Nickel and copper complexes with few amide-based macrocyclic and open-chain ligands

The present work shows three new amide-based ligands H2L1, H2L2 and H2L3 and their nickel and copper complexes. The X-ray structural analysis substantiate that the ligands constitute a square-based basal plane around the metal center. The crystal structures also show interesting solid state packing due to hydrogen-bonding and various weak C⋯H interactions. The solution-based spectral studies support the solid-state geometry observed for these complexes. The electrochemical results show that the Ni3+/2+ and Cu3+/2+ redox couple primarily depends on the N4 donors composed of Namide and Namine atoms. It was observed that the ligands H2L1 and H2L2 are better suited to stabilize the Cu(III) species whereas ligand H2L3 is ideal for the stabilization of Ni(III) species. On the basis of electrochemical findings, transient Ni3+ species were generated and characterized by the absorption spectroscopy.