Ligands derived from o-benzoquinone: statistical correlation between oxidation state and structural features

Abstract

The known crystal structures of co-ordination compounds containing o-benzoquinone, tetrachloro-o-benzoquinone and 3,5-di-tert-butyl-o-benzoquinone derivatives in the form of catecholates I, semiquinonates II or benzoquinones III have been examined. Since forms I–III differ both in oxidation state and structural features, a simple method is proposed to correlate the oxidation states of these ligands with their structural parameters, thus allowing the determination of the oxidation state on the basis of crystallographic data. By this procedure it is possible to confirm that the o-benzoquinone complexes in most cases assume charge-localized electronic structures, and the same conclusion is reached by factor analysis. The results are compared with literature oxidation-state assignments, and the periodic trend in the charge distribution across a transition series is discussed for homoleptic complexes.