Halogenated Benzene Cation Radicals

The benzene cation radicals [C6F5-CF3](+), [1,4-C6F4(CF3)(2)](+), [1,2,4,5-C6H2Cl4](+), [C6F5-C6F5](+), and [C6Br6](+) have been obtained as salts with fluoroarsenic and fluoroantimony counterions. Their structures have been obtained by single-crystal structure determinations, and supported by ESR measurements and DFT calculations. [C6F5-CF3](+), [1,4-C6F4(CF3)(2)](+), and [1,2,4,5-C6H2Cl4](+) have the predicted bisallyl type structure. [C6F5-C6F5](+) can be described as having a quinoid form with a strengthened central C-C bond and a smaller dihedral angle as compared to the neutral C6F5-C6F5. [C6Br6](+) is the missing link between [C6F6](+), [C6Cl6](+), and [C6I6](+). It has a Jahn-Teller distortion, though weaker than [C6F6](+) and [C6Cl6](+), in contrast to [C6I6](+), which remains in a regular hexagon structure.