Volume 17, Issue 35
Organoelement Compounds
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ChemInform Abstract: Trivalent Nickel Bis(triaza macrocyclic) Complexes. Ligand Ring Size and Medium Effects on the Nickel(III)/Nickel(II) Redox Couple Potential.

First published: September 2, 1986

Abstract

The formation of the Ni(III) title complexes (IV) with the ligands (IIId)-(IIIf) (preparation to be seen in the scheme) h-as been investigated in MeCN, DMSO, and water.

ChemInform Abstract

The formation of the Ni(III) title complexes (IV) with the ligands (IIId)-(IIIf) (preparation to be seen in the scheme) h-as been investigated in MeCN, DMSO, and water. ESR spectra of frozen MeCN solutions of (IVd)-(IVf) are typical of a low-spin d7 cation and display a rhombic [in the case of (IVd) and (IVe)] or axial (IVf) pattern. Examination of the half-wave potential of the Ni(II)/Ni(III) couples determined by voltam- 142 metric techniques, shows that the easiest attainment of the trivalent state occurs with the smallest ring size macrocycle (IIId). The complex (IVd) is formed at an even less positive potential than the [Ni(cyclam)]3+ complex considered until now as the most stable Ni(III) species among polyaza macrocyclic complexes. This demonstrates the superiority of six-coordination in stabilizing the Ni(III) oxidation state. The role of the solvent in the formation of trivalent complexes concerning the coordination and the solvation sphere and the presence and absence of water in the redox equilibrium has been investigated and discussed. The results are compared with those previously obtained for tetra-, penta-, and hexaaza ligand complexes.

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