Fe-N system at high pressure reveals a compound featuring polymeric nitrogen chains.

Area of Science:

• Materials Science
• High-Pressure Physics
• Inorganic Chemistry

Background:

• Poly-nitrogen compounds are attractive high energy density materials due to numerous N-N bonds.
• Synthesizing stable, high-nitrogen content materials is challenging as stability and nitrogen content are often mutually exclusive.
• High pressure is a viable method to stabilize these energetic compounds.

Purpose of the Study:

• To synthesize and characterize novel iron-nitrogen compounds under high pressure.
• To investigate the structural properties and stability of these high-nitrogen materials.

Main Methods:

• Direct reaction between iron (Fe) and nitrogen (N2) gas.
• Synthesis conducted in a laser-heated diamond anvil cell at high pressures.
• Crystal structure determination using single-crystal synchrotron X-ray diffraction.

Main Results:

• Three iron-nitrogen compounds were successfully synthesized: Fe3N2, FeN2, and FeN4.
• Fe3N2 (at 50 GPa) is isostructural to Cr3C2.
• FeN2 exhibits a marcasite structure with covalently bonded dinitrogen units.
• FeN4 (at 106 GPa) contains polymeric [N4^2-]n units, identified as catena-poly[tetraz-1-ene-1,4-diyl] anions.

Conclusions:

• The study demonstrates the successful synthesis of unprecedented iron-nitrogen compounds under high pressure.
• The discovery of FeN4 with polymeric nitrogen chains opens new avenues for high-nitrogen energetic materials.
• Structural and theoretical analyses confirm the unique nitrogen bonding in the synthesized materials.