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Crystal structures of 2,4,6-collidinium and 3,5- lutidinium halogenides’ cocrystals with 1,4- diiodotetrafluorobenzene

Halogen and hydrogen bonds are attractive non- covalent interactions between the Lewis base (acceptor) and the Lewis acid region of covalently bonded halogen and hydrogen atoms (donors). Among neutral acceptors (oxygen, nitrogen, halogen, π- electrons, etc.), halogenide anions stand out with their negative charge and sphericity, making them better acceptors with no sterical hinderance which would disrupt the approach of one or more donors of same or different interactions. Although halogen and hydrogen bonds with halogenides were excessively investigated separately in solid state [1, 2], joint research remains scarce. Halogenopyridinium halogenides are an example of simplest systems that encompass the aformentioned [3], followed by their cocrystals with halogen bond donors [4]. However, to the best of our knowledge, no systematic research on systems with neutral molecules as the only donors of halogen bond, cations as the only donors of hydrogen bonds, and halogenides as the only acceptors has been performed to date. In order to examine the potential of halogenide anions to act simlultaneously as acceptors of halogen and hydrogen bonds, we prepared cocrystals of 2, 4, 6-collidinium and 3, 5-lutidinium halogenides with 1, 4-diiodotetrafluorobenzene (14tfib). Each halogenide salt (X = F, Cl, Br, I) and 14tfib were dissolved in ethanol in 1:1 ratio. All crystallization experiments yielded single crystals with the exception of the 3, 5-lutidinium fluoride cocrystal. The obtained single crystals were suitable for X-ray diffraction experiments, which enabled the determination of their molecular and crystal structures. In all the prepared solids, the halogenide anion forms two C−I⋯X– halogen bonds with two 14tfib molecules, and one N−H⋯X– hydrogen bond with a cation. The halogen bonding between 14tfib (a ditopic donor) and halogenides acting as a ditopic acceptors results in infinite chains. Additionally, 14tfib molecules form C−H⋯F−C contacts with cations. Although the cations and halogenides differ, halogen and hydrogen bonded motifs are preserved in spite of the changes in the crystal packing. [1] G. Gilli and P. Gilli, The Nature of the Hydrogen Bond, Oxford University Press, Oxford, 2009. [2] G. Cavallo, P. Metrangolo, R. Milani, T. Pilati, A. Priimagi, G. Resnati and G. Terraneo, Chem. Rev. 116 (2016) 2478–2601. [3] L. Fotović and V. Stilinović, CrystEngComm 22 (2020) 4039–4046. [4] L. Posavec, V. Nemec, V. Stilinović and D. Cinčić, Cryst. Growth. Des. 21 (2021) 6044–6050.

halogen bond ; cocrystal ; collidinium halogenide ; lutidinium halogenide

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