Moderate Pressure Stabilized Pentazolate Cyclo-N₅^- Anion in Zn(N₅)₂ Salt

Stabilization of the pentazole anion only by acidic circumstances entrapment impedes the realization of a full-nitrogen substance; however, compression of nitrogen-rich nitrides has been recommend as an alternative way that has more controllable advantages to acquire the atomic nitrogen states. Through the structure searches are in conjunction with first-principle calculations, moderate pressure stabilized nitrogen-rich zinc nitrides with abundant extended nitrogen structures, e.g., cyclo-N₅, infinite -(N₄)- chains, three-point stars N(N₃), and N₂ dumbbells, are predicted. The resonance between alternating σ bonds and π bonds in poly nitrogen sublattices takes charge of the coexistence of single and double bonds. The Zn(N₅)₂ salt has a noteworthy energy density (6.57 kJ/g) among the reported binary metal nitrides and synthesized pentazolate hydrates. An excellent Vicker's hardness (34 GPa) and detonation performance is unraveled. Although Zn(N₅)₂ salt is not expected to be recoverable at ambient conditions, it is worth noting that Zn(N₅)₂ is found to be stable at a very low pressure of ∼30 GPa, which is only half of those pressures required to synthesize CsN₅. We clarified that the metal-centering octahedral pentazolate framework was entrapped by dual ionic-covalent bonds. More importantly, the covalent bonding can effectively enhance the chemical insensitivity and thermal stability, further preventing the autodecomposition of monatomic solid N₅^- anions into dinitrogen. Meanwhile, a unique topological pseudogap that attached to a metastable phase of ZnN₄ salt is exposed for the first time, due to the dual effects of strong covalent sp² hybridization interaction and the origin of ionic states.