Crystal and molecular structure of 8-hydroxyquinoline betaine monohydrate studied by X-ray, FTIR, NMR and DFT

Abstract

Molecular structure and properties of 8-hydroxyquinoline betaine monohydrate (1-carboxymethyl-8-hydroxyquinolinium inert salt monohydrate) were studied by X-ray diffraction, DFT calculations, FTIR and NMR spectra. In the crystals, 8-hydroxyquinoline betaine and water are bonded by an intermolecular and asymmetric COO···H2O hydrogen bond of 2.782(3) Å. The water molecules are disordered so that one of the proton is shared between two half occupied sites. The hydroxyl group of quinoline is bonded to the neighboring molecule by the O−H···OOC hydrogen bond of 2.571(3) Å. The molecular geometry, Hirshfeld surface, Mulliken atomic charge distribution, molecular electrostatic potential, frontier molecular orbitals, vibrational wavenumbers, magnetic isotropic shielding constants were determined using the density functional theory (DFT/B3LYP) with 6–311++G(d,p) basis set. The FTIR spectrum shows a characteristic ABC structure, typical of medium-short hydrogen bonds. The potential energy distribution (PED) was used to assign the bands in the vibrational spectrum. 1H and 13C NMR spectra were analyzed.