Effects of Pressure on Actinide Compounds and Their Lanthanide Analogues

The pressure behavior of the actinides, like the rest of the chemistry of the actinides, is not well studied or understood. Chapter 1 gives a brief description of the prior work that has gone into studying the pressure behavior of the actinides. A short description of the much more expansive research into the pressure behavior of the lanthanides is also given as a comparison to the work on the actinides. Chapter 2 is unique in that no lanthanides are involved, and instead focuses on the specific case of Cs2UO2Cl4 and how the uranyl bond is affected by pressure. A previous computational prediction of the pressure behavior is contradicted by the experimental evidence. Chapters 3, 4, and 5 discuss the impact of two different ligand systems on the trivalent actinide series: a soft dithiocarbamate ligand and a hard mellitate ligand. Through examining the UV Vis NIR absorption and luminescence spectra the role of the 4f orbitals of the lanthanides and the 5f of the actinides in bonding is probed under pressure. Both the softness of the ligand and metal are shown to be important in the type and magnitude of effects seen. Chapter 6 analyses three lanthanide compounds under pressure crystallographically and spectroscopically lays the groundwork for analysis of the actinides in the same system. The 2,2 dihydroxymesoxalate ligand is used for its uniform crystallization across the trivalent lanthanides and the trivalent actinides that have been produced, as well as its high symmetry to assist in high pressure crystallography. Chapter 7 is also a structural analysis using Raman spectroscopy on several lanthanides with the thiocyanate ligand, as well as the curium thiocyanate. The C=N stretching frequency is examined as a function of pressure, revealing the extent of backbonding in these systems. Chapter 8 provides a conclusion to the work and a summary of the trends in the results found in the dissertation.