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We have synthesized the first hydrous sp³-carbonate by laser-heating Ba[CO3], CO2 and H2O in a diamond anvil cell at 40(3) GPa. The crystal structure of Ba[H4C4O10][H3C4O10][H2CO3][HCO3] was determined by synchrotron single crystal X-ray diffraction. The experiments were complemented by DFT-based calculations. This compound is the first example of a carbonate containing both trigonally-coordinated carbon in [CO3]2−-groups and tetrahedrally coordinated carbon in [CO4]4−-groups. The [CO4]4−-groups polymerize by corner-sharing to form pyramidal [C4O10]4−-groups, which can bind three or four hydrogen atoms. As the pyramidal [C4O10]4−-groups are a constituent of several anhydrous sp³-carbonates, we now expect that further high-pressure hydrous carbonates can be obtained. [ABSTRACT FROM AUTHOR]

The anhydrous pyrocarbonate and the first hydrogen pyrocarbonate Li[HC2O5] have been synthesized in a laser‐heated diamond anvil cell at moderate pressures (≈25 ${ \approx 25}$ GPa). The structures of the two compounds have been obtained from single crystal X‐ray diffraction data. Raman spectroscopy and DFT calculations have been employed to further characterize their structure‐property relations. The present results significantly enlarge the group of inorganic pyrocarbonates by the discovery of the hydrogenated pyrocarbonate anion Li[HC2O5]−. In the structure of Li[HC2O5] there is a symmetric O−H−O arrangement at high pressures, which converts to a conventional O−H⋯ ${ \cdots }$ O hydrogen bond upon pressure release. [ABSTRACT FROM AUTHOR]

The anhydrous pyrocarbonate and the first hydrogen pyrocarbonate Li[HC2O5] have been synthesized in a laser‐heated diamond anvil cell at moderate pressures (≈25 ${ \approx 25}$ GPa). The structures of the two compounds have been obtained from single crystal X‐ray diffraction data. Raman spectroscopy and DFT calculations have been employed to further characterize their structure‐property relations. The present results significantly enlarge the group of inorganic pyrocarbonates by the discovery of the hydrogenated pyrocarbonate anion Li[HC2O5]−. In the structure of Li[HC2O5] there is a symmetric O−H−O arrangement at high pressures, which converts to a conventional O−H⋯ ${ \cdots }$ O hydrogen bond upon pressure release. [ABSTRACT FROM AUTHOR]

The anhydrous pyrocarbonate and the first hydrogen pyrocarbonate Li[HC2O5] have been synthesized in a laser‐heated diamond anvil cell at moderate pressures (≈25 ${ \approx 25}$ GPa). The structures of the two compounds have been obtained from single crystal X‐ray diffraction data. Raman spectroscopy and DFT calculations have been employed to further characterize their structure‐property relations. The present results significantly enlarge the group of inorganic pyrocarbonates by the discovery of the hydrogenated pyrocarbonate anion Li[HC2O5]−. In the structure of Li[HC2O5] there is a symmetric O−H−O arrangement at high pressures, which converts to a conventional O−H⋯ ${ \cdots }$ O hydrogen bond upon pressure release. [ABSTRACT FROM AUTHOR]

The anhydrous pyrocarbonate and the first hydrogen pyrocarbonate Li[HC2O5] have been synthesized in a laser‐heated diamond anvil cell at moderate pressures (≈25 ${ \approx 25}$ GPa). The structures of the two compounds have been obtained from single crystal X‐ray diffraction data. Raman spectroscopy and DFT calculations have been employed to further characterize their structure‐property relations. The present results significantly enlarge the group of inorganic pyrocarbonates by the discovery of the hydrogenated pyrocarbonate anion Li[HC2O5]−. In the structure of Li[HC2O5] there is a symmetric O−H−O arrangement at high pressures, which converts to a conventional O−H⋯ ${ \cdots }$ O hydrogen bond upon pressure release. [ABSTRACT FROM AUTHOR]

Understanding the fate of subducted carbonates is a prerequisite for the elucidation of the Earth's deep carbon cycle. Here we show that the concomitant presence of Ca[CO3] with CO2 in a subducting slab very likely results in the formation of an anhydrous mixed pyrocarbonate, Ca 3 C 2 O 5 2 CO 3 , at moderate pressure (≈ 20 GPa) and temperature (≈ 1500 K) conditions. We show that at these conditions Ca 3 C 2 O 5 2 CO 3 can be obtained by reacting Ca[CO3] with CO2 in a laser-heated diamond anvil cell. The crystal structure was obtained from synchrotron-based single crystal X-ray diffraction data. Density Functional Perturbation Theory calculations in combination with experimental Raman spectroscopy results unambiguously confirmed the structural model. The crystal structure of Ca 3 C 2 O 5 2 CO 3 is characterized by the presence of CO 3 2 − - and C 2 O 5 2 − -groups. The results presented here imply that the formation of Ca 3 C 2 O 5 2 CO 3 needs to be taken into account when constructing models of the deep carbon cycle of the Earth. Carbonates are transported into the deep Earth by subduction of the oceanic lithosphere, but the stability fields of subducted carbonates as a function of pressure, temperature, and composition remain incompletely described. Here, the authors synthesize the anhydrous, mixed pyrocarbonate Ca3[C2O5]2[CO3] from Ca[CO3] and CO2 in a laser-heated diamond anvil cell at moderate pressure and elucidate its structural features. [ABSTRACT FROM AUTHOR]

The anhydrous alkaline earth metal carbonate Be(CO3) was synthesized in a laser-heated diamond anvil cell at moderate pressures and temperatures (20(2) GPa and 1500(200) K) by a reaction of BeO with CO2. It crystallizes in the acentric, trigonal space group P3121 with Z = 3. The crystal structure was obtained from synchrotron single crystal X-ray diffraction data and confirmed by density functional theory-based calculations in combination with Raman spectroscopy. Second harmonic generation measurements were employed to verify the acentric space group symmetry. The crystal structure of Be(CO3) is characterized by the presence of isolated [CO3]2−-groups and BeO4-tetrahedra. This is a new structure type and such a topology has not been observed in carbonates before. Be(CO3) can be recovered to ambient conditions and is not undergoing a phase transition during decompression. [ABSTRACT FROM AUTHOR]

The anhydrous alkaline earth metal carbonate Be(CO3) was synthesized in a laser-heated diamond anvil cell at moderate pressures and temperatures (20(2) GPa and 1500(200) K) by a reaction of BeO with CO2. It crystallizes in the acentric, trigonal space group P3121 with Z = 3. The crystal structure was obtained from synchrotron single crystal X-ray diffraction data and confirmed by density functional theory-based calculations in combination with Raman spectroscopy. Second harmonic generation measurements were employed to verify the acentric space group symmetry. The crystal structure of Be(CO3) is characterized by the presence of isolated [CO3]2−-groups and BeO4-tetrahedra. This is a new structure type and such a topology has not been observed in carbonates before. Be(CO3) can be recovered to ambient conditions and is not undergoing a phase transition during decompression. [ABSTRACT FROM AUTHOR]

The inorganic pyrocarbonate salt Na2[C2O5] crystallizes in the acentric, monoclinic space group P21 with Z = 2. It contains monovalent alkali metal cations together with isolated pyrocarbonate anions. The [C2O5]2−-groups consist of two planar [CO3]2−-groups which are slightly tilted with respect to each other around the bridging oxygen atom. Na2[C2O5] was synthesized in a laser-heated diamond anvil cell at 20(2) GPa by heating a mixture of Na2[CO3] + CO2 to ≈800(200) K. Its crystal structure was obtained by single crystal synchrotron X-ray diffraction and confirmed by density functional theory-based calculations in combination with Raman spectroscopy. Second harmonic generation measurements verified the acentric space group symmetry. The crystal structure is characterized by alternating layers of Na+-cations and [C2O5]2−-complex anions. [ABSTRACT FROM AUTHOR]

The inorganic pyrocarbonate salt Na2[C2O5] crystallizes in the acentric, monoclinic space group P21 with Z = 2. It contains monovalent alkali metal cations together with isolated pyrocarbonate anions. The [C2O5]2−-groups consist of two planar [CO3]2−-groups which are slightly tilted with respect to each other around the bridging oxygen atom. Na2[C2O5] was synthesized in a laser-heated diamond anvil cell at 20(2) GPa by heating a mixture of Na2[CO3] + CO2 to ≈800(200) K. Its crystal structure was obtained by single crystal synchrotron X-ray diffraction and confirmed by density functional theory-based calculations in combination with Raman spectroscopy. Second harmonic generation measurements verified the acentric space group symmetry. The crystal structure is characterized by alternating layers of Na+-cations and [C2O5]2−-complex anions. [ABSTRACT FROM AUTHOR]

The inorganic pyrocarbonate salt Ba[C2O5] contains twisted pyrocarbonate anions ([C2O5]2−), an atomic arrangement previously not observed in other pyrocarbonates. This unexpected additional structural degree of freedom points towards an enlarged chemical variability in this novel group of compounds. Ba[C2O5] was synthesized in a laser-heated diamond anvil cell at 30(2) GPa by heating a mixture of Ba[CO3] + CO2 to ≈ 1500(200) K. Its crystal structure was solved from single crystal synchrotron X-ray diffraction data and confirmed by density functional theory-based calculations. The two planar [CO3]2−-groups of the [C2O5]2−-anion are strongly twisted around the bridging oxygen atom. Ba[C2O5] has been observed in the pressure range of 5–30 GPa, where its symmetry is P6/m with Z = 12. [ABSTRACT FROM AUTHOR]

High‐pressure single‐crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator‐to‐semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory‐based calculations show that at ambient conditions the channels in the structure host the stereochemically‐active Pb 6s2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands. [ABSTRACT FROM AUTHOR]

High‐pressure single‐crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator‐to‐semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory‐based calculations show that at ambient conditions the channels in the structure host the stereochemically‐active Pb 6s2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands. [ABSTRACT FROM AUTHOR]