Solubilization of doubly charged iron(II) complexes in aqueous neutral micellar aggregates. A kinetic investigation

Abstract

The incorporation of doubly charged iron(II) complexes FeL²⁺₃[with L = 4,4′-dimethyl-2,2′-bipyridine or 4,4′-bis(alkoxycarbonyl)-2,2′-bipyridine, where alkoxy = methoxy, ethoxy or propoxy] into micellar aggregates of non-ionic surfactants C_iE_j(C₁₀E₆, C₁₂E₆, C₁₄E₆, C₁₂E₁₀ and C₁₂E₂₃) has been studied at 20 °C by examining the kinetics of the cerium(IV) oxidation of these complexes. Binding of the iron(II) complexes to the neutral micelles increases as the co-ordinated ligand becomes increasing hydrophobic. Solubilization is also favoured by an increase (at constant i) in the number of ethoxy groups on the surfactant, while the extent of binding remains substantially unchanged when the hydrocarbon alkyl surfactant chain becomes longer (at constant j). Binding of the solubilized iron(II) complexes would occur at the interface of the hydrophobic core and the wet outer poly(ethoxy) sheath of the micelle with a probable large projection of the solubilizate into the latter micellar region.