Synthesis, characterization and electrochemical studies of unsymmetrical macrocyclic mono and binuclear nickel(II) complexes

A series of nickel(II) complexes of general formula [Ni2L](ClO4)(2) with unsymmetrical compartmental macrocyclic ligands was synthesized by stepwise method using 6,6'-piperazine-1,4-diyldimethylenebis(4-X-2-formylphenol) (X = CH3 or Br), nickel(II) ions and diamines. In this macrocyclic system there are two different N2O2 compartments, one has two piperazinyl nitrogens and two phenolic oxygens and the other compartment has two azomethine nitrogens and two phenolic oxygens as coordinating sites. The complexes were characterized by elemental and spectral analysis. The electrochemical properties of the complexes indicate that all the complexes undergo two quasi-reversible one electron transfer processes in the cathodic potential region (0 to - 1.3 V) and two quasi-reversible one electron transfer processes in the anodic potential region (0 to + 1.3 V). In both reduction and oxidation process the first electron transfer process is shifted towards anodic potential region as the macrocyclic ring size increases. The reduction and oxidation process also changes with the substituent at the para position of the phenolic oxygen atoms. (C) 2003 Elsevier Science B.V. All rights reserved.