The Crystal Structure of Carbonic Acid

• Main Authors: Benz, Sebastian, Chen, Da, Möller, Andreas, Hofmann, Michael, Schnieders, David, Dronskowski, Richard
• Other Authors: Deutsche Forschungsgemeinschaft
• Format: Other/Unknown Material
• Language: unknown
• Published: American Chemical Society (ACS) 2022
• Subjects: Carbonic acid
• Online Access: http://dx.doi.org/10.26434/chemrxiv-2022-vw55l; https://chemrxiv.org/engage/api-gateway/chemrxiv/assets/orp/resource/item/62963bf197e76a533fc0a2bd/original/the-crystal-structure-of-carbonic-acid.pdf

Ubiquitous carbonic acid, H2CO3, a key molecule in biochemistry, geochemistry, and also extraterrestrial chemistry, is known from a plethora of physicochemical studies. Its crystal structure has now been determined from neutron-diffraction data on a deuterated sample in a specially built hybrid clamped cell. At 1.85 GPa, D2CO3 crystallizes in the monoclinic space group P21/c with a = 5.392(2), b = 6.661(4), c = 5.690(1) Å, β = 92.66(3)°, Z = 4, with one symmetry-inequivalent anti-anti shaped D2CO3 molecule forming dimers, as previously predicted. Quantum chemistry evidences π bonding within the CO3 molecular core, very strong hydrogen bonding between the molecules, and a massive influence of the crystal field on all bonds; phonon calculations emphasize the locality of the vibrations, being rather insensitive to the extended structure.