Synthesis and structural characterization of a double helical dinuclear copper(II) complex with tetradentate biacetyl bis(benzoylhydrazone)

The reaction of tetradentate hydrazone ligand H₂babh with Cu(CH₃COO)₂ in methanol solvent leads to the formation of the mono-nuclear complex [Cu(babh)]. However, on being dissolved in dichloromethane solvent and on addition of ethanol solvent, a dinuclear complex of [Cu₂(μ_1,3-babh)₂(C₂H₅OH)₂] is obtained. The X-ray crystallography indicates that the dinuclear helical complex formation is caused due to the unsymmetrical twisting of the H₂babh ligand. One oxygen and two nitrogen atoms from the ligand and one oxygen atom from the other ligand coordinate to each copper(II) center. Both the copper(II) centers in a dinuclear unit are penta-coordinate with a slightly distorted square pyramidal geometry. The IR spectra of mono- and dinuclear copper(II) complexes have different bands. The absorption spectra of mono- and di-nuclear complexes are quite similar in methanol solvent. However, the electronic absorption spectra of the two complexes are basically different in the solid state.