Solubilities of salts and kinetics of reaction between hydroxide ions and iron(II)–di-imine complexes in water–methanol mixtures. Derivation of single-ion transfer chemical potentials and their application to analysis of solvent effects on kinetic parameters

Abstract

Kinetic data are reported for the reaction at 298 K and ambient pressure between two iron(II)–di-imine complex cations and hydroxide ions in water–methanol mixtures. Solubility data are reported for a range of inorganic salts containing simple and complex ions. Methods for calculating transfer chemical potentials of single ions are examined and, depending on the extrathermodynamic assumption, shown to predict different trends in the properties of ions in these aqueous mixtures. Further, calculated initial- and transition-state solvation effects on the kinetics are different: in some cases dramatically so. The solvation characteristics are compared for various ions in methanol–water mixtures as calculated using the tetraphenylphosphonium tetraphenylborate (TPTB) assumption, which sets the transfer chemical potential of tetraphenylphosphonium ions equal to that of tetraphenyl-boronate ions. Arguments are advanced for adopting single-ion transfer chemical potentials based on this assumption. Relationships are examined between the transfer parameters for H⁺, H₃O⁺, ROH⁺₂ and H₉O⁺₄ ions in binary aqueous mixtures, ROH + H₂O.