A novel Ni(II) complex with an asymmetric monoamino-monoamidato-dithioether square-planar coordination (1) was prepared as a model compound of the active center of NiSOD and characterized by spectroscopic and electrochemical methods. EPR data indicate that the structure of complex 1 in the high oxidation state can be significantly altered upon binding of imidazole, a stronger donor ligand than the original supporting ligand.