Polynuclear Oxalate-bridged Nickel Complexes based on Bis(macrocyclic) Building Blocks: Synthesis, Spectral and Electrochemical Studies

Abstract

Several polymeric, oxalate-bridged supramolecular structures based on dinickel complexes of bis(macrocyclic) pentaaza ligands having a polymethylene or xylylene spacer between macrocyclic subunits were synthesized and characterized by means of UV VIS, IR spectroscopy and cyclic voltammetry. Electrochemical data reveal that bis(macrocyclic) amine ligands do not stabilize the nickel(III) oxidation state as effectively as does the related monomacrocycle. For most of the compounds studied, the stability of the mixed-valent Ni^III-Ni^II state relative to the isovalent ones (comproportionation equilibrium) does not depend on the structure of the spacer except for two complexes which display lower stability in this state. In the complex having the shortest dimethylene bridge, electronic interactions in the binuclear core may account for the observed effect while steric repulsions play an important role in the m-xylylene-bridged derivative.

Key Words:

• Polynuclear complexes
• bis(macrocycles)
• redox potentials
• nickel(III/II) couple
• comproportionation equilibria