Effect of organised surfactant systems on the kinetics of metal–ligand complex formation and dissociation

Abstract

The kinetics and mechanism of a range of metal–ligand complexation reactions have been studied in water, sodium dodecylsulphate micellar solutions and aerosol-OT-stabilised water-in-oil microemulsions. A generalised theory is developed for the interpretation of kinetic measurements in these dispersions and it is tested for metal-complex formation. In most cases the rate of complex formation is only affected by the concentration-enhancement effect of the surfactant/water interface on the reactants. Then the volume within the solution available for reaction can be deduced and reasonable values are obtained. For the reaction between Ni(phen)²⁺ and PADA, other factors influence the kinetics. As a result the nature of the micelle surface where reaction occurs can be investigated. For the ligand PAN there is evidence that it can partition between more than two pseudo-phases, with a consequent reduction in the rate of complex formation. The dissociation rates of the complexes at the interfaces are increased by up to a factor of ten as compared with bulk water.