Nitrogen-rich Energetic Salts Research Articles

First-principle calculations of the electronic, vibrational, and thermodynamic properties of nitrogen-rich salt of 3,6-dinitramino-1,2,4,5-tetrazine [(NH4)2(DNAT)

Energy-containing materials such as explosives have attracted considerable interest recently. In the field of high-energy materials, tetrazine and its derivatives can largely meet the requirements of high nitrogen content and oxygen balance. Nitrogen-rich energetic salts are important research subjects. Nitrogen-rich salt of 3,6-dinitramino-1,2,4,5-tetrazine is a high-energy nitrogen-rich material, but there are few related studies. This paper systematically studies the crystal structure and electronic, vibrational, and thermodynamic properties of (NH4)2(DNAT). The lattice parameters of (NH4)2(DNAT) are observed to align well with the experimental values. The properties of electrons are analyzed by band structure and density of states (DOS). The phonon dispersion curves indicate that the compound is dynamically stable. The vibrational modes of bonds and chemical groups are described in detail, and the peaks in the Raman and infrared spectra are assigned to different vibration modes. Based on the vibration characteristics, thermodynamic properties such as enthalpy (H), Helmholtz free energy (F), entropy (S), Gibbs free energy (G), constant volume heat capacity (CV), and Debye temperature (Θ) are analyzed. This article can pave the way for subsequent work or provide data support to other researchers, promoting further research. In this study, we utilized the density functional theory (DFT) for our calculations. The exchange-correlation potential and van der Waals interactions were characterized based on the GGA-PBE + G function calculation. We obtained Brillouin zone integrals using Monkhorst-Pack k-point grids, with the k-point of the Brillouin zone set to a 2 × 2 × 2 grid. During the self-consistent field operation, we set the total energy convergence tolerance to 5 × 10-6eV per atom. The cut-off energy for the calculation was established at 830eV. Additionally, the states of H (1s1), C (2s2 2p2), N (2s2 2p3), and O (2s2 2p4) were treated as valence electrons in our study.

Bistriazolotriazole-tetramine: commendable energetic moiety and cation.

Various 7H,7'H-[6,6'-bi[1,2,4]triazolo[4,3-b][1,2,4]triazole]-3,3',7,7'-tetramine (A) based nitrogen-rich energetic salts were designed and their properties explored. All energetic salts possess relatively high nitrogen content (> 48%), positive heats of formation (> 429kJ/mol) and stability owing to a significant contribution from fused backbone. The cationic component shows a very high heat of formation (2516kJ/mol); therefore, it is highly suitable for enthalpy enhancement in new energetic salts. The cation was paired with the energetic anions nitrate (NO3-), perchlorate (ClO4-), dinitromethanide (CH(NO2)2-), trinitromethanide (C(NO2)3-), nitroamide (NHNO2-), and dinitroamide (N(NO2)2-) to improve oxygen balance and detonation performance. Designed salts show moderate detonation velocities (7.9-8.7 km/s) and pressures (23.8 - 33.1 GPa). The distribution of frontier molecular orbitals, molecular electrostatic surface potentials, QTAIM topological properties, and noncovalent interactions of designed salts were simulated to understand the electronic structures, charge distribution in molecules, hydrogen bonding, and other nonbond interactions. The predicted safety factor (SF) and impact sensitivity (H50) of designed salts suggest their insensitivity to mechanical stimuli. This work explored the 7H,7'H-[6,6'-bi[1,2,4]triazolo[4,3-b][1,2,4]triazole]-3,3',7,7'-tetramine as a suitable cationic component which could be promising and serve exemplarily in energetic materials. The optimization and energy calculations of all the designed compounds were carried out at the B3LYP/6-311 + + G(d,p) and M06-2X/def2-TZVPP levels, utilizing the Gaussian software package. The molecular surface electrostatic potential, quantum theory of atoms in molecules (QTAIM), reduced density gradient (RDG), and noncovalent interaction (NCI) analysis were performed by employing Multiwfn software. The EXPLO5 (v 7.01) thermochemical code and PILEM web application were used to predict the detonation properties.

Application of machine learning in developing a quantitative structure-property relationship model for predicting the thermal decomposition temperature of nitrogen-rich energetic ionic salts.

While thermal decomposition temperature (T d) is one of the most important indexes for energetic materials, the most common way of determining and evaluating T d requires laboratory experiments that are complicated, time-consuming and expensive. In the present study, the quantitative structure-property relationship (QSPR) model of T d for 21 nitrogen-rich energetic ionic salts was built and used for T d prediction through 13 descriptors and principal component analysis. The relatively small dataset of 21 samples may lead to overfitting. In the case of small datasets, possible overfitting was reduced by the support vector machine to derive the non-linear QSPR model. The obtained correlation coefficient (R 2) of 96.31% and root-mean-square error (RMSE) of 15.72 indicate the relative reliability of the QSPR model developed in this work. Moreover, T d values of 6 newly designed nitrogen-rich energetic ionic salts were predicted using the new QSPR model. The predicted T d values range from 194 to 225 °C, which are better than that of 4-amino-3,5-dinitro-1H-pyrazole (LLM-116: 178 °C), and no. 1, 2 and 5 are comparable to that of the traditional explosive 1,3,5-trinitro-1,3,5-triazinane (RDX: 230 °C), indicating the excellent properties of the designed energetic ionic salts, which can be used for the preparation of potential energetic materials.

Synthesis and detonation characters of 3,4,5-1H-trinitropyrazole and its nitrogen-rich energetic salts.

The development of energetic materials is still facing challenges due to the inherent contradiction between energy and sensitivity. Two new nitrogen-rich energetic salts of 3,4,5-1H-trinitropyrazole (HTNP) were synthesized. They are fully characterized by X-ray diffraction, NMR, MS and IR spectroscopy. The DSC and BAM tests were carried out as well. These TNP salts show high thermostability and high positive heat of formation. Their detonation performances were calculated by the EXPLO5 program. Most noteworthy is that DATr salt exhibits superior sensitivity and detonation performance comparable to secondary explosive RDX, making it promising for use as a new-generation green energetic material.

Synthesis of Advanced Pyrazole and N-N-Bridged Bistriazole-Based Secondary High-Energy Materials.

In this work, we have synthesized 3,5-dihydrazinyl-4-nitro-1H-pyrazole (2), 9-nitro-1H-pyrazolo[3,2-c:5,1-c']bis([1,2,4]triazole)-3,6-diamine (3), and N-N-bonded N,N'-{[4,4'-bi(1,2,4-triazole)]-3,3'-diyl}dinitramide (5) and its stable nitrogen-rich energetic salts in one and two steps in quantitative yields from commercially available inexpensive starting material 4,6-dichloro-5-nitropyrimidine (1). Along with characterization via nuclear magnetic resonance, infrared, differential scanning calorimetry, and elemental analysis, the structures of 2 and 4-8 were confirmed by single-crystal X-ray diffraction. Interestingly, 5-8 show excellent thermal stability (242, 221, 250, and 242 °C, respectively) compared to that of RDX (210 °C). Detonation velocities of 2, 4, 6, and 7 range from 8992 to 9069 m s-1, which are better than that of RDX (8878 m s-1) and close to that of HMX (9221 m s-1). All of these compounds are insensitive to impact (10-35 J) and friction (360 N) sensitivity. These excellent energetic performances, stabilities, and synthetic feasibilities make compounds 2, 4, 6, and 7 promising candidates as secondary explosives and potential replacements for the presently used benchmark explosives RDX and HMX.

Base-promoted decarboxylative gem-diazo-C-coupling: Synthesis, characterization and performance of nitrotriazolylformazans

Formazans, containing the characteristic chain of atoms –NN-CRN–NH- (R ​= ​–CN or tetrazyl) are nitrogen-rich and conjugated compounds exhibiting unique properties. In this work, new cyano and tetrazylformazans and their series of nitrogen-rich energetic salts were synthesized via base-promoted gem-diazo coupling reaction. The resulting derivatives were well characterized, and their performances were further investigated. The experimental results indicated that the decomposition temperatures of 1–12 lie between 159 ​°C and 279 ​°C. All of them are much less impact sensitive (≥20 ​J) than trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). They have relatively high positive heats of formation between 987.7 and 1457.3 ​kJ ​mol-1, which are much higher than those of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), RDX and HMX. The calculated detonation pressures (p) range between 23.2 and 30.2 ​GPa and calculated detonation velocities (D) between 7480 and 8274 ​m ​s-1. Interestingly, compound 4 shows excellent laser ignition combustion performance.

FOX-7 based nitrogen rich green energetic salts: Synthesis, characterization, propulsive and detonation performance

New 1,1-diamino-2,2-dinitroethene (FOX-7)-based energetic salts are reported in this study. A variety of bases including hydrazine, hydroxylamine, ammonia, amino guanidine and metal hydroxides (MOH) were found to react with FOX-7 to give the following salts: hydrazinium (E)-2-amino-2-hydrazinylidene-1,1-dinitroethan-1-ide (1) dihydroxylammonium mono((Z)-2-amino-2-(hydroxyimino)-1,1-dinitroethan-1-ide) (2) ammonium (1-amino-2,2-dinitrovinyl)amide (3), potassium/sodium/lithium(I)-[(Z)-2-amino-2-hydrazineylidene-1,1-dinitroethan-1-ide] (4–6), and aminoguanidine-(Z)-2-amino-2-hydrazinylidene-1,1-dinitroethan-1-ide (7). The title compounds were fully characterizedusing IR, NMR, and elemental analysis. The structures of the salts 2 and 7 were further confirmed by single crystal X-ray analysis. These salts have experimental densities in the range between 1.59 gcm−3 to 1.92 g cm−3. Thermal stabilities of these salts were measured by DSC and TGA analysis and their decomposition temperatures were found between 85 °C and 177 °C. Enthalpies of formation (ΔHf°) were calculated (Gaussian 03) and with their experimental densities, the propulsive and detonation properties of the nitrogen-rich green energetic salts were evaluated. These compounds exhibit high density, high positive enthalpy (ΔHf°), balanced nitrogen and oxygen contents with excellent propulsive (Isp) and good detonation properties (DP and DV) which are superior to that of RDX, ammonium perchlorate (AP), and comparable to TKX-50. The energetic salts (1, 2, 5 and 6) show potential as highly promising secondary explosives. These energetic salts have potential as promising solid propellants.

Novel family of nitrogen-rich energetic (1,2,4-triazolyl) furoxan salts with balanced performance.

Nitrogen-rich energetic materials comprised of a combination of several heterocyclic subunits retain their leading position in the field of materials science. In this regard, a preparation of novel high-energy materials with balanced set of physicochemical properties is highly desired. Herein, we report the synthesis of a new series of energetic salts incorporating a (1,2,4-triazolyl) furoxan core and complete evaluation of their energetic properties. All target energetic materials were well characterized with IR and multinuclear NMR spectroscopy and elemental analysis, while compound 6 was further characterized by single-crystal X-ray diffraction study. Prepared nitrogen-rich salts have high thermal stability (up to 232°C), good experimental densities (up to 1.80 g cm−3) and high positive enthalpies of formation (344–1,095 kJ mol−1). As a result, synthesized energetic salts have good detonation performance (D = 7.0–8.4 km s−1; p = 22–32 GPa), while their sensitivities to impact and friction are quite low.

Theory of impact sensitivity revisited: mechanical-to-vibrational energy transfer phenomenon

A revision of the mechanism of mechanical-to-vibrational energy transfer in crystals of energetic materials undergone impact loading is proposed. The new approach takes into account previous inaccuracies of normalization of the number of couplings between phonon overtones and conformational vibrational fundamentals (ζ), which is critical for comparison of molecules that differ greatly in the number of atoms. Moreover, it introduces two very important damping factors, namely a and b. The a factor allows differentiation of the phonon overtones by their coupling strength; the lower the overtone interacts, the stronger the coupling is. Meanwhile, the b factor is aimed to distinguish the coupling strength itself. This factor is the denominator in the exponent of a Gaussian-type function and determines the rate at which the coupling strength decays with the rise of difference between the interacting phonon overtones and conformational vibrational fundamentals. After a careful regression analysis of ζ against impact sensitivities (h50) of 30 common nitroexplosives, we have determined the numerical values of these damping factors as a = 2.5 and b = 40 cm–1. The proposed approach is extrapolated on the vibrational spectra of 21 crystalline energetic materials with Z' ≥ 1 and a general applicability along with limitations of the method are discussed for the family of nitroexplosives and nitrogen-rich (cyclo-pentazolate and 5,5′-bitetrazole) energetic salts as an example.

Thermal Decomposition Mechanism and Energy Release Law of Novel Cyclo-N5--Based Nitrogen-Rich Energetic Salt.

Detonation energy of novel cyclo-N5--based nitrogen-rich energetic salts is expected to exceed 3 times the equivalent of TNT. PHAC([(N5)6(H3O)3(NH4)4Cl]) was selected as the prototype to investigate the thermal decomposition reaction of PHAC in the solid phase for the first time by the first-principles molecular dynamics method. At about 38 ps, the final state of the reaction was reached. It was found that there were mainly five final products, among which the proportion of N2 molecules was the maximum and accounted for 60% (mole fraction) of all final products. The reaction pathways of PHAC were analyzed, and more than 30 elementary reactions were found. The initial reaction of the PHAC thermal decomposition was the ring-opening of cyclo-N5- ion and proton transfer. The energy release of PHAC thermal decomposition is divided into two stages. The first stage is a slow release of energy before the formation of the HN3 molecule. The second stage is the rapid release of energy after the formation of HN3 molecules. The HN3 molecule is an essential junction, and the unimolecular dissociation of HN3 is the rate-determining step. Such an understanding of reaction mechanism and energy release law greatly promotes the application and synthesis of novel cyclo-N5--based nitrogen-rich energetic salts.

Theoretical investigation of impact sensitivity of nitrogen rich energetic salts

The higher impact sensitivity of many energetic materials has become one of the major obstacles which diminishes its wide range of applications in various fields. Salt formation is an effective approach that enhances the stability of the molecules towards impact. In this study quantum mechanical calculations have been employed in order to predict the impact sensitivity trends for the series of nitrogen rich energetic salts: 3-Amino-1,2,4(4H)-oxadiazol-5-one (AOD) and 4-Nitramino-1,2,4-Triazole (NRTZ). Quantum mechanically derived criteria, namely, HOMO-LUMO energy gap, ratio of the bond dissociation energy to molecular total energy, the electrostatic potential at bond mid-point, bond topological parameters were computed, and the quality of results are assessed against experimental BAM fall hammer test results. Several sets of DFT functionals and basis sets were tested to identify the best level of theory for the selected nitrogenous salts. The results demonstrated an excellent qualitative prediction of the impact sensitivity by using CAMB3LYP/6-31G(d)/IEFPCM = water level of theory. Hence, quantum mechanical predictions are an ideal preliminary approach to design advanced energetic salts based on AOD and NRTZ with enhanced stability prior to the synthesis, which facilitates reducing the great cost and risk to safety.

Insight into the thermostability and low sensitivity of energetic salts based on planar fused-triazole cation

A new family of nitrogen-rich fused-triazole energetic salts based on 3,6-diamino-1H-[1,2,4]triazolo[4,3-b][1,2,4]triazole were synthesized and fully characterized by infrared spectroscopy (IR), 1H and 13C nuclear magnetic resonance, elemental analysis, differential scanning calorimetry (DSC). Structures of 3 and 4·H2O were confirmed by single-crystal X-ray diffraction analyses and their crystal packing characteristics were thoroughly analysed. All new compounds show good thermal stability (Td > 223 °C) and tend to be insensitive to external mechanical stimulus. The densities of these salts ranged from 1.72 to 1.93 g cm−3. Theoretical performance calculations (Gaussian 09 and EXPLO 5) provided detonation pressures and velocities within the ranges of 20.8 to 32.9 GPa and 7599 to 8719 m s−1, respectively. The perchlorate salt 3 exhibits the highest density (1.93 g cm−3) and best oxygen balance (−30.0%), good thermal stability (Td = 258 °C), low sensitivities, and excellent detonation velocity (8719 m s−1) and pressure (32.9 GPa), which suggest that it has the potential to be used as High-energy–density material.

Withdrawal notice to: Guanidinium dicyanamide-based nitrogen-rich energetic salts as additives of hypergolic ionic liquids [Combustion and Flame 226 (2021) 243–247

Withdrawal notice to: Guanidinium dicyanamide-based nitrogen-rich energetic salts as additives of hypergolic ionic liquids [Combustion and Flame 226 (2021) 243–247

The photostability and degradation pathways of TKX-50 as a representative of nitrogen-rich energetic salts in aqueous solution

The dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50), as an outstanding representative of nitrogen-rich energetic salts, has recently attracted increasing interest due to its excellent performances. However, it is unclear about the photostability and degradation pathways of TKX-50 in aqueous solution. In this paper, the photostability and the degradation process of TKX-50 in aqueous solution have been comprehensively studied for the first time. TKX-50 can keep stable toward visible light. However, it presented a rapid degradation with rate constant of 0.0054 s−1 under 254-nm light irradiation. TKX-50 also demonstrated much faster photodegradation than traditional nitro explosives. Further, degradation products of TKX-50 were analyzed by high-resolution mass spectrum with theoretical calculations. The photodegradation pathways are proposed that 5,5′-bistetrazole-1,1′-diolate (BTO) anion of TKX-50 can been fragmented into the nitrile by losing N2 and HNO, and then hydroxylammonium (NH3OH+) from TKX-50 reacts with the nitrile through the nucleophilic addition. Besides as a solvent, water also may accelerate the photodegradation of TKX-50 probably by hydrolyzing the intermediary nitrile products. In a word, this study provides comprehensive understanding about the photostability of TKX-50 in aqueous solution, and it is helpful to study the photochemistry of other energetic ionic salts based on BTO.

Structural and Vibrational Spectroscopic Elucidation of Nitrogen Rich Energetic Salt: 2,4-Diamino-6-methyl-1,3,5-triazinium Levulinate Dihydrate

A novel nitrogen rich energetic salt 2,4-diamino-6-methyl-1,3,5-triazinium levulinate dihydrate (DMTLDH) has been grown by slow evaporation method at room temperature. The grown synthesized salt crystallizes in the centrosymmetric space group P21/n of monoclinic system. The intermolecular hydrogen bond N–H···N, N–H···O, C–H···O, O–H···O type interactions stabilizes the structure and leads to three dimensional network. In addition to that the crystal structure also possesses C–O···Cg interactions. Also, quantum chemical computational studies using DFT-B3LYP/6-311++G(d,p) and PBEPBE/6-31G(d,p) basis set is used to analyze the structural parameters and vibrational frequencies of grown crystal. Frontier molecular orbital analysis describes the charge transfer within the molecule and also other electronics parameters were calculated. The natural bonding orbital analysis has also been performed to study the stability of the molecule. Further, the crystal packing behaviour of DMTLDH was studied quantitatively with the aid of Hirshfeld surface analysis.

Crystal structures and properties of high-nitrogen energetic salts based on (Z)-1,1-diamino-2-nitro-2-(1H-tetrazol-5-yl)ethene

Forming hydrogen bond interactions between a nitro group (Tz-FOX), a tetrazole moiety (Tz-FOX), and amino groups (G, AG, and TAG) led to three nitrogen-rich energetic salts (2, 3, and 5).

Insight into the Thermostability and Low Sensitivity of Energetic Salts Based on Planar Fused-Triazole Cation

A new family of nitrogen-rich fused-triazole energetic salts based on 3,6-diamino-1H-[1,2,4]triazolo[4,3-b][1,2,4]triazole were synthesized and fully characterized by infrared spectroscopy (IR), 1H and 13C nuclear magnetic resonance, elemental analysis, differential scanning calorimetry (DSC). Structures of 3 and 4·H2O were confirmed by single-crystal X-ray diffraction analyses and their crystal packing characteristics were thoroughly analysed. All new compounds show good thermal stability (Td> 223°C) and tend to be insensitive to external mechanical stimulus. The densities of these salts ranged from 1.72 to 1.93 g cm-3. Theoretical performance calculations (Gaussian 09 and EXPLO 5) provided detonation pressures and velocities within the ranges of 20.8 to 32.9 GPa and 7599 to 8719 m s-1, respectively. The perchlorate salt 3 exhibits the highest density (1.93 g cm-3) and best oxygen balance (-30.0%), good thermal stability (Td = 258 °C), low sensitivities, and excellent detonation velocity (8719 m s-1) and pressure (32.9 GPa), which suggest that it has the potential to be used as High-energy-density material.

WITHDRAWN: Guanidinium dicyanamide-based nitrogen-rich energetic salts as additives of hypergolic ionic liquids

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy ). This article has been withdrawn at the request of the editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. This error bears no reflection on the article or its authors. The publisher apologizes to the authors and the readers for this unfortunate error.

Guanidinium Dicyanamide-Based Nitrogen-Rich Energetic Salts as Additives of Hypergolic Ionic Liquids

In this paper, four kinds of guanidinium dicyanamide-based energetic salts were prepared and investigated as energetic additives to hypergolic ionic liquid 1-ethyl-3-methyl imidazolium dicyanamide ([EMIM][DCA]) for the first time. Their densities, viscosities, heat of formation, specific impulse, ignition delay time, melting point, charge distribution, and decomposition temperature were tested and calculated. The results showed that these salts possessed high nitrogen content (>66 wt %), high density, and high specific impulse. Their addition can bring significant improvement in the density and specific impulse of [EMIM][DCA] and hardly affect its ignition delay time.

A simple and efficient strategy for constructing nitrogen-rich isomeric salts and cocrystal through pKa calculation

Nitrogen-rich energetic salts and cocrystal have attracted considerable attention in recent years. To assess the formation of cocrystal or salt, acid dissociation constant (pKa) values of the isomeric co-formers were calculated in this work and significant differences were observed. Two salts and one cocrystal based on H2BT (1H, 1′H-5,5′-bitetrazole), DATr (4,5-diamino-4H-1,2,4-triazole), 1MAT (1-methyl-5-aminotetrazole) and 2MAT (2-methyl-5-aminotetrazole) were synthesized, which corresponding to the different pKa values of three isomeric coformers. Single crystal structure analysis reveals that all compounds are formed by layered stacking structure with π-π stacking and rich hydrogen bonds, resulting in the insensitivity towards impact and friction (impact sensitivity > 40 J, friction sensitivity > 360 N). To the best of our knowledge, it is the first time to report the cocrystal of H2BT. The study results provide a utility method to seek for suitable coformers and design energetic cocrystal through the calculation of pKa.