X-ray and spectroscopic studies of the molecular structure of bis(8-oxy-1-methylquinolinium) hydroiodide

Bis(8-oxy-1-methylquinolinium) hydroiodide has been studied by X-ray diffraction, FT-IR, ¹H and ¹³C NMR spectroscopy. In the crystalline state a homoconjugated OH  O⁻ hydrogen bond is formed. As indicated by the X-ray data this hydrogen bond is very short (2.457 Å) and structurally symmetrical. The existence of this bond is manifested in the FT-IR spectra by an intense and broad band in the 1500–400 cm⁻¹ region. This type of absorption indicates that this hydrogen bond can be described by one very broad potential energy minimum in which the proton shows a large proton polarizability due to its fast fluctuations, i.e., it shows the so-called Zundel’s polarizability.