Solubility of salts of hexachlororhenate(IV) ions with complex cations in water and in water + alcohol mixtures: free energies of transfer of the complex ions
Abstract
It is shown that when the solubilities of two salts of the same valence type with a common anion are known in water and in mixtures of water with a co-solvent, and when the free energies of transfer ΔGt⊖ from water into the mixture are known for one of the cations, ΔGt⊖ for the other cation can be calculated. Solubilities of {a,f-[Co(py)4Cl2]}2[ReCl6] in the mixtures water + ButOH and water + methanol and the solubilities of {a,f-[Co(4Me-py)4Cl2]}2[ReCl6] and of {a,b-[Co(SCN)Cl(en)2]}2[ReCl6] in water ButOH have been measured at 25.0 °C (py = pyridine, 4Me-py = 4-methylpyridine, en = ethylenediamine). These values have been combined with literature data for the solubility of Cs2[ReCl6] and for ΔGt⊖(Cs+) in these mixtures to produce values for ΔGt⊖ for the complex cations. ΔGt⊖ Values found for a,f-[Co(py)4Cl2]+ in water + methanol, together with kinetic data for the solvolysis of the cation and with values for ΔGt⊖(Cl–) in the same mixtures, have been used to derive values for ΔGt⊖ for the cation in the solvolytic transition state, [Co(py)4Cl]2+. This confirms that the effect of solvation of the cation in the transition state dominates over that of the cation in the initial state.