Non-covalent interactions in solid p-C6F4Cl2 and C6F5Cl

This study investigates the crystal structure and phase behaviour of two organofluorine aromatic compounds, para-dichlorotetrafluorobenzene (p-C ₆F ₄Cl ₂) and chloropentafluorobenzene (C ₆F ₅Cl), 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 p-C ₆F ₄Cl ₂ showed no solid-state phase transitions, C ₆F ₅Cl 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 C ₆F ₅Cl is due to a change from twofold disorder to an antiferroelectric arrangement of the molecular dipole moment. Phase II of C ₆F ₅Cl is isomorphous to the structure of p-C ₆F ₄Cl ₂. A comparison of the different solid-state structures of mono- and para-di-halide-substituted hexafluorobenzenes is given.