Vibrational analysis of thiosaccharin and thiosaccharinate anion. A gradient-corrected density functional and experimental study

A gradient-corrected density functional (DFT) study of thiosaccharin molecule and of the corresponding nitranion was carried out using various combinations of exchange and correlation functionals, with a special emphasis on the vibrational analysis of the studied species. The employed DFT methodologies included the B3LYP, mPW1PW91, HCTH and the OLYP combinations of functionals, using the 6-31+G(d,p) basis set for orbital expansion in solving the Kohn–Sham SCF equations. Full geometry optimizations of thiosaccharin molecule and the corresponding nitranion were carried out employing Schlegel's gradient optimization algorithm. Subsequently, harmonic vibrational analyses were carried out for the minima located on the corresponding molecular/ionic potential energy hypersurfaces. Also, Fourier transform infrared (FT IR) spectra of thiosaccharin and a series of metal thiosaccharinates (those of Na, K, Mg, Mn, Co, Ni, Cu, Zn, Cd, Hg and Pb) were recorded at room and liquid nitrogen boiling temperature. Experimental FT IR vibrational spectra of the studied systems were analyzed in the light of the computed density functional harmonic force fields for free thiosaccharin molecule and its nitranion. The performances of various DFT methodologies employed were compared.