pH-metric and thermodynamic studies of rare earth metal chelates

Proton ligand stability constants of hydroxybenzoic acid containing nitro group (2-Hydroxy-4-nitrobenzoic acid and 3-Hydroxy-4-nitrobenzoic acid) were determined through Irving-Rossoti pH titration technique. The stability constants of rare earth metal chelates containing 2-Hydroxy-4-nitrobenzoic acid and 3-Hydroxy-4-nitrobenzoic acid as ligands were studied in aqueous medium at different ionic strength (μ=0.01, 0.05 and 0.1 mol/L) and temperatures (298, 308 and 318± 0.1 K). The values of stability constant were evaluated through different computational methods like successive approximation, least square treatment, correction term method, and convergence method. The observed value of thermodynamic parameters (ΔG°, ΔH° and ΔS°) favors the complex formation between metal and ligands. The order of stability constant was found to be Pr(III)