Ion association between hexaamminecobalt (III) ion and monovalent anions in methanol-water mixtures from 10 to 50 degrees C

Abstract

The conductivities of chloride, bromide, iodide, nitrate, and perchlorate of hexaamminecobalt(III) complex were measured in 10-80 wt.% methanol-water mixtures at varying temperatures from 10 to 50degreesC. The ion association constants were estimated by analyzing conductivity data in terms of the Robinson-Stokes equations. Ion-association constants calculated for all complex salts in methanol-water mixtures increased, depending on the percentage of methanol. This was equivalent to the ion-association constants increasing with a decrease in the the dielectric constant of the mixtures. K-A values increased with increasing temperature for the chloride, bromide, and iodide of [Co(NH3)(6)](3+). It was observed that these values indicated some disorder, dependent on the temperature, for nitrate and perchlorate. Thermodynamic parameters (Gibbs' free energy, entropy and enthalpy of ion association) were estimated from the temperature dependence of the ion-association constant. The limiting molar conductivities of complex ion and monovalent anions in the mixed solvents were determined from our experimental data by using the Kohlraush equation.