Experimental and theoretical investigation of 5-para-nitro-benzylidene-thiazolidine-2-thione-4-one molecule

Abstract

Experimental methods (FT-IR, Raman and NMR spectroscopies, and X-ray diffraction technique) coupled with quantum chemical calculations based on density functional theory (DFT) are used for structural and electronic characterization of 5-para-nitro-benzylidene-thiazolidine-2-thione-4-one (5pN-BTT). X-ray diffraction technique indicates that this compound crystallizes with one tetrahydrofuran (THF) solvent molecule, forming a 1:1 5pN-BTT·THF complex, in the monoclinic space group C2/ c, with Z = 8 and cell parameters a = 29.496(9) Å, b = 7.276(2) Å, c = 14.873(4) Å, α = 90.0°, β = 95.161(6)° and γ = 90.0°. The lowest energy optimized geometry of the investigated compound in gas-phase corresponds to thionic tautomer being consistent with that obtained by X-ray technique. Tautomeric equilibrium between the thione, thiol and enol forms of the compound have been considered and analyzed by theoretical methods. The continuum PCM solvation model fails to reproduce the experimental chemical shift associated with the NH proton in the thione form, but a very good correlation between experiment and theory was obtained by taking into account the specific solute–solvent interactions. Proton NMR spectrum of 5pN-BTT in DMSO solution shows an unexpected proton chemical shift at 14 ppm which is attributed to the proton bound to the nitrogen atom and explained by assuming a relatively strong hydrogen bond between 5pN-BTT and the solvent molecule, realized through NH group. The molecular vibrations of 5pN-BTT were investigated by FT-IR and FT-Raman spectroscopies and the vibrational spectrum of the solid state 5pN-BTT compound has been assigned based on DFT calculations at B3LYP level of theory using the standard 6-31G(d) basis set.