Solubilities in aqueous mixtures oft-butanol andtrans-dichlorotetra(3-alkylpyridine) cobalt(III) hexachlororhenate(IV): Gibbs energies of transfer of the complex cations

Abstract

The solubilities of the hexachlororhenate(IV) salts of the complex cations trans-[Co(3Mepy)4Cl2]+ and trans-[Co(3Etpy)4Cl2]+ have been determined in water+t-butyl alcohol mixtures. By reference to the solubilities of Cs2ReCl6 and the Gibbs energies of transfer of Cs+ from water into water+t-butyl alcohol mixtures, ΔG t o (Cs+), ΔG t o [Co(3Mepy)4Cl 2 + ] and ΔG t o [Co(3Etpy)4Cl 2 + ] are calculated. These latter values, when introduced into the equation for a free energy cycle applied to the process of the initial state going to the transition state for the solvolyses of these two cations, produces values for ΔG t o [Co(3Mepy)4Cl2+*] and ΔG t o [Co(3Etpy)4Cl2+*] for the Co3+ cations in the transition state. These values are compared with (ΔG t o (i) for i=[Co(Rpy)4Cl2]+, [Co(Rpy)4Cl]2+*, [Coen2XCl]+ and [Coen2X]2+* to investigate the influence of the hydrophobicity of the surface of the complex on its stability in the mixtures. ΔG t o (i) (solvent sorting) are compared with ΔG t o (i) (TATB).