Synthesis, characterization and reactivity of trinuclear Cu(II) complexes derived from disalicylaldehyde malonoyldihydrazone

•Homotrimetallic copper(II) complexes have been synthesized from disalicylaldehyde malonoyldihydrazone.•The dihydrazone ligand is present in enol form in the complexes.•The ground state for the complexes is a mixture of the quartet state (S = 3/2) and doublet state (S = 1/2) at room temperature.•All of the complexes show a reversible one-electron redox couple in their cyclic voltammogram.•The complexes have catalyzed the H2O2 mediated oxidation of benzyl alcohol to benzaldehyde in 53% yield.

Three new homotrinuclear copper(II) complexes [Cu3(slmh)(μ-Cl)2(CH3OH)3]⋅0.5CH3OH (1), [Cu3(slmh)(NO3)2(CH3OH)5]⋅1.5CH3OH (2) and [Cu3(slmh)(μ-ClO4)2(CH3OH)3]⋅2CH3OH (3) from disalicylaldehyde malonoyldihydrazone have been synthesized and characterized. The composition of the complexes has been established on the basis of data obtained from analytical and thermoanalytical data. The structure of the complexes has been discussed in the light of molar conductance, electronic, FT-IR and far-IR spectral data, magnetic moment and EPR spectral studies. The molar conductance values for the complexes in DMSO solution indicate that all of them are non-electrolyte. The magnetic moment values for the complexes suggest considerable metal–metal intramolecular interaction between metal ions in the structural unit of the complexes. The EPR spectral features reveal that at RT, the ground state for the complexes is a mixture of the quartet state (S = 3/2) and doublet state (S = ½). At lower temperature, the ground state for the complexes is dx2−y2 with considerable contribution from dz2 orbital. Dihydrazone ligand is present in enol form in all of the complexes. The complexes have distorted square pyramidal stereochemistry. The electron transfer reactions of the complexes have been investigated by cyclic voltammetry. Hydrogen peroxide mediated oxidation of benzyl alcohol catalyzed by complex 1 has been studied.

Graphical abstractThe reaction of disalicylaldehyde malonoydihydrazone in methanol with CuX2⋅nH2O (X = Cl, ClO4) maintaining H4slmh: KOH: CuX2⋅nH2O (X = Cl, NO3 and ClO4) molar ratio at 1:4:3.2 yielded the complexes of the composition [Cu3(slmh)(μ-X)2(CH3OH)3]⋅nCH3OH [n = 0.5, X = Cl (1); n = 2, X = ClO4(3)] and [Cu3(slmh)(NO3)2(CH3OH)5]⋅1.5CH3OH (2).Figure optionsDownload full-size imageDownload as PowerPoint slide