Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)



Committee Chair

Suzanne C. Bart

Committee Member 1

Jonathan Wilker

Committee Member 2

Jianguo Mei

Committee Member 3

David R. McMillin


The complex bonding and redox properties of actinide elements are much less understood compared to common main group and transition metal elements. This is likely the result of fewer chemical studies, due to the challenges of working with these radioactive elements. Nevertheless, understanding the chemical behavior of these elements, and how they differ from the lanthanide series, is crucial for nuclear materials processing and waste management. Along these lines, the first chapter discusses the interactions of an ONO-chelating redox-active ligand with uranium. Uranium derivatives of a dioxophenoxazine ligand, (DOPOq)2UO2, (DOPOsq)UI2(THF)2, (DOPOcat)UI(THF)2, and Cp*U(DOPOcat)(THF)2 (DOPO = 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate), have been synthesized from U(VI) and U(III) starting materials. Full characterization of these species show uranium complexes bearing ligands in three different oxidation states. The electronic structures of these complexes have been explored using 1H NMR and electronic absorption spectroscopies, and where possible, X-ray crystallography and SQUID magnetometry. The second chapter describes the stability imparted by this dioxophenoxazine ligand in the formation of tris(DOPO) complexes. This chapter involves the discussion of the first non-aqueous isostructural series of coordination compounds for members across the f-block, including thorium uranium, plutonium, americium, berkelium, and californium, which is the broadest, most well-studied series of trivalent metals known. While californium would be expected to show purely electrostatic contributions to bonding due to its location in the series, spectroscopic, structural, and computational analyses shows higher degrees of covalent bonding compared to its neighbors to the left. This work provides a greater understanding of bonding between organic ligands and actinides, which can aid in the design of new ligands for encapsulation and separation of metals at the bottom of the periodic table.

The third chapter addresses subtle electronic characteristics associated with redox-active ligand uranium complexes. Uranium complexes (MesDAE)2U(THF) (1-DAE) and Cp2U(MesDAE) (2-DAE), bearing redox-innocent α-diamine ligands, have been synthesized and characterized for a full comparison with previously published, redox-active α-diamine complexes, (MesDABMe)2U(THF) (1-DAB) and Cp2U(MesDABMe) (2-DAB). These redox-innocent analogues maintain a similar steric environment to their redox-active ligand counterparts to facilitate a study aimed at determining the differing electronic behavior around the uranium center. Structural analysis by X-ray crystallography showed 1-DAE and 2-DAE have a very similar structural environment to 1-DAB and 2-DAB, respectively. The main difference occurs with coordination of the ene-backbone to the uranium center in the latter species. Electronic absorption spectroscopy reveals these new DAE complexes are nearly identical to each other. X-ray absorption spectroscopy of all four species notes that there is a significant difference between the bis(diamide)-THF uranium complexes as opposed to those that only contain one diamide and two cyclopentadienyl rings, but there is little difference in valency between the two ligand systems. Finally, magnetic measurements reveal that all complexes display temperature dependent behavior consist with uranium(IV) ions that are not supported by ligand radicals. Overall, this study determines that there is no significant bonding difference between the redox-innocent and redox-active ligand frameworks on uranium. Furthermore, there is no data to suggest covalent bonding character using the latter ligand framework on uranium, despite what is known for transition metals. The fourth chapter describes the synthesis of redox-active pyridine(diimine) (PDI) lanthanide complexes with an aim to bring redox activity to the notoriously redox non active metal centers. A full reduction series of the MesPDIMe ligated to neodymium was accomplished using NdI3(THF)3.5 as a starting material. This series included the three electron reduced dimer, [MesPDIMeNd(THF)]2, which is an interesting structural analogue to known uranium compounds. Also, this dimer has demonstrated high reactivity towards a variety of substrates, making it an exciting platform with which to explore redox chemistry at a lanthanide center. The fifth chapter describes the synthesis and reactivity of new uranyl complexes containing novel alkyl amide ligands. New uranyl derivatives featuring the amide ligand, -N(SiHMe2)tBu, were synthesized and characterized by X-ray crystallography, multinuclear NMR spectroscopy, and absorption spectroscopies. Steric properties of these complexes were also quantified using the computational program Solid-G. The increased basicity of the free ligand -N(SiHMe2)tBu was demonstrated by direct comparison to -N(SiMe3)2, a popular supporting ligand for uranyl. Substitutional lability on a uranyl center was also demonstrated by exchange with the -N(SiMe3)2 ligand. Reactions of these complexes with substituted anilines promotes new reactivity, and sets the ground work for the isolation of a uranyl imido. Finally, the sixth chapter discusses the development of new molecular neptunium halide complexes that can be used as an entry into nonaqueous chemistry. Solvent exchange of NpCl4(DME)2 with THF yielded the THF adduct, NpCl4(THF)3, whereas PuCl4(DME)2 appears to be unstable in THF, partially decomposing through disproportionation to the mixed valent plutonium salt, [PuCl2(THF)5][PuCl5(THF)]. Reduction of NpCl4(THF)3 led to the isolation and structural and spectroscopic characterization of NpCl3(py)4, which is a rare example of a trivalent neptunium halide that was sourced from neptunium oxides rather than Np0.