Stabilization of the [C₂N₅]^7- Anion in Recoverable High-Pressure Eu₄Fe_0.864(6)(C₂N₅)₂ Pyronitridocarbonate

Area of Science:

• Materials Science
• Inorganic Chemistry
• High-Pressure Synthesis

Background:

• Nitrogen-rich anions are challenging to synthesize under ambient conditions.
• Extreme conditions, such as high pressure, can stabilize unusual chemical species.
• Previous research has not explored the synthesis of pyronitridocarbonates or oxygen-free rare-earth guanidinates.

Purpose of the Study:

• To synthesize novel nitrogen-rich carbon-nitrogen anions under extreme conditions.
• To characterize the crystal structures and chemical bonding of newly synthesized compounds.
• To investigate the recoverability and stability of these materials at ambient conditions.

Main Methods:

• Direct reaction between europium azide (Eu(N3)2) and europium carbide (EuC2) with iron (Fe) in a laser-heated diamond anvil cell (DAC).
• Synthesis conducted at extreme pressures of 50(3) GPa.
• Crystal structure determination using synchrotron single-crystal X-ray diffraction (SCXRD).
• Validation of crystal structures and electronic structure analysis using density functional theory (DFT) calculations.

Main Results:

• Successfully synthesized the first inorganic hydrogen-free pyronitridocarbonate, Eu4Fe_x(C2N5)2 (x = 0.864(6)), featuring novel [C2N5]7- anions.
• Synthesized the first stoichiometric oxygen-free rare-earth metal guanidinate, Eu5(CN3)3.
• Eu4Fe_x(C2N5)2 was found to be recoverable to near-ambient pressures.
• Upon recovery, half of the [C2N5]7- units decomposed into guanidinate [CN3]5- and carbodiimide [CN2]2- anions.

Conclusions:

• Established a synthetic pathway to a new class of inorganic nitridocarbonates.
• Demonstrated the feasibility of synthesizing highly charged, novel anions under high pressure.
• Highlighted the potential for discovering new materials with unique properties through extreme condition synthesis.