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Issue 5, 1997
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Stabilization of copper(III) complexes bydisubstituted oxamides and related ligands


The electrochemical behaviour of a family of monomeric copper(II) complexes of the related tetraanionic chelating ligands N,N ′-o-phenylenebis(oxamate) (L 1 ) and its methylamide (L 2 ) and bis(methylamide) (L 3 ) has been investigated by cyclic voltammetry in acetonitrile at 25 °C and 0.1 mol dm -3 NEt 4 ClO 4 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)–L 1 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 Cu III –Cu II potentials and the visible absorption maxima of the copper(II) complexes. The relative gain in crystal-field stabilization energy for the change from the d 9 (Cu II , square planar) to the low-spin d 8 (Cu III , square-planar) electronic configuration is the main factor in the overall thermodynamic stability of the copper(III) complexes. The molecular structure of the stable copper(III) complex [PPh 4 ][CuL 3 ]·MeCN has been determined 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 Å) typical of trivalent copper.

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Article type: Paper
DOI: 10.1039/A607572J
Citation: J. Chem. Soc., Dalton Trans., 1997,0, 745-752
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    Stabilization of copper(III) complexes by disubstituted oxamides and related ligands

    R. Ruiz, C. Surville-Barland, A. Aukauloo, E. Anxolabehere-Mallart, Y. Journaux, J. Cano and M. Carmen Muñoz, J. Chem. Soc., Dalton Trans., 1997, 0, 745
    DOI: 10.1039/A607572J

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