Diiodine arenes

The additions of other (polycyclic) aromatic donors to solutions of dichlorine, dibromine or diiodine afford similar new bands, which show significant red shifts with increasing strength of the arene donor. For example, the absorption maximum of the dibromine complexes varies from 280 nm (with chlorobenzene) to 369 nm (with hexamethylbenzene) and similar variations of the new absorption maxima are observed with diiodine complexes (Fig. 2). 

The only reported X-ray structure of a it-bonded diiodine exists in the 12/coronene associate [75], which shows the I2 to be located symmetrically between the aromatic planes and to form infinite donor/acceptor chains. -Coordination of diiodine over the outer ring in this associate is similar to that observed in the bromine/arene complexes (vide supra), and the I - C separation of 3.20 A is also significantly contracted relative to the stun of their van der Waals radii [75]. For the highly reactive dichlorine, only X-ray structures of its associates are observed with the n-type coordination to oxygen of 1,4-dioxane [76], and to the chlorinated fullerene [77]. 

Table 5.6 Equilibrium constants Kc (I mol 0 and diiodine basicity scales pKt arenes, heteroarenes and alkenes.

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