Mononuclear copper(II) complexes containing a macrocyclic ditopic ligand: synthesis, structures and properties

Abstract : Three different mononuclear copper(II) complexes 1-3 bearing ditopic macrocyclic ligands (L1 or L2) have been prepared. Both ligands include two coordinating cores, namely tris(methylpyridyl)amine (TPA) and pyridine-dicarboxamide (PydCA). Complexes 1-3 have been characterized in solid state, and in solution by UV-Vis and EPR spectroscopies, as well as by cyclic voltammetry. X-ray diffraction analyses of crystals of complexes 1 and 3 show that the Cu(II) ion is preferably coordinated in the TPA site. Moreover, the coordination sphere of the copper center fully depends on the Cu(II) salt used for the synthesis (CuCl2 for 1 and 2, Cu(OTf)2 for 3). Hence, the tetracoordinated bis-chloro complex 1 adopts a distorted square-planar geometry at solid state, whereas the pentacoordinated bis-aqua complex 3 displays an almost perfect square pyramidal conformation. Both complexes 1 and 3 react with H2O2 in acetonitrile, leading to the formation of copper(II)-hydroperoxo species according to the UV-Vis spectroscopic studies.