Formation of Benzimidazoisoquinolinium and Benzimidazoisoindolinum Cyclic Systems by the Reaction of 2‑(2-Alkynylphenyl)benzimidazoles with Iodine and Iodine–Iodine Interaction Including Halogen Bonding in Their Crystal Structures

The reaction of 2-(2-alkynyl­phenyl)­benz­[d]­imidazoles with molecular iodine constructed 5- and 6-membered rings as novel organic salts in high yield. The constituted number of ring systems was influenced by the substituent at the triple bond: 6-membered rings were formed from compounds bearing aryl substituents, whereas 5-membered ones were obtained from compounds with hydrogen or alkyl substituents. The products were obtained with triiodide as a counteranion; however, compounds with iodide were also obtainable under certain conditions. We also revealed that they had an iodine–iodine interaction included in halogen bonding between an iodo moiety of the cation and a triiodide or iodide of the counteranion. The iodine–iodine interaction was formed with greater preference than the electrostatic interaction between the cationic atom and triiodide or iodide.