Project Details Critical evaluation of equilibrium constants of 4f-metal mixed complexes with acidic chelate and organophosphorus O-donor ligands

Project No.:
Start Date:
01 May 2016
End Date:


** Series title: Critical evaluation of stability constants of metal complexes in solution

Compilation and critical evaluation of equilibrium constants of mixed complexes of 4f-ions with acidic chelates and organophosphorus O-donor ligands in various molecular or ionic diluents will be done. Reliable stability constants for such complexes are extremely important for academic and industrial research and are widely used in analytical chemistry for estimating interferences. The expected results are particularly important for the prediction and optimization of liquid/liquid extraction systems of interest to the rare earths industry and are required to improve current “state of the art” technologies. Solvent extraction has become the reference technique for reprocessing of spent nuclear fuels at industrial scale. Ionic liquids are now more and more integrated in the industrial field as well.


During the years many IUPAC Technical Reports have been published on equilibrium constants of metal complexes formation in solution with one complexing reagent, but no synergistic systems (that involves more than one ligand in the solvent) has been analyzed. Compilation and critical evaluation of equilibrium constants of mixed complexes of 4f-metal ions with mixtures of acidic chelate and organophosphorus O-donor ligands will be done during the execution of the proposed project.

There are no previous, concurrent or planned interactions with bodies outside IUPAC that are relevant to the project. Therefore, developing a reliable database containing useful information of already applied extraction systems for lanthanoids will offer opportunities to the scientists of various fields in chemistry and chemical technology to make comparison, conclusions and chose better options when planning next research methodologies. It is expected to provide information for the practical applicability of the used systems but it is hoped that general rules could be derived for intelligent design of the next generation of ionic liquid extraction systems. Sustained interest in improved nuclear-fuel-reprocessing methods and growing concern for the fate of actinides at potential waste-disposal provide continuous motivation for investigating the complexation and separation behavior of the two f-families. In traditional liquid-liquid separation processes great volumes of contaminated solvents are generated. In terms of the increase of safety, prevention of pollution and improvement in extraction efficiency, the research, development and implementation of innovative chemical technologies is indispensable. Comparison between conventional molecular and ionic diluents must be done today. The very limited set of data concerning metal extraction in ionic liquids raise the hope to much greater extraction efficiencies and increased selectivity at the same time. The main contribution is the improvement of the state of the art concerning concepts for classical solvent extraction by transfer of know-how of ionic liquids as innovative diluents in a separation field of 4f- and 5f-ions. The design of new efficient macrocyclic extractant containing chelating/phosphinoyl part due to the known powerful extracting ability that these molecules usually show in extraction and coordination chemistry is the original point. In addition, this will be very essential for the researchers of coordination, analytical organic and separation chemistry as already mentioned above with special attention to exposure to the industry sector.


Sep 2016 – Project announcement published in Chem. Int. Sep 2016, p. 24;

Jan 2021 update – The text document is being finalized for submission in Pure and Applied Chemistry.

Jan 2022 update – The Technical Report has been submitted to PAC and in under review.

Page last updated 14 Jan 2022