Binding of carbon dioxide to cobalt and nickel tetra-aza macrocycles

Abstract

Cyclic voltammetry of cobalt and nickel complexes of the macrocycle 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene in 0.10M tetraethylammonium perchlorate in dimethyl sulphoxide in the presence of carbon dioxide shows a strong positive shift of the Co^II/I reduction potential, leading to an equilibrium constant of 7 × 10⁴ for CO₂ binding, whereas the nickel complex shows a very low affinity for CO₂ binding in either the Ni^II or Ni^I oxidation states.