Inorganic Chemistry, Vol.35, No.18, 5188-5200, 1996
Models of the Cytochromes - Redox Properties and Thermodynamic Stabilities of Complexes of Hindered Iron(III) and Iron(II) Tetraphenylporphyrinates with Substituted Pyridines and Imidazoles
The Fe-III/Fe-II and Fe-II/Fe-I reduction potentials of a series of model hemes have been measured by cyclic voltammetry in dimethylformamide at 25 degrees C as a function of the concentration of added axial ligands. The six porphyrinate ligands utilized were tetraphenylporphyrin (TPP), tetramesitylporphyrin (TMP), and a series of "hindered" tetraphenylporphyrins having substituents (OCH3, F, Cl, Br) on both ortho positions of each of the four phenyl rings. The perchlorato salts of the iron(III) porphyrinates were utilized for the titrations. The axial ligands utilized were N-methylimidazole, 2-methylimidazole, and pyridines of basicities ranging in pK(a)(PyH(+)) from 9.7 to 1.1.
Keywords:TRANSITION-METAL PORPHYRINS;AXIALLY COORDINATED IMIDAZOLES;ELECTRON-PARAMAGNETIC-RES;SPIN FERRIC COMPLEXES;FORMATION-CONSTANTS;(PORPHINATO)IRON(III) COMPLEXES;METHYLOPHILUS-METHYLOTROPHUS;LIGAND ORIENTATION;CHEMICAL-SHIFTS;SERIES