Vibrational and DFT study of 5-(3-pyridyl-methylidene)-thiazolidine-2-thione-4-one

The molecular vibrations of 5-(3-pyridyl-methylidene)-thiazolidine-2-thione-4-one (5-3-PMTT) were investigated by FT-IR, FT-Raman and SERS spectroscopies. In parallel, quantum chemical calculations based on density functional theory (DFT) are used to determine the geometrical, energetic and vibrational characteristics of the molecule. The three possible tautomers of 5-3-PMTT (thione, thiol and enol) have been analyzed by theoretical methods and their relative stability is discussed. The vibrational spectrum of the solid state 5-3-PMTT compound has been assigned based on DFT calculations at B3LYP level of theory using the standard 6-31G(d) basis set. The experimental vibrational bands were assigned to the calculated normal modes and a very good correlation was achieved between the experimental and theoretical data. SERS spectra suggest an important deformation of the adsorbed molecule on silver colloid surface; the six-membered ring is almost perpendicular while the thiazolidine ring lies almost parallel to Ag colloid surface. The molecular electrostatic potential of the molecule has been calculated and used for predicting site candidates of electrophilic attack.