Structural, spectroscopic, and theoretical studies of a very short OHO hydrogen bond in bis(4-(N-methylpiperidinium)-butyrate) hydrobromide

The molecular structure of bis(4-(N-methylpiperidinium)-butyrate) hydrobromide, (MPBu)(2)HBr, has been characterized by single crystal X-ray diffraction, infrared and NMR spectroscopies, and by DFT calculations. The crystals of the title compound at 140 K are monoclinic, space group C2/c, with a=11.7118(4), b=7.8737(2), c=23.9240(8) angstrom, beta=90.431(3)degrees, V=2206.1(1) angstrom(3), and Z = 4. Two 4-(N-methylpiperidinium)-butyrate moieties are joined by a very short and centrosymmetric O center dot H center dot O hydrogen bond of 2.436(2) angstrom. The piperidine ring adopts a chair conformation with the methyl group in the equatorial and the bulky -(CH2)(3)COO substituent in the axial position. The broad absorption band below 1500 cm(-1) in the FTIR spectrum confirms the existence of a very short O center dot H center dot O hydrogen bond. The H-1 and C-13 NMR spectra are interpreted on the basis of 2D experiments and the calculated GIAO/B3LYP/6-31G(d,p) magnetic isotropic shielding tensors. In the optimized structure of the complex, a 4-(N-methylpiperidinium)-butyrate zwitterion interacts with a 4-(N-methylpiperidinium)-butyric acid cation forming an O center dot center dot center dot H-O hydrogen bond of 2.580 angstrom Copyright (C) 2008 John Wiley & Sons, Ltd.