Temperature-triggered phase transition in pyridazine hexafluorophosphate

The pyridazine hexafluorophosphate [C4H5N2]+[PF6]− (1) undergoes a reversible phase transition around 140 K, which was confirmed by the DSC measurement. Variable-temperature crystal structures determined at 293 K and 93 K show that the compound crystallizes in the same space group P21/c, indicating that 1 undergoes an iso-structural phase transition. As the temperature decreases, dielectric measurement of the title compound shows no significant change around the phase transition temperature. Classic hydrogen bonds are found between molecules at 293 K and 93 K with similar packing arrangement. The most distinct difference between the low temperature and room temperature structures is the order–disorder transition of the hexafluorophosphate anion, which is probably the driving force of the phase transition.

The most distinct difference between the low-temperature and room-temperature structures is the order–disorder transition of the hexafluorophosphate anion, which is probably the driving force of the phase transition.Figure optionsDownload as PowerPoint slide