Conductometric and Potentiometric Studies on Zinc(II)-, Cadmium(II)-and Mercury(I, II)-Phenanthroline- Salicylaldoxime-Benzamide Complexes

Abstract

Conductometric and potentiometric studies on the complexes of Zn(II). Cd(II) and Hg(1, II) with 1,10-phenanthroline, salicylaldoxime (SD) and benzamide (BAM) in aqueous solution at 35 and 45 ºC provided evidence of formation of (1:1), (1:2) and (1:3) Zn(II)-, Cd(II)-, Hg(II)-₂ and Hg(II)-Phen, SD and BAM, (1:1:1) Zn(II)-, Cd(II)-, Hg(II)₂-, and Hg(II)-Phen-SD, phen-BAM, and BAM–SD, and (1:1:1) Zn(II)-, Cd(II)-, Hg(II)-, and Hg(II)- Phen-SD-BAM complexes in which the metal ions are coordinated through two coordinate bonds with the two protonated nitrogen atoms of Phen, two covalent bonds with the two deprotonated atoms of phenolic OH and oximic NOH groups of SD, and one coordinate and one covalent bonds with one protonated and one deprotonated atoms of benzoyl CO and amide NH groups of BAM. Proton-ligand (pK) dissociation constants, metal-ligand and metal-mixed ligands formation stability constants (K_f) were determined in aqueous medium using 5 mL HNO₃ (1 x 10^-2 M), 1:15 metal:ligands(s) ratio and 0.01 M NaOH (titrant) solution at a fixed ionic strength (I = 0.01 M NaNO₃). Free energy changes (∆ºG), enthalpy (∆H) and entropy (∆S) values at 35 and 45 ºC for binary, ternary and quaternary complexes were also evaluated. The data show that the magnitude of K_f, ∆ºG, ∆H and ∆S values increase with increasing temperature, stoichiometric ratio and with the tendency of the formation of polymeric and metal-mixed ligands’ chelates. The increase of stability constants of the complexes is in the order: Cd(II) > Zn(II) > Hg(II)₂ > Hg(II) complexes.