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Crystal packings were modeled for salts of substituted formamidines including formamidinium, guanidinium, azidoformamidinium and nitroformamidinium. The enthalpies of formation for substituted formamidines with various anions were calculated.

Based on various calculation methods, the enthalpies of formation for a number of salts of nitric and perchloric acids were estimated. Relationships between the thermochemical characteristics of salts depending on various cations are considered. Calculations have been made and the efficiency of using a number of quantum-chemical methods in estimating the formation enthalpy of compounds in the gas phase has been analyzed. Based on a combination of quantum chemistry methods and Atom-Atom Potentials, the crystal structure of salts was simulated and the enthalpy of sublimation was estimated for subsequent use in calculations by the recently developed MICCM method. This method surpasses all the most commonly used calculation schemes in terms of accuracy in estimating the enthalpies of salt formation. Among the compounds considered, the calculations of the salts enthalpies of three amino-1,2,4-triazoles showed a significant discrepancy with the experimental data.

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.

Based on a combination of quantum chemistry and atom–atom potentials methods, we developed a technique for modeling the structure and estimating the complexation energy of a binary organic complex in gas and crystal phases. The efficiency of this technique was illustrated by an example of the benzotrifuroxan–benzene molecular complex. For both phases, the same molecular binary structure (π-stacking) was obtained with a parallel arrangement of the planes of BTF and benzene molecules and complexation energies of −11.9 and −11.7 kcal mol−1 for a gas phase and a crystal cluster, respectively.

The crystal structure prediction for two isomeric forms of tetrazino-tetrazine tetraoxide (TTTO), viz., [1,2,3,4]tetrazino[5,6-e][1,2,3,4]tetrazine 1,3,6,8-tetraoxide and [1,2,3,4] tetrazino [5,6-e] [1,2,3,4] tetrazine 1,3,5,7-tetraoxide was performed using an original procedure to obtain the optimized point charges that approximate the molecular electrostatic potential. The best computational models were used for simulation of the crystal packing of the molecules within the framework of the atom-atom potential function method with the refined Lennard-Jones potential parameters (6-12) by optimizing the unit cell parameters and localizing the minima on the potential energy surfaces of the crystal structures.

A computer simulation of cocrystal structures of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine-4,6-dioxide (FTDO) with benzotrifuroxan (BTF) in ratios of (1 : 1), (2 : 1) and (3 : 1) was performed, and their thermodynamic stability and physical–chemical characteristics were calculated. According to calculations, the (3 : 1) cocrystal is thermodynamically most stable. Therefore, it is the most preferable for cocrystallization, and we successfully obtained a cocrystal only for the (3 : 1) ratio. The cocrystal was characterized by X-ray diffraction and vibrational spectroscopy. In the vibrational spectra, some new bands were observed compared with the parent compounds spectra. In addition, some bands of pure FTDO and BTF disappeared, which is typical for a molecular complex formation. The thermal decomposition and sensitivity to impact and friction of the cocrystal were investigated. The impact sensitivity (2.8 J) turned out to be equal to the sensitivity of the less sensitive component (BTF). In addition, the sensitivity to friction (14 N) decreased by three times compared with the highly sensitive FTDO, which is unusual for cocrystals of high-energy compounds. The (3 : 1) cocrystal had a high density of 1.888 (calc.) and 1.865 g cm−3 (exp.). The calculated detonation velocity (9.14 km s−1) and Chapman–Jouguet pressure (38.08 GPa) are high, and indicate favorable prospects for using this cocrystal.

Nitronium borates of NO2[B(OX)4] type with X = CF3CO and NO2 as ligands were synthesized, and their structures were determined by powder X-ray diffraction. Crystalline NO2[B(ONO2)4] is relatively stable at room temperature and undergoes transformation to B2O3 upon heating. The [B(CF3COO)4]− anion was obtained for the first time and characterized as a structural fragment of a solid compound. The possibility of reversible modification of the complex anion by replacement of the nitrate or trifluoroacetate ligand was demonstrated for the first time by the mutual transformations of NO2[B(ONO2)4] and NO2[B(CF3COO)4].

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.

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.

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: $$\hbox {IC}_{50} = 2.20$$ , 2.29, 0.47 and $$3.11\,{\upmu }\hbox {M}$$ , respectively). The $$\hbox {IC}_{50}$$ value of compound 4i against normal human embryonic kidney cells HEK293 was $$19.34\,{\upmu }\hbox {M}$$ , which appeared to be 6–41-fold higher than $$\hbox {IC}_{50}$$ values of 4i against human cancer cells.

Regularities in the Raman ( v NO 2 s ) and 14N NMR spectra of acetyl nitrates containing various electron-withdrawing α-substituents were established by quantum chemical calculations. The experimental data on (poly)-α-haloacetyl nitrates (in solutions) revealed no reliable relationship between the halogen nature/number and the spectral characteristics, whereas the computed values of δN and O–NO2 bond lengths disclose the substituent effect on the polarization of O–N bond and hence on the nitrating power of acyl nitrates.

The thermodynamic stability of the furoxan ring annullated with 1,2,3,4-tetrazine 1,3-dioxide cycle was studied. Crystal structure prediction based on global energy minimization in the framework of the atom-atom potential functions method was performed for isomeric furoxano-tetrazinedioxides (FuxTDOs): [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 1,5,7-trioxide (1) and [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 1,4,6-trioxide (2). The Coulomb energy was calculated with advanced point charge models fitted with high accuracy to the molecular electrostatic potentials of these molecules. The pressure and velocity of detonation of compounds 1 and 2 were estimated using the calculated enthalpy of formation and predicted molecular crystal density, which allows us to consider these compounds as high energetic materials.

The enthalpies of formation for bitetrazole guanidinium salts in the gas and solid phases were calculated using the standard approach and isodesmic reaction method. A comparative analysis of the quality of the methods and the basis sets (HF, 3-21G, 6-31G, 6-311++G(d, p); DFT/B3LYP, 3-21G, 6-31G(d)) was performed for the calculation of the molecular volumes necessary for modeling the enthalpies of formation in solid phase, and the optimum set was recommended. The calculated values of enthalpies of formation of the compounds obtained by the isodesmic reaction method are three times lower than the results obtained using standard procedures.

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.

A novel general approach towards various nitroazoles via tandem process involving dinitrofuroxan cycloreversion followed by [3+2] cycloaddition of generated in situ nitroformonitrile oxide is developed. The reaction is promoted by addition of catalytic amounts of ionic liquids. Plausible mechanisms of the described processes based on quantum chemical calculations are proposed.

The regularities of AlkNHBr consumption in the reaction of formation of 1,2-dialkyldiaziridines in aqueous media were studied for the first time by UV spectrometry. The rate constants of particular steps of the reaction were estimated starting from the possibility of formation of the precursor of 1,2-dialkyldiaziridine, N-halogenaminal, due to the amination of the intermediate iminium cation along with the parallel halogenation of the intermediate gem-diamine. The quantum chemical calculations (DFT, B3LYP, 6–31++G(d,p) and 3–21G basis sets) were performed for the spatial and electronic structures of the compounds and indices of the local reactivity and global electrophilicity of the key intermediates of the reactions. The results of the calculations allowed us to explain the retardation of the reaction when using EtNHBr instead of MeNHBr.

Pentathiepinopyrroles reacted with methyl propiolate and triphenylphosphine to give regioselectively dithiinopyrroles in agreement with the electron distribution in the proposed reaction intermediate. Thieno[2,3-f][1,2,3,4,5]pentathiepin when treated with methyl propiolate and triphenylphosphine gave a pair of regioisomers where the higher yielding regioisomer contained the same mode of junction as in the case of pentathiepinopyrroles. X-ray crystal structures are provided for the thieno[2,3-b][1,4]dithiine carboxylate isomers. Quantum-chemical calculations B3LYP/6-31G(d) and B3LYP/6-311++G(d,p) have been carried out for better understanding of the reaction mechanisms; the index of synchronism of the Sh addition and the index of a relative difference in bond orders in transition states are in good agreement with the formation of the regioisomers by the reaction of unsymmetrical pentathiepins with alkynes containing one electron-withdrawing group.

The enthalpies of formation were calculated for a number of bitetrazole salts using classical quantum chemistry methods and an improved method of isodesmic reactions, and the latter was found most accurate in the assessment of this characteristic.

The oxidations of N 2 O 4 to N 2 O 5 with ozone or molecular oxygen were simulated using quantum chemistry (DFT) and computer modeling (Gaussian 98 program package) methods.