ELECTRONIC STRUCTURE AND MOLECULAR GEOMETRIES OF METAL COMPLEXES WITH DFT AND MULTIREFERENCE METHOD

Metal complexes are ubiquitous for their diverse applications including catalysis, sensing, medicine, and environmental applications. For effective use of metal complexes, understanding their electronic structure is essential. In most cases, molecules can be represented as a single electron configuration. However, in some cases, especially transition metal and actinide complexes, multireference electronic structures are observed. This is because the valence d (and f) orbitals in metals are often nearly degenerate, leading to close-lying energy states and the subsequently more frequent presence of multiconfigurational electronic structures. The traditional approach to modeling these systems is to use density functional theory to optimize the geometry of the molecule. In most cases, this assumption holds; however, we are interested in cases where it is less obvious. This thesis focuses on the relationship between molecular geometry and electronic structure in metal complexes using DFT and multireference methods. In some cases, high-level multireference methods are used to obtain geometries and compute vibrational frequencies. Specifically, the copper corrole was studied, which has been the subject of long-standing debate due to its unique geometry and electronic structure. Complete active space multireference methods were employed to optimize unsubstituted and a set of meso-functionalized copper corroles, and their electronic structure was studied with a larger active space, comparing the results with available DFT and experimental data. On the other hand, other questions involving changes in molecular geometry can be addressed using structures from density functional theory. Specifically, a series of uranium-arenide complexes were investigated to understand their ground state electronic configurations and bonding between uranium and anthracene ligands. Finally, the nature of uranium-pnictogen bonds was explored and a unique metal-ligand structural distortion observed in the solid state was understood