Structural, spectroscopic and theoretical study of an o-vanillin Schiff base derivative

REINALDO PIS DIEZ; GUSTAVO A. ECHEVERRÍA; OSCAR E. PIRO; JORGE L. JIOS; BEATRIZ S. PARAJÓN COSTA

NEW JOURNAL OF CHEMISTRY

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2016 vol. 40 p. 2730 - 2740

1144-0546

The potassium salt of the Schiff base obtained by condensation of 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) and 2-aminoethanesulfonic acid (Taurine) in a methanolpotassium hydroxide solution, was characterized by crystallographic, spectroscopic and DFTmethods. The compound crystallizes in the monoclinic C2/c space group with a = 37.539(4), b =5.9129(4), c = 26.321(5) Å, β = 121.10(2)° and Z =8 molecules per unit cell. The crystallographic data reveals that two different anionic molecules, which constitute a tautomeric pair, coexist in the crystal. This finding is supported by FTIR, Raman and electronic measurements in methanol solution. The main crystallographic differences between the bonding structures occur along the shortest chemical path linking the oxygen and the nitrogen atom of the OH and CN group. Both tautomeric forms are stabilized by strong O-H?N and N-H?.O intramolecular hydrogen bonds. Optimized geometrical parameters and calculated spectroscopic features obtained by DFT calculations show a very good agreement with the experimental data. Moreover, 1H NMR, 13C NMR and electronic measurements in DMSO solution show the prevalence of the enol-imine tautomer in this solvent.