Nickel(II) complexes with different chromospheres containing macrocyclic ligands: Spectroscopic and electrochemical studies

The mixed donor tetradentate (L1 = N2O2) and pentadentate (L2 = N2O2S) ligands have been prepared by the interaction of 1,3-diaminopropane and thiodiglycolic acid with diamine. These ligands possess two dissimilar coordination sites. Different types of complexes were obtained which have different stoichiometry depending upon the type of ligands. Their structural investigation have been based on elemental analysis, magnetic moment and spectral (ultraviolet, infrared, 1H NMR, 13C NMR and mass spectroscopy methods). The Ni(II) complexes show magnetic moments corresponding to two unpaired electrons except [Ni(L1)](NO3)2 which is diamagnetic. Ligand field parameters of these complexes were compared. N2O2S donor ligand complexes show higher values of ligand field parameters, which are used to detect their geometries.The redox properties and stability of the complexes toward oxidation waves explored by cyclic voltammetry are related to the electron-withdrawing or releasing ability of the substituents of macrocyclic ligands moiety. The Ni(II) complexes displayed Ni(II)/Ni(I) couples irreversible waves associated with Ni(III)/Ni(II) process.