Charge-assisted chalcogen bonding in 2-(4-substituted benzoyl)thiazolo[3,2-a]pyridin-4-ium bromides

Abstract

A series of 2-(4-substituted benzoyl)thiazolo[3,2-a]pyridin-4-ium bromides [−OCH3 (1), –H (2), –F (3), −Cl (4)] was obtained by the heterocyclization reaction of the corresponding 2-bromo-1-(4-substituted phenyl)-3,3-diethoxypropan-1-ones with pyridine-2-thiol in dry isopropyl alcohol under reflux for 2 h. The new compounds 1–4 were characterized by elemental analysis, 1H and 13C NMR spectroscopy and single crystal X-ray diffraction. Both the negative charge-assisted (S⋯Br−) and normal (S···π) chalcogen bonds were found in the crystal packing of 2−4, whereas one of the hydrogen atoms of an electron-donating –OCH3 group in 1, behaves as a bifurcated hydrogen bond donor centre towards a sulfur atom of the thiazolo ring and an oxygen atom of CO group of a neighboring molecule leading to the intermolecular hydrogen bonds. The optical properties of 1−4 in DMSO, DMF and MeOH were investigated by UV–vis absorption spectroscopy, with λmax being dependent on the solvent polarity and attached substituents (−OCH3, –H, –F, −Cl) at the para-position of the aromatic moiety.