Crystal structure of silver pentazolates AgN₅ and AgN₆

Area of Science:

• Materials Science
• Inorganic Chemistry
• Computational Chemistry

Background:

• Silver pentazolate, a high energy density material, has been synthesized but its crystal structure remains undetermined due to sensitivity.
• Understanding the structural properties of energetic materials is crucial for their synthesis and application.

Purpose of the Study:

• To predict and characterize novel silver-nitrogen crystalline compounds under varying pressures.
• To elucidate the stability and structural features of potential high energy density materials.
• To provide data aiding experimental identification of these compounds.

Main Methods:

• First-principles evolutionary crystal structure searching with variable stoichiometry was employed.
• Calculations were performed for conditions ranging from ambient to 100 GPa.
• Thermodynamic stability and formation enthalpies were computed.

Main Results:

• Newly discovered AgN5 and AgN6 were identified as the only thermodynamically stable silver-nitrogen compounds between 42 and 80 GPa.
• AgN6 contains both cyclo-N5- anions and N2 molecules, distinguishing it from AgN5.
• Both AgN5 and AgN6 are metastable at ambient conditions with positive formation enthalpies.
• Enhanced aromaticity due to charge transfer from silver to nitrogen rings contributes to cyclo-N5- stability.
• Calculated Raman spectra for AgN5 align with experimental measurements.

Conclusions:

• The study successfully predicted novel silver-nitrogen compounds, AgN5 and AgN6, with potential for high energy density applications.
• The findings provide critical insights into the stability and structural characteristics of these energetic materials under pressure.
• The calculated Raman spectra offer valuable guidance for experimental verification and identification.