Synthesis, characterization and electrocatalytic behavior of cobalt and iron phthalocyanines bearing chromone or coumarin substituents

<div><p>Cobalt and iron phthalocyanines (Pcs) bearing peripherally tetra-substituted chromone (chr) or coumarin (cou) moieties were formulated and characterized by UV–Vis and FTIR spectroscopy, ESI-TOF mass spectrometry, and elemental analysis. The structural elucidations of the ligands, 4-(chromone-7-oxy)phthalonitrile (<b>1</b>) and 4-(4-(trifluoromethyl)-coumarin-7-oxy)phthalonitrile (<b>2</b>) were complemented by NMR spectroscopy and single crystal X-ray analysis (for <b>1</b>). The redox properties of the complexes were investigated via voltammetry and the subsequent voltammetric assignments were corroborated by UV–Vis spectroelectrochemistry. Each metal complex displayed four redox processes of which their Pc ring oxidations are irreversible and the remaining redox couples are quasi-reversible. Utilizing the respective metallophthalocyanines, modified working electrodes were prepared by electropolymerization and their electrocatalytic activities toward nitrite oxidation were explored. All the metal complexes showed an increase in nitrite oxidation currents and a minor decrease in oxidation potentials which is indicative of electrocatalysis. The trend of electrocatalytic activity was found to be as follows: CoPc–chr (<b>3</b>) > FePc–cou (<b>4</b>) > CoPc–cou (<b>5</b>).</p></div