Synthesis, characterization, mixed-ligand complex formation reactions, and equilibrium studies of Co(II) with 2,2′-dipyridylamine and some selected biorelevant ligands

Abstract

Binary and ternary cobalt(II) complexes involving 2,2′-dipyridylamine and various biologically relevant ligands containing different functional groups are investigated. The ligands used are dicarboxylic acids, amino acids, and DNA unit constituents. The ternary complexes are formed by simultaneous reactions. The results showed the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. The stability of ternary complexes formed with dicarboxylic acids was quantitatively compared with their corresponding binary complexes in terms of the ∆log10 K parameters. The concentration distribution of the complexes in solution was evaluated. The solid complexes of Co(II) dipyridylamine cyclobutane-1,1-dicarboxylate, or malonate, oxalate, and succinate have been synthesized and characterized by elemental analysis, infrared spectra, magnetic, and conductance measurements. Spectroscopic studies and M eff values suggest a tetrahedral geometry for the cobalt(II) complexes. The effect of temperature on the formation constant of the complexes was studied, and the thermodynamic parameters were calculated. Formation of the metal complexes has been found to be spontaneous, exothermic, and entropically favorable.