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

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·H2O, 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, OCOH⋯Cl− = 2.993(2) Å and with neighboring H2O 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 CO bond of OCOH 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·H2O 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 H2O molecules, and the νCO 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 OH·O hydrogen bonds between COO groups.