Tetranuclear Copper(II) and Nickel(II) Complexes Incorporating a New Imidazole-Containing Ligand

The ligating properties of a new tridentate imidazole‐ and phenol‐containing ligand H3L towards nickel(II) and copper(II) ions have been studied. The ligand generates, in the presence of air and base, iminosemiquinone radical anions, which are not stable in the presence of the metal ions. The amine bond >C−NH− of the parent ligand becomes oxidized to >C=N− bonds upon coordination with NiII or CuII. The imidazole N atom becomes deprotonated and the resulting imidazolate group acts as a bridging ligand to generate tetranuclear complexes [CuII4L′4] and [NiII4L′4], where [L′]2− is the dianionic new Schiff base formed after oxidation of the parent ligand. The square‐planar tetranickel(II) complex is diamagnetic, as expected, whereas the four copper centres bridged by imidazolate anions in the complex [CuII4L′4] are antiferromagnetically exchange coupled (J = −49 cm−1), which has been supported by the EPR measurements. A simple magnetostructural correlation for the imidazolate‐bridged copper(II) complexes is yet to emerge. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)