Keele Research Repository

The project investigates the reactions of selected aromatic nitrogen compounds with selected di- and interhalogens in order to obtain crystalline N···I halogen-bonded complexes according to the equation:
A + B → AB

where reactant A is a pyridine derivative (3,5- difluoropyridine, 3,5-dichloropyridine, 2,6-dichloropyridine, 2,6-dimethoxypyridine, 4-methoxypyridine, 3-fluoropyridine, 2-fluoro-3-iodopyridine, 2-fluoro-4 -iodopyridine, 2-fluoro-5-iodopyridine, 2-cyanopyridine) or a heterocyclic compound (quinoxaline, 2-chloroquinoline, 1,10 phenanthroline). Reactant B represents iodine monochloride, iodine monobromide or iodine, while AB is the product. All the reactions were carried out in 1:1 molar ratio in ethanol as a solvent, starting at room temperature and subsequently cooling the reaction mixture down to 0 °C. Products can be classified into two groups, the first one (the majority of samples) consists of N···I halogen-bonded complexes with the crystals that form almost instantaneously after the reagents are mixed. These crystals are stable at the room temperature and have a relatively high melting point.
The second group includes pyridinium ion-polyhalogen ion complexes and reactant polymorphs. The formation of these crystals requires placing the reaction mixture in the freezer for more than 12 hours or cooling the reaction mixture down to -45 °C or -75 °C. All the crystalline products were characterised by ATR-FTIR spectroscopy, UV-Visible spectroscopy and where possible due to crystal size, by single-crystal X-ray diffraction.