Short and symmetrical OHO hydrogen bond in bis(quinuclidine betaine) hydrochloride

The molecular structure of bis(quinuclidine betaine) hydrochloride, (QNB)2HCl, has been characterized by single crystal X-ray diffraction, infrared spectroscopy and by DFT calculations. The crystals are centrosymmetric, monoclinic, space group C2/c. Two QNB moieties are joined by a very short and centered O⋯H⋯O hydrogen bond of 2.461(2) Å. Its existence is confirmed by the broad absorption band below 1500 cm−1 in the FTIR spectrum. In the structure of (QNB)2HCl optimized at the B3LYP/6-31G(d,p) level of theory, the quinuclidine betaine units are non-equivalent. The protonated quinuclidine betaine interacts with the QNB inner salt by the OH⋯O hydrogen bond of 2.494 Å. In the structure of (QNB)2H homoconjugated cation, optimized by the B3LYP/6-31G(d,p) approach, the OHO bond is shorter than in the crystal (2.415 Å). A study of the motion of the proton along the OH⋯O bridge has been carried out by the semiempirical PM3 method.