Non-covalent interactions in solid -CFCl and CFCl.

This study investigates the crystal structure and phase behaviour of two organofluorine aromatic compounds, -dichlorotetrafluorobenzene (-CFCl) and chloropentafluorobenzene (CFCl), with a focus on solid-state phase transitions and non-covalent interactions. The thermal and structural properties of these compounds were investigated using a combination of differential scanning calorimetry (DSC), variable-temperature powder X-ray diffraction (VT-PXRD), and single-crystal X-ray diffraction (SXD). While -CFCl showed no solid-state phase transitions, CFCl exhibited three solid-state phases, including a reversible solid-solid transition at low temperature and an elusive transition just below the melt. The phase II-III transition in CFCl is due to a change from twofold disorder to an antiferroelectric arrangement of the molecular dipole moment. Phase II of CFCl is isomorphous to the structure of -CFCl. A comparison of the different solid-state structures of mono- and -di-halide-substituted hexafluorobenzenes is given.