Synthetic, Electrochemical, Optical, and Conductivity Studies of Coordination Polymers of Iron, Ruthenium, and Osmium Octaethylporphyrin

A series of ligand-bridged metalloporphyrin polymers, [M(OEP)(L-L)]„ (M = Fe, Ru, Os; L-L = pyrazine, 4,4′-bipyridine, l,4-diazabicyclo[2.2.2]octane), have been synthesized and characterized. When partially oxidized, these polymers are highly conductive. The conductivity of these polymers depends on the extent of doping, the nature of the central transition metal, and the bridging ligand. The doped polymers exhibit strong infrared absorptions due to mixed-valence transitions, the features of which correlate with the bulk conductivity. The infrared spectra of the doped [Os(OEP)(pyz)]„ samples reveal the presence of a coupling between an IR-silent vibrational mode of the bridging ligand and a mixed-valence transition, which suggests that the bridging ligand participates in the conduction process. Electrochemical studies of the polymers have been carried out with carbon cloth electrodes. These studies demonstrate that the doping reactions are metal-centered and corroborate the assertion that the porphyrin 7r-electrons are not involved in the conduction pathway. This feature contrasts with most of the previous work with porphyrinic conductors in which the conduction pathway is dominated by the macrocycle.