Effect of the Micellar Electric Field on Electron-Transfer Processes. A Study of the Metal-to-Metal Charge Transfer within the Binuclear Complex Pentaammineruthenium(III)−(μ-Cyano)pentacyanoruthenium(II) in Micellar Solutions of Sodium Dodecylsulfate (SDS) and Hexadecyltrimethylammonium Chloride (CTACl)

Abstract

The metal-to-metal charge-transfer band within the binuclear complex pentaammineruthenium(III)−(μ-cyano)pentacyanoruthenium(II), a Robin−Day class II complex, was studied in solutions containing sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium chloride (CTACl). The redox potentials of both ruthenium centers were also measured. From the optical and electrochemical (redox) data, both the reorganization free energy and the reaction free energy corresponding to the electron transfer were obtained. It was found that in solutions containing the anionic surfactant the relevant parameters for the electron-transfer process, that is, the free energies of reorganization and reaction, are quite similar to those corresponding to aqueous electrolyte solutions. In the case of the solutions containing the cationic surfactant, these parameters are quite different from those of the aqueous electrolyte solutions. The results are interpreted taking into account the effects of the micellar electric field on both the binuclear complex and the medium (solvent) surrounding it. These effects depend on the (average) position of the binuclear complex in relation to the micelle: in the case of cationic micelles the binuclear complex penetrates the Stern layer. When the micelles are anionic, the binuclear complex is, on the average, outside this layer, but a residual influence of the micellar field seems to be operative.