Ambient-Pressure Recoverable Polynitrogen Solids Assembled by Pentazolate Rings with High Energy Density.

Crystal structure predictions and first-principles calculations were used to predict three polynitrogen solids ( aP 8-N, aP 12-N, and oP 24-N) that possess competitive enthalpies as compared to the synthesized open-chain N 8 phase at pressures in the range of 0-60 GPa. aP 8-N, aP 12-N, and oP 24-N contain edge-shared, N 2 -linked, and N-bridged pentazolate rings and form molecular N 8 , molecular N 12 , and quasi-one-dimensional N ∞ ribbons, respectively. The calculations of formation enthalpies show that the three polynitrogen solids can be synthesized by compressing cyclo-N 5 salts in hydrogen-saturated environments. Molecular simulations suggest that the three polynitrogen solids have the ability of quench recoverability under ambient conditions once being synthesized at high pressure. With estimated energy densities in the range of 5.6-6.5 kJ/g, these three polynitrogen phases show notable promise for applications as high-energy-density materials.