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A novel Schiff base N′-[1-(3-aminophenyl)ethylidine]isonicotinohydrazide was prepared and its complexation behavior towards some selected lanthanides had been studied employing pH-metric and calorimetric titration and spectral techniques. pH-metric studies were carried out for the trivalent La, Pr, Nd, Sm, Eu, and Gd complexes in 30% aqueous-dioxane medium at constant ionic strength of 0.05 mol/L NaClO4 and at different temperatures of 293, 303 and 313 K. The proton-ligand formation constants of the ligand indicated the presence of only one dissociable proton while the metal-ligand formation constants were compatible with the formation of 1:1 Ln(Ⅲ) complexes. The sta-bility of the complexes followed the order: La3+Gd3+, showing a break at gadolinium. The thermodynamic parame-ters, ΔG, ΔH and ΔS associated with protonation and complexation reactions were negative which suggested that all reactions were exother-mic and enthalpy-driven. Isothermal calorimetric studies of Gd3+-aeINH systems at 303 K also showed exothermic nature of the complexation reaction and formation of 1:1 complex in agreement with the pH-metric data. Formation of 1:1 complexes was confirmed by the characteriza-tion of Nd(Ⅲ) complex. A seven coordinated geometry was assigned for the complex based on its elemental and spectral data.
A novel Schiff base N ’- [1- (3-aminophenyl) ethylidine] isonicotinohydrazide was prepared and its complexation behavior towards some selected lanthanides had been studied either pH-metric and calorimetric titration and spectral techniques. PH-metric studies were carried out for the trivalent La, Pr, Nd, Sm, Eu, and Gd complexes in 30% aqueous-dioxane medium at constant ionic strength of 0.05 mol / L NaClO4 and at different temperatures of 293, 303 and 313 K. The proton-ligand formation constants of the ligand indicates the presence of only one dissociable proton while the metal-ligand formation constants were compatible with the formation of 1: 1 Ln (III) complexes. The sta-bility of the complexes followed the order: La3 + Gd3 +, showing a break at gadolinium. The thermodynamic parame-ters, ΔG, ΔH and ΔS associated with protonation and complexation reactions were negative which suggested that all reactions were exother-mic and enthalpy-driven. Isothermal calorimetric studies of Gd3 + -aeINH systems at 303 K also showed exothermic nature of the complexation reaction and formation of 1: 1 complex in agreement with the pH-metric data. Formation of 1: 1 was was by the characteriza tion of Nd (III ) complex. A seven coordinated geometry was assigned for the complex based on its elemental and spectral data.