Electroactive Ru(NH 3) 63+ gallery cations in clay-modified electrodes

Abstract

Ru(NH 3) 6 3+ -Laponites® and -montmorillonite films supported on graphite electrodes exhibited cyclic voltammograms with a well-defined Ru(NH 3) 6 3+/2+ wave even when the complex ion loading was less than the cation exchange capacity of the clay film. Coulometry indicated that more than 80% of the Ru(NH 3) 6 3+ electrostatically bound at the cation exchange sites of the gallery surfaces was electroactive. Further confirmation of the presence of electroactive gallery exchange cations was obtained by comparing the electrochemical behavior of the Ru(NH 3) 6 3+ montmorillonite with montmorillonite containing Fe(bpy) 3 2+ exchange ions and [Fe(bpy) 3 2+][SO 4 2−] ion pairs. In this latter system the ion-paired [Fe(bpy) 3 2+] [SO 4 2−] centers are electroactive but the gallery Fe(bpy) 3 2+ exchange cations are rigorously electroinactive. The concentration and nature of the cation in the supporting electrolyte greatly affected the peak currents of the Ru(NH 3) 6 3+ clay, whereas the electroactivity of the [Fe(bpy) 3 2+][SO 4 2−] centers were not affected by the electrolyte cation. The decrease in the electroactivity of Ru(NH 3) 6 3+ montmorillonite with increasing electrolyte concentration was attributable to the exchange of Ru(NH 3) 6 3+ by electrolyte cations. A mechanism has been suggested for maintaining electrical neutrality upon electron transfer in these clay films.