Studies on lanthanon(III) complexes ofN-methylisatin-β-amidinohydrazone

Summary The consecutive formation constants of 11 and 21 chelate species made by interaction ofN-methylisatin--amidinohydrazone (-MIAG) with tripositive lanthanons were determined potentiometrically at different ionic strengths (0.02, 0.05, 0.1 and 0.2 M NaClO₄) and at different temperatures (30, 40, 45 and 50 °C) in 50% v/v dioxan-H₂O. The formation constants log _n (calculated by a weighted least-squares method) for the complexes have been found to increase with the atomic number of the lanthanon, with a break at gadolinium. Thermodynamic parameters G, H and S of these complexation reactions were also evaluated.