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 nu(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); DELTA-H-degrees and DELTA-S-degrees values of 8.4 +/- 0.5 kJ mol-1 and 31.5 +/- 2 J mol-1, respectively, were determined.