Peculiar properties of homoleptic Cu complexes with dipyrromethene derivatives

Abstract

In view of preparing Cu polynuclear complexes with dipyrromethene ligands, the mononuclear complexes [Cu(II)(dipy)₂] (dipyH = 5-phenyldipyrromethene) and [Cu(II)(dpdipy)₂] (dpdipyH = 1,5,9-triphenyldipyrromethene) have been prepared and characterized by X-ray crystallography, mass spectrometry and EPR spectroscopy. Their peculiar redox and spectroscopic (absorption/emission) behaviours are discussed. In contrast to Cu^II complexes of 1,1′-bidypyrrin, the reduction electrolysis of [Cu(II)(dpdipy)₂] leads to decomposition products on a time scale of a few hours. Moreover in relation to this observation, [Cu(I)(dpdipy)₂]⁻ could not be synthesized in spite of the Cu^I core protection by the phenyl substituents in ortho position of the nitrogen atoms. Theoretical calculations provide some explanations for this instability. Interestingly [Cu(II)(dipy)₂] and [Cu(II)(dpdipy)₂] display weak luminescence at room temperature, attributed to a ligand centered emission.