High-Pressure and Low-Temperature Polymorphism in C–H···F–C Hydrogen Bonded Monofluorotoluenes
datasetposted on 01.05.2013, 00:00 by Joe Ridout, Michael R. Probert
Three fluorotoluene isomers, all liquids under ambient conditions, have been crystallized using two distinct in situ methods: cryo-crystallization (by decreasing the temperature below the freezing point) and through the application of high-pressure. In all three isomers, crystallization from high-pressure results in different polymorphic forms to those observed at low-temperature: cryo-crystallization and compression of the pure liquid results in the formation of two distinct polymorphs of both 3- and 4-fluorotoluene, but only one polymorph of 2-fluorotoluene. However, compression of a 1:1 mixture of 2- and 3-fluorotoluenes results in a different polymorph of 2-fluorotoluene to that seen when crystallizing the pure liquid. The effects of temperature and pressure on the crystallization process in systems that have only weak C–H···F–C hydrogen bonds are confirmed to be very different.