Homoleptic, mononuclear transition metal complexes of 1,2-dioxolenes: Updating their electrochemical-to-structural (X-ray) properties

This review updates the electrochemical and structural aspects of homoleptic quinoidal (or pseudo-quinoidal) molecules coordinated to (single) transition metal ions. In fact, since 1,2-dioxolenes are redox-active molecules able to shuttle reversibly through the sequence quinone/hydroquinone/catechol, their metal complexes can display both the ligand-centred and the metal-centred electron transfers, which in some cases can overlap or trigger internal charge reorganizations. Such extended electron transfer ability makes it difficult in some cases to ascertain the oxidation states of both the ligands and the metal. Joint structural and electrochemical investigation can in most cases succeed in solving the dilemma, but in a wider horizon further experimental (for instance, magnetic measurements) or theoretical supports (enlightenment on the composition of frontier orbitals) would be desirable. (c) 2005 Elsevier B.V. All rights reserved.