Related Experiment Video
Updated: Sep 26, 2025
13:21
Preparation, Purification, and Characterization of Lanthanide Complexes for Use as Contrast Agents for Magnetic Resonance Imaging
Published on: July 21, 2011
15.1K
The solution structures and relative stability constants of lanthanide-EDTA complexes predicted from computation.
Ravi D O'Brien1, Thomas J Summers1, Danil S Kaliakin1
1Department of Chemical and Materials Engineering, University of Nevada, Reno, Reno, NV 89557, USA. dcantu@unr.edu.
Physical Chemistry Chemical Physics : PCCP
|April 19, 2022
Summary
Understanding lanthanide (Ln) ion selectivity is crucial for rare earth element separation. Computational methods accurately predict Ln-EDTA complex stability across different pH and temperatures, aiding separation strategies.
Area of Science:
- Inorganic Chemistry
- Computational Chemistry
- Materials Science
Background:
- Lanthanide (Ln) ion selectivity is critical for separating rare earth elements.
- Ligand selectivity can be quantified using relative stability constants or binding energies.
- Ethylenediaminetetraacetic acid (EDTA) is a common chelating agent for Ln ions.
Purpose of the Study:
- To predict relative stability constants of EDTA with various Ln ions (La, Eu, Gd, Lu) using computational methods.
- To investigate the influence of pH (∼7 and ∼11) and temperature (25 °C and 90 °C) on Ln-EDTA complex structures and stabilities.
- To correlate structural variations in solution with complex stability at different conditions.
Main Methods:
- Electronic structure calculations incorporating relativistic effects.
- Density functional theory molecular dynamics simulations to model Ln-EDTA complexes in solution.
- Analysis of molecular structures and variations with temperature and protonation state.
Main Results:
- Predicted relative stability trends for different Ln ions with EDTA at pH ∼11.
- Predicted relative stability trends for La with EDTA at pH ∼7 and ∼11.
- Demonstrated significant impact of EDTA protonation state on complex structure and stability.
- Correlated increased complex stability with reduced structural variations at higher temperatures.
Conclusions:
- Computational predictions of Ln-EDTA complex stability align with experimental observations.
- EDTA protonation state critically influences Ln-EDTA complex solution structures and stabilities.
- Temperature-induced structural stability of Ln-EDTA complexes is linked to overall complex stability.
Related Concept Videos
01:09EDTA: Conditional Formation Constant
1.2K
Each EDTA molecule has six binding sites: four carboxyl groups and two amino groups. The fully protonated form of EDTA is represented as H6Y2+. However, it can exist in different forms, H5Y+, H4Y, H3Y−, H2Y2−, and HY3−, depending on the pH of the solution. In very basic solutions with pH > 10.17, the fully deprotonated form, Y4−, is the predominant species that readily complexes with metal ions in a 1:1 ratio.
For the equilibrium reaction of the metal with the...
For the equilibrium reaction of the metal with the...
1.2K
01:22EDTA: Chemistry and Properties
2.3K
Polydentate ligands are most widely used in complexometric titrations because they form more stable complexes with the metal ions than mono- or bidentate ligands due to the chelate effect. Examples of polydentate ligands are ethylenediaminetetraacetic acid (EDTA), crown ethers, and cryptands. The most important feature of optimal polydentate ligands is the ability to form 1:1 complexes in a single-step process. Amino carboxylic acid derivatives are frequently used as complexing agents. EDTA is...
2.3K
01:26EDTA: Auxiliary Complexing Reagents
700
EDTA titrations are usually carried out in highly basic conditions, where the fully deprotonated form of EDTA, Y4−, actively complexes with the free metal ions in the solution. Several metal ions precipitate as hydrous oxide (hydroxides, oxides, or oxyhydroxides) under these conditions, lowering the concentration of free metal ions in the solution. For this reason, auxiliary complexing agents or ligands such as ammonia, tartrate, citrate, or triethanolamine are used in EDTA titrations to...
700
01:09Complexation Equilibria: Factors Influencing Stability of Complexes
502
In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
502
01:19Complexation Equilibria: The Chelate Effect
702
In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...
702
01:20Complexometric EDTA Titration Curves
1.1K
EDTA titration curves determine the free metal ion concentration. The titration curve represents the change in concentration of free metal ions (p function) as a function of the volume of EDTA added. This curve consists of three regions: before, at, and after equivalence points. Excess free metal ions are present before the equivalence point. Equal concentrations of metal ions and EDTA are present at the equivalence point. After the equivalence point, excess EDTA exists. This means slight...
1.1K