Crystallisation of paracetamol and piperazine from ethanol at a pressure of 0.57 GPa produced an ethanol solvate of a 2:1 co-crystal of paracetamol:piperazine. This contrasts with crystallisation from ethanol at ambient pressure for which only an unsolvated 2:1 co-crystal of paracetamol:piperazine has been obtained. The hydrogen bonding arrangements of the two compounds are very different and a striking feature of the solvate is the presence of an unusually short hydrogen bond between the phenolic and amine groups.
Oswald, I. D. H., & Pulham, C. R. (2008). Co-crystallisation at high pressure - an additional tool for the preparation and study of co-crystals. CrystEngComm, 10(9), 1114-1116. https://doi.org/10.1039/b805591b