Synthesis and Structure of Pb[C 2 O 5 ]: An Inorganic Pyrocarbonate Salt.

We have synthesized Pb[C 2 O 5 ], an inorganic pyrocarbonate salt, in a laser-heated diamond anvil cell (LH-DAC) at 30 GPa by heating a Pb[CO 3 ] + CO 2 mixture to ≈2000(200) K. Inorganic pyrocarbonates contain isolated [C 2 O 5 ] 2- groups without functional groups attached. The [C 2 O 5 ] 2- groups consist of two oxygen-sharing [CO 3 ] 3- groups. Pb[C 2 O 5 ] was characterized by synchrotron-based single-crystal structure refinement, Raman spectroscopy, and density functional theory calculations. Pb[C 2 O 5 ] is isostructural to Sr[C 2 O 5 ] and crystallizes in the monoclinic space group P 2 1 / c with Z = 4. The synthesis of Pb[C 2 O 5 ] 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 sp 2 and sp 3 carbonates.