A theoretical approach to a chemical system convertible into a storage cell: carbon_carbon bonds functioning as electron donor and electron acceptor units

Density functional calculations have been performed on nickel Schiff base complexes and nickel porphyrinogen complexes in order to understand the behaviour of these systems in redox processes. In nickel Schiff base complexes C–C sigma bonds are formed upon reduction, while in 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. The lack of variation in the oxidation state of the metal is the first step towards the reversibility of the redox process. The complementary behaviour in redox processes of nickel Schiff base complexes and nickel porphyrinogen complexes can be considered in a reversible electrochemical cell with the discharge process based on C–C bonds breaking and the recharge based on C–C bonds formation.