Resonance Raman Spectra of Tetrapyrrole Complexes of Oxomolybdenum(V)

The resonance Raman spectra of MoO(MEC) and MoO(OEP)(OMe) have been measured in the solid state. Due to low symmetry of the tetrapyrrole core, the former exhibits about 2 times more bands than the latter in the 1650-400-cm-1 region. Excitation profile studies on MoO(MEC) show that some tetrapyrrole core vibrations give maxima at the α(O-O) band and that two bands at 950 cm-1 (Mo=0 stretching) and 320 cm-1 are enhanced more than the core vibrations as the exciting frequency approaches the strong band at 455 nm. These results suggest that the 455-nm band is largely due to a ligand-metal charge-transfer transition and that the 320-cm-1 band is assignable to the Mo-N stretching vibration enhanced via such charge transfer. The spectral change caused by laser irradiation of MoO(OEP)(OMe) in the solid state has been attributed to polymerization through the formation of the methoxy bridge between two metal atoms.