188727-93-7Relevant academic research and scientific papers
Stabilization of copper(III) complexes by disubstituted oxamides and related ligands
Ruiz, Rafael,Surville-Barland, Celine,Aukauloo, Ally,Anxolabehere-Mallart, Elodie,Journaux, Yves,Cano, Joan,Munoz, M. Carmen
, p. 745 - 751 (2007/10/03)
The electrochemical behaviour of a family of monomeric copper(II) complexes of the related tetraanionic chelating ligands N,N′-o-phenylenebis(oxamate) (L1) and its methylamide (L2) and bis(methylamide) (L3) has been investigated by cyclic voltammetry in acetonitrile at 25°C and 0.1 mol dm-3 NEt4ClO4 as supporting electrolyte. The copper(III)-copper(II) reduction potentials have been found to span a potential range from +0.41 to -0.02 V (vs. saturated calomel electrode), being reversible for all cases except the copper(II)-L1 complex. The trend in formal potentials along this series is explained in terms of the stronger donor properties of the deprotonated-amido nitrogen atoms than those of the carboxylate oxygen ones. Hence, the stabilization of the trivalent oxidation state of copper is attributed to the increasing number of deprotonated-amido donor groups. A perfect correlation has been observed within this family between the CuIII-CuII potentials and the visible absorption maxima of the copper(II) complexes. The relative gain in crystal-field stabilization energy for the change from the d9 (CuII, square planar) to the low-spin d8 (CuIII, square-planar) electronic configuration is the main factor in the overall tnermodynamic stability of the copper(III) complexes. The molecular structure of the stable copper(III) complex [PPh4][CuL3J·MeCN has been'deterfnined by single-crystal X-ray analysis. The metal is in a nearly square-planar environment formed by the four amido nitrogen atoms of the chelating ligand, with short Cu-N bond distances (1.84-1.88 A) typical of trivalent copper.
