Dinuclear Complexes Formed by Hydrogen Bonds: Synthesis, Structure and Magnetic and Electrochemical Properties.

The synthesis is reported of a series of homo-and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis( 1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between co-ordinated alcohols and coordinated alkoxides. Homonuclear divalent (MMII)-M-II, mixed-valent (MMIII)-M-II and heteronuclear (MM)-M-II'(III) species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O center dot center dot center dot O distances for the hydrogen bonds. Magnetic measurements show the hydrogen-bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves, which are attributed to rapid intramolecular proton transfer facilitated by the hydrogenbonded structure.