New ‘side-off’ coordination asymmetric homobinuclear Ni(II) and heterobinuclear Ni(II)Zn(II) complexes as models for hydrolysis of p-nitrophenylphosphate: Synthesis, characterization and electrochemical studies

A series of new phenol based coordination asymmetric side-off homobinuclear Ni(II) and heterobinuclear Ni(II)Zn(II) complexes have been synthesized and characterized by elemental analysis and spectral analysis. The electronic spectra of all the complexes show “Red shift” in LMCT band, for the ligand H2L2 having electron donating C2H5 groups as N-substituents in the free side arms compared to ligand H2L1 having relatively lower electron donating CH3 groups. 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 complexes of the ligand H2L2 due to the presence of higher electron donating C2H5 N-substituents in the later case than the relatively lower electron donating N-substituents in the former case. Hydrolysis of p-nitrophenylphosphate using homobinuclear Ni(II) and heterobinuclear Ni(II)Zn(II) complexes as catalysts showed that the homobinuclear complexes have higher rate constant values than that of the corresponding heterobinuclear complexes. A comparison of the spectral, electrochemical and catalytic behavior of the complexes of the ligands is discussed on the basis of the electron donating nature of the N-substituents at the free side arms.

Graphical abstractA series of new phenol based coordination asymmetric side-off homobinuclear Ni(II) and heterobinuclear Ni(II)Zn(II) complexes have been synthesized and characterized by elemental analysis and spectral analysis. Electrochemical behavior of the complexes has been studied. These complexes exhibit good activity against the hydrolysis of 4-nitrophenylphosphate. Remarkable changes observed in electrochemical and 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 coordination asymmetric side-off binuclear complexes. ► Their spectral and electrochemical behavior have been studied. ► Interesting changes in the above studies depending upon the various N-substituents. ► They exhibit good activity against hydrolysis of 4-nitrophenylphosphate.