Resonance Raman spectrum of a (2)A(1u) ferryl porphyrin pi-cation radical

Resonance Raman spectra are reported for the iron complex of tetramethyltetramesitylporphine (TMTMP) in its ferric, ferryl, and ferryl pi-cation forms. For comparison, the spectra of the copper complex and its corresponding pi-cation radical are included. Vibrational assignments have been made based on depolarization ratio measurements and isotopic frequency shifts associated with methine deuteration. The observed behavior of the v(2) and v(11) RR ''marker bands'', which shift to higher frequency upon oxidation of the macrocycle, is consistent with previously reported NMR studies wherein these radicals were shown to have predominately (2)A(1u) ground states. The v(Fe-O) stretching modes of the ferryl species (both five- and six-coordinate) and (OFeTMTMP(.+))(ClO4-) are identified by their O-16/O-18 isotope shifts. This is the first observation of the v(Fe-O) mode for a (2)A(lu), type ferryl pi-cation radical. Its frequency (833 cm(-1)) is virtually identical with that of the corresponding derivative of nzeso-tetramesitylporphyrin (TMP), (O=FeTMP(+))(ClO4-), a (2)A(2u), radical, which exhibits its v(Fe-O) mode at 835 cm(-1). These data imply that the v(Fe-O) modes of ferrylporphyrin pi-cation radicals are rather insensitive to radical type ((2)A(lu) vs (2)A(2u))-behavior which is surprisingly different from the previously observed sensitivity of the v(V-O) modes of corresponding vanadylporphyrin pi-cation radicals.