Anion influence on the packing of 1,3-bis(4-ethynyl-3-iodopyridinium)-benzene halogen bond receptors

Rigid and directional arylethynyl scaffolds have been widely successful across diverse areas of chemistry. Utilizing this platform, we present three new structures of a dicationic 1,3-bis(4-ethynyl-3-iodopyridinium)-benzene halogen bonding receptor with tetrafluoroborate, nitrate, and hydrogen sulfate. Structural analysis focused on the receptor conformation, anion shape, solvation, and long range packing of these systems. Coupled with our previously reported structures, we concluded that anions can be classified as building units within this family of halogen bonding receptors. Two kinds of antiparallel dimers were observed for these dicationic receptors. An off-centered species was most frequent, present among geometrically diverse anions and assorted receptor conformations. In contrast, the centered antiparallel dimers were observed with receptors adopting a bidentate conformation in the solid-state. While anions support the solid-state formation of dimers, the molecular geometry and characteristics (planarity, rigidity, and directionality) of arylethynyl systems increase the likelihood of dimer formation by limiting efficient packing arrangements. The significantly larger cation may have considerable influence on the solid-state packing, as similar cationic arylethynyl systems also display these dimers.