Synthesis and characterization of new unsymmetrical ‘side-off’ tetra and hexa coordinate homobinuclear Cu(II) and heterobinuclear Cu(II)–Zn(II) complexes: Magnetic, electrochemical and kinetic studies

A new class of phenol based unsymmetrical side-off tetra and hexa coordinate homobinuclear Cu(II) and heterobinuclear Cu(II)–Zn(II) complexes have been synthesized and characterized by elemental and spectral analysis. The electronic spectra of all the complexes show “Red shift” in LMCT band, for the ligand H2L2 compared to that of the ligand H2L1 due to the relatively higher electron donating nature of their substitutents. The homobinuclear Cu(II) complexes (1 and 2) illustrate an antiferromagnetic interaction (μeff: 1.58 and 1.60 BM) at 298 K with a broad EPR signal. Variable temperature magnetic moment study of the binuclear copper (II) complexes shows that the extent of antiferromagnetic coupling is greater in the case of H2L2 complexes than H2L1 complexes (−2 J values: 192 cm−1 and 184 cm−1 respectively). The heterobinuclear Cu(II)–Zn(II) complexes (3 and 4) have a magnetic moment value close to the spin only value with four hyperfine EPR signals. Electrochemical studies of the complexes reveal that all the binuclear complexes show two irreversible one-electron transfer reduction waves in the cathodic region. There is an “anodic shift” in the first reduction potential of the complexes, of the ligand H2L1 when compared to that of the ligand H2L2 due to the presence of relatively higher electron donating N-substituents in the later case than in the former case. The catecholase activity of the complexes reveals that the homobinuclear Cu(II) complexes show higher catalytic activity than the corresponding heterobinuclear Cu(II)–Zn(II) complexes. In the hydrolysis of 4-nitrophenylphosphate, the heterobinuclear Cu(II)–Zn(II) complexes show better catalytic activity than the corresponding homobinuclear Cu(II) complexes.

Graphical abstractA new class of phenol based unsymmetrical side-off tetra and hexa coordinate homobinuclear Cu(II) and heterobinuclear Cu(II)–Zn(II) complexes have been synthesized and characterized by elemental analysis and spectral analysis. Their magnetic and electrochemical behavior have been studied. These complexes exhibit good catecholase activity as well as the hydrolysis of 4-nitrophenylphosphate. Moreover, the noteworthy changes observed in magnetic, electrochemical and in the kinetics, depending upon the various N-substituents at the free side arms were clearly studied and explained.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of phenol based unsymmetrical side-off homo and hetero binuclear complexes. ► Their spectral, magnetic and electrochemical behavior have been studied. ► Interesting changes in the above studies depending upon the various N-substituents. ► They exhibit good catecholase activity and hydrolysis of 4-nitrophenylphosphate.