Unique properties of transition metal quinone complexes of the MQ(3) series

Transition metal complexes of ligands derived from o-benzoquinones have bee n shown to exhibit unique versatility in their electronic, structural and m agnetic properties. Examples of these properties are described for complexe s of the MQ(3) series with ligands coordinated in the form of semiquinonate (SQ) radical anions, catecholate dianions (Cat), and unreduced benzoquinon es (BQ). Electrochemical activity may occur at either the metal or ligand; SQ complexes exhibit temperature dependent magnetic properties resulting fr om M-SQ, SQ-SQ, and intermolecular exchange coupling; equilibria between M- I(SQ)/M-II(Cat) redox isomers has been observed to occur in solution and in the solid state; charge localization has resulted in the formation of comp lexes containing mixed-valence ligands; strong pi donation from Cat oxygens has been found to stabilize metal ions in unusually high oxidation states. Examples of these properties from among compounds of the MQ(3) series are described. (C) 2001 Elsevier Science B.V. All rights reserved.