A DFT study of cage compounds: 3, 5, 8, 10, 11, 12-hexanitro-3, 5, 8, 10, 11, 12-hexaazatetracyclo [5.5.1.12,6.04,9] dodecane and its derivatives as high energetic materials

A new cage compound, 3, 5, 8, 10, 11, 12-hexanitro-3, 5, 8, 10, 11, 12-hexaazatetracyclo [5.5.1.1^2,6.0^4,9] dodecane (HNHATCD, I) as well as its –ONO₂ (II) and –N₃ (III) derivatives were proposed in the present work. Their molecular structures were optimized at the B3LYP/6-31G(d,p) level of density functional theory. Heat of formation, strain energy, detonation performance, and thermal stability were studied. Results show that the –N₃ group greatly increases the heat of formation, but decreases the strain energy and density, and it is much more helpful for enhancing the detonation energy than the –NO₂ and –ONO₂ groups. An analysis of bond dissociation energies (BDEs) of the weakest bonds implies that the BDE of –N₃ derivatives is the smallest but it is still larger than 120 kJ mol^?1, revealing that these designed compounds have a high thermal stability. Considering the detonation performance and thermal stability, I and II may be potential candidates of high energy density materials.     

Computational studies on 3,5,7,10,12,14,15,16-octanitro-3,5,7,10,12,14,15,16-octaaza-pentacyclo[7.5.1.12,8.04,13.06,11]hexadecane as potential high-energy-density compound

The B3LYP/6-31G(d) method of density functional theory was used to study molecular geometry, electronic structure, infrared spectrum, and thermodynamic properties. Detonation properties were evaluated using Kamlet–Jacobs equations based on the calculated density and heat of formation. Thermal stability of 3,5,7,10,12,14,15,16-octanitro-3,5,7,10,12,14,15,16-octaaza-pentacyclo[7.5.1.1^2,8.0^4,13.0^6,11]hexadecane (cage-HMX) was investigated by calculating the bond dissociation energy at unrestricted B3LYP/6-31G(d) level. The calculated results show that the first step of pyrolysis is the rupture of the N–NO₂ bond. The crystal structure obtained by molecular mechanics belongs to P2₁ space group, with lattice parameters a = 8.866 Å, b = 11.527 Å, c = 13.011 Å, Z = 4, and ρ = 2.219 g cm^?3. Both the detonation velocity of 9.79 km s^?1 and the detonation pressure of 45.45 GPa are better than those of CL-20. According to the quantitative standard of energetics and stability as a high-energy-density compound, cage-HMX essentially satisfies this requirement. These results provide basic information for molecular design of novel HEDCs.     

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.     

多硝基六氮杂金刚烷结构和相对稳定性的理论研究

The density function theory at the B3LYP/6-31G* level was employed to study the structures, including the total energies (EZPE), the geometries, the oxygen balances (OB100), the dipole moments, of polynitrohexaazaadamantanes (PNHAAs) and the potential candidates of high energy density compounds (HEDCs).The structural parameters of PNHAAs, such as the the maximum N-NO2 bond length (LBmax), the least N-N Mulliken population (BN-N), the least negative charge on the nitro group (QNO2) and OB100, were studied to predict their relative stability or sensitivity (the easiness for initiating a detonation, high sensitivity means low stability). It was found that the same conclusion was drawn from the four parameters.With the number of nitro groups increasing, the stabilities of these compounds decrease. OB100 failed in identifying the isomers, but the EZPE energy and the dipole moment were considered to give more reliable results for the isomers.     

Theoretical investigation of a high density cage compound 1,3,5,7,9,11-hexanitrotetradecahydro-1H-1,3,4,5,7,7b,9,11,12a,12b1,12b2,13-dodecaaza-4,8,12-(epimethanetriyl)cyclohepta[l]cyclopenta[def] phenanthrene

The B3LYP/6-31G** method was used to investigate IR and Raman spectra, heat of formation, and thermodynamic properties of a new designed polynitro cage compound 1,3,5,7,9,11-hexanitrotetradecahydro-1H-1,3,4,5,7,7b,9,11,12a,12b¹,12b²,13-dodecaaza-4,8,12-(epimethanetriyl)cyclohepta[l]cyclopenta[def]phenanthrene. The detonation and pressure were evaluated using the Kamlet–Jacobs equations based on the theoretical density and HOFs. The bond dissociation energies and bond orders for the weakest bonds were analyzed to investigate the thermal stability of the title compound. The results show that N₈–NO₂ bond is predicted to be the trigger bond during pyrolysis. There exists an essentially linear relationship between the WBIs of N–NO₂ bonds and the charges – $ Q_{{{\text{NO}}_{ 2} }} $ on the nitro groups. The crystal structure obtained by molecular mechanics belongs to the P2₁ space group, with lattice parameters Z = 2, a = 11.4658 Å, b = 15.2442 Å, c = 10.2451 Å, ρ = 2.07 g cm^?3. The designed compound has high thermal stability and good detonation properties and is a promising high-energy density compound.     

Substituent effects on the properties related to detonation performance and sensitivity for 2,2',4,4',6,6'-hexanitroazobenzene derivatives

To look for superior and safe high energy density compounds (HEDCs), 2,2',4,4',6,6'-hexanitroazobenzene (HNAB) and its -NO(2), -NH(2), -CN, -NC, -ONO(2), -N(3), or -NF(2) derivatives were studied at the B3LYP/6-31G* level of density functional theory (DFT). The isodesmic reactions were applied to calculate the heats of formation (HOFs) for these compounds. The theoretical molecular density (ρ), detonation energy (E(d)), detonation pressure (P), and detonation velocity (D), estimated using the Kamlet-Jacobs equations, showed that the detonation properties of these compounds were excellent. The effects of substituent groups on HOF, ρ, E(d), P, and D were studied. The order of contribution of the substituent groups to P and D was -NF(2) > -ONO(2) > -NO(2) > -N(3) > -NH(2). Sensitivity was evaluated using the nitro group charges, frontier orbital energies, and bond dissociation enthalpies (BDEs). The trigger bonds in the pyrolysis process for all these HNAB derivatives may be Ring-NO(2), Ring-N═N, Ring-NF(2), or O-NO(2) varying with the attachment of different substituents. BDEs of trigger bonds except those of -ONO(2) derivatives are relatively large, which means these compounds suffice the stability request of explosives. Taking both detonation properties and sensitivities into consideration, some -NF(2) and -NO(2) derivatives may be potential candidates for HEDCs.     

Synthesis of Amino,Azido, Nitro,and Nitrogen‐Rich Azole‐Substituted Derivatives of 1H‐Benzotriazole for High‐Energy Materials Applications

The amino, azido, nitro, and nitrogen‐rich azole substituted derivatives of 1H‐benzotriazole have been synthesized for energetic material applications. The synthesized compounds were fully characterized by ¹H and ¹³C NMR spectroscopy, IR, MS, and elemental analysis. 5‐Chloro‐4‐nitro‐1H‐benzo[1,2,3]triazole ( 2 ) and 5‐azido‐4,6‐dinitro‐1H‐benzo[1,2,3]triazole ( 7 ) crystallize in the Pca2₁ (orthorhombic) and P2₁/c (monoclinic) space group, respectively, as determined by single‐crystal X‐ray diffraction. Their densities are 1.71 and 1.77 g cm^?3, respectively. The calculated densities of the other compounds range between 1.61 and 1.98 g cm^?3. The detonation velocity (D) values calculated for these synthesized compounds range from 5.45 to 8.06 km s^?1, and the detonation pressure (P) ranges from 12.35 to 28 GPa.     

Theoretical studies on the structures, densities, detonation properties and pyrolysis mechanism of energetic compounds containing pyridine ring

Density function theory has been employed to study a series of compounds containing pyridine ring at the B3LYP/6-31G* level. Detonation performance was evaluated by using the Kamlet–Jacobs equations based on the calculated densities and heats of formation. Some compounds have high densities (ca. 1.9 g cm⁻³) and good performance (detonation velocities over 9 km s⁻¹, detonation pressures about 39 GPa) and may be the potential candidates of high energy density materials. The thermal stability and the pyrolysis mechanism of the title compounds were investigated by the bond dissociation energies and the impact sensitivity predicted. Solvent effect has been investigated and it makes the title compounds more stable in solutions.     

Theoretical investigations on the structure, density, thermodynamic and performance properties of amino-, methyl-, and nitroimidazoles and their N-oxides

Density functional theory calculations at the B3LYP/aug-cc-pVDZ level have been performed to explore the structure, stability, heat of explosion, density, and the performance properties of amino-, methyl-, and nitroimidazoles. N-Nitroimidazoles have shown lower densities compared with those of C-nitroimidazoles. Detonation properties of title compounds were evaluated by using Kamlet–Jacob semi-empirical equations based on the predicted densities and the calculated heats of detonation. It has been found that some compounds with the calculated densities 2.0 g/cm³, detonation velocities over 9.10 km/s and detonation pressures of about 45 GPa (some even over 50 GPa) may be novel potential high energy materials. The higher performance of nitroimidazole-N-oxides is apparently due to their higher densities (2.0–2.515 g/cm³). Heat of explosion, stability, density, and performance properties are related to the number and relative positions of –NO₂, –NH₂, and –CH₃ groups of the imidazole ring. The designed nitroimidazoles satisfy the criteria of high energy materials.     

Computational study on the crystal structure, thermodynamic properties, detonation performance and pyrolysis mechanism of a novel high density cage compound 10-(5-nitrimino-1,2,3,4-tetrazol-1-yl)methyl-2,4,6,8,12-pentanitrohexaazaisowurtzitane

A novel polynitro cage compound 10-(5-nitrimino-1,2,3,4-tetrazol-1-yl)methyl-2,4,6,8,12-pentanitro-hexaazaisowurtzitane, composed of CL-20 and tetrazole framework, has been designed. DFT-B3LYP/6-31G(d) and molecular mechanics methods are employed to calculate its IR spectrum, heat of formation, thermodynamic properties, and crystal structure. Besides, the stability of this compound is evaluated using the bond dissociation energy. The result shows that the initial step of thermal decomposition is the rupture of N–NO₂ bond in the side chain. This compound is most likely to crystallize in the P-1 space group, and corresponding cell parameters are Z = 2, a = 7.65 Å, b = 14.30 Å, c = 10.36 Å, α = 91.53°, β = 50.83°, γ = 89.44°, and ρ = 2.025 g cm^?3. Detonation velocity and detonation pressure of this compound are estimated to be 9.090 km s^?1 and 38.078 GPa using the Kamlet–Jacobs equation, similar to those of CL-20. Considering detonation performance and thermal stability, this compound meets the requirements of exploitable high energy density materials.     

Computational DFT studies on a series of toluene derivatives as potential high energy density compounds

Based on the full optimized molecular geometric structures at B3LYP/6-31G**, B3LYP/6-31+G**, B3P86/6-31G**, and B3P86/6-31+G** levels, the densities (ρ), detonation velocities (D), and pressures (P) for a series of toluene derivatives, as well as their thermal stabilities, were investigated to look for high energy density compounds (HEDCs). The heats of formation (HOFs) are also calculated via designed isodesmic reactions. The calculations on the bond dissociation energies (BDEs) indicate that the BDEs of the initial scission step are between 48 and 59 kcal/mol, and pentanitrotoluene is the most reactive compound, while 2,4,6-trinitrotoluene is the least reactive compound for toluene derivatives studied. A good linear relationship between BDE/E and impact sensitivity is also obtained. The condensed phase HOFs are calculated for the title compounds. These results would provide basic information for the further studies of HEDCs. The detonation data of pentanitrotoluene show that it meets the requirement for HEDCs.     

Triazole‐Substituted Nitroarene Derivatives: Synthesis,Characterization, and Energetic Studies

A series of dense and energetic polynitroaryl‐1,2,4‐triazoles were synthesized through the nitration of aryl‐1,2,4‐triazoles. The Cu‐catalyzed/base‐mediated coupling reactions of haloarenes with 1,2,4‐triazoles delivered N‐aryl‐1,2,4‐triazoles. These new nitro‐rich‐aryltriazoles were characterized by analytical and spectroscopic methods. The solid‐state structures of most of these compounds were established by X‐ray diffraction analysis. Their thermal properties were determined by differential scanning calorimetry–thermogravimetric analysis. Their heats of formation (HOFs) and crystal densities were also calculated. The densities of the synthesized compounds ranged from 1.40 to 1.85 g cm^?3. Some of these newly synthesized compounds exhibited high positive HOFs, good thermal stabilities, high densities, and reasonable detonation velocities and pressures.     

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.     

Theoretical Study on Nitroso-Substituted Derivatives of Azetidine as Potential High Energy Density Compounds

At the B3 PW91/6-311+G(d,p)//MP2/6-311+G(d,p) level, molecular densities, detonation velocities, and detonation pressures of nitroso substituted derivatives of azetidine with their thermal stabilities were investigated to look for high energy density compounds(HEDCs). It was found that the azetidine derivatives had high heat of formation(HOF) and large bond dissociation energy(BDE). Intramolecular hydrogen bonds were located in three molecules(1, 4, and 5), and the molecular stability were improved markedly as well. For 5 and 6, the detonation performances(D= 9.36 km/s and 10.80 km/s, P= 44.42 GPa and 60.70 GPa, respectively) meet requirements as high energy density compounds. This work may provide basic information for further study of title compounds.     

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.     

Computational studies on tetrazole derivatives as potential high energy materials

The tetrazole is an important functionality of the most of energetic materials due to 80% nitrogen content, stability, and high enthalpy of formation. The present structure–property relationship study focuses on the optimized geometries of tetrazole derivatives obtained from density functional theory (DFT) calculations at B3LYP/6-31G* levels. The heat of formation (HOF) of tetrazole derivatives have been calculated by designing the appropriate isodesmic reactions. The increase in nitro groups on azole rings shows the remarkable increase in HOF. Density has been predicted by using CVFF force field. Increase in the nitro group increases the density. Detonation properties of the designed compounds were evaluated by using the Kamlet–Jacobs equation based on predicted densities and HOFs. Designed tetrazole derivatives show detonation velocity (D) over 8 km/s and detonation pressure (P) of about 32 GPa. Thermal stability was evaluated via bond dissociation energies (BDE) of the weakest C–NO₂ bond at B3LYP/6-31G* level. Charge on the nitro group has been used to assess the sensitivity correlation. Overall, the study implies that designed compounds of this series are found to be stable and expected to be the novel candidates of high energy materials (HEMs).     

A theoretical investigation on the structures,densities, detonation properties,and pyrolysis mechanism of the nitro derivatives of phenols

The nitro derivatives of phenols are optimized to obtain their molecular geometries and electronic structures at the DFT‐B3LYP/6‐31G* level. Detonation properties are evaluated using the modified Kamlet–Jacobs equations based on the calculated densities and heats of formation. It is found that there are good linear relationships between density, detonation velocity, detonation pressure, and the number of nitro and hydroxy groups. Thermal stability and pyrolysis mechanism of the title compounds are investigated by calculating the bond dissociation energies (BDEs) at the unrestricted B3LYP/6‐31G* level. The activation energies of H‐transfer reaction is smaller than the BDEs of all bonds and this illustrates that the pyrolysis of the title compounds may be started from breaking O? H bond followed by the isomerization reaction of H transfer. Moreover, the C? NO₂ bond with the smaller bond overlap population and the smaller BDE will also overlap may be before homolysis. According to the quantitative standard of energetics and stability as a high‐energy density compound, pentanitrophenol essentially satisfies this requirement. In addition, we have discussed the effect of the nitro and hydroxy groups on the static electronic structural parameters and the kinetic parameter. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Furazans with Azo Linkages: Stable CHNO Energetic Materials with High Densities,Highly Energetic Performance,and Low Impact and Friction Sensitivities

Various highly energetic azofurazan derivatives were synthesized by simple and efficient chemical routes. These nitrogen‐rich materials were fully characterized by FTIR spectroscopy, elemental analysis, multinuclear NMR spectroscopy, and high‐resolution mass spectrometry. Four of them were further confirmed structurally by single‐crystal X‐ray diffraction. These compounds exhibit high densities, ranging from 1.62 g cm^?3 up to a remarkably high 2.12 g cm^?3 for nitramine‐substituted azofurazan DDAzF ( 2 ), which is the highest yet reported for an azofurazan‐based CHNO energetic compound and is a consequence of the formation of strong intermolecular hydrogen‐bonding networks. From the heats of formation, calculated with Gaussian 09, and the experimentally determined densities, the energetic performances (detonation pressure and velocities) of the materials were ascertained with EXPLO5 v6.02. The results suggest that azofurazan derivatives exhibit excellent detonation properties (detonation pressures of 21.8–46.1 GPa and detonation velocities of 6602–10 114 m s^?1) and relatively low impact and friction sensitivities (6.0–80 J and 80–360 N, respectively). In particular, they have low electrostatic spark sensitivities (0.13–1.05 J). These properties, together with their high nitrogen contents, make them potential candidates as mechanically insensitive energetic materials with high‐explosive performance.     

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.     

Theoretical studies on a series of 1,2,3-triazoles derivatives as potential high energy density compounds

Based on the full-optimized molecular geometric structures at B3LYP/6-31G* and B3P86/6-31G* levels, the densities (ρ), detonation velocities (D), and pressures (P) for a series of 1,2,3-triazole derivatives, as well as their thermal stabilities, were investigated to look for high energy density compounds (HEDCs). The heats of formation (HOFs) are also calculated via designed isodesmic reactions. The calculations on the bond dissociation energies (BDEs) indicate that the BDEs of the initial scission step are between 53 and 70 kcal/mol, and 4-nitro-1,2,3-triazole is the most reactive compound, while 1-(2′,4′-dinitrophenyl)-5-nitro-1,2,3-triazole is the least reactive compound for 1,2,3-triazole derivatives studied. The condensed phase heats of formation are also calculated for the title compounds. These results would provide basic information for the further studies of HEDCs. The detonation data of 1-(3′,4′-dinitrophenyl)-4-nitro-1,2,3-triazole and 1-(2′,4′-dinitrophenyl)-4-nitro-1,2,3-triazole show that they meet the requirement for HEDCs.