Surface ion association of the hexacyanoferrate(III)/(II) ion bound by 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23 H-porphine or 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21H ,23H-porphine adsorbed on a graphite electrode

Abstract

A monolayer or submonolayer of the positively charged molecule of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23 H-porphine (H ₂ TMPyP) or 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21H ,23H-porphine (H ₂ TAPP) irreversibly adsorbed on a graphite electrode can associate with a hexacyanoferrate(III) or hexacyanoferrate(II) ion in solution to form surface ion pairs which have been examined by surface cyclic voltammetry. The electrochemical responses of adsorbed H ₂ TMPyP, H ₂ TAPP, and associated [Fe(CN) ₆ ] ^3-/4- were employed to estimate the surface coverage which was then used to evaluate quantitatively the ion association equilibria between adsorbed porphine and solution hexacyanoferrate(III) or hexacyanoferrate(II) ions. The competing association of other common anions such as Cl ^- and [SO ₄ ] ^2- with [Fe(CN) ₆ ] ^3-/4- was also examined.