Spectroscopic studies, cyclic voltammetry and synthesis of nickel(II) complexes with N4, N2O2 and N4S2 donor macrocyclic ligands

All the complexes show magnetic moments corresponding to two unpaired electrons except [Ni(L1)](NO3)2 and [Ni(L2)](NO3)2 complexes which are diamagnetic. Electronic spectroscopy was used to analyse the differences between the paramagnetic and diamagnetic forms. Electrochemical properties have been studied extensively for Ni(III/II) and Ni(II/I) couples. The equilibrium between the paramagnetic and diamagnetic forms and the nickel(III/II) couple are strongly dependent on the electrolyte. It has been observed that the sulphate group coordinated selectively on the apical position of the nickel(II) centers of the compounds. The structural and electrochemical studies suggest that cooperative effects, involving coordination of sulphate to one nickel center, is responsible for the recognition of this anion. Various ligand field parameters have been calculated and discussed.