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 (λ i r r = 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 (λ i r r = 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 5 T 2 g ligand-field excited state.