Halogen Derivatives of Toluene under High Pressure

Crystal structures of 4-chlorotoluene and 4-bromotoluene under high pressure have been determined. In the case of 4-chlorotoluene, two high-pressure forms of this compound exist in the same range of pressure. However, no direct phase transition between them at high pressure has been observed. It has been confirmed that the symmetry of the high-pressure structure of 4-iodotoluene is the same as its symmetry determined at low temperature. Finally, we have extended the pressure range in which the high-pressure structure of 4-fluorotoluene was investigated. We have found that the space group previously reported (Pna21) as the proper one for the high-pressure form of 4-fluorotoluene is not correct as Pnma seems to be a better choice. 4-Bromotoluene formed only P21/c space group crystals isostructural with the α form of 4-chlorotoluene. For the single crystals of 4-iodotoluene under high pressure, we only managed to determine the cell parameters. These values correspond with those determined previously at low temperature measurement.