Investigating the Electronic Structure of Uranium Complexes

Abstract

As research within the field of actinide chemistry grows, the importance of accurately calculating the electronic structure becomes more crucial. This is especially true when considering potential speciation of nuclear waste using optical spectroscopy. Within the literature, TD-DFT is the most prevalent method for these calculations despite being a single configurational approach. However, due to orbital degeneracy and relativistic effects a multiconfigurational approach should be more accurate. Therefore, herein we present three pieces of work that aim to examine the accuracy of multiconfigurational methods and dynamical correlation, to predict experimental spectra and magnetism for uranium molecules with various oxidation states. From our work, we found that there is no black-box approach when calculating the electronic structure of uranium. Starting from U(VI), as electrons are added the level of theory required is increased and the importance of multiconfigurational methods as well as dynamical correlation becomes more apparent. In paper one we investigated the electronic structure of three uranium molecules in the more common oxidation states (+4, +5 and +6) and determined the effectiveness of our approach by simulating optical spectra and comparing with experimental and TD-DFT data found in the literature. In paper two we re-evaluated recently synthesised low oxidation state uranocenes using multiconfigurational methods compared to their DFT analysis. We investigated the possibility of a multiconfigurational ground state and attempted to clarify the interpretation of their reported EPR spectrum and χMT data by simulating our own spectra. Finally, in paper three, we show that computational methods such as CASSCF and DFT can confirm the oxidation state of newly synthesised di-uranium complexes and disambiguate the nature of bonding via NPA and QTAIM analysis.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Louise Natrajan (Supervisor) & Nicholas Chilton (Supervisor)