The unusual combination of beauty and power of furoxano-1,2,3,4-tetrazine 1,3-dioxides: a theoretical study of crystal structures

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 DH_f⁰ 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 DH_f⁰of 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).

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.

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.

Time for quartet: the stable 3 : 1 cocrystal formulation of FTDO and BTF – a high-energy-density material

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 (3–1 : 1) was performed. Theoretically and experimentally was shown: a (3 : 1) cocrystal is formed.

The Ingenious Synthesis of a Nitro-Free Insensitive High-Energy Material Featuring Face-to-Face and Edge-to-Face π-Interactions

Density, detonation property, and sensitivity may be the most valued features when evaluating an energetic material. By reasoning structure–property relationships, a nitro-free planar energetic material with high nitrogen and oxygen content, 7-hydroxy-difurazano[3,4-b:3′,4′-f]furoxano[3″,4″-d]azepine (4), was synthesized using a unique and facile approach. The structure was fully characterized by IR and NMR spectra, elemental analysis, differential scanning calorimetry (DSC), and single-crystal X-ray diffraction. The expected properties of 4, including a high density of 1.92 g cm⁻³, high detonation velocity of 8,875 m s⁻¹, and low mechanical sensitivities (impact sensitivity, 21 J and friction sensitivity, >360 N), confirm our strategy. Interestingly, the single-crystal structures of 4 reveal expected face-to-face and edge-to-face π-interactions in the crystal stacking. The remarkable differences in crystal stacking of 4 provide unequivocal evidence that face-to-face π-π interactions contribute significantly to closer assembly and higher density.