Molecular structure and spectroscopic properties of the 1:1 complex of quinuclidine betaine with l-tartaric acid

The 1:1 complex of quinuclidine betaine (QNB) with l(+)-tartaric acid (TA) (1-carboxymethyl-1-azoniumbicyclo[2.2.2]octane semi-tartrate) has been synthesized and characterized by X-ray diffraction, FTIR, Raman and NMR spectroscopy, and DFT calculations. QNB–TA crystallizes in monoclinic space group P21. In the crystal quinuclidine betaine is protonated and interacts with semi-tartrate anion by the short O–H···O hydrogen bond of 2.472(4) Å. The semi-tartrate anions form infinite chains through the COOH···OOC hydrogen bond of 2.585(5) Å. The FTIR spectrum shows broad bands in the 2700–2200 and 2000–500 cm−1 regions typical of such short hydrogen bonds and are consistent with the X-ray results. In the optimized structures of the title complex at the B3LYP/6-31G(d,p) level of theory both in the monomer, QNB–TA, and dimer, (QNB–TA)2, the betaine molecules are not protonated. The 1H and 13C NMR spectra elucidate the structure of the complex investigated in aqueous solutions.