Tungstoarsenate(III) polyoxoanions as inorganic ligands for polynuclear copper complexes

A trinuclear copper(II) complex and a tetranuclear copper(II) complex that each incorporate a 9-tungstoarsenate(III) polyoxoanion ligand and several 2,2′-bipyridine (2,2′-bpy) ligands co-crystallize as the acid form: H4[{Cu(2,2′-bpy)}3(α-AsW9O33)] · [{Cu(2,2′-bpy)2}{Cu(2,2′-bpy)}3(α-AsW9O33)] · 38H2O (1). Compound 1 was obtained from a hydrothermal reaction employing the trivacant lacunary polyoxometalate [α-AsW9O33]9− as a precursor. The α-isomeric form of the parent ion is retained in both product anions. Four different coordination modes are observed for the seven copper centers, with unusual structural distortions imposed by the steric bulk of the polyanion. Intra- and intermolecular π-stacking of the 2,2′-bpy ligands are both evident. Variable temperature magnetic susceptibility, magnetization and EPR data are consistent with very weak antiferromagnetic interactions between the copper centers that are likely mediated by the π-stacking of the 2,2′-bpy ligands.

[{Cu(2,2′-bpy)}3(α-AsW9O33)]3− and [{Cu(2,2′-bpy)2}{Cu(2,2′-bpy)}3(α-AsW9O33)]− are the first two complexes of 3d metal centers to feature inorganic tungstoarsenate ligands and organic 2,2′-bpy ligands. They co-crystallize following the hydrothermal reaction between [α-AsW9O33]9−, Cu(II) and 2,2′-bipyridine in acetate buffer. Very weak antiferromagnetic exchange interactions are evident between the copper centers in the two complexes.Figure optionsDownload as PowerPoint slide