Bis-bipyridine hexa-aza-macrocycle complexes of zinc(II) and nickel(II) and the catalytic reduction of carbon dioxide

Aza-macrocyclic complexes have gained importance in catalysis for the activ ation of small molecules, like carbon dioxide. Bis-bipyridine hexa-aza-macr ocycles efficiently co-ordinate as a tetradentate ligand, to give complexes of Zn(II), Ni(II) and other transition metal ions that are essentially pla nar. Spectroscopic, electrochemical and chemical characterizations of these systems are presented in this article. Electrochemical studies performed i n a carbon dioxide atmosphere render preliminary information about its elec trocatalytical reduction. Quantum chemical calculations are used to underst and the origin of the manifested properties of both the ligands and the met al complexes. They show, in this case, the importance of delocalized pi int eractions, which are responsible for their different structural and electro nic characteristics in protic and non-protic media. (C) 3000 Elsevier Scien ce B.V. All rights reserved.