Synthesis, crystal structures, spectroscopic and electrochemical studies on Cu(II) and Ni(II) complexes with compartmental nitrogen–oxygen mixed donor ligands

• Subtle changes on ligands influences the coordination geometry of metal.
• Cu complexes with Schiff base and its reduced form have different electrochemistry.
• A novel tetranuclear Ni4 unit with face-fused double cubane.
• The phenolic oxygens participate as anionic oxygens in complexation.

The synthesis and characterization of two new N2O4 donor type ligands, 2-{[(2-{3-[2-({[(2-hydroxyphenyl)methylidene]amino}methyl)phenoxy]propoxy}benzyl)imino]methyl}phenol (H2L1) and 2-[({2-[3-(2-{[(2-hydroxybenzyl)amino]methyl}phenoxy)propoxy]benzyl}amino)methyl]phenol (H2L2), and their metal complexes with Cu(II) and Ni(II) metal ions are reported. The ligands and complexes have been characterized by 1H NMR, FT-IR, UV–Vis absorption spectroscopy, single-crystal X-ray diffraction, CHN elemental analysis and cyclic voltammetry (CV). The redox behavior of the two complexes has been studied by CV. Copper and nickel complexes of Schiff base (H2L1) and reduced Schiff base (H2L2) showed different behaviors because the structure of the complexes depends of the ligand. The complex [Cu2L12]·2CH3OH (1) is dinuclear with the two metal centers bridged exclusively by the ligands, consisting of two distorted square planar CuN2O2 chromophors with large intermetallic separation (8.879 Å). Complex [Ni4L22(CH3COO)4]·4CH3OH (2) consists of tetranuclear Ni4 unit of two symmetry related hexacoordinated nickel atoms having distorted octahedral NiN2O4 and NiO6 environments, and contains two types of acetate coordination modes, namely, bridging bidentate (μ2-η1, η1), and asymmetric chelating bridging (μ2-η2, η1).

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