One- and two-electron reduction of metalloporphyrins. Radiation chemical, photochemical, and electrochemical studies. Kinetics of the decay of. pi. -radical anions
One- and two-electron reduction products of several metalloporphyrins have been studied by steady-state and pulse radiolysis in aqueous and methanolic solutions and by photochemistry and electrochemistry in aqueous solutions. This study concentrates on the TMPyP (tetrakis(N-methyl-4-pyridyl)porphyrin) complexes of Ga/sup III/, Ge/sup IV/, and In/sup III/, and the TPyP (tetra(3-pyridyl)porphyrin complex of Sb/sup V/, and compares them with the previously studied complexes of Zn/sup II/, Al/sup III/, and Sn/sup IV/. All these porphyrins undergo one-electron reduction on the ligand to form ..pi..-radical anions. The rates of formation and decay of these species have been studied under various conditions. The lifetimes of these radicals were found to vary greatly; those of Sb/sup V/ and Sn/sup IV/ are completely stable while some others decay in the millisecond range. The stability decreases in the order Sb/sup V/, Sn/sup IV/, In/sup III/, Ge/sup IV/, Ga/sup III/, Al/sup III/, Zn/sup II/, which was found to correspond to the order of the porphyrin ring reduction potentials determined under similar conditions. Increased lifetime of the radical upon increase in electronegativity of the metal was found to be due to inhibition of porphyrin ring protonation, which is a necessary step in the formation of final products. The final two-electron reduction products are mainly phlorin anions. The same products were observed upon photochemical reduction. The potentials for the first and second one-electron reduction of the porphyrins were determined by cyclic voltammetry. The separation between the first and second wave gives an indication of the stability of the ..pi..-radical anion.
- Research Organization:
- National Bureau of Standards, Gaithersburg, MD
- OSTI ID:
- 5697003
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 90:11
- Country of Publication:
- United States
- Language:
- English
Similar Records
Reduction reactions of water soluble cyano-cobalt(III)-porphyrins: Metal versus ligand centered processes
Oxidation and reduction of manganese porphyrins in aqueous solutions by free radicals: a pulse radiolysis investigation
Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANIONS
ELECTROCHEMISTRY
LIFETIME
PHOTOCHEMISTRY
RADIOLYSIS
ANTIMONY COMPLEXES
BISMUTH COMPLEXES
GALLIUM COMPLEXES
INDIUM COMPLEXES
LEAD COMPLEXES
ORGANOMETALLIC COMPOUNDS
PORPHYRINS
EXPERIMENTAL DATA
PHOTOLYSIS
VOLTAMETRY
CARBOXYLIC ACIDS
CHARGED PARTICLES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DATA
DECOMPOSITION
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
IONS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
RADIATION CHEMISTRY
RADIATION EFFECTS
400600* - Radiation Chemistry
400500 - Photochemistry
400400 - Electrochemistry