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

Abstract

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 orthovanillin. 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.

Evaluation of Concomitant Halogen and Pnictogen Bonds in Cocrystals of Imines Derived from 2-Nitrobenzaldehyde and 4-Haloaniline

“…Traditionally, imines have been studied as ligands in coordination compounds, as model systems for study of tautomerism, − biological macromolecules, synthetic intermediates, and anion receptors . More recently, however, imines and their coordination compounds also started drawing attention in crystal engineering, particularly halogen-bonded cocrystals. − Mostly, this includes functionalizing the imine with halogen bond acceptor groups, such as a piperidinyl ,, or nitrile nitrogen atom or a carbonyl, , methoxy, ,, hydroxyl, − morpholinyl, , or nitro oxygen atom, although there are few studies where appropriately functionalized imines have been used as halogen bond donors. , Thus, a combination of a nitro group and halogen atoms in the same imine could afford data on the interrelationship between NO 2 ···NO 2 interactions and a halogen bond. To the best of our knowledge, only one systematic study of a series of such imines combining nitro groups and iodine has been published to date. , Within the studied series of compounds (nine nitrobenzylideneiodoaniline isomers, some appearing in several polymorphic forms), the I···O nitro halogen bond was observed in three and the I···N imine halogen bond in one structure, while the NO 2 ···NO 2 interactions were also found in only one structure.…”