Density functional investigations on the C-C bond formation and cleavage in molecular batteries

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 electrons reservoirs, but also as a buffer for the oxidation state of the metal. In the molybdenum Schiff base complexes a preferential formation of metal-metal bonds upon reduction is calculated, while in the niobium analogues the formation of C-C bonds competes with that of M-M bonds, the latter being the first ones to be involved in electron-transfer reactions