Optical and photoinduced electron transfer in tris(ethylenediamine)cobalt(III)-cyanometallate ion pairs

The ion pairs {[Co(en)(3)](3+); [M(CN)(x)](4-)}, where M=Fe, Ru, Os (x=6) and M=Mo, W (x=8), and {[Co(en)(3)](3+); [Mn(CN)(5)NO](3-)}, in aqueous solution show up ion pair charge-transfer (IPCT) transitions in the visible and near-ultraviolet spectral regions. On excitation of the IPCT transitions (lambda(irr)=405 nm), trinuclear complexes trans-{(en)(2)Co[NC-M(CN)((x-1))](2)](5-) are formed subsequent to an optical electron-transfer step with quantum yields close to unity. Excitation of the longest-wavelength ligand-field transition (lambda(irr)=510 nm) of ion paired [Co(en)(3)](3+) results in a photoinduced electron-transfer reaction leading to the formation of binuclear pentacoordinate [(en)(2)Co-NC-M(CN)(5)](-) (M=Fe, Ru, Os) and trinuclear hexacoordinate trans- {(en)(2)Co[NC-M(CN)(7)](2)}(5-) (M= Mo, W) complexes. The redox-reactive excited state of [Co(en)(3)](3+) has a lifetime shorter than 3 ns and is tentatively assigned to the T-5(2g) ligand-field excited state. (C) 1997 Elsevier Science S.A.