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

Abstract

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 {ΔGto(Co(3Rpy)4Cl2+)−ΔGto(Cs+)} can be determined where ΔGto is the standard Gibbs free energy of transfer from water to an aqueous mixture. ΔGto(Cs+) from the solvent sorting scale and from the TPTB scale are then used to calculate ΔGto(Co(3Rpy)4Cl2+). These two sets of values for ΔGto(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 ΔGto(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.