Ion association and solvation of thiocyanates in water–dimethylformamide mixtures: an ultrasonic study

Abstract

Ultrasonic relaxation spectra of LiNCS and NH₄NCS in water–DMF mixtures have been measured in the frequency range 1–700 MHz. No ultrasonic relaxation of NH₄NCS in DMF was observed in this range. Ultrasonic relaxation for LiNCS solutions was observed at concentrations >60 mol% in DMF and was ascribed to ion-pair formation, expressed by the Eigen mechanism. The difference in ultrasonic relaxation spectra of LiNCS and NH₄NCS solutions is discussed with respect to their different solvation properties. This information was obtained from the partial molar volume and adiabatic compressibility. The kinetic parameters and the adiabatic volume change due to the ionic association process for LiNCS in DMF are estimated using the formation constant obtained by analysis of the Raman bands.