Ultraviolet/visible spectra have been recorded for chlorine, bromine, and iodine atom π-molecular complexes with a number of aromatic compounds. The visible spectra of the I •/arene complexes show charge-transfer (CT) bands whose transition energy correlates linearly with the vertical ionization potential of the corresponding arene. Comparison of the spectra of these complexes with the spectra of the corresponding Cl 2/arene, Br 2/arene, and I 2/arene complexes leads to the conclusion that the I •/arene complexes are classical hexahapto π-molecular complexes. The CT transition energies of the Cl •/arene and the Br •/arene complexes correlate well with one another, yet the CT transition energies of these complexes are seemingly independent of the vertical ionization potential of the arene.
The Journal of Physical Chemistry93, no. 2 (1989): 564–570.