Nickel and cobalt complexes of 15,15-disubstituted 1,4,7,10,13-pentaazacyclohexadecane-14,16-dione ligands

The synthesis of the novel Co(III)(15,15-difluoro-1,4,7,10,13-pentaazacyclohexadecane-14,16-dione) acetate complex from different cobalt sources is described. Furthermore, the corresponding nickel complex and its new analog with the 15-fluoro-15-methyl-1,4,7,10,13-pentaazacyclohexadecane-14,16-dione ligand were studied in great detail including cyclic voltammetry and single crystal analyses of a total of 6 complexes. The results for the nickel compounds showed that depending upon ligand substitution and solvent, an N3 or, after a double deprotonation, an N5 coordination mode could be observed and characterized in the solid state and in solution. Moreover, cyclic voltammetric analyses were performed revealing that the Ni(II/III) oxidation potentials are becoming more positive with the increasing number of fluorine atoms. This effect is due to the electron withdrawing property of fluorine that is reducing the electron richness of the metal ion. (C) 2011 Elsevier B.V. All rights reserved