Cadmium(II) complexes of 5-nitro-salicylaldehyde and -diimines: synthesis, structure and interaction with calf-thymus DNA

Abstract

Five Cd( II) complexes with the anion of 5- NO2- salicylaldehydeH ( 5- NO2- saloH) in the absence or presence of the alpha-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)] center dot 2CH3OH center dot H2O (2), [Cd(5- NO2- salo) 2( dpam.)] (3), [Cd-3(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.