Study of the interactions of Sodium Thiocyanate, Potassium Thiocyanate and Ammonium Thiocyanate in water + N,N-dimethylformamide mixtures by Raman spectroscopy

Raman spectra of water + N,N-dimethylformamide (DMF) mixtures and their solutions with NaNCS, KNCS and NH4NCS were obtained. The bands of ν(CO) stretching, δ(OCN) bending, r(CH3) rocking and ν(N–CH3)ν(N–CH3) stretching of the DMF molecule with and without salts were studied. The dependence of the vibration frequencies and Raman intensities of the bands on the composition of the mixed solvent was discussed. The change of the band frequencies as a result of the presence of the salts and the solvation of the cations by the solvent molecules was examined. The stronger cation solvation by the aprotic solvent molecules instead of the water molecules in DMF concentrated solutions was discussed. The ν(CN) and ν(CS) vibrations of the SCN− ions were observed as a function of the cation present and the solvent composition. The presence of the SCN− ions as “free”, contact ion pairs, or solvent separated pairs, was discussed.