Dinuclear Metal Complexes. Part 2. Synthesis, Characterisation, and Electrochemical Studies of Macrocyclic Dicopper(II) Complexes

Article abstract of DOI:10.1039/DT9830002429

The synthesis, characterisation, and electrochemical studies of dicopper(II) complexes 1>2.nH2O of the macrocycle 7,11;19,23-dimetheno-9,21-dimethyl<1,5,13,17>-tetra-azacycloicosa-5,7,9,12,17,19,21,24-octaene-25,26-diol (H2L¹), and of some 6,12,18,24-substituted (Me4; Prⁿ4; Ph4; Ph, Me, Ph, Me) derivatives have been carried out.These compounds undergo sequential one-electron transfers at two different potentials.For all of these compounds, except for 1>2.2H2O, two reversible or almost reversible reduction steps have been observed in acetonitrile medium using a hanging mercury drop electrode.In the case of 1>2.2H2O, the second couple became obscured due to the presence of an adsorption phenomenon or secondary electrode reaction.However, in NN-dimethylformamide (dmf) medium, satisfactory voltammograms have been obtained only with 1>2.2H2O.The mixed-valent complexes are considerably more stable in acetonitrile than is IICu^IL¹>⁺ in dmf.The potentials of the first reduction step (E₁) remain practically invariant throughout the series and are independent of the extent of magnetic interactions in the dicopper(II) complexes.The potentials of the second reduction step (E₂) vary with the alkyl and aryl groups present, and a linear plot has been obtained for E₂ vs. the Hammett function ?_m.On the basis of previously reported observations and the present study it is inferred that in acetonitrile medium the unpaired electron in the mixed-valent complexes remains localised on one of the copper atoms.

Full text of DOI:10.1039/DT9830002429

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