Redefining the Actinide Series

This dissertation focuses on probing the fundamental chemistry of the actinide series, specifically the structure and bonding in complexes of transuranium elements. The actinides consist of the elements from actinium to lawrencium in the periodic table, best known for uranium and plutonium, which were used to develop nuclear weapons and power. Today, nuclear power is used to generate over 17% of the electricity across the world.[1, 2] Although an effective means of generating electricity, the waste generated from nuclear reactors is a major issue with relatively little progress being made to reduce the amount and radiotoxicity of the waste. Overall, this problem stems from the chemical complexity and highly radioactive nature of the actinides. Because of this the actinides are understudied, particularly beyond uranium, and as a result much of the fundamental chemistry is poorly understood. The goal of this work is to prepare coordination complexes that can be used as probes for elucidating changes in structure and bonding across the actinide series. Over the past couple decades, neutral nitrogen donating ligands have shown to have a greater affinity towards the actinides over the lanthanides.[1] The work discussed in this dissertation has focused on using nitrogen-containing carboxylates to explore periodic trends through the lanthanide and actinide series. The first step of this project was to explore structure and bonding differences between the lanthanide (4f) and actinide (5f) series. The early lanthanides, such as Ce and Nd are often used as surrogates for the actinides because they possess f orbitals and are relatively similar in size to that of their actinide analogs.[3] Depending on the coordinating ligand, the structure and bonding between the 4fs and 5fs can either mimic each other or diverge greatly. In some cases the structure of the actinides and lanthanides are very similar, but the electronic properties are vastly different. In chapters 3 and 4, unique structures and electronic properties of Pu and Ce complexes are explored. The second portion of this research was to investigate the differences in structure and bonding between of the transplutonium actinides, americium through californium (Am-Cf). Traditionally these later actinides were believed to mimic the lanthanides in both their structure and bonding characteristics, but as we explore the actinides more we find this might not be true. Our approach used a pyridine dicarboxylate derivative to make an isomorphous series of both the trivalent actinides and lanthanides. It was found that the late actinides, starting at Cf, have different electronic properties that are not paralleled by any of the lanthanides or early actinides. Much to our surprise, it seems that Cf represents a second transition in the actinide series, which is discussed in chapters 5 through 7. Overall, this dissertation focuses on exploring the structure and bonding of the f elements through solid-state chemistry utilizing a variety of characterization techniques.