Metalloporphyrin Mixed-Valence π-Cation Radicals: Solution Stability and Properties

Abstract

Solution equilibria and optical spectra of several metallooctaethylporphyrin π-cation radicals have been examined in methylene chloride solution. The several π-cation radical species, [M(OEP•)]Y (M = Cu, Ni, Zn, Pd, or VO; Y = ClO4- or SbCl6-), are found to dimerize to form [M(OEP•)]22+. These dimeric species are characterized by the appearance of a new, strongly concentration-dependent near-infrared absorption band. This band is found in the region of 900−960 nm for all compounds except for the vanadyl complex which absorbs farther to the red at 1375 nm. The equilibrium constants for the dimerization reaction (2[M(OEP•)]+ (KD) [M(OEP•)]22+) have been evaluated from multiple-wavelength, concentration-dependent absorption data. Equimolar solutions of these π-cation radicals and their analogous neutral M(OEP) derivatives react to form new binuclear species, [M(OEP•/2)]2+, in which the single radical electron is delocalized over both porphyrin rings. These new species, for which we suggest the term “mixed-va...