RESONANCE RAMAN-SPECTRUM OF A (2)A(1U) FERRYL PORPHYRIN PI-CATION RADICAL

Resonance Raman spectra are reported for the iron complex of tetrameth yltetramesitylporphine (TMTMP) in its ferric, ferryl, and ferryl pi-ca tion 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 be havior of the v(2) and v(11) RR ''marker bands'', which shift to highe r frequency upon oxidation of the macrocycle, is consistent with previ ously reported NMR studies wherein these radicals were shown to have p redominately (2)A(1u) ground states. The v(Fe-O) stretching modes of t he ferryl species (both five- and six-coordinate) and (OFeTMTMP(.+))(C lO4-) are identified by their O-16/O-18 isotope shifts. This is the fi rst observation of the v(Fe-O) mode for a (2)A(lu), type ferryl pi-cat ion radical. Its frequency (833 cm(-1)) is virtually identical with th at 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 ferry lporphyrin pi-cation radicals are rather insensitive to radical type ( (2)A(lu) vs (2)A(2u))-behavior which is surprisingly different from th e previously observed sensitivity of the v(V-O) modes of corresponding vanadylporphyrin pi-cation radicals.