Midway between Energetic Molecular Crystals and High-Density Energetic Salts: Crystal Engineering with Hydrogen Bonded Chains of Polynitro Bipyrazoles

Abstract

A new strategy for supramolecular synthesis of energetic salts is reported. It is still a challenge to address packing patterns and crystal morphologies of such materials due to the lack of reliable supramolecular synthons, which are applicable to polynitro substituted species. 3,5-Dinitro-4,4′-bipyrazole (1), 3,3′,5-trinitro-4,4′-bipyrazole (2), and 3,3′,5,5′-tetranitro-4,4′-bipyrazole (3) are excellent functional models that provide a higher degree of control over the structure by manipulating robust self-assembly molecular building blocks of lower dimensionality. A variety of K+, Cs+, and nitrogen-rich salts (e.g., ammonium, aminoguanidinium, hydrazinium, and hydroxylammonium) 4–17, prepared by single deprotonation of NH-acidic 1–3, are based upon polar anionic chains sustained with strong NH···N bonding of conjugate acidic and basic pyrazole/pyrazolate sites. A gradual increase of NH-acidity (dinitropyrazolyl > nitropyrazolyl ≫ pyrazolyl) productively contributes to the strength of NH···N bonds and reliability of such supramolecular synthon. New synthesized energetic materials were fully characterized by NMR (1H, 13C, and 14N) spectroscopy, infrared spectroscopy, differential thermal analysis (DTA), and elemental analysis, and the heats of formation were calculated using the atomization method based on CBS-4 M enthalpies. Several detonation parameters, such as detonation pressure, velocity, and energy, were calculated by using the X-ray densities and the calculated standard molar enthalpies of formation. The sensitivities toward external stimuli were tested according to the BAM standards. In addition, the toxicity toward Vibrio fischeri bacteria of the monopotassium salt 9·H2O is reported.