Spectro-electrochemistry of cobalt and iron tetrasulphonated phthalocyanines

Abstract Cobatl and iron derivatives of tetrasulphonated phthalocyanine (TsPc) have been studied by spectroelectrochemistry in aqueous solution at pH 2–10. For CoTsPc, two reduced species are observed: yellow [Co(I)TsPc(−2)] − and pink [Co(I)TsPc(−3)] 2− , over the entire pH range. In acid, oxidation gives a monomeric [Co(III)TsPc(−2)] + species; in base, in equilibrium exists between monomeric and dimeric forms of [Co(III)TsPc(−2)] + , whose relative concentration depends upon concentration of CoTsPc, ionic strength, pH and temperature. Reduction of [Fe(III)TsPc(−2)] + solutions gives green Fe(II)TsPc(−2) and pink [Fe(I)TsPc(−2)] − over the entire pH range. Oxidation gives a product which appears to be an [Fe(IV)TsPc] 2+ species. Differences between the spectra of the species and in the species obtained at different pH values, and aggregation effects are discussed with reference to the nature of axial coordination to the central metal atoms.