Europium(III) Meets Etidronic Acid (HEDP): A Coordination Study Combining Spectroscopic, Spectrometric, and Quantum Chemical Methods

Abstract

Etidronic acid (1-Hydroxyethylidene-1,1-diphosphonic acid, HEDP, H4L) is a proposed decorporation agent for U(VI). This paper studied its complex formation with Eu(III), an inactive analog of trivalent actinides, over a wide pH range, at varying metal-to-ligand ratios (M:L) and total concentrations. Combining spectroscopic, spectrometric, and quantum chemical methods, five distinct Eu(III)−HEDP complexes were found, four of which were characterized. The readily soluble EuH2L+ and Eu(H2L)2− species with log β values of 23.7 ± 0.1 and 45.1 ± 0.9 are formed at acidic pH. At near-neutral pH, EuHL0s forms with a log β of ~23.6 and, additionally, a most probably polynuclear complex. The readily dissolved EuL− species with a log β of ~11.2 is formed at alkaline pH. A six-membered chelate ring is the key motif in all solution structures. The equilibrium between the Eu(III)–HEDP species is influenced by several parameters, i.e., pH, M:L, total Eu(III) and HEDP concentrations, and time. Overall, the present work sheds light on the very complex speciation in the HEDP–Eu(III) system and indicates that, for risk assessment of potential decorporation scenarios, side reactions of HEDP with trivalent actinides and lanthanides should also be taken into account.

Equilibrium Thermodynamics of Macropa Complexes with Selected Metal Isotopes of Radiopharmaceutical Interest

“…For the p K a determination, samples with 1 mM macropa in a 0.1 M NaCl D 2 O solution covering the pD range from 0.8 to 9.6 were prepared. p K a values of the ligand were determined according to procedures successfully applied to other ligand systems. − …”

“…p K a values of the ligand were determined according to procedures successfully applied to other ligand systems. 48 − 50 …”

Performance of ionic liquid functionalized metal organic frameworks in the adsorption process of phenol derivatives

“…The electron-rich groups of the HEDP hydroxyl and phosphonic acid groups have been demonstrated to have strong interactions with metal ions. [30][31][32] In addition, HEDP has low toxicity to aquatic organisms, but causes eutrophication of water. 33 The use of ILs on certain solid supports not only allows their advantages to be exploited, but it is also inexpensive because of the small quantities used.…”