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

1998; Elsevier BV; Volume: 44; Issue: 2-3 Linguagem: Inglês

10.1016/s0013-4686(98)00118-2

1873-3859

K. Vengatajalabathy Gobi, Takeo Ohsaka,

Molecular Junctions and Nanostructures

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). The thermodynamic equilibrium between yellow and blue species was studied, and the thermodynamic parameters for the yellow–blue conversion were determined. Comparing the formal potentials (E0′) of [M2(bispen)]4+ [M=Cu(II), Ni(II)] and those of 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 E0′ of [Ni2(bispen)]4+ was found to shift towards the less positive potential region in presence of coordinating anions, and the shift in the E0′ is attributed to the coordination of electrolyte anions only to the tervalent nickel metal center. The observed 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 voltammetry measurements.