The Effect of Adsorption of the Hexaamineruthenium(II/III) Redox Pair Ions on the Process of Octanethiol Self-Assembling on a Gold Electrode

Abstract

The effect of components of the Ru(NH₃)₆Cl₃/Ru(NH₃)₆Cl₂ redox-pair on the dynamics of octanethiol monolayer formation on gold from aqueous thiol-containing solutions in 0.1 M NaClO₄ is studied by cyclic voltammetry. In this work, the method for assessing the adsorption activity of the components of the [Ru(NH₃)₆]^3+/2+ redox-pair by the octanethiol dense monolayers on gold formation time was used. The introduction of the redox pair components into a thiol-containing solution is shown to lead to an increase in the formation time of octanethiol-monolayer insulating films and to the less stable monolayers’ formation. The inhibitory effect of hexaamineruthenium(II)/(III) ions decreased with increasing of octanethiol concentration in the solution. A difference in the adsorption activity of the ions composing the [Ru(NH₃)₆]^3+/2+ redox-pair on gold in the presence of octanethiol is found: [Ru(NH₃)₆]³⁺ ions are better adsorbed than [Ru(NH₃)₆]²⁺ ones. A comparative assessment of the adsorption activity of two redox-pairs—[Ru(NH₃)₆]^3+/2+ and \({\text{Fe(CN}})_{6}^{{{{3 - } \mathord{\left/ {\vphantom {{3 - } {4 - }}} \right. \kern-0em} {4 - }}}}\)—is performed. It was shown that a typical redox pair [Ru(NH₃)₆]^3+/2+, in contrast to the redox pair \({\text{Fe(CN}})_{6}^{{{{3 - } \mathord{\left/ {\vphantom {{3 - } {4 - }}} \right. \kern-0em} {4 - }}}}\), can be considered a test one, since the ions of this system are weakly adsorbed on the gold surface and make but insignificant impact on the thiol monolayer self-assembling process. The octanethiol and the hexaamineruthenium(II)/(III) and ferro-ferricyanide ions can be ranged, according to their adsorption activity on the gold electrode, as follows: octanethiol > [Fe(CN)₆]^3– ≈ [Fe(CN)₆]^4– \( \gg \) [Ru(NH₃)₆]³⁺ > [Ru(NH₃)₆]²⁺.