A theoretical approach to molecular batteries: C-C bonds functioning as electron shuttles

Density functional calculations have been performed on titanium, nickel, molybdenum and niobium-Schiff base complexes and titanium, nickel-porphyrinogen complexes in order to understand the behavior of these systems in redox processes. In titanium and nickel-Schiff base complexes C-C sigma bonds are formed upon reduction, while in titanium and nickel-porphyrinogen complexes C-C sigma bonds are formed upon oxidation. In both systems, the formation or the cleavage of C-C bonds avoids a variation in the oxidation state of the metal and these C-C bonds act not only as electron reservoirs, but also as a buffer for the oxidation state of the metal. The possibility of intramolecular electron transfer from C-C bonds to M-M bonds and vice versa has been investigated for molybdenum and niobium-Schiff base complexes. (C) 2003 Elsevier B.V. All rights reserved.