Experimental Discovery and Electronic Structure of Free State Aminopentazole N

All-nitrogen compounds (ANC) that are environment-friendly and promising high-energy-density materials (HEDMs). N5NH2, an all-nitrogen building block with functional groups, can be converted into bridged-pentazole N10, azopentazole N12, etc. But N5NH2 synthesized by previous methods was bound in supramolecular frameworks and not isolated for further research. In this article, we synthesized free-state N5NH2 through radical amination of cyclo-N5 ‒ and its cation N5NH3 + 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, N5NH3 +Cl‒ is stable below ‒20 °C for 12 hours. Harmonic oscillator model of aromaticity (HOMA), electron localization function (ELF), NICSZZ(1)π, localized orbital locator (LOL), and anisotropy of the induced current density (ACID) show N5NH2 and N5NH3 + have aromaticity, and the order of aromaticity and stability is N5NH3 + < N5NH2 < cyclo-N5 ‒, consistent with experiments. The HOMO-LUMO energy gaps of N5NH2 (ΔE = 10.05 eV) and N5NH3 + (ΔE = 10.14 eV) is lower than that of cyclo-N5 ‒ (ΔE = 11.46 eV), indicating higher reaction activity. The synthesis of free-state N5NH2 is a crucial step in all-nitrogen construction and promotes the energetic materials field toward all-nitrogen.