Metalloporphyrin Mixed-Valence π-Cation Radicals:  Solid-State Structures

The synthesis and structural characterization of three mixed-valence π-cation radical derivatives of (octaethylporphinato)metal(II) species, [M(OEP • /2 )] 2 +, (M = Ni, Cu, and (Zn,H 2 )), are reported. The species thus have the same formal ring oxidation level as the photooxidized special pair of photosynthetic reaction centers. The complexes display unique binuclear structures with cofacial porphyrin rings with mean plane separations of 3.20−3.32 Å, ring center to ring center distances of 3.50−3.55 Å, and lateral shifts between the two rings of 1.16−1.53 Å. These inter-ring geometries are distinctly different from either those of “classical” π-cation radical derivatives or those of dimers formed by neutral species. The different inter-ring geometries suggests that there are inherent inter-ring geometries that depend principally on the oxidation level of the porphyrin rings.