The stability of some lanthanide complexes with itaconate in aqueous solutions

✍ Scribed by H. Schurmans; H. Thun; F. Verbeek; W. Vanderleen

• Publisher: Elsevier Science
• Year: 1972
• Weight: 612 KB
• Volume: 38
• Category: Article
• ISSN: 0022-0728
• DOI: 10.1016/s0022-0728(72)80106-2

✦ Synopsis

Complex formation between lanthanide or transition metal ions and dicarboxylate ligands have been investigated potentiometrically by a few workers only. Practically all these 1 -3 investigations have been restricted to complexes of the type ML,. However in the case of itaconate the low ratio of the acid dissociation constants KA1/KA2 causes the ligand species H2L, HL-, L 2 -to exist together in solution 4 in the range 2 < -log [H] < 6 where complex formation in the case of lanthanide ions takes place. Consequently two complexing species, HL-and L 2-are present and protonated complexes of the general form MHjL, may be expected when the stability constants of unprotonated and protonated complexes are of the same order of magnitude. Indeed, Lai et al. 5 observed a protonated lead itaconate complex by polarographic means.

The present investigation describes the determination of stability constants of the various lanthanide itaconate complexes formed in aqueous solution at 25.0°C and unit ionic strength in NaC104. The equilibrium studies are made by potentiometric pH-methods, which show the presence of mononuclear protonated metal complexes. To identify these species and evaluate their stability constants the calculation procedure of 0sterberg 6 was used. The concentrations of itaconic acid did not exceed 50 mM so as to avoid self-association of the acid and subsequent tedious calculation 7.

CALCULATION PROCEDURE

General considerations

In considering the formation of mononuclear metal ion complexes of the type MHjL, in solution, equilibria can be represented generally by: