ELECTROCHEMICAL AND SPECTRAL PROPERTIES OF NOVEL DINICKEL(II) AND DICOPPER(II) COMPLEXES WITH N,N-LINKED BIS(PENTAAZACYCLOTETRADECANE)

The nickel(II) and copper(II) complexes of bis(pentaazamacrocyclic) li gand (bispen) are synthesized by the template condensation of bis(2-am inoethyl)-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 yel low-blue conversion were determined. Comparing the formal potentials ( E-0') of [M-2(bispen)](4+) [M = Cu(II), Ni(II)] and those of the corre sponding cyclam complexes, a destabilization effect on the M(III) stat e was observed and is ascribed to the strain in the pentaazamacrocycle caused by the presence of the uncoordinated tertiary N-atom in the ma crocycle. The E-0' of [Ni-2(bispen)](4+) was found to shift towards th e less positive potential region in presence of coordinating anions, a nd the shift in the E-0' is attributed to the coordination of electrol yte anions only to the tervalent nickel metal center. The observed ord er of anions for the stabilization of tervalent nickel metal ions was found parallel to that of their spectrochemical series. Equilibrium bi nding constants for the axial coordination of inorganic anions were de termined by cyclic voltammetry measurements. (C) 1998 Elsevier Science Ltd. All rights reserved.