Je. Bollinger et Dm. Roundhill, COMPLEXATION OF INDIUM(III), GALLIUM(III), IRON(III), GADOLINIUM(III), AND NEODYMIUM(III) IONS WITH AMINO DIPHOSPHONIC ACIDS IN AQUEOUS-SOLUTION, Inorganic chemistry, 32(13), 1993, pp. 2821-2826
The compounds (Me2N)CH(PO3H2)2(MAMDP) and MeC(NH2)(PO3H2)2(AEDP) have
been synthesized. These compounds have been titrated with base and the
protonation constants determined. Titration data of pH against added
acid or base show that AEDP acts as a ligand toward In3+ and that MAMD
P binds as a ligand to In3+, Ga3+, Fe3+, Gd3+, and Nd3+. From a least-
squares fit of the pH titration curves, the stability and protonation
constants have been obtained for solutions containing these ligands an
d these trivalent metal ions. The ligands bind to the trivalent metal
ions via the phosphonate oxygens, although it is likely that hydrogen
bonding occurs between water and the phosphonate ligand. For the ions
In3+, Ga3+, and Fe3+, the logarithms of the stability constants log K1
01 and log K102 (where K101 = [ML2(5-)]/[M3+][L4-] and K102 = [ML2(5-)
]/[M3+][L4-12) have the respective values of 30.0, 25.8, 28.8 and 35.8
, 33.7, 34.3. For the lanthanide ions Nd3+ and Gd3+ the values are low
er at 16.0, 17.6 and 20.4, 20.7, respectively. This pattern of stabili
ty constants follows the trend for the complexation of EDTA with these
trivalent metal ions. The compound MAMDP remains coordinated to the m
etal ions in solutions of low acidity because protonation occurs at th
e free rather than the complexed phosphonate oxygens.