Effect of temperature and ionic strength on the formation constants of 2-acetylpyridine(n-benzoyl)glycine hydrazone with lanthanide(iii) ions

Ranita Devi Naosekpam, Promila Devi Thangjam, Sharmeli Yumnam and Rajkumari Lonibala

Formation of 2-Acetylpyridine(N-Benzoyl)Glycine Hydrazone, 2-ApBzGH with Ln(III) ions (Ln = La, Pr, Nd, Sm, Eu, Gd) was studied pHmetrically at temperatures 283, 293, 303, 313 and 323 K and ionic strengths 0.05, 0.10, 0.15, 0.20 M using KNO3 as the background electrolyte. The pH titration and the proton-ligand formation curves of the ligand showed the presence of one ionizable proton in the ligand. The ligand formed 1:1 and 1:2 complexes with La(III) ion while 1:1, 1:2 and 1:3 complexes were formed with other Ln(III) ions in 30 % (v/v) aqueous-dioxane medium and the corresponding formation constants (log  ) were determined from the formation curves. The formation constant values decreased with increase in temperature and ionic strength indicating that complex formation was more favorable at lower temperature and ionic strength. The trend in the constants along the lanthanide series was: La < Pr < Nd < Sm < Eu > Gd, showing a break at Gd. Changes in free energy, enthalpy and entropy associated with the protonation and complexation reactions were evaluated. All reactions were spontaneous, exothermic and enthalpy-driven processes.      

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