Inorganic Tricarbonate : High-Pressure Synthesis and Structure of K₂C₃O₇

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Aslandukov, Andrii ; Aslandukova, Alena ; Akbar, Fariia Iasmin ; Yin, Yuqing ; Akilli, Ridvan ; Garbarino, Gaston ; Spahr, Dominik ; Winkler, Bjoern ; Bykov, Maxim ; Dubrovinskaia, Natalia ; Dubrovinsky, Leonid:
Inorganic Tricarbonate : High-Pressure Synthesis and Structure of K₂C₃O₇.
In: Journal of the American Chemical Society. (24 März 2026) .
ISSN 1520-5126
DOI: https://doi.org/10.1021/jacs.5c19614

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Abstract

The synthesis of carbonates with novel types of anions is important for geoscience, chemistry, and materials science. Herein, we present the first inorganic tricarbonate salt, K2C3O7, discovered in laser-heated diamond anvil cells at 55(3) and 45(2) GPa. The crystal structure of K2C3O7 was determined in situ by using synchrotron single-crystal X-ray diffraction from a polycrystalline sample. It features nonplanar [C3O7]2– anions, which consist of three corner-sharing planar CO3 groups rotated relative to one another. This anion extends the homologous series of sp2-carbonates: [CO3]2–─[C2O5]2–─[C3O7]2–. Raman spectroscopy establishes the characteristic vibrational fingerprint of the [C3O7]2– anion. Density functional theory (DFT) calculations corroborate the experimental results and suggest a thermodynamic stability of K2C3O7 between 10 and 55 GPa. DFT calculations predict a phase transition between 80 and 90 GPa associated with polymerization of the [C3O7]2– groups, accompanied by a change in the coordination polyhedra of two carbon atoms from triangles to tetrahedra. These results imply that other sp2-and mixed sp2/sp3-carbonates might be stabilized at a high pressure.The synthesis of carbonates with novel types of anions is important for geoscience, chemistry, and materials science. Herein, we present the first inorganic tricarbonate salt, K2C3O7, discovered in laser-heated diamond anvil cells at 55(3) and 45(2) GPa. The crystal structure of K2C3O7 was determined in situ by using synchrotron single-crystal X-ray diffraction from a polycrystalline sample. It features nonplanar [C3O7]2– anions, which consist of three corner-sharing planar CO3 groups rotated relative to one another. This anion extends the homologous series of sp2-carbonates: [CO3]2–─[C2O5]2–─[C3O7]2–. Raman spectroscopy establishes the characteristic vibrational fingerprint of the [C3O7]2– anion. Density functional theory (DFT) calculations corroborate the experimental results and suggest a thermodynamic stability of K2C3O7 between 10 and 55 GPa. DFT calculations predict a phase transition between 80 and 90 GPa associated with polymerization of the [C3O7]2– groups, accompanied by a change in the coordination polyhedra of two carbon atoms from triangles to tetrahedra. These results imply that other sp2-and mixed sp2/sp3-carbonates might be stabilized at a high pressure.