Experimental Discovery and Electronic Structure of Free State Aminopentazole NNH and its Cation.

All-nitrogen compounds (ANC) that are environment-friendly and promising high-energy-density materials (HEDMs). NNH, an all-nitrogen building block with functional groups, can be converted into bridged-pentazole N, azopentazole N, etc. But NNH synthesized by previous methods was bound in supramolecular frameworks and not isolated for further research. In this article, we synthesized free-state NNH through radical amination of cyclo-N and its cation NNH by the directional hydrolysis of imido-pentazoles. The new structures were verified by MS, IR, NMR and powder diffraction, and their aromaticity, HOMO-LUMO, ESP, etc. were calculated by DFT. Experimental results show these compounds are only stable at low temperature. For instance, NNH Cl is stable below ‒20 °C for 12 hours. Harmonic oscillator model of aromaticity (HOMA), electron localization function (ELF), NICS(1), localized orbital locator (LOL), and anisotropy of the induced current density (ACID) show NNH and NNH have aromaticity, and the order of aromaticity and stability is NNH < NNH < cyclo-N , consistent with experiments. The HOMO-LUMO energy gaps of NNH (ΔE = 10.05 eV) and NNH (ΔE = 10.14 eV) is lower than that of cyclo-N (ΔE = 11.46 eV), indicating higher reaction activity. The synthesis of free-state NNH is a crucial step in all-nitrogen construction and promotes the energetic materials field toward all-nitrogen.