Synthesis, Characterisation and Electrochemical Behaviour of some Nickel(II) Complexes with Linear and Tripodal Tetradentate Ligands Derived From Schiff Bases

Abstract

A number of new six-coordinate Ni(II) complexes with linear and tripodal tetradentate ligands having the general formula [Ni(H2L)(H2O)2]Cl2.xH2O have been synthesized. Microanalysis, molar conductance, IR spectra, thermogravimetric analysis, magnetic measurements, and electronic spectra have been used to elucidate their structure. The experimental data show that the ligands are bonded in a non-deprotonated form and are coordinated in a tetradentate manner, the other axial sites being occupied by the aquo molecules. On the basis of electronic results it is concluded that tripodal ligands exert the strongest ligand field and the ligand substituents affect the ligand field strength which increases with the electron donating effect of the R group. The electrochemical behaviour of the nickel(II) complexes was determined by cyclic voltammetry which shows that chelate structure, ligand geometry and electron donating effect of the ligand substituents are among the factors influencing the redox potentials of the complexes. Also, we note that the ligands used in the present study can stabilize both the nickel(I) and the nickel(III) states. Referee I: H. N. Po Referee II: D. Dollimore