Structure of 1-methyl-6-oxyquinolinium betaine dihydrate studied by X-ray diffraction, DFT calculations, vibrational and NMR spectra

The crystals of 1-methyl-6-oxyquinolinium betaine dihydrate, 6QB·2H2O, are triclinic, space group P1¯. The oxygen atom of 6QB exhibits an extremely rare capability of accepting four hydrogen bonds. It is engaged in four hydrogen bonds to water molecules of the 2.823, 2.825, 2.833 and 2.849 Å; each water molecule interacts with two neighbouring 6QB molecules linking them into infinite sheets. Differences in geometrical parameters between the X-ray and calculated molecules reflect changes in their structures between zwitterion and quinonoid forms. The probable assignments of the experimental FTIR solid spectrum have been made on the basis of B3LYP/6-311G(d,p) calculated frequencies in vacuum. Both 1H and 13C chemical shifts are solvent dependent. Linear correlations between the experimental 1H and 13C NMR chemical shifts of 6QB·2H2O in solutions and the GIAO/B3LYP/6-311G(d,p) calculated magnetic isotropic shielding tensors (σcal) using the screening solvation model, δexp = a + bσcal, are reported.