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A series of R-[1,2,5]oxadiazolo[3,4-c]cinnoline 5-mono- and 1,5-dioxides containing substituents (R = CH3, F, Br, CF3) at different positions were synthesized by an N-nitration–annulation process occurring upon treatment of 3-amino-4-(R-aryl)furazans and 4-amino-3-(R-aryl)furoxans with the HNO3–H2SO4–Ac2O system. The regioselectivity of the ring closure step was determined for the unsymmetrically substituted R-aryl precursors. Unexpected acylation at position 6 of 7-bromo-[1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxide occurred as a result of the increased duration of the synthesis. The crystal structures of five new compounds were determined by X-ray diffraction analysis, and their crystal packings were compared with each other and with those of previously studied molecules, revealing common motifs regardless of the type or position of the substituent. Specifically, the fluorine derivative forms layers isostructural with those in unsubstituted mono- and dioxides, differing only in their arrangement within the P21 and P21/c space groups. Two methyl derivatives, on the other hand, exhibit a structure with flat layers. While the crystal environments of different R-substituents are generally distinct, the unsubstituted part of the heterocyclic core tends to form repeating isostructural motifs, such as dimers, chains, and layers. Although substituents disrupt the crystal packing, they still allow for the combination of these motifs in different crystal structures. [ABSTRACT FROM AUTHOR]

A comparative study of experimentally established structures, stability and energetic performance of ammonium and hydrazinium salts of 4H-[1,2,3]triazolo[4,5-c][1,2,5]oxadiazole (triazolofurazan, TF) as well as its N-oxide and N-nitroimide was performed. The aim of this study was to reveal the structure–property relationships of heterocyclic systems by the example of triazolofurazan derivatives. It was shown that the introduction of N-oxide oxygen into position 5 of the TF anion led to a small loss in enthalpy of formation (4 kcal mol−1) while the introduction of the N–NO2 (N-nitroimido) group in the same position added a significant amount of energy into the molecule (36 kcal mol−1). Both substituents improved the oxygen balance and increased the density (0.065–0.22 g cm−3) of the final salts; however, only N-oxide enhanced the thermal stability by ca. 35–45 °C, while N-nitroimide either remained unchanged or decreased the heat resistance compared to unsubstituted analogues. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the potential of cinnoline oxides and their nitro derivatives as explosive materials. Thus, the study includes the synthesis, crystal structure prediction, single-crystal X-ray structure determination, crystal packing analysis and calculation of the detonation properties of [1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxide, 1,5-dioxides and their nitro derivatives. It was found that the exocyclic oxygen atom of the 1,2,5-oxadiazole ring affects the nitration reaction of the benzene ring of cinnoline oxides: its absence requires more hard nitration conditions, but at the same time makes it possible to obtain a dinitro cinnoline derivative. 7,9-Dinitro-[1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxide was obtained for the first time. Previously unknown experimental crystal structures were established for six compounds. For all of the compounds studied, crystal structure prediction was used to obtain information about crystal packing, even in the absence of experimental data. It was shown that crystal structure prediction based on the grid algorithm for structure generation and a force field approach with a charge-shifted model of electrostatic interactions for energy minimization and ranking yielded reliable results for this class of compounds. Crystal packing analysis was used to reveal supramolecular synthons, and to find differences and similarities in crystal structures. For example, the crystals of cinnoline 1,5-dioxides, molecules with an exocyclic oxygen atom of the 1,2,5-oxadiazole ring, are isostructural or nearly isostructural to the corresponding cinnoline 5-oxides, but their density and oxygen balance are higher. The calculated detonation parameters indicated the moderate performance of the [1,2,5]oxadiazolo[3,4-c]cinnoline oxides as explosives. [ABSTRACT FROM AUTHOR]