Intermolecular interactions in clusters of ethylammonium nitrate and 1-amino-1,2,3-triazole

The intermolecular interaction energies, including hydrogen bonds (H-bonds), of clusters of the ionic liquid ethylammonium nitrate (EAN) and 1-amino-1,2,3-triazole (1-AT) based deep eutectic propellants (DeEP) are examined. 1-AT is introduced as a neutral hydrogen bond donor (HBD) to EAN in order to form a eutectic mixture. The effective fragment potential (EFP) is used to examine the bonding interactions in the DeEP clusters. The resolution of the Identity (RI) approximated second order Møller-Plesset perturbation theory (RI-MP2) and coupled cluster theory (RI-CCSD(T)) are used to validate the EFP results. The EFP method predicts that there are significant polarization and charge transfer effects in the EAN:1-AT complexes, along with Coulombic, dispersion and exchange repulsion interactions. The EFP interaction energies are in good agreement with the RI-MP2 and RI-CCSD(T) results. The quasi-atomic orbital (QUAO) bonding and kinetic bond order (KBO) analyses are additionally used to develop a conceptual and semi-quantitative understanding of the H-bonding interactions as a function of the size of the system. The QUAO and KBO analyses suggest that the H-bonds in the examined clusters follow the characteristic hydrogen bonding three-center four electron interactions. The strongest H-bonding interactions between the (EAN)1:(1-AT)n and (EAN)2:(1-AT)n (n = 1-5) complexes are observed internally within EAN; that is, between the ethylammonium cation [EA]+ and the nitrate anion ([NO3]-). The weakest H-bonding interactions occur between [NO3]- and 1-AT. Consequently, the average strengths of the H-bonds within a given (EAN)x:(1-AT)n complex decrease as more 1-AT molecules are introduced into the EAN monomer and EAN dimer. The QUAO bonding analysis suggests that 1-AT in (EAN)x:(1-AT)n can act as both a HBD and a hydrogen bond acceptor simultaneously. It is observed that two 1-AT molecules can form H-bonds to each other. Although the KBOs that correspond to H-bonding interactions in [EA]+:1-AT, [NO3]-:1-AT and between two 1-AT molecules are weaker than the H-bonds in EAN, those weak H-bond networks with 1-AT could be important to form a stable DeEP.

π-Electronic ion pairs: building blocks for supramolecular nanoarchitectonics viaiπ-iπ interactions

The pairing of charged π-electronic systems and their ordered arrangement have been achieved by iπ-iπ interactions that are derived from synergetically worked electrostatic and dispersion forces. Charged π-electronic systems that provide ion pairs as building blocks for assemblies have been prepared by diverse strategies for introducing charge in the core π-electronic systems. One method to prepare charged π-electronic systems is the use of covalent bonding that makes π-electronic ions and valence-mismatched metal complexes as well as protonated and deprotonated states. Noncovalent ion complexation is another method used to create π-electronic ions, particularly for anion binding, producing negatively charged π-electronic systems. Charged π-electronic systems afford various ion pairs, consisting of both cationic and anionic π-systems, depending on their combinations. Geometries and electronic states of the constituents in π-electronic ion pairs affect the photophysical properties and assembling modes. Recent progress in π-electronic ion pairs has revealed intriguing characteristics, including the transformation into radical pairs through electron transfer and the magnetic properties influenced by the countercations. Furthermore, the assembly states exhibit diversity as observed in crystals and soft materials including liquid-crystal mesophases. While the chemistry of ion pairs (salts) is well-established, the field of π-electronic ion pairs is relatively new; however, it holds great promise for future applications in novel materials and devices.

Structural Properties of HEHN- and HAN-Based Ionic Liquid Mixtures: A Polarizable Molecular Dynamics Study

Molecular dynamics simulations of binary mixtures comprising 2-hydroxyethylhydrazinium nitrate (HEHN) and hydroxylammonium nitrate (HAN) were conducted using the polarizable APPLE&P force field to investigate fundamental properties of multimode propulsion (MMP) propellants. Calculated densities as a function of temperature were in good agreement with experiments and similar simulations. The structural properties of neat HEHN and HAN-HEHN provided insights into their inherent, protic nature. Radial distribution functions (RDFs) identified key hydrogen bonding sites located at N-H···O and O-H···O within a first solvation shell of approximately 2 Å. Angular distribution functions further affirmed the relatively strong nature of the hydrogen bonds with nearly linear directionality. The increased hydroxylammonium cation (HA+) mole fraction shows the influence of competitively strong hydrogen bonds on the overall hydrogen bond network. Dominant spatial motifs via three-dimensional distribution functions along with nearly nanosecond-long hydrogen bond lifetimes highlight the local bonding environment that may precede proton transfer reactions.

Synthesis and characterization of promising insensitive energetic salts based on 3-amino-5-hydrazinopyrazole

The development of green energetic materials is based on environmental friendliness, safety and performance improvement. It is of great significance to design and synthesize new nitrogen rich salts for a new generation of green energetic materials. In the present work, a series of 3-amino-5-hydrazinopyrazole energetic salts comprising energetic anions were synthesized and were characterized using elemental analysis, IR spectroscopy and differential scanning calorimetry (DSC). Compounds 1-5 were further confirmed by single crystal X-ray diffraction and the sensitivities were measured by the standard BAM methods. Additionally, the structure-property relationship was elucidated from the experimental results and theoretical calculations. Energetic salts of 2 and 5 exhibited high heat of formation (5, 1160.06 kJ mol-1), high decomposition temperature (2, 172 °C; 5, 186 °C), excellent detonation performance (2, Dv, 9076 m s-1, P 34.1 GPa; 5, Dv, 8974 m s-1, P 31.9 GPa), moderate sensitivity towards outer stimuli and high nitrogen contents (2, 41.03%; 5, 63.84%). This work increases future prospects for the design of insensitive and novel high-energy green energetic material.

Taming nitroformate through encapsulation with nitrogen-rich hydrogen-bonded organic frameworks

Owing to its simple preparation and high oxygen content, nitroformate [^-C(NO₂)₃, NF] is an extremely attractive oxidant component for propellants and explosives. However, the poor thermostability of NF-based derivatives has been an unconquerable barrier for more than 150 years, thus hindering its application. In this study, the first example of a nitrogen-rich hydrogen-bonded organic framework (HOF-NF) is designed and constructed through self-assembly in energetic materials, in which NF anions are trapped in pores of the resulting framework via the dual force of ionic and hydrogen bonds from the strengthened framework. These factors lead to the decomposition temperature of the resulting HOF-NF moiety being 200 °C, which exceeds the challenge of thermal stability over 180 °C for the first time among NF-based compounds. A large number of NF-based compounds with high stabilities and excellent properties can be designed and synthesized on the basis of this work.

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen is uniquely situated in the periodic table to form kinetically stable compounds often with chemically stable N-N bonds but which are thermodynamically unstable in that the formation of stable multiply bonded N₂ is usually thermodynamically preferable. This unique placement in the periodic table makes catenated nitrogen compounds of interest for development of high-energy-density materials, including explosives for defense and construction purposes, as well as propellants for missile propulsion and for space exploration. This review, designed for a chemical audience, describes foundational subjects, methods, and metrics relevant to the energetic materials community and provides an overview of important classes of catenated nitrogen compounds ranging from theoretical investigation of hypothetical molecules to the practical application of real-world energetic materials. The review is intended to provide detailed chemical insight into the synthesis and decomposition of such materials as well as foundational knowledge of energetic science new to most chemists.

Azo-triazolide bis-cyclometalated Ir(iii) complexes via cyclization of 3-cyanodiarylformazanate ligands

In this work we describe the synthesis of sterically encumbered 1,5-diaryl-3-cyanoformazanate bis-cyclometalated iridium(iii) complexes, two of which undergo redox-neutral cyclization during the reaction to produce carbon-bound 2-aryl-4-arylazo-2H-1,2,3-triazolide ligands. This transformation offers a method for accessing 2-aryl-4-arylazo-2H-1,2,3-triazolide ligands, a heretofore unreported class of chelating ligands. One formazanate complex and both triazolide complexes are structurally characterized by single-crystal X-ray diffraction, with infrared spectroscopy being the primary bulk technique to distinguish the formazanate and triazolide structures. All complexes are further characterized by UV-Vis absorption spectroscopy and cyclic voltammetry, with the triazolide compounds having similar frontier orbital energies to the formazanate complexes but much less visible absorption.

A promising cation of 4-aminofurazan-3-carboxylic acid amidrazone in desensitizing energetic materials

For the development of energetic materials, insensitive compounds have attracted considerable attention due to their improved safety and lower cost than those of sensitive energetic compounds during production, transportation, and application. In this study, insensitive 4-aminofurazan-3-carboxylic acid amidrazone was used as a cation to obtain four derivatives which were determined by X-ray single crystal diffraction. It is interesting to note that all four derivatives are insensitive to impact and friction, while the velocities of detonation for derivatives are superior to that of insensitive TATB (1,3,5-triamino-2,4,6-trinitrobenzene). Multi-factors analysis shows that the cation of 4-aminofurazan-3-carboxylic acid amidrazone is a promising furazan-based cation in desensitizing energetic compounds.

4-Aminofurazan-3-carboxylic acid amidrazone was used to obtain four derivatives confirmed by X-ray diffraction. The derivatives are insensitive to impact and friction, while the velocities of detonation are superior to that of 1,3,5-triamino-2,4,6-trinitrobenzene.

A comparative study of thermal stability of TNT, RDX, CL20 and ANTA explosives using UV 266 nm-time resolved photoacoustic pyrolysis technique

The paper reports the potential use of UV based pulsed photoacoustic spectroscopy to study the thermal stability of some well-known premier explosives such as TNT, RDX, CL20, and ANTA between 30 and 350 °C range. The thermal PA spectra of samples were recorded using fourth harmonic wavelength i.e. 266 nm of pulse duration 7 ns and repetition rate 10 Hz obtained from Q-switched Nd: YAG laser system. Under the influence of UV radiation, the explosive molecules in vapor phase follow the photodissociation process and converted into their byproducts such as NO, NO₂ and N₂O etc. due to π* ← n transitions, which are responsible for the generation resultant PA signal at 266 nm wavelength. The results obtained from PA spectra as a function of temperature are cross verified with Thermo gravimetric-differential thermal analysis (TG-DTA) to ascertain the thermal stability of these samples. The comparative PA spectra of samples were analyzed and shown the behavior of acoustic modes with respect to incident laser energy, and data acquisition time. Finally, the thermal quality factor "Q" is measured to test the stability of reported explosives.

A comparative study of the structure, stability and energetic performance of 5,5′-bitetrazole-1,1′-diolate based energetic ionic salts: future high energy density materials

The structure–property–performance interrelationship of energetic ionic salts based on 5,5′-bitetrazole-1,1′-diolate was thoroughly investigated using ab initio calculations.

Comparative Study of Ultraviolet Laser-Based Time-Resolved Photoacoustic Fingerprint Spectra and Thermal Decomposition Mechanisms of Energetic 1,2,3-1H-Triazole Derivatives Under Controlled Pyrolysis

We report the comparative study of photoacoustic (PA) fingerprint spectra, thermal decomposition, and stability mechanism of some phenyl and bis series energetic compounds named 1-(2-methoxy,-3,5-dinitrophenyl)-1H-1,2,3-triazole ( S₅), 1-(3-methoxy, 2, 6 dinitrophenyl) 1H-1, 2, 3 triazole ( S₁₀), 1-(4-nitrophenyl)-1H-1,2,3-triazole ( S₈), and 2,6-bis ((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl) pyridine ( S₉). Fourth harmonic wavelength, i.e., 266 nm of pulse duration 7 ns and 10 Hz repetition rate obtained from Q-switched Nd: YAG laser, was used to record the thermal PA spectra of these compounds under controlled pyrolysis condition in the range of 30-350 ℃. The PA fingerprint spectra are produced due to entire molecule vapor along with principal functional byproduct NO₂ molecule. NO₂ molecule is a major gas released during thermal decomposition due to weakest nature of C-NO₂ bond. Further, NO₂ molecules are involved in photodissociation process due to π*← n transition and converted into NO molecules inside the PA cell due to excitation by 266 nm wavelength. The combined results of PA and gas chromatography-mass spectrometry (GC-MS) spectra along with thermo gravimetric-differential thermal analysis (TG-DTA) data confirm the thermal decomposition mechanism process that can be completed in multiple steps. In addition, GC-MS spectra also confirm the release of NO and NO₂ molecules. The effect of incident laser energy and data acquisition time has been carried out for understanding the behavior of acoustic modes. Finally, the thermal quality factor "Q" is measured to test the stability of compounds.

Structures and properties of energetic cations in energetic salts

Energetic cations play important roles in energetic performance, which may attribute to the diverse backbones and substituted groups of energetic cations. This review emphasizes the roles of backbones and substituted groups in the energetic performance of energetic salts.

Hydrazine 5,5′-bitetrazole-1,1′-diolate: a promising high density energetic salt with good properties

The salt HA·BTO has proved to be a good insensitive explosive alternative, and has promising application as an RDX replacement.

Energetic salts based on 3-hydrazino-4-amino-1,2,4-triazole (HATr): synthesis and properties

The synthesized energetic salts of 3-hydrazino-4-amino-1,2,4-triazole were fully characterized with respect to their prospective use in energetic applications.

A novel insensitive cocrystal explosive BTO/ATZ: preparation and performance

A new insensitive co-crystal explosive, BTO/ATZ, has a promising future for use as an insensitive explosive.

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.

Energetic salts from nitroformate ion

Development of new energetic salts is the key factor in replacing low performance compounds in conventional formulations of high explosives as well as propellants. Ten salts based on the nitroformate anion and various nitrogen-rich cations were designed and their geometric optimizations carried out using the density functional method. With reasonable oxygen balance (from -36% to 0%), heats of formation (47-624 kJ mol(-1)) and high densities (1.81-1.89 g cm(-3)), the detonation velocity (D) and pressure (P) values of salts were calculated as 8.62-9.36 km s(-1) and 33.10-40.01 GPa, respectively. Lastly, the nitroformate salts studied in this work are of prospective interest as high performance explosives.

New thermally stable energetic materials: synthesis and characterization of guanylhydrazone substituted furoxan energetic derivatives

The synthesis and characterization of guanylhydrazone substituted furoxan energetic derivatives with good thermal stabilities and detonation performance are now reported.

3,4-Diamino-1,2,4-triazole based energetic salts: synthesis, characterization, and energetic properties

A series of energetic salts based on 3,4-diamino-1,2,4-triazole with promising detonation performances have been synthesized using a metathesis reaction method or a protonation reaction method.

A new design strategy on cage insensitive high explosives: symmetrically replacing carbon atoms by nitrogen atoms followed by the introduction of N-oxides

A new insensitive high explosive with the special double cage structure.

A theoretical study on the stability and intramolecular interaction in 5-nitrotetrazolates with the DFT and DFT-D methods

Two new salts 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate and 1-methyl-3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate were designed based on the structures of experimentally synthesized 3-azido-1,2,4-triazolium 5-nitro-tetrazolate and 1-methyl-3-azido-1,2,4-triazolium 5-nitro-tetrazolate, to explore new promising candidates for energetic materials and to investigate the influences of the substituents (- CH 3 and - N 3) and solvent (water) on the intramolecular interactions and properties. The intramolecular hydrogen bonding interactions were investigated by the natural bond orbital (NBO) and the quantum theory of atoms in molecules (QTAIM) analyses using the density functional theory (DFT) and the dispersion correction DFT (DFT-D) methods. The low-lying singlet electronic transitions were estimated using the time-dependent DFT. All four examined salts exist as ionic structures in aqueous solution while acid–base molecular complexes form in gas phase. The hydrogen bond energy (E H ) obtained with the DFT-D method is larger than that obtained with the DFT method, but the trend is consistent, i.e. - N 3 increases while - CH 3 decreases E H . In addition, the position of the strongest electronic absorption peak has a little correlation with the number of - N 3 and - CH 3 groups. 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate is a valuable energetic salt with the highest nitrogen content, oxygen coefficient and density and the second highest heat of formation and chemical stability.

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.

Conjugated energetic salts based on 3,3′-((1E,1′E)-(2,4,6-trinitro-1,3-phenylene)bis(ethene-2,1-diyl))bis(2,4,6-trinitrophenol)

Highly conjugated energetic salts exhibit remarkable thermostability and insensitivity.

Synthesis and characterization of 5-nitro-2-nitratomethyl-1,2,3,4-tetrazole: a high nitrogen energetic compound with good oxygen balance

The synthesis of 5-nitro-2-nitratomethyl-1,2,3,4-tetrazole (4) and its full characterization are given here. Compound 4 was synthesized through the nitration of 5-nitro-2-hydroxymethyl-tetrazole (3) with fuming nitric acid and acetic anhydride and its structure was characterized by MS, FT-IR, ¹H-NMR and ¹³C-NMR techniques. The crystal structure of 4 was determined by X-ray single crystal diffraction analysis. The compound belongs to the orthorhombic system with space group Pna2(1), and its crystal parameters were a = 2.121(8) nm, b = 0.5281(19) nm, c = 0.6246(2) nm, Z = 4, V = 0.6995(4) nm³, Dc = 1.805 g/cm³, F(000) = 384, μ = 0.174 mm⁻¹. A theoretical study of 4 has been performed, using quantum computational density functional theory (B3LYP methods) with 6-31G* basis sets as implemented in the Gaussian 03 program suite. The obtained heat of formation (HOF) for 4 was 228.07 kJ·mol⁻¹, the detonation pressure (P) values calculated for 4 was 37.92 GPa, the detonation velocity (D) can reach 9260 m·s⁻¹, and the oxygen balance was zero (Q), making 4 a competitive energetic compound.