Stability constants of europium complexes with a nitrogen heterocycle substituted methane-1,1-diphosphonic acid

摘要

Even in moderately acidic solutions ((H(sup +)) > 0.01 M), N-piperidinomethane- 1,1-diphosphonic acid (H(sub 4)PMDPA) is a strong complexant of trivalent lanthanide ions that shows enhanced complex solubility over previously studied 1,1-diphosphonic acids. The protonation constants of PMDPA in 2.0 M H/NaClO(sub 4) were determined by potentiometric and NMR titrations, and the stability constants for formation of complexes with Eu(sup 3+) were determined by solvent extraction. Difference in protonation equilibria induced by addition of the nitrogen heterocycle results in an increase in the complexation strength of PMDPA. In solutions containing 0.1 M H(sup +) and ligand concentrations greater than 0.02 M, PMDPA is the most effective 1,1-diphosphonic acid for europium complexation studied thus far.