Cu-Ln complexes involving non-symmetrical ligands able to introduce asymmetric centres in the vicinity of Ln ions

Abstract

The present work confirms the difficulty to prepare main ligands able to coordinate 3d and 4f ions and to bring asymmetric centres in the vicinity of the Ln ions. Although our two first examples were not realized with pure enantiomers, we have shown that introduction of 3d ions in these ligands was possible but problems arise with the complexation of the LnIII ions. Due to these difficulties, we used an original reaction pathway. A trianionic ligand possessing one amide, one imine, two phenol functions reacts with CuII ions to yield an anionic complex that crystallizes in a non-centrosymmetric space group, due to the presence of a stereogenic CuII centre. Further reaction with LnIII ions in presence of ancillary ligands yields tetranuclear complexes made of two LCuGd units in a head-to-tail arrangement. Ferromagnetic Cu-Ln interactions, resulting from an alternate distribution of the CuII and LnIII ions, are the only ones to be active. But this tetranuclear complex is no more chiral, the conformation change of the ligand diamino chain around one CuII ion yielding two CuII ions of opposite chiralities.