Two new neutral mixed-ligand cobalt(II) complexes, [CoCl2(dmdphphen)] 1and [Co(NCS)2(dmdphphen)] 2 where dmdphphen is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, were synthesized and characterized by an elemental analysis, UV-Vis, IR, TG/DTA, cyclic voltametry CV and single X-ray diffraction. Complex 2 crystallized as monoclinic with a space group P21/c. Co(II) ions are located in a distorted tetrahedral environment. TG/DTA result shows that these complexes are very stable and decomposed through one step reaction. The two complexes exhibit a quasi-reversible one electron response at-550 and 580mV vs. Cp2Fe/Cp2Fe+, which has been assigned to Co(I)/Co(II) and Co(II)/Co(III) couples. Absorption spectral studies reveal that the such complexes exhibit hypochromicity during their interaction with CT-DNA.