METAL-COMPLEXES OF 1,2-DIAMINOBENZENE DERIVATIVES - DETERMINATION OF THE OXIDATION-STATE OF THE LIGANDS THROUGH CRYSTALLOGRAPHIC DATA

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.