Fluorine-Enhanced Self-Assembled Bromotetrafluorobenzene–Acetonitrile Systems

The in situ low-temperature single crystal growth technique was used to cocrystallize acetonitrile, CH3CN, with both 1-bromo-2,3,5,6-tetrafluorobenzene, BrC6F4H (1) and 1-bromo-2,3,5,6-tetrafluoro-4-(trifluoromethyl)benzene, BrC6F4CF3 (2). Cocrystals of BrC6F4H·(CH3CN)2 (3) and (BrC6F4CF3)3·(CH3CN)2 (4) were obtained from the liquid mixtures of their components in a 1:5 molar ratio. The structures of these crystals (1 and 2) and cocrystals (3 and 4) were determined by X-ray diffraction at various low temperatures down to 100 K. The bromotetrafluorobenzene molecules in both 2 and 4 are temperature independently disordered, whereas the disorder of the acetonitrile methyl groups is temperature dependent in 3 and associated with the transition to the ordered phase. In 1–4, various types of contacts are present with the main contributions being F···F/C/H and Br···F/H. The interactions in cocrystals 3 and 4 are pronounced in particular. The role played by close and directional C–H···N hydrogen and/or C–Br···N halogen bonds is clearly seen. The intermolecular contacts in 1–4, including their appearance and evolution with temperature, were studied by the Hirshfeld surface analysis supported by quantum-chemical calculations.