Thermodynamical study on the formation of some mixed ligand complexes of non-transition metal ions in solution I. The formation and the stability of some Pb(II) mixed ligand complexes

The stability constants of the binary complexes of type PbB, PbB₂, and the mixed ligand complexes of type PbAB have been studied by potentiometric pH titration technique at ionic strength I = 0.10 (KNO₃) and at temperature 15, 25, 35 and 45°C respectively, where A = 2,2′-bipyridyl (bipy) or 1,10-phenanthroline (phen); B = malonate (mal), succinate (suc), or anthranilate (anth). The equalibrium constants ΔlogK,¹ ΔΔG, ΔΔH, and ΔΔS of the reaction PbA + PbB = PbAB + Pb²⁺ have been calculated. The results show that the discriminating effects² between the primary ligand (bipy or phen) and the secondary ligand (mal, suc or anth) in those non-transition metal mixed ligand complexes are also evident, and as a measurement of this effect, ΔΔH is more appropriate than ΔlogK. The possible reasons which lead to these results have been discussed.