ABSTRACT
We have synthesized Pb[C2O5], an inorganic pyrocarbonate salt, in a laser-heated diamond anvil cell (LH-DAC) at 30 GPa by heating a Pb[CO3] + CO2 mixture to ≈2000(200) K. Inorganic pyrocarbonates contain isolated [C2O5]2- groups without functional groups attached. The [C2O5]2- groups consist of two oxygen-sharing [CO3]3- groups. Pb[C2O5] was characterized by synchrotron-based single-crystal structure refinement, Raman spectroscopy, and density functional theory calculations. Pb[C2O5] is isostructural to Sr[C2O5] and crystallizes in the monoclinic space group P21/c with Z = 4. The synthesis of Pb[C2O5] demonstrates that, just like in other carbonates, cation substitution is possible and that therefore inorganic pyrocarbonates are a novel family of carbonates, in addition to the established sp2 and sp3 carbonates.
ABSTRACT
The synthesis of a novel type of carbonate, namely of the inorganic pyrocarbonate salt Sr[C2O5], which contains isolated [C2O5]2--groups, significantly extends the crystal chemistry of inorganic carbonates beyond the established sp2- and sp3-carbonates. We synthesized Sr[C2O5] in a laser-heated diamond anvil cell by reacting Sr[CO3] with CO2. By single crystal synchrotron diffraction, Raman spectroscopy, and density functional theory (DFT) calculations, we show that it is a pyrocarbonate salt. Sr[C2O5] is the first member of a novel family of inorganic carbonates. We predict, based on DFT calculations, that further inorganic pyrocarbonates can be obtained and that these will be relevant to geoscience and may provide a better understanding of reactions converting CO2 into useful inorganic compounds.
ABSTRACT
We have synthesized the orthocarbonate Sr3[CO4]O in a laser-heated diamond anvil cell at 20 and 30 GPa by heating to ≈3000 (300) K. Afterward, we recovered the orthocarbonate with [CO4]4- groups at ambient conditions. Single-crystal diffraction shows the presence of [CO4]4- groups, i.e., sp3-hybridized carbon tetrahedrally coordinated by covalently bound oxygen atoms. The [CO4]4- tetrahedra are located in a cage formed by corner-sharing OSr6 octahedra, i.e., octahedra with oxygen as a central ion, forming an antiperovskite-type structure. At high pressures, the octahedra are nearly ideal and slightly rotated. The high-pressure phase is tetragonal (I4/mcm). Upon pressure release, there is a phase transition with a symmetry lowering to an orthorhombic phase (Pnma), where the octahedra tilt and deform slightly.
