Photochemical reactions of fac-[Mn(CO)3(phen)imidazole]+: evidence for long-lived radical species intermediates.
The electronic absorption spectrum of fac-[Mn(CO)(3)(phen)imH](+), fac-1 in CH(2)Cl(2) is characterized by a strong absorption band at 378 nm (epsilon(max) = 3200 mol(-1) L cm(-1)). On the basis of quantum mechanical calculations, the visible absorption band has been assigned to ligand-to-ligand charge-transfer (LLCT, im-->phen) and metal-to-ligand charge-transfer (MLCT, Mn-->phen) charge transfer transition. When fac-1 in CH(2)Cl(2) is irradiated with 350 nm continuous light, the absorption features are gradually shifted to represent those of the meridional complex mer-[Mn(CO)(3)(phen)imH](+), mer-1 (lambda(max) = 556 nm). The net photoreaction under these conditions is a photoisomerization, although, the presence of the long-lived radical species was also detected by (1)H NMR and FTIR spectroscopy. 355 nm continuous photolysis of fac-1 in CH(3)CN solution also gives the long-lived intermediate which is readily trapped by metylviologen (MV(2+)) giving rise to the formation of the one-electron reduced methyl viologen (MV(*+)). The UV-vis spectra monitored during the slow (45 min) thermal back reaction exhibited isosbestic conversion at 426 nm. On the basis of spectroscopic techniques and quantum mechanical calculations, the role of the radicals produced is analyzed.
de Aguiar
Inara
I
Departamento de Química, Universidade Federal de São Carlos, CP 676, 13565-905, São Carlos, SP, Brasil.
Inglez
Simone D
SD
Lima
Francisco C A
FC
Daniel
Juliana F S
JF
McGarvey
Bruce R
BR
Tedesco
Antônio C
AC
Carlos
Rose M
RM
D004579:Electron Transport; D005609:Free Radicals / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D008027:Light; D008345:Manganese / Q000737:chemistry*; D008670:Metals / Q000737:chemistry; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010777:Photochemistry; D010782:Photolysis; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
D005609:Free Radicals; D007093:Imidazoles; D008024:Ligands; D008670:Metals; D009942:Organometallic Compounds; D008345:Manganese