Raman spectroscopic determination of the dissociation constants of an acetonitrile–zinc complex in aqueous solution and the enthalpy and entropy of complex dissociation

The dissociation constants for an acetonitrile‐zinc complex, (CH3CN)Zn2+, were measured in aqueous solutions containing zinc salts (40‐80%, w/w) and acetonitrile by Raman spectroscopy. Quantitative measurements of the intensity of the free and complexed ν(CN) Raman bands at 2264 and 2320 cm−1, respectively, were used to determine the average enthalpy and entropy of the complex dissociation to free acetonitrile in the temperature range 293‐343 K for a 70% (w/w) solution of zinc chloride (0.052 mol) in an aqueous solution containing acetonitrile (0.024 mol); δH° and δS° values of 8.4 ± 0.5 kJ mol−1, respectively, were determined.