Unveiling the Structure of Polytetraruthenated Nickel Porphyrin by Raman Spectroelectrochemistry

The structure of polytetraruthenated nickel porphyrin was unveiled for the first time by electrochemistry, Raman spectroelectrochemistry, and a hydroxyl radical trapping assay. The electrocatalytic active material, precipitated on the electrode surface after successive cycling of [NiTPyP­{Ru­(bipy)₂Cl}₄]⁴⁺ species in strong aqueous alkaline solution (pH 13), was found to be a peroxo-bridged coordination polymer. The electropolymerization process involves hydroxyl radicals (as confirmed by the characteristic set of DMPO/^•OH adduct EPR peaks) as reaction intermediates, electrocatalytically generated in the 0.80–1.10 V range, that induce the formation of Ni–O–O–Ni coordination polymers, as evidenced by Raman spectroelectrochemistry and molecular modeling studies. The film growth is halted above 1.10 V due to the formation of oxygen gas bubbles