Quantum Coherence and Covalency in Organometallic Lanthanide Complexes Investigated by Pulse EPR Techniques

Abstract

Quantum coherence and covalency in organometallic lanthanide complexes investigated by pulse EPR techniques: a thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science and Engineering. The research presented in this thesis uses continuous-wave and pulsed electron paramagnetic resonance (EPR) techniques for the investigation of the electronic structure, relaxation and quantum coherence properties of a number of organometallic complexes of C3 symmetry. The compounds include either a di- or trivalent lanthanide or transition metal ions bound by three cyclopentadienyl (Cp' = C5H4SiMe3, Cp'' = C5H3(SiMe3)2-1,3, Cptt = C5H3(CMe3)2- 1,3), silyl-amide (N'' = N(SiMe3)2) or aryloxide (OArAd,Ad,Me = 2,6-Ad2-4-Me-C6H2O) ligands, where Me and Ad refer to methyl and adamantane substituents. Studies on [Ln(Cp')3]- (LnII = LaII, LuII or YII), [Sc{N(SiMe3)2}3]-, [La(Cp'')3]-, La(Cptt)3]- and [Y(OArAd,Ad,Me)3]- have revealed robust quantum coherence properties that could be monitored up to 120 K in frozen solutions and to 300 K in the solid-state single crystals. Nutation experiments enabled Rabi oscillations being observed for all possible electronuclear transitions, indicating the potential of the molecules as quantum bits despite their rich nuclear spin environment. Advanced pulse hyperfine EPR techniques, such as HYSCORE and ENDOR, are employed to characterize the environment of the metal ion in greater detail probing the electronic spin density trasfered to ligand nuclei. Continuous wave and pulse EPR spectroscopy are also involved to study a family of Ln(III) complexes of formula [Ln(Cptt)3] (LnIII = CeIII, NdIII, SmIII). Analysis of the results provided information on their electronic structure and relaxation times. These complexes do not display long coherence times due to the nature of their SOMO 4f-orbitals, leading to faster relaxation properties of the electrons. Hyperfine sublevel correlation (HYSCORE) spectroscopy is further used to study the weak interactions of the unpaired electron with the ligand 1H and 13C nuclei, probing that the metal ligand bonding is primarily ionic in these cyclopentadienyl trivalent lanthanide complexes.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Eric Mcinnes (Supervisor), Floriana Tuna (Supervisor) & David Mills (Supervisor)