LAUSR

Potentiometric and spectroscopic techniques are used to study the interaction of N′-[1-(2-hydroxyphenyl)ethylidene]Isonicotinohydrazide (HpEH) with trivalent Pr, Nd, Gd, Tb, and Ho ions. Potentiometric titrations, carried out keeping the Ln3+/HpEH molar ratios at 1:2 and 1:4 at different temperature and a constant ionic strength of 0.1 mol·dm−3 KNO3 in aqueous dioxane (40%) medium, show two protons of the ligand in equilibrium and complex formation of 1:1, 1:2 and 1:3 Ln3+/HpEH stoichiometry. The conditional stability constants of the Ln3+–HpEH complexes increase in the order: Pr < Nd < Gd < Tb < Ho. The negative values of the standard state thermodynamic parameters (ΔG°, ΔH°, and ΔS°) associated with both protonation and complexation reactions for all the systems show the reactions are spontaneous, exothermic and of unfavorable entropy. Changes in the absorption bands indicate interactions of HpEH and Ln3+. Photoluminescence study of the Tb3+ and HpEH complex reveals that HpEH is florescent and has no sensitizing effect on Tb3+ luminescence in ethanol, while in the isolated solid Tb3+–HpEH complex the luminescence intensity was found to be greatly sensitized. The synthesized Tb3+–HpEH complex, characterized on the basis of elemental analysis, magnetic susceptibility, molar conductivity, thermal analysis and spectral measurements is paramagnetic, acts as a 2:1 electrolyte and is of 1:3 Ln3+/HpEH stoichiometry.