Single crystal diffraction study of Ba[H4C4O10][H3C4O10][H2CO3][HCO3], a hydrous mixed sp2/sp3-carbonate

Abstract

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.