Thermodynamics, Chemical Speciation and Complex Formation Equilibria Studies of Binary and Mixed Ligand Complexes of Cu(II) with 2,2′-Bipyridyl and Some Aromatic Diamines

Abstract

The formation of mixed ligand complexes of Cu(II) with 2,2′-bipyridyl (Bipy) in the presence of some selected aromatic diamines (L) (L = 3,4-diamino benzoic acid (DABA), 2-hydazinopyridine (hzpy) or 4-chloro-o-phenylenediamine has been studied by pH-metric titrations. Potentiometric measurements show that ternary complexes are formed in a simultaneous manner. The pH-titrations of the reaction mixtures are shown to yield 1:1:1 ternary complex formation. The equilibrium and formation constants of the resulting ternary complexes have been calculated at I = 0.1 mol·dm−3 of NaNO3. The order of stability in terms of the secondary ligands has been found to be DABA > hzpy > CAPA. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters Δlog10K, Δlog10β and log10X. The concentration distributions of various species formed in solution were also evaluated as a function of pH. In addition, the effect of temperature on both the ionization process of the ligands and complex formations for Cu–Bipy–L ternary systems was studied. The thermodynamic parameters were calculated from the temperature dependence of the equilibrium constants and are discussed. The structure of the Cu(II) complexes have been geometrically optimized using the parameterized PM3 semiempirical method.