| Abstract
| - Resonance Raman spectra are reported for the iron complex oftetramethyltetramesitylporphine (TMTMP)in its ferric, ferryl, and ferryl π-cation forms. Forcomparison, the spectra of the copper complex and itscorrespondingπ-cation radical are included. Vibrational assignments have beenmade based on depolarization ratio measurementsand isotopic frequency shifts associated with methine deuteration.The observed behavior of the ν2 andν11 RR“marker bands”, which shift to higher frequency upon oxidation ofthe macrocycle, is consistent with previouslyreported NMR studies wherein these radicals were shown to havepredominately 2A1u ground states. Theν(Fe−O)stretching modes of the ferryl species (both five- and six-coordinate)and(OFeTMTMP•+)(ClO4-)are identified bytheir 16O/18O isotope shifts. This is thefirst observation of the ν(Fe−O) mode for a2A1u type ferryl π-cationradical.Its frequency (833 cm-1) is virtuallyidentical with that of the corresponding derivative ofmeso-tetramesitylporphyrin(TMP),(OFeTMP+)(ClO4-), a2A2u radical, which exhibits itsν(Fe−O) mode at 835 cm-1. Thesedata imply thatthe ν(Fe−O) modes of ferrylporphyrin π-cation radicals arerather insensitive to radical type (2A1u vs2A2u)behaviorwhich is surprisingly different from the previously observedsensitivity of the ν(V−O) modes of correspondingvanadylporphyrin π-cation radicals.
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