The curious case of proton migration under pressure in the malonic acid and 4,4′-bi­pyridine cocrystal

Patyk-Kaźmierczak, E.; Izquierdo-Ruiz, F.; Lobato, A.; Kaźmierczak, M.; Moszczyńska, I.; Olejniczak, A.; Recio, J.M.

doi:10.1107/S2052252524000344

Figure 3
Pressure dependence of the C=O and C—O bond lengths (black triangles and red circles, respectively), as well as the O⋯N and C⋯N distances (blue squares and green diamonds, respectively). Full symbols joined with solid lines mark the compression series for the C2/c phase and the data for the carboxylic group C12(=O2)O1H of the P2₁/c phase. Open symbols connected by dotted lines mark the decompression series for the C2/c phase and data for the carboxylic group C14(=O4)O3H of the P2₁/c phase. The lower graph shows the difference in the length of carbon–oxygen bonds of the carboxylic group, with a dashed red horizontal line marking the difference limit of 0.04 Å. All values were calculated using ShelXL (Sheldrick, 2015a