Combined X-ray Crystallographic and Periodic DFT Study of Supramolecular Organization and Intermolecular Interactions in Crystalline Peroxosolvates of (Nitropyrazolyl)furazans

Abstract

Hydrogen peroxide is a source of active oxygen, which can optimize the negative oxygen balance of energy compounds and improve their detonation properties due to the formation of crystalline peroxosolvates. This approach has been recently proposed but remains unexplored because the number of hydrogen peroxide adducts and energetic compounds is very limited. Due to its acidic nature, hydrogen peroxide usually forms stable peroxosolvates with basic or amphoteric coformers. Herein, peroxosolvates of amphoteric energetic compounds, (nitropyrazolyl)furazanes C₆H₅N₅O₃·H₂O₂ (1·H₂O₂), C₆H₄N₆O₅·H₂O₂ (2·H₂O₂), and 5(C₅H₂N₆O₅)·H₂O₂ (3·1/5H₂O₂), were obtained, and their crystal structures were determined. Crystal packings of 1–3 are based on the same supramolecular synthon formed by a peroxide molecule and three adjacent coformers. In this unit, H₂O₂ forms three hydrogen bonds: one with the furazan ring as the proton donor and two with pyrazolyl fragments as both a proton donor and a proton acceptor. Analysis of the metric parameters of H-bonds in previously published isostructural crystalline hydrates 1·H₂O and 2·H₂O indicates the predominant acidic nature of amphoteric coformers. Periodic density functional theory (DFT) calculations reveal that the total sum of hydrogen bonds as a proton donor of the hydrogen peroxide molecule is up to 10 kJ mol^–1 higher than the hydrogen bond energy as a proton acceptor, reflecting the acidic nature of H₂O₂. The contribution of hydrogen bonds of hydrogen peroxide molecules to the lattice energy of the resulting peroxosolvates is about 40–45%. 1·H₂O₂ exhibits improved oxygen balance and estimated detonation parameters in comparison to unsolvated 1, whose structure was also determined.