Trans-4-(trifluoromethyl) cinnamic acid: Structural characterisation and crystallographic investigation into the temperature induced phase transition

The crystal structure of trans-4-(trifluoromethyl) cinnamic acid (1) has been determined in the triclinic space group P1(-). Differential scanning calorimetry showed that 1 undergoes a single fully reversible temperature induced phase transition at around 132/131 K (cooling/heating). Single crystal structure determinations, carried out at 200, 145 and 120 K, revealed that the volume of the unit cell quadruples as the crystal is cooled through the phase transition with Z' increasing from 2 to 8. The structures are stabilised by the presence of O-H center dot center dot center dot O hydrogen bonding and C-H center dot center dot center dot O interactions. The results of DSC, single crystal and powder X-ray diffraction studies on 1 are reported.