Molecular structure, hydrogen bonding, basicity and spectroscopic properties of 3-hydroxypyridine betaine hydrochloride monohydrate

Abstract

The effect of hydrogen bonding, inter- and intramolecular electrostatic interactions on the structure of 3-hydroxy-pyridine betaine hydrochloride monohydrate (1-carboxymethyl-3-hydroxypyridinium chloride monohydrate), 3-HO-PBH·Cl·H 2O, has been studied by X-ray diffraction, 1H and 13C NMR and FTIR spectroscopies, and by the B3LYP/6-31G(d,p) calculations. In the crystal, the Cl − anion is connected with protonated betaine via the hydrogen bond, O C O H⋯Cl − = 2.993(2) Å and with neighboring H 2O molecules via the 3.111(1) and 3.578(1) Å bonds, while the 3-OH group interacts with water molecule by the hydrogen bond of 2.566(2) Å, forming an aggregate along the [b] direction. The water molecule additionally forms hydrogen bonds of 2.888(3) Å to the C O bond of O C OH group. On recrystallization the 1:1 complex slowly converts into the 2:1 complex, bis(3-hydroxy-pyridine betaine) hydrochloride, [bis(1-carboxymethyl-3-hydroxypyridinium) chloride], [(3-HO-PB) 2H·Cl]. The geometries of 3-HO-PBH·Cl·H 2O in the gas phase (vacuum), DMSO and water solutions have been optimized by the B3LYP/6-31G(d,p) level of theory using the COSMO model. Good linear correlations between 13C and 1H experimental chemical shifts and GIAO/ B3LYP/6-31G(d,p) calculated magnetic isotropic shielding tensors ( σ) have been obtained. The FTIR spectrum of the 1:1 complex shows a broad and intense absorption in the 3100–2500 cm −1 region due to the stretching vibration of hydrogen bonds between the Cl − anion and COOH, OH substituents and H 2O molecules, and the νC O band at 1739 cm −1. The spectrum of the 2:1 complex shows an additional broad absorption in the 1900–800 cm −1 region due to the O H·O hydrogen bonds between COO groups.