Coordination compounds of 1,4-dihydroxybenzoquinone and its homologues. Structures and properties

Metal complexes of 1,4-dihydroxy-benzoquinone and its homologues (H2C6X2O4) are reviewed, focusing on assembled structures based on their X-ray crystallographic structures reported so far. A wide variety of crystal structures based on mononuclear, binuclear, polynuclear complexes and extended structures of coordination polymers or hydrogen bond linked networks are listed in relation to the coordination modes such as the monodentate, bidentate, and bis-bidentate form of the ligands. Their physico-chemical properties such as redox, UV-vis, EPR and magnetic properties are described. The ligand, H2C6X2O4, discussed here is one of the most useful multifunctional ligands, affording not only various self-assembled frameworks via coordination, hydrogen, and coulomb linkages, but also unique electronic structures, which are accompanied by charged and spin states. Their characteristics are mentioned in detail. (C) 2002 Elsevier Science B.V. All rights reserved.