The deprotonated amido vs. the amino group in the stabilization of coordinated trivalent copper and nickel cations. An electrochemical evaluation.

The M2+/M3+ redox change in the Cu and Ni complexes with 2 types of 14-membered tetraaza macrocycles contg. (1) 4 amine N atoms (cyclam) and (2) 2 amine N atoms and 2 deprotonated amido groups was studied by voltammetric techniques. Replacement of 2 amino groups by 2 deprotonated amido groups involves a dramatic decrease of the CuIII/CuII redox potential (of ∼0.8 V), but does not affect greatly the potential of the NiIII/NiII redox change. This behavior is related to the enhanced donor properties of the type dioxocyclam and benzyldioxocyclam macrocycles and to the more or less favorable CFSE (crystal field stabilization energy) contribution from which the M2+/M3+ change profits.