Surface electrochemistry of N,N',N″,N‴-tetramethyl-tetra-3,4-pyridinoporphyrazinocobalt(II)

The complex N,N',N″,N‴-tetramethyl-tetra-3,4-pyridinoporphyrazinocobalt(II) ([CoIITMPz[4+])4+ adsorbed on a graphite electrode undergoes spontaneous reduction, forming a surface containing CoI. Five reversible surface peaks are observed at low pH, two of which are two-electron concerted processes. At high pH, one of these two-electron processes splits into two one-electron waves. Both oxidation and reduction of the central metal can be observed, along with successive reduction steps involving the porphyrazine ligand. Notable is the marked shift to positive potentials of these processes, relative to unsubstituted cobalt phthalocyanine, due to the positive charge localized on the porphyrazine. The electrocatalytic activity of this complex modified electrode toward the reduction of hydrogen peroxide is also reported. We demonstrate that a series of different surfaces exist which are obtained by variation of pH and polarization potential and that these surfaces possess differing electrocatalytic activity. Sur...