Experimental and theoretical studies of 4-hydroxy-1-methylpiperidinium perchlorate

The structure of 4-hydroxy-1-methylpiperidinium perchlorate has been characterized by X-ray diffraction, FTIR, Raman and NMR spectroscopies, and by DFT calculations. The crystals belong to orthorhombic Pbca group. The piperidine ring has a chair conformation with the hydroxyl and methyl groups in the equatorial positions. The hydroxyl group interacts by bifurcated O-H···O hydrogen bonds with the ClO4− anion of 2.905(5) and 3.045(5) Å. Two optimized structures of the title compound have been calculated by the B3LYP/6-31G(d,p) approach. In one of them the ClO4- anion is involved in the N+-H···O hydrogen bonds of 2.629 Å, while in the other the ClO4- anion interacts electrostatically with the N+ atom of the 4-hydroxy-1-methylpiperidinium cation. In aqueous solution two 4-hydroxy-1-methylpiperidinium perchlorates are in the conformational equilibrium. Their conformations are discussed on the basis of the NMR spectra. The solid state FTIR spectrum is consistent with the X-ray data.