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

Abstract

AbstractThe molecular structure of bis(4‐(N‐methylpiperidinium)‐butyrate) hydrobromide, (MPBu)2HBr, 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) Å3 , β = 90.431(3)°, V = 2206.1(1) Å3, and Z = 4. Two 4‐(N‐methylpiperidinium)‐butyrate moieties are joined by a very short and centrosymmetric O.H.O hydrogen bond of 2.436(2) Å3 . The piperidine ring adopts a chair conformation with the methyl group in the equatorial and the bulky (CH2)3COO 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 H O hydrogen bond. The 1H and 13C 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 .HO hydrogen bond of 2.580 Å3 . Copyright © 2008 John Wiley & Sons, Ltd.