Solubility of dichlorotetraalkylpyridinecobalt III hexachlororhenate(IV) in water + methanol mixtures: Free energies of transfer of the complex cation from water into the mixtures

The solubility of salts [Co(3Rpy)₄Cl₂]₂]ReCl₆] has been determined in water + methanol mixtures. By comparing these with the solubilities of the salt Cs₂ReCl₆ and using calculated activity coefficients for the ions in the water+methanol mixtures, values for {G_t^o(Co(3Rpy)₄Cl₂⁺)–G_t^o(Cs⁺)} can be determined where G_t^o is the standard Gibbs free energy of transfer from water to an aqueous mixture. G_t^o(Cs⁺) from the solvent sorting scale and from the TPTB scale are then used to calculate G_t^o(Co(3Rpy)₄Cl₂⁺). These two sets of values for G_t^o(Co(3Rpy)₄Cl₂⁺) on the differing scales are then inserted into a free energy cycle applied to the bond extension Co(3Rpy)₄Cl₂⁺ (initial state)Co(3Rpy)₄Cl²⁺+Cl^– (transition state) for the solvolysis in water and in water + methanol mixtures to produce values for G_t^o(Co(3Rpy)₄Cl²⁺) using both scales. Data for the solubilites of [Copy₄Cl₂]₂[ReCl₆] and [Co(4Rpy)₄Cl₂]₂[ReCl₆] have been re-calculated to compare free energies of transfer for these complex cations with those specified above.