Nickel(II) complexes of N,N′-dimethyl-N,N′-bis(pyridyl-2yl-methyl)ethylene-diamine (L 1 ), N,N′-dimethyl-N,N′-bis(pyridyl-2-ylmethyl)-1,2-diaminopropane (L 2 ) and N,N′-dimethyl-N,N′-bis(pyridyl-2-ylmethyl)-1,3-diaminopropane (L 3 ) were prepared and their spectroscopic and redox properties studied. The distorted octahedral structure was determined for [NiL 3 ClCH 3 OH](ClO 4 ) by using X-ray crystallography. The electronic spectral behavior of the complexes at different pHs was analyzed; it is shown that a new band grew at the expense of the other band intensity in acid media. The redox properties of ligands and their complexes show the peaks of Ni(II)→Ni(III) and Ni(II)→Ni(0) as these were detected at low concentration while Ni(II)→Ni(I) process was detectable clearly at high concentration. Furthermore, the interaction studies of 2-mercaptoethanesulfonic acid as a simulator of coenzyme M reductase (CoM) with NiN 4 chromophores are discussed.