Computational Studies of the Electronic Structure and Bonding in Heavy Element Compounds

This thesis reports the results of studies of a selection of heavy element molecular compounds involving the actinides, lanthanides and main group metals using density functional theory. A wide variety of tools are employed, including molecular orbital, population, charge and electron density analysis, and comparison of computed with experimental spectroscopic methods (NMR, IR, UV-Vis and ESR) is performed. A description of the methods used in this thesis is given in Chapter 1. The formation of uranyl species by the reaction between uranyl (VI) and organic compounds such as α-isosaccharinate and D-gluconate in low level nuclear waste repositories can have important implications for the environment. Most notably, the high mobilities of soluble uranyl species can contaminate underground geological environments such as the water and soil. The complexation of uranyl and the organic acids as a function of pH is studied computationally and compared to experimental data in Chapter 2. Chapter 3 explores variations of D-Gluconic acid using different functionals. The main uranyl species present were identified and overall there was good agreement with experiment. The nature and degree of covalency in actinide/lanthanide–Group 13 element bonds is assessed in Chapter 4 using a variety of analysis methods. The extent of covalency was found to strongly depend on the method employed. Chapter 5 studies novel systems featuring divalent members of Group 14; Ge(II), Si(II) and Sn(II), with emphasis on the structural and electronic effects of the lone pair of electrons. Finally, a study on Tl in a very unusual oxidation state, Tl(II), is performed in Chapter 6. ESR properties are calculated to account for the presence of an unpaired electron of two experimentally proposed Tl(II) compounds. In one case the presence of the Tl(II) radical is verified, whereas in the other it is disproved