Towards improving the characteristics of high-energy pyrazines and their N-oxides

CONTEXT

Based on the methods of quantum chemistry and atom-atom potentials, the molecular and crystal structure of a number of high-energy pyrazines was modeled: unsubstituted diazines, as well as fully nitrated 1,4-diazabenzenes, their oxides and polymorphs. The enthalpies of formation, densities of molecular crystals, and some performance characteristics of these compounds were determined. The parameters of decomposition of substances were estimated. It has been established that tetranitropyrazine-1,4-dioxide has maximum energy content and excellent performance characteristics, which determine the prospects for using this compound as a high-energy one in the considered series of compounds.

METHODS

In this work, DFT calculations were conducted through the software Gaussian 09 using B3LYP functional with basis set aug-cc-PVDZ and the Grimme dispersion correction D2. For crystal structure optimization, the atom-atom potential methods with PMC program (Packing of Molecules in Crystal) were used. Charges for molecular electrostatic potential were fitted by FitMEP and enthalpies of formation in gas phase were assessed by G3B3.

Computational insight into the crystal structures of cubane and azacubanes

CONTEXT

Using quantum chemistry and atom-atom potential methods, the molecular and crystal structures of cubane 1 and all types of unsubstituted azacubanes 2-22 were calculated. Alternative possible polymorphs of cubane 1 have been proposed. The thermochemical properties of azacubanes in the gas and solid phases were assessed. Thermodynamic aspects of stability are considered, and a significant decrease in stability is revealed upon transition from cubane 1 to octaazacubane 22. It has been shown that the density and energetic properties of azacubanes depend nonlinearly on the number of nitrogen atoms in the structure and the density of octaazacubane 22 at room temperature is 1.546 g cm-3, which is significantly lower than the previously given estimate.

METHODS

In this work, DFT calculations were conducted through the software Gaussian 09 using B3LYP functional with basis set aug-cc-PVDZ and the Grimme dispersion correction D2. For crystal structure optimization, the atom-atom potential methods with PMC (packing of molecules in crystal) program were used. Charges for molecular electrostatic potential were fitted by FitMEP, and enthalpies of formation in gas phase were assessed by G3B3.

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.

From Minerals to Simplest Living Matter: Life Origination Hydrate Theory

Long since, people tried to solve the mystery of the way that led to the appearance and propagation of living entities. However, no harmonious understanding of this mystery existed, because neither the scientifically grounded source minerals nor the ambient conditions were proposed and because it was groundlessly taken that the process of living matter origination is endothermal. The Life Origination Hydrate Theory (LOH-Theory) first suggests the chemical way capable of leading from the specified abundant natural minerals to origination of multitudes of multitudes of simplest living entities and gives an original explanation for the phenomena of chirality and racemization delay. The LOH-Theory covers the period up to origination of the genetic code. The LOH-Theory is grounded on the following three discoveries based on the available information and on the results of our experimental works performed using original instrumentation and computer simulations. (1) There is the only one triad of natural minerals applicable for exothermal thermodynamically possible chemical syntheses of simplest living-matter components. (2) N-base, ribose, and phosphdiester radicals and nucleic acids as whole are size-compatible with structural gas-hydrate cavities. (3) The gas-hydrate structure arises around amido-groups in cooled undisturbed systems consisting of water and highly-concentrated functional polymers with amido-groups.The natural conditions and historic periods favorable for simplest living matter origination are revealed. The LOH-Theory is supported by results of observations, biophysical and biochemical experiments, and wide application of original three-dimensional and two-dimensional computer simulations of biochemical structures within gas-hydrate matrix. The instrumentation and procedures for experimental verification of the LOH-Theory are suggested. If future experiments are successful, they, possibly, could be the first step on the way to industrial synthesis of food from minerals, i.e., to execution of the work that is performed by plants.

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).

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.

An Alliance of Polynitrogen Heterocycles: Novel Energetic Tetrazinedioxide-Hydroxytetrazole-Based Materials

Energetic materials constitute one of the most important subtypes of functional materials used for various applications. A promising approach for the construction of novel thermally stable high-energy materials is based on an assembly of polynitrogen biheterocyclic scaffolds. Herein, we report on the design and synthesis of a new series of high-nitrogen energetic salts comprising the C-C linked 6-aminotetrazinedioxide and hydroxytetrazole frameworks. Synthesized materials were thoroughly characterized by IR and multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction and differential scanning calorimetry. As a result of a vast amount of the formed intra- and intermolecular hydrogen bonds, prepared ammonium and amino-1,2,4-triazolium salts are thermally stable and have good densities of 1.75–1.78 g·cm⁻³. All synthesized compounds show high detonation performance, reaching that of benchmark RDX. At the same time, as compared to RDX, investigated salts are less friction sensitive due to the formed net of hydrogen bonds. Overall, reported functional materials represent a novel perspective subclass of secondary explosives and unveil further opportunities for an assembly of biheterocyclic next-generation energetic materials.

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.

Quest: structure and properties of BTF–nitrobenzene cocrystals with different ratios of components

Using the methods of quantum chemistry and AAP, the structure of BTF cocrystals with nitrobenzene, 1,2-, 1,3-, 1,4-dinitrobenzene, 1,3,5-trinitrobenzene, and hexanitrobenzene with different ratios of components (1 : 1, 1 : 2, 1 : 3, 2 : 1, 3 : 1) is modeled.

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.

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

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.

Temperature-accelerated method for exploring polymorphism in molecular crystals based on free energy

The ability of certain organic molecules to form multiple crystal structures, known as polymorphism, has important ramifications for pharmaceuticals and high energy materials. Here, we introduce an efficient molecular dynamics method for rapidly identifying and thermodynamically ranking polymorphs. The new method employs high temperature and adiabatic decoupling to the simulation cell parameters in order to sample the Gibbs free energy of the polymorphs. Polymorphism in solid benzene is revisited, and a resolution to a long-standing controversy concerning the benzene II structure is proposed.