Transfer chemical potentials, solubilities and reactivities in binary aqueous mixtures of two complex iron(II) cations: tris[(3-methoxyphenyl)iminophenyl-2-pyridylmethane] iron(II) and 1,8-bis[(2-quinolylmethylene)amino]-3,6-diazaoctane iron(II)

Abstract

Solubilities are reported for perchlorates of two low-spin iron(II)–di-imine complex cations in binary aqueous mixtures at ambient pressure and 298 K where the organic cosolvents are methanol, ethanol, propan-2-ol, acetone and dimethyl sulphoxide. The two cations are tris[(3-methoxyphenyl)iminophenyl-2-pyridylmethane] iron(II) and 1,8-bis[(2-quinolylmethylene)amino]-3,6-diazaoctane iron(II), [Fe(bsb-3-OMe)₃]²⁺, [Fe(hxsbq)]²⁺. These contain bi- and hexa-dentate ligands derived from 3-methoxyaniline (m-anisidine) and 2-benzoylpyridine, and from triethylenetetramine and quinoline-2-aldehyde, respectively. Solubility data are analysed using the TATB (or TPTB) extrathermodynamic assumption to yield transfer chemical potentials for the two complex cations. Both iron(II) complex cations are strongly stabilised by organic cosolvents owing to the markedly hydrophobic character of the ligands. Rate constants are reported for reactions between hydroxide ions and the above iron(II) complex cations in binary aqueous mixtures. Derived transfer parameters for these cations, together with those for hydroxide ions, lead to an interesting comparison of the effects of different cosolvents on initial and transition states for the reaction involving [Fe(bsb-3-OMe)₃]²⁺ cations. The analysis confirms the important role played by the hydrophobic ligands in determining the overall kinetic patterns.