PHOTOCHEMICAL REACTIONS OF NITROPENTAAMMINECOBALT(3) ION

The photochemical behavior of Co(NH3)5NO22+ has been investigated in aqueous solution and in the solid state. Excitations have been performed by radiations at 254, 313, 365, and 442 mμ, corresponding to charge-transfer and ligand-field bands of the complex. The nature of the photoreactions has been established by spectrophotometric measurements in the uv, visible, and ir spectral regions and by chemical analyses of some of the reaction products. In aqueous solution at all of the wavelengths of irradiation, the oxidation-reduction decomposition involving the NO2- ligand and the nitro → nitrito linkage isomerization occur simultaneously. In the solid state the nitro → nitrito isomerization occurs at all of the wavelengths of irradiation, accompanied at 254 mμ by a minor oxidation-reduction decomposition. For aqueous solutions the quantum yields of the two photoreactions have been determined. They decrease with decreasing energy of the exciting radiations, but their ratio is almost wavelength independent. The mechanisms of the photoreactions are discussed, and it is proposed that the same photoreactive excited state is involved, independent of the wavelength of irradiation. On the basis of the data obtained, it is also concluded that, even in solution, the linkage photoisomerization must occur through an intramolecular mechanism. © 1968, American Chemical Society. All rights reserved.