Structural, spectroscopic and theoretical studies of short OHO hydrogen bonds in 2:1 complexes of 1-methyl-6-oxyquinolinium betaine with mineral acids

Bis(1-methyl-6-oxyquinolinium) hydroiodide, (6QB)2HI (1), has been characterized by X-ray diffraction, B3LYP calculations, FTIR and NMR spectroscopy. The complex crystallizes in triclinic P 1¯ space group. A pair of 6QB molecules is bridged by the O·H·O hydrogen bond of 2.450(2) Å. The anion I- electrostatically interacts with both positively charged nitrogen atoms of the neighboring 6QB molecules. The isolated entities of the complex were analyzed at the B3LYP/6-311G(d,p) level of theory in order to determine the influence of counter ions (X− = I−, Br−, Cl− and ClO4-) on the hydrogen bond in (6QB)2HX (2-5). The FTIR spectra of (6QB)2HI and (6QB)2HClO4 show a broad and intense absorption in the 1500-400 cm−1 region, typical for short hydrogen bonds. Both 1H and 13C chemical shifts depend on the acid-base stoichiometry and counter ions.