Metal complexes of 1,2-diaminobenzene derivatives. Determination of the oxidation state of the ligands through crystallographic data

Abstract

The known crystal structures of metal complexes containing 1,2-diaminobenzene derivatives in the form of the benzenediamine dianion I, benzosemiquinone diimine monoanion II or neutral benzoquinone diimine III have been examined. Since the 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. It thus becomes possible to deduce the oxidation state of a 1,2-diaminobenzene derivative just by considering its crystal structure. The available data indicate that the 1,2-diaminobenzene derivatives considered, once complexed to a metal ion, generally do not assume charge-localized structures, like I–III, but intermediate ones. In most cases, these forms are near to II or intermediate between II and III. The results are compared with literature oxidation-state assignments, and discussed in terms of the back-bonding ability of the ligands.