Electrochemical and spectral properties of novel dinickel(II) and dicopper(II) complexes with N,N-linked bis(pentaazacyclotetradecane)

摘要

The nickel(II) and copper(II) complexes of bis(pentaazamacrocyclic) ligand (bispen) are synthesized by the template condensation of bis(2-aminoethyl)-1,3-propanediamine, formaldehyde and 2-aminoethyl disulfide (a primary diamine). Thethermodynamic equilibrium between yellow and blue species was studied, and the thermodynamic parameters for the yellow-blue conversion were determined. Comparing the formal potentials (E{sup}0') of [M{sub}2(bispen)]{sup}4+ [M = Cu(II), Ni(II)] and thoseof the corresponding cyclam complexes, a destabilization effect on the M(III) state was observed and is ascribed to the strain in the pentaazamacrocycle caused by the presence of the uncoordinated tertiary N-atom in the macrocycle. The E{sup}0' of[Ni{sub}2(bispen)] {sup}4+ was found to shift towards the less positive potential region in presence of coordinating anions, and the shift in the E{sup}0' attributed to the coordination of electrolyte anions only to the tervalent nickel metal center. Theobserved order of anions for the stabilization of tervalent nickel metal ions was found parallel to that of their spectrochemical series. Equilibrium binding constants for the axial coordination of inorganic anions were determined by cyclic voltammetrymeasurements.