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 P2(1). In the crystal quinuclidine betaine is protonated and interacts with semi-tartrate anion by the short O-H center dot center dot center dot O hydrogen bond of 2.472(4) angstrom. The semi-tartrate anions form infinite chains through the COOH center dot center dot center dot OOC hydrogen bond of 2.585(5) angstrom. 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 H-1 and C-13 NMR spectra elucidate the structure of the complex investigated in aqueous solutions. (C) 2009 Elsevier B.V. All rights reserved.