Concomitant cocrystal and salt: no interconversion in the solid state.

A cocrystal and a molecular salt of β-alanine and DL-tartaric acid, C3H8NO2+·C4H4O6-, of the same chemical composition, were studied over a wide temperature range by single-crystal and powder X-ray diffraction. Neither the interconversion between the two phases nor any polymorphic transitions were observed in the temperature range from 100 K to the melting points. This contrasts with the solvent-mediated phase transition from the salt to the cocrystal in a slurry that has been documented earlier.