Exploring the F-Block through Non-Aqueous Coordination Chemistry

The knowledge of actinide chemistry significantly lags behind the rest of the periodic table. Understanding the fundamental behavior of these elements is crucial for actinide separations and nuclear waste storage. Many separation strategies utilize various ligands to effectively coordinate specific actinides, however this remains an underdeveloped area of research. It is generally accepted that actinides have slightly more diffuse f-orbitals which allow for more covalent character in the bonds they form with ligands, resulting in more stable complexes with softer donor ligands. This has resulted in the design of selective ligands to specifically bind actinides for effective separation. By carefully selecting solvents, a wide variety of ligands can be utilized in order to understand the relative participation of actinide frontier orbitals (6p, 6d, 5f, 7s, 7p) in bonding, and understanding these bonding differences is important for how they may be utilized for future designs of ligand systems for actinide separations. The first part of this work focuses on f-element Schiff base coordination complexes in order to produce a clearer picture of the bonding between actinides and ligands. Schiff base ligands and their derivatives are of popular interest because of their ability to coordinate many different metal ions and stabilize them in a variety of oxidation states. First, a series of homoleptic tetravalent f-element and transition metal complexes have been synthesized, allowing for a comparison of coordination complexes containing metal cations in the formal 4+ oxidation state by structural, spectroscopic, and theoretical analysis. Utilizing the same ligand, this study was extended to the uranyl and neptunyl dications in the 6+ oxidation state. Furthermore, a series of heteronuclear complexes featuring a trivalent f-element and divalent transition metal were examined through crystallographic, spectroscopic, and magnetic analysis. The second part of this work focuses on periodic trends in bonding and Lewis-acid catalysis of the lanthanides and mid actinides utilizing a neutral nitrogen donor cryptand ligand. An imine-cleavage methodology is used to generate bimetallic complexes from the ligand across the f-block. In this study, a divergence of coordination activity is observed between the early and late lanthanides in structure and bonding, and is extended to the actinides. Synthetic methods also show the importance of the starting material as well as the pH, in the generation of mono vs. bimetallic complexes. Lastly, a similar study was conducted utilizing different starting materials to focus on the monometallic cryptand complexes of Ce and Pu.