Lanthanide Complexes with D-Penicillamine Methyl Ester: Formation Constants, Spectral and Thermal Properties

Abstract

Abstract The complex-formation of the lanthanide(III) cations with D-penicillamine methyl ester have been investigated in acidic and neutral media. The macroscopic protonation constants of the ligand and the formation constants of [Ln·Pme]2+, [Ln·(Pme)2]+, [Ln·Pme·OH]+ and [Ln·Pme·(OH)2] complexes have been determined from pH-metric data using BEST computer program. Species distribution diagrams of the complexes were obtained and plotted using SPE and SPEPLOT computer programs. Elemental analyses of the solid complexes indicate the formation of 1:1 metal:ligand species. Infrared spectra show that coordination takes place through the NH2, the SH and the C=O groups of the ligand. The complexes decompose in four steps as shown by their TG and DTA analysis with the formation of Ln2(SO4)3 as a final product. Activation energy values (ΔEa) are correlated with the atomic radii of the metal ions. The mechanism of the thermal decomposition is proposed.