Inorganic Tricarbonate: High-Pressure Synthesis and Structure of K₂C₃O₇.

Area of Science:

• Geoscience
• Chemistry
• Materials Science

Background:

• The synthesis of novel carbonate anions is crucial for advancing geoscience, chemistry, and materials science.
• Previous research has focused on simpler carbonate structures, leaving complex anions unexplored.

Purpose of the Study:

• To synthesize and characterize a novel inorganic tricarbonate salt.
• To investigate the structural and thermodynamic properties of this new compound under high pressure.

Main Methods:

• High-pressure synthesis using laser-heated diamond anvil cells.
• In situ crystal structure determination via synchrotron single-crystal X-ray diffraction.
• Vibrational fingerprinting using Raman spectroscopy.
• Theoretical validation using density functional theory (DFT) calculations.

Main Results:

• The first inorganic tricarbonate salt, K2C3O7, was successfully synthesized at high pressures (45-55 GPa).
• The crystal structure reveals nonplanar [C3O7]2- anions, extending the sp2-carbonate homologous series.
• Raman spectroscopy and DFT calculations confirmed the anion's structure and thermodynamic stability (10-55 GPa).

Conclusions:

• The discovery of K2C3O7 expands the known family of inorganic carbonates.
• High pressure can stabilize novel carbonate structures with complex anions.
• DFT predicts a phase transition at 80-90 GPa, suggesting potential for other high-pressure carbonate stabilization.