Acid–base and spectroscopic properties of a novel supramolecular porphyrin bonded to four pentacyanoferrate(II) groups

The synthesis and characterization of a new supermolecular porphyrin obtained by the coordination of four pentacyanoferrate(II) groups to the pyridyl N-atoms of meso-(3-pyridyl)porphyrin are reported. The redox potential and the 57Fe Mössbauer isomeric shift indicated that the pyridylporphyrin behaves as an electron-withdrawing group. The binding of pentacyanoferrate(II) groups induced a remarkable increase in the basicity of the porphyrin ring, in contrast to the [Ru(bipy)2Cl]+ groups. In the presence of Ni(II) ions, the pentacyanoferrateporphyrin complex precipitated forming a Prussian blue type material. The voltammograms of a carbon paste electrode of this material exhibited two broad redox waves around 0.43 and 0.63 V ascribed to two distinct iron sites, as confirmed by 57Fe Mössbauer spectroscopy.