71 g/cm³. The calculated detonation velocities and detonation pressures indicate that the nitro group is very helpful for enhancing the detonation performance for the designed compounds. Thermal stabilities have been evaluated from the bond dissociation energies. Charge on the nitro group was used to assess the impact sensitivity in this study. According to the results of the calculations, tri- and tetra-nitro substituted derivatives reveal high performance with better thermal stability.     

Bis(4‐nitraminofurazanyl‐3‐azoxy)azofurazan and Derivatives: 1,2,5‐Oxadiazole Structures and High‐Performance Energetic Materials

Bis(4‐nitraminofurazanyl‐3‐azoxy)azofurazan ( 1 ) and ten of its energetic salts were prepared and fully characterized. Computational analysis based on isochemical shielding surface and trigger bond dissociation enthalpy provide a better understanding of the thermal stabilities for nitramine‐furazans. These energetic compounds exhibit good densities, high heats of formation, and excellent detonation velocity and pressure. Some representative compounds, for example, 1 (v_D: 9541 m s^?1; P: 40.5 GPa), and 4 (v_D: 9256 m s^?1; P: 38.0 GPa) exhibit excellent detonation performances, which are comparable with current high explosives such as RDX (v_D: 8724 m s^?1; P: 35.2 GPa) and HMX (v_D: 9059 m s^?1; P: 39.2 GPa).     

Molecular design of prismane-based potential energetic materials with high detonation performance and low impact sensitivity

To develop new energetic materials, the eleven nitroester substitution derivatives of prismane were investigated at the B3LYP/6-311G** level of density functional theory (DFT). The gas phase heats of formation were calculated by isodesmic reactions and the solid-state heats of formation were obtained by the Politzer approach using the heats of sublimation for the designed compounds. The detonation velocities and pressures of all molecules were calculated by Kamlet–Jacobs equations based on molecular density and heat of detonation. The results show that the nitroester group in prismane is helpful for enhancing molecular detonation properties and power index. Among all molecules, 1,2,3,4-tetrnitroesterprismane has excellent detonation properties (detonation pressure = 40.05 GPa, detonation velocity = 9.28 km/s) and large power index value. The molecular stabilities were evaluated by calculating bond dissociation energies and characteristic heights (H₅₀). The results indicate that the bond dissociation energies of all molecules are above 80 kJ/mol, and all molecules have a larger H₅₀ value than hexanitrohexaazaisowurtzitane (CL-20, 12 cm). The obtained structure–property relationships may provide basic information for the molecular design of novel high-energy materials.     

Molecular design and property prediction of a series of novel cyclotetramethylene tetranitramine derivatives as high energy density compounds

We constructed five novel cyclotetramethylene tetranitramine (HMX) derivatives based on the skeleton of HMX ring. The molecules were fully optimized at the B3LYP/6-311G (d) level. We designed isodesmic reactions to calculate their enthalpies of formation. Then, their heats of detonation, detonation velocities, and detonation pressures were calculated using the Kamlet-Jacobs equations on the theoretical densities and enthalpies of formation. Their oxygen balances were computed to estimate whether the title compounds are oxygen-enriched or oxygen-poor. Finally, their impact sensitivity values were evaluated via a simple equation reported in previous studies. In terms of the quantitative standard as high energy density compounds (HEDCs), the potential candidates of HEDCs were selected.