Cadmium(II) complexes of 5-nitro-salicylaldehyde and α-diimines: synthesis, structure and interaction with calf-thymus DNA
Five Cd(II) complexes with the anion of 5-NO2-salicylaldehydeH (5-NO2-saloH) in the absence or presence of the α-diimine 1,10-phenanthroline (phen), 2,2′-dipyridylamine (dpamH), 2,2′-dipyridine (bipy), or 2,9-dimethyl-1,10-phenanthroline (neoc) were synthesized and characterized as [Cd(5-NO2-salo)2(CH3OH)2] (1), [Cd(5-NO2-salo)2(phen)]·2CH3OH·H2O (2), [Cd(5-NO2-salo)2(dpamΗ)] (3), [Cd3(5-NO2-salo)6(bipy)2] (4), and [Cd(5-NO2-salo)(neoc)(NO3)]2 (5). Based on spectroscopic results (IR, UV, NMR), elemental analysis and conductivity measurements an octahedral geometry around cadmium metal ion is suggested, with the 5-NO2-salicylaldehyde ligand having different coordination modes. The structures determined by X-ray crystallography verified neutral mononuclear 1–3 and trinuclear 4. Simultaneous TG/DTG–DTA technique was used to analyze the thermal behavior of 1, 2, and 3. The complexes bind tightly to calf-thymus DNA mainly by intercalation, as concluded by DNA viscosity measurements and exhibit significant displacement of EB from the EB-DNA complex.
