Halogen Bonds of Halotetrafluoropyridines in Crystals and Co-crystals with Benzene and Pyridine.

Mitzel NW, Trapp P, Stammler H-G, et al. Halogen Bonds of Halotetrafluoropyridines in Crystals and Co-crystals with Benzene and Pyridine. Chemistry . 2019;25(30):7339-7350.The structures of the three para-substituted halotetrafluoropyridines with chlorine, bromine and iodine have been determined in the solid state (X-ray diffraction). The structures of these compounds and that of pentafluoropyridine were also determined in the gas phase (electron diffraction). Structures in the solid state of the bromine and iodine derivative exhibit halogen bonding as a structure deter-mining motif. On the way to an investigation on the formation of the halogen bond of halotetrafluoropyridines in the solid state with the stronger Lewis base, e.g. a better halogen-bond acceptor, pyridine, co-crystals of benzene adducts were investigated. These co-crystals show halogen bonding only for the two heavier halotetrafluoropyridi-nes. In the pyridine co-crystals halogen bonding was observed for all three para-halotetrafluoropyridines. The formation of homodimers and heterodimers with pyridine is also supported by quantum-chemical calculations of electron-density topologies and natural-bond orbitals. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim