Photodecomposition of cis-azidoamminebis(2,4-pentanedionato)cobalt(III). The photoactive state

Article abstract of DOI:10.1021/ic50222a041

The photodecomposition of cis-Co(acac)₂N₃NH₃ (acac = 2,4-pentanedionate) occurs with the formation of Co(acac)₂ and azide radicals. This reaction has been effected with the use of exciting radiations throughout the 250-580-nm region, and in the 250-470-nm region the quantum efficiency for this reaction is surprisingly wavelength independent. Examination of the optical spectra of Co(acac)₂N₃NH₃ and Co(acac)₃ and the respective optical electronegativities of the azide and 2,4-pentanedionate ligands suggests that photooxidation of the 2,4-pentanedionato group should be favored over that of the azido group. Yet photooxidation of the azido group is the only observed reaction. This observation, the relative constancy of the quantum efficiency, and the energy of the threshold for the onset of redox photodecomposition ((21.3-17.2) × 10³ cm^-1) suggest that the photoactive state is a triplet charge-transfer state involving the azido group. The photoreaction has an apparent activation energy of 11.7 kcal/mol, and solvent assistance in the loss of the azide radical is implicated.