Halogen-bonded halide networks from chiral neutral spacers

Abstract

Chiral, ditopic, halogen bond donor molecules are prepared from the reaction of C₆F₅I with three different enantiopure chiral diols, namely, (R,R)-2,3-butanediol, (R,R)-hydrobenzoin and S-binaphthol, with displacement of the fluorine atom para to the iodine atom in C₆F₅I, to give (R,R)-1, (R,R)-2 and (S)-3, respectively. Chiral, halogen-bonded networks with halide anions are investigated upon co-crystallisation of (R,R)-1 with (Et₃S⁺, I⁻), (Et₄N⁺, Br⁻), (n-Bu₄N⁺, Br⁻) and (n-Pe₄N⁺, Br⁻). In the first three salts with 1 : 1 stoichiometry, the halide anions are coordinated by two iodine atoms with short I⋯X⁻ (X⁻ = I⁻, Br⁻) distances and acute (75–80°) I⋯X⁻⋯I angles, leading to the formation of chains, eventually organized into helices around twofold screw axes as in [(R,R)-1]·[Bu₄NBr]. Co-crystallisation with tetrapentylammonium bromide affords a 2 : 1 stoichiometry salt, [(R,R)-1]₂·[Pe₄NBr], with a fourfold coordination around the Br⁻ anion and the formation of a square lattice network built out of interconnected helices.