Modulation of Rotational Dynamics in Halogen-Bonded Cocrystalline Solids

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-C6F4Cl2) and chloropentafluorobenzene (C6F5Cl), 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-C6F4Cl2 showed no solid-state phase transitions, C6F5Cl 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 C6F5Cl is due to a change from twofold disorder to an antiferroelectric arrangement of the molecular dipole moment. Phase II of C6F5Cl is isomorphous to the structure of p-C6F4Cl2. A comparison of the different solid-state structures of mono- and para-di-halide-substituted hexafluorobenzenes is given.

σ-Hole Effect-Induced Electroluminescence of Halogen Cocrystals for Determination of Iodide in Seawater

Developing new electrochemiluminescence (ECL) luminators with high stability, wide applicability, and strong designability is of great strategic significance to promote the ECL field to the frontier. Here, driven by the I···N bond, 1,3,5-trifluoro-2,4,6-triiodobenzene (TFTI) and 2,4,6-trimethyl-1,3,5-triazine (TMT) self-assembled into a novel halogen cocrystal (TFTI-TMT) through slow solution volatilization. Significant difference of charge density existed between the N atoms on TMT and the σ-hole of the I atoms on TFTI. Upon the induction of σ-hole effect, high-speed and spontaneous charge transferring from TMT to the σ-hole of TFTI occurred, stimulating exciting ECL signals. Besides, the σ-hole of the I atoms could capture iodine ions specifically, which blocked the original charge transfer from the N atoms to the σ-hole, causing the ECL signal of TFTI-TMT to undergo a quenching rate as high as 92.9%. Excitingly, the ECL sensing of TFTI-TMT toward I- possessed a wide linear range (10-5000 nM) and ultralow detection limit (3 nM) in a real water sample. The halogen cocrystal strategy makes σ-hole a remarkable new viewpoint of ECL luminator design and enables ECL analysis technology to contribute to addressing the environmental and health threats posed by iodide pollution.