High-Pressure Synthesis of Two Pb₃(C₃N₆) Polymorphs Featuring Fully Deprotonated [C₃N₆]^6- Melaminate Anions

Area of Science:

• Materials Science
• Solid-State Chemistry
• High-Pressure Synthesis

Background:

• Graphitic carbon nitride (g-C3N4), melamine, and derivatives are crucial in catalysis, energy storage, and materials science.
• The synthesis and characterization of novel compounds with unique structural properties are of significant scientific interest.

Purpose of the Study:

• To synthesize and characterize new Pb-C-N compounds under high pressure.
• To investigate the crystal structures and properties of these novel materials.

Main Methods:

• High-pressure synthesis using laser-heated diamond anvil cells.
• Synchrotron single-crystal X-ray diffraction for crystal structure determination.
• Density functional theory (DFT) calculations for electronic structure analysis.

Main Results:

• Two new Pb3(C3N6) polymorphs, tP48-Pb3(C3N6) and hP72-Pb3(C3N6), were synthesized at 40-48 GPa.
• The crystal structures were solved in noncentrosymmetric space groups P4̅21m and P6122, respectively.
• A novel hydrogen-free [C3N6]6- melaminate anion was identified, and the compounds are recoverable to ambient conditions. DFT calculations indicate they are direct narrow band gap semiconductors.

Conclusions:

• The study successfully synthesized and characterized two new Pb3(C3N6) polymorphs containing a novel melaminate anion.
• These materials exhibit semiconductor properties and are recoverable, suggesting potential applications in materials science.
• The findings expand the understanding of high-pressure synthesis and the structural diversity of C-N compounds.