Access Type
Open Access Embargo
Date of Award
January 2023
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Chemistry
First Advisor
Matthew J. Allen
Abstract
ABSTRACTCRYPTAND-BASED LOW-VALENT F-BLOCK COMPLEXES TOWARD STABILIZATION AND SEPARATION OF ACTINIDES AND LANTHANIDES DESHIKA NUWANGI KULASEKARA August 2023 Advisor: Dr. Matthew J. Allen Major: Chemistry (Inorganic) Degree: Doctor of Philosophy This thesis consists of six chapters that include studies of the understanding of ligand environment on the stabilization and separation of low-valent lanthanides and actinides. The studies explain the trends in structural, spectroscopic, and electrochemical properties of lanthanide and actinides with respect to changes in donor atoms, denticity, basicity, and counter ions. This dissertation also discusses a ligand-modified solid–liquid extraction method to separate lanthanide from each other. A brief overview of the dissertation is presented in Chapter 1. Chapter 2 describes the effect of ligands on the different properties of low-valent actinides and lanthanides. It explains the trends in rational design of ligands in order to obtain desirable catalytic, electrochemical, magnetic, spectroscopic, and luminescence properties of low-valent lanthanides and actinides. The focus of this chapter is to provide an introduction of how to tune the properties of low-valent f-block metals by changing donor atoms, geometry, denticity, basicity, and functional groups with respect to the properties of ligands. This chapter also provides information about the role of ligands in selective separation of lanthanides from each other or from actinides. Chapter 3 of this thesis discusses a study of the influence of ligand environments on the structural, spectroscopic, magnetic, and electrochemical properties of trivalent uranium cryptates. Three cryptands are studied that vary in denticities and basicities. X-ray crystallography, UV–visible and near-IR spectroscopy, cyclic voltammetry, and magnetic moments support the trends in different properties of trivalent uranium in different cryptands. The results of the study display that cryptands with smaller denticities show greater affinity for UIII than larger denticities, evidenced by shorter bond lengths and more negative electrochemical potentials. Further, the trends in electrochemical potentials of UIII-containing cryptates indicate shifting of oxidation potentials of UIII/IV to more positive values with decreasing basicity of the donor atoms. These studies provide information about rational design of ligands using cryptands and other non-redox active neutral ligands. Chapter 4 of this thesis describes a study evaluating a new cryptand-modified solid–liquid material to separate Eu from Gd using differences in electrochemical properties of the ions. With the demand for green-energy technologies and Eu being a critical material, improving separation methods to isolate Eu is important. The method discussed in this chapter overcomes challenges associated with the separation of Eu and Gd due to their similar coordination chemistries in the +3 oxidation state. A competitive adsorption study in the cryptand system between EuII/EuIII and GdIII shows greater affinity for EuII relative to GdIII. After separation from GdIII, Eu is released with 99.3% purity by oxidizing EuII to EuIII. This method resulted high-purity (>99%) Eu after one cycle of separation and recovered a total of 94% of loaded Eu. The purity of the separated Eu is unaffected between pH 3 and pH 5.5. Overall, the method that is described in this chapter is capable of separating Eu from Gd. Understanding the factors affecting on the coordination and stabilization of low-valent f-block elements is important in rational designing of ligands. The role of donor atoms, denticity and flexibility in cryptands in encapsulating and stabilization of low-valent f-block elements (UIII and LaIII) were studied in this chapter using 2.2.2-cryptands and tris[2-(2-methoxyethoxy)ethyl]amine. Incorporating flexibility to cryptands enhanced the coordination ability of UIII and removing one tertiary amine shifted the oxidation potential of UIII/IV couple to more positive than 2.2.2-cryptands. The greater affinity of actinides towards more softer donor atoms was observed with shorter bond length between UIII and nitrogen donor atoms compared to lanthanides (LaIII). These findings provide information about the stabilization ability of low-valent f-block elements by introducing flexibility to cryptand-type ligands. Chapter 6 summarizes all the chapters and provides future outlook for each chapter.
Recommended Citation
Kulasekara, Deshika Nuwangi, "Cryptand-Based Low-Valent F-Block Complexes Toward Stabilization And Separation Of Actinides And Lanthanides" (2023). Wayne State University Dissertations. 3885.
https://digitalcommons.wayne.edu/oa_dissertations/3885