Structural, spectroscopic and theoretical studies of 8-hydroxyquinolinium bromide and its monohydrate

Abstract Molecular structures and properties of 8-hydroxyquinolinium bromide (1) and its monohydrate (2) have been characterized by X-ray diffraction, B3LYP/6-311++G(d,p) calculations and FTIR spectroscopy. In the anhydrate 1 the ions of 8-hydroxyquinolinium cation and bromide anion are hydrogen-bonded into centrosymmetric dimers through the N···Br and O(8)···Br bonds of the distances of 3.220(3) and 3.157(2) A, respectively. In monohydrate 2 the water molecule mediates in hydrogen bonds OH···O and OH···Br between the bromide and 8-hydroxyquinolinium ions. The types of intermolecular hydrogen bonds in 8-hydroxyquinolinium cation is connected to the conformational preference of the hydroxyl group. The theoretically optimized models of 8-hydroxyquinolinium bromide anhydrous dimer 1b and dimer hemihydrate 2b better reproduce all interionic hydrogen bonds than these models of monomers 1a and 2a, consistent with the experimental and theoretical infrared spectra. The potential energy distribution (PED) have been used to assign the vibrational spectra.