Photochemical and photophysical data are reported for a series of fac-[Mn(CO)3(phen)(Im–R)](SO3CF3) complexes, where phen is 1,10-phenanthroline and Im is imidazole. Intraligand and metal-to-ligand charge transfer (MLCT) transitions are observed in the electronic absorption spectra of these complexes and are sensitive to the nature of the ligand substituent. At room temperature the emission spectra show a clear progression from broad structureless MLCT to highly structured π–π* emission on going from R = -H, -CH3, -C6H5, to -Metro, where Metro is 2-methyl-5-nitroimidazole. Even at low temperatures the latter complexes show only the π–π* emission. The trend in the photophysical properties found in the emission spectra parallels the changes in the photochemical properties with the electron-donating or electron-withdrawing power of the substituent on the imidazole ligand. Although MLCT irradiation of the complexes with R = -H, -CH3 leads to the mer-[Mn(CO)3(phen)(Im–R)] isomers, the complexes with the imidazole ligand substituted by -C6H5 or -Metro release the Im–R ligand and produce the stereoretentive fac-[Mn(CO)3(phen)(S)] complexes. The stereochemical fate and mechanistic implications of the photolysis reactions are discussed in terms of the nature of ligand substitution.
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Vol. 80 • No. 2