Influence of organic cations on the stacking of semiquinone radical anions

A series of seven novel salts of tetrachloro-and tetrabromosemiquinone radical anions with organic cations is prepared and structurally characterised by single-crystal X-ray diffraction. Four types of stacks of radical anions have been identified: i) stacks of pancake-bonded dimers (Peierls-distorted stacks), ii) stacks of pancake-bonded trimers, iii) stacks of equidistant radicals and iv) a novel type of equidistant stacks of partially charged radicals (charge: -1/2, imposed by a stoichiometry of 1 : 2). Cations play an important role in stabilisation of the stacks of radical anions; the structures with stacks of equidistant radicals include columns of cations. However, the structures having pancake-bonded dimers and trimers are accompanied by isolated pairs of cations.