Nitric Acid Concentration-Controlled Chemoselective Divergence of a Nitrogen-Rich 5,6,5-Fused Tricyclic Scaffold to Thermally Stable Salts and High-Energy Diazonium Materials

Abstract

A nitric acid concentration- and temperature-controlled aqueous chemoselective divergence strategy is reported using a nitrogen-rich 5,6,5-fused tricyclic parent compound 1. In the nitric acid system, 70% nitric acid induces only monoprotonation to afford nitrate salt 2 (Tdec = 225.88 °C), whereas fuming nitric acid at 80 °C triggers protonation, diazotization, and one-pot multicomponent cocrystal self-assembly to give diazonium cocrystal 4 ([C6H4N9+]2·[NO3–]2·HNO3·H2O, Tdec = 181 °C). As an extension of the protonation pathway, treatment with perchloric acid affords perchlorate salt 3 (Tdec = 294.85 °C). Further neutralization of 4 gives neutral diazonium inner salt 5 (Tdec = 179.5 °C, Dv = 8822 m s–1, ΔHf = 1644.77 kJ mol–1). Single-crystal X-ray diffraction, ESP, NCI/IGMH, and Hirshfeld analyses indicate that nitric acid/water molecules in 4 participate in a multicomponent noncovalent network through hydrogen bonding and polar contacts, while π–π stacking occurs between adjacent fused-ring skeletons. This strategy demonstrates that nitric acid concentration can serve as an effective switch for selectively constructing protonated salts, diazonium cocrystals, and neutral diazonium inner salts from a single fused-ring scaffold.