Electron spin resonance study of the structure of the alkali-metal complexes of symmetric dithienobenzoquinones

The formation of ion pairs was detected upon reducing the thiophen analogues of anthraquinone and phenanthraquinone with alkali-metals in ethereal solvents. Different structures of the ion pair are observed for the two classes of compounds. The thiophen analogues of phenanthraquinone give complexes where the alkali-metal is located on the molecular plane and chelated by the oxygen lone pairs. In the analogues of anthraquinone the counterion is located near only one of the carbonyl oxygen atoms at a given time. When the two carbonyl groups are non-equivalent, as in (V), the ion pair may exist in two different isomeric forms, both of which have been detected in one case.