What are the prospects of [1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxides, 1,5-dioxides and their nitro derivatives as high-energy-density materials? Synthesis, experimental and predicted crystal structures, and calculated explosive properties

Abstract

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.