Fate of nickel and cobalt sulfophthalocyanines under oxidizing conditions: a spectroscopic investigation

Two water-soluble metal sulfophthalocyanines, namely Ni(II)PcS and Co(II)PcS, were structurally characterized by electrospray ionization mass spectrometry (ESI-MS) and UV-vis and NMR spectroscopy. The dominant ion in ESI-MS was a penta-protonated monomeric Ni(II) complex and a tetra-protonated form with the Co(II) ion being oxidized to Co(III), confirming the facile oxidation of the central cobalt atom of the phthalocyanine ring by a soft ionization method as ESI. Experiments at various ESI voltages were also performed to ascertain the target of the oxidation, whether it was the metal or the phthalocyanine unsaturated system. Addition of small amounts of oxidizing agents, like potassium persulfate, resulted in a definite attenuation of the Q band in the UV-vis spectra, while ESI-MS detected a variety of complexes, containing at least one oxygen atom, which rapidly replaced the initial complexes.