Perhalogenated Hydroxyl Aryl Imines as Halogen Bond Donors in Cocrystals with Nitrogen-Containing Acceptors

In this study, we investigate the halogen bond donor potential of two novel halogen bond donors, peripherally perhalogenated imines derived from 2,3,5,6-tetrafluoro-4-iodoanilline, and salicylaldehyde or ortho-vanillin. A series of six cocrystals derived from synthesized imines and selected ditopic nitrogen bases (4,4′-bipyridine, 1,2-bis(4-pyridyl)ethane and 1,4-diazabicyclo[2.2.2]octane) have been prepared by both liquid-assisted grinding and crystallization from solution. Crystal structure determination based on single crystal X-ray diffraction has revealed that all six cocrystals exhibit molecular trimers containing two imine molecules and one acceptor molecule interconnected by I···N halogen bonds. Solid-state thermochromic studies revealed that both Schiff bases and their cocrystals show reversible thermochromic behavior that is not accompanied by significant changes in molecular structure and crystal packing.