Substituted tetrazoles with N-oxide moiety: critical assessment of thermochemical properties.

Modeling of the structure of molecules and simulation of crystal structure followed by the calculation of the enthalpies of formation for 21 salts of three high-energy tetrazole 1N-oxides: 5-nitro-1-hydroxy-1H-tetrazole 1a-1g, 5-trinitromethyl-1-hydroxy-1H-tetrazole 2a-2g and 6-amino-3-(1-hydroxy-1H-tetrazol-5-yl)-1,2,4,5-tetrazine 1,5-dioxide 3a-3g was performed. The methods of quantum chemistry and the method of atom-atom potentials were used. Structural search for optimal crystal packings was carried out in 11 most common space symmetry groups. The enthalpies of formation were obtained and analyzed using two different approaches: VBT and MICCM methods, which allowed to evaluate the quality of these calculation methods. In addition, the results obtained indicate high values of thermochemical characteristics for some of the considered compounds, which have a positive effect on their explosive properties and unveil their future application potential.

Di- and trioxides of triazolotetrazine: Computational prediction of crystal structures and estimation of physicochemical characteristics.

Simulation of crystal structures of series 1(2)-R-1(2)H-[1,2,3]triazolo[4,5-e][1,2,3,4]tetrazine 5,7-dioxides, 1,5,7-trioxides, 4,6-dioxides and 3,4,6-trioxides was carried out using an original technique based on the method of atom-atom potentials and quantum chemistry. The effect of the position of the substituent in the triazole ring on the change in the crystal structures of these compounds and their thermochemical characteristics was studied for the first time. For some of synthesized compounds, thermochemical characteristics were investigated and differential scanning calorimetry curves were obtained. Detonation parameters were calculated, on the basis of which the prospects for the use of the considered compounds were assessed.

New Method for Predicting the Enthalpy of Salt Formation.

A new efficient method for calculating the enthalpies of salt formation is proposed. The method is based on a fundamentally new cocrystal model, consisting of a mixture of cations and anions and a "quasi-salt" of neutral components, in fact, of the salt itself, and the enthalpy of formation is calculated as the average value between the enthalpies of formation of these two structural components. Unlike correlation and additive schemes, this method is based on the construction of a real physical model of a salt crystal, for which the molecular geometry of the ions and neutral salt components is preliminarily optimized by quantum chemistry methods. Further, based on the obtained data, the initial models of crystal lattices in the statistically most probable structural classes are constructed with their subsequent optimization by the method of Atom-Atom potentials. For a number of compounds of various chemical classes, the effectiveness of the method for estimating the enthalpy of salts is shown, which surpasses the known methods in terms of calculation accuracy.

Design and Synthesis of Nitrogen-Rich Azo-Bridged Furoxanylazoles as High-Performance Energetic Materials.

A series of novel energetic materials comprising of azo-bridged furoxanylazoles enriched with energetic functionalities was designed and synthesized. These high-energy materials were thoroughly characterized by IR and multinuclear NMR (1 H, 13 C, 14 N) spectroscopy, high-resolution mass spectrometry, elemental analysis, and differential scanning calorimetry (DSC). The molecular structures of representative amino and azo oxadiazole assemblies were additionally confirmed by single-crystal X-ray diffraction and X-ray powder diffraction. A comparison of contributions of explosophoric moieties into the density of energetic materials revealed that furoxan and 1,2,4-oxadiazole rings are the densest motifs while the substitution of the azide and amino fragments on the nitro and azo ones leads to an increase of the density. Azo bridged energetic materials have high nitrogen-oxygen contents (68.8-76.9 %) and high thermal stability. The synthesized compounds exhibit good experimental densities (1.62-1.88 g cm-3 ), very high enthalpies of formation (846-1720 kJ mol-1 ), and, as a result, excellent detonation performance (detonation velocities 7.66-9.09 km s-1 and detonation pressures 25.0-37.7 GPa). From the application perspective, the detonation parameters of azo oxadiazole assemblies exceed those of the benchmark explosive RDX, while a combination of high detonation performance and acceptable friction sensitivity of azo(1,2,4-triazolylfuroxan) make it a promising potential alternative to PETN.

Nitrodiaziridines: Unattainable yet, but Desired Energetic Materials.

Using quantum chemical methods and the original technique based on atom-atom potential methods, the molecular and crystal structure simulation of all possible structural forms of nitrodiaziridines were carried out. The possible pathways of thermal decomposition of nitrodiaziridines were modeled, and the most stable forms were identified. Thermodynamic stability, physicochemical characteristics, and detonation properties were also estimated. The obtained results enable a huge potential of the nitrodiaziridine-based compounds as high-energy materials for a variety of applications.

Assembly of Tetrazolylfuroxan Organic Salts: Multipurpose Green Energetic Materials with High Enthalpies of Formation and Excellent Detonation Performance.

A series of highly energetic organic salts comprising a tetrazolylfuroxan anion, explosophoric azido or azo functionalities, and nitrogen-rich cations were synthesized by simple, efficient, and scalable chemical routes. These energetic materials were fully characterized by IR and multinuclear NMR (1 H, 13 C, 14 N, 15 N) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). Additionally, the structure of an energetic salt consisting of an azidotetrazolylfuroxan anion and a 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazolium cation was confirmed by single-crystal X-ray diffraction. The synthesized compounds exhibit good experimental densities (1.57-1.71 g cm-3 ), very high enthalpies of formation (818-1363 kJ mol-1 ), and, as a result, excellent detonation performance (detonation velocities 7.54-8.26 kms-1 and detonation pressures 23.4-29.3 GPa). Most of the synthesized energetic salts have moderate sensitivity toward impact and friction, which makes them promising candidates for a variety of energetic applications. At the same time, three compounds have impact sensitivity on the primary explosives level (1.5-2.7 J). These results along with high detonation parameters and high nitrogen contents (66.0-70.2 %) indicate that these three compounds may serve as potential environmentally friendly alternatives to lead-based primary explosives.

The influence of substituents on the reactivity and cytotoxicity of imidazothiazolotriazinones.

A series of tetrahydroimidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine-2,7(1H, 6H)-diones were synthesized via the reaction of imidazotriazinethiones and bromoacetic acid followed by condensation with isatins. Amidine skeletal rearrangement of 3,3a,9,9a-tetrahydroimidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine-2,7 (1H, 6H)-diones into 1,3a,4,9a-tetrahydroimidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine-2,8 (3H, 7H)-diones under KOH treatment has been studied. The influence of substituents at positions 1,3,3a,6,9a of imidazothiazolotriazine on the ability to undergo rearrangement was analyzed based on experimental data and theoretical calculations. Both imidazothiazolo[3,2-b]triazines and their rearrangement products were evaluated for their cytotoxic activity against rhabdomyosarcoma, A549, HCT116 and MCF7 human cancer cell lines by MTT assay. Among the derivatives, 1,3-diethyl-6-[1-(2-propyl)-2-oxoindolin-3-ylidene]-3,3a,9,9a-tetrahydroimidazo [4,5-e]thiazolo[3,2-b]-1,2,4-triazine-2,7(1H, 6H)-dione 4i was found to have the highest antiproliferative activity toward the tested cell lines (4i: [Formula: see text], 2.29, 0.47 and [Formula: see text], respectively). The [Formula: see text] value of compound 4i against normal human embryonic kidney cells HEK293 was [Formula: see text], which appeared to be 6-41-fold higher than [Formula: see text] values of 4i against human cancer cells.

Is everything correct? The formation enthalpy estimation and data revision of nitrate and perchlorate salts.

CONTEXT:   In modern searches for the structure of high-energy-density compounds with high operational, detonation, and physicochemical characteristics, a special place belongs to salts, which have a number of significant advantages over neutral compounds. The development of this area of HEDM is hampered by the lack of effective calculation schemes for estimating the enthalpy of formation DHf0 of salts, as a key parameter in assessing the prospects for their use. Based on the author's method (MICCM), which is superior in accuracy to currently available calculation methods, the enthalpies of formation of various salts of nitrates and perchlorates for a promising class of high-energy amino-1,2,4-triazoles are calculated and the accuracy of calculations is estimated by other methods. Relationships between the thermochemical characteristics of salts depending on various cations are considered. Among the considered compounds, calculations of the enthalpies of salts of three amino-1,2,4-triazoles showed a significant discrepancy with the experimental data. METHODS: Calculations DHf0of salts were performed using three methods: volume-base thermodynamic (Jenkins/Bartlett method), the method of adding of ions contributions (MAIC, Matyushin's method), and the method of ions and cocrystals contribution mixing (MICCM, Khakimov's method). Calculations by the MICCM method were carried out on the basis of quantum chemistry methods (when estimating the enthalpies of formation in the gas phase) and the method of atom-atom potentials (AAP) when calculating the enthalpy of sublimation of salts. We have optimized all the structures in the gas phase using the Becke three hybrid exchange and Lee-Yang-Parr correlation functional with Grimme's dispersion correction, B3LYP-D2, and aug-cc-pVDZ basis set using the Gaussian16 software. The AAP calculations were performed using the FitMEP software packages (for adjusting the charges of the molecular electrostatic potential) and PMC (for the procedure for constructing crystal packings and searching for optimal ones).

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.