Anion dependent supramolecular architectures in Cu(II) complexes containing N₂O-donor Schiff-base and 4,4′-bipyridine ligands: structural analyses and theoretical studies

Three new copper(II) complexes, [Cu2L2Cl2 (4,4′-bpy)]•2.7H2O (1), [CuL(4,4′-bpy)(H2O)]NO3 (2) and [CuL(4,4′-bpy)(H2O)]ClO4 (3), where HL = 1-[1-(2-Dimethylamino-ethylimino)-ethyl]-naphthalen-2-ol, have been synthesized and characterized by elemental analysis, IR, UV–Vis spectroscopy and single crystal X-ray diffraction studies. Complex 1 is a centrosymmetric dinuclear species in which 4,4′-bipyridine acts as bridging bidentate linker between the two copper(II) ions whereas, complexes 2–3 are rare mononuclear complexes in which the 4,4′-bpy ligand shows monodentate coordination mode stabilized by H-bonding interactions through its electronegative non-coordinated N-atom. These interactions involve imine and methylene hydrogen atoms of the Schiff-base ligand for 2, whereas a single H-bond with one of the hydrogen atoms of the coordinated water is established in 3. In addition, several non-covalent interactions like hydrogen bonding and π-based interactions (C–H/π, anion–π and π– π stacking) are also observed in crystal packing of all three complexes. These interactions have been investigated by means of DFT calculations and assigned with discrete interaction energies. The strong influence of the coordination of the 4,4′-bpy ligand to the copper(II) centers upon the binding strength of the π-based interactions has also been demonstrated