Single crystal diffraction study of Ba[HCO][HCO][HCO][HCO], a hydrous mixed sp/sp-carbonate.

We have synthesized the first hydrous sp-carbonate by laser-heating Ba[CO], CO and HO in a diamond anvil cell at 40(3) GPa. The crystal structure of Ba[HCO][HCO][HCO][HCO] was determined by synchrotron single crystal X-ray diffraction. The experiments were complemented by DFT-based calculations.

High-Pressure Synthesis of an Iron Carbonate, Fe[CO].

We synthesized an iron carbonate, Fe[CO], by reacting FeO with CO at high temperatures and pressures of approximately 33(3) GPa. The structure was solved by single-crystal X-ray diffraction. Full geometry optimizations based on density functional theory reproduced the crystal structure.

Ca[CO][CO] is a pyrocarbonate which can be formed at p, T-conditions prevalent in the Earth's transition zone.

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[CO] with CO in a subducting slab very likely results in the formation of an anhydrous mixed pyrocarbonate, , at moderate pressure ( ≈ 20 GPa) and temperature ( ≈ 1500 K) conditions. We show that at these conditions can be obtained by reacting Ca[CO] with CO in a laser-heated diamond anvil cell.

6-Fold-Coordinated Beryllium in Calcite-Type Be[CO].

The anhydrous beryllium carbonate Be[CO] with calcite-type crystal structure was obtained by a reaction of BeO with CO in a laser-heated diamond anvil cell at pressures between 30 GPa and 80 GPa and elevated temperatures. Its calcite-type crystal structure (3̅ with = 6) is characterized by 6-fold-coordinated beryllium atoms forming [BeO] octahedra and by trigonal-planar [CO] groups. The crystal structure was determined by synchrotron-based single-crystal X-ray diffraction and confirmed by density-functional-theory-based calculations in combination with experimental Raman spectroscopy.