Magnetic and Spectroscopic Studies on Lanthanide Compounds and Heterometallic Rings

Abstract

Molecular magnets have emerged as promising candidates for revolutionary applications in high-density information storage and quantum computing. This thesis presents a comprehensive investigation into the synthesis, structural characterization, magnetic properties, and electronic structures of diverse lanthanide-based compounds, with a particular focus on chromium-lanthanide heterometallic systems and lanthanide-only complexes. The research adopts a multifaceted approach, integrating synthetic inorganic chemistry, magnetometry, advanced spectroscopic techniques, and theoretical modelling to elucidate the fundamental properties of these molecular systems. The primary objectives of this study are twofold: firstly, to probe the exchange interactions and local anisotropy in heterometallic rings through advanced spectroscopic techniques, and secondly, to explore the magnetic properties of lanthanide compounds under varied doping levels and in different diamagnetic hosts, such as yttrium and lutetium. A series of 3d-4f heterometallic rings, featuring chromium(III) and lanthanide ions {CrIII6LnIII2} (Ln = Ce, Gd, Tb, Yb and Y) and {CrIII6CeIII}, were synthesized and characterized. These compounds were studied using SQUID magnetometry and EPR spectroscopy. Strong antiferromagnetic interactions between chromium(III) ions and weak interactions involving lanthanide ions were quantified using a full microscopic spin Hamiltonian. Simplified models were also developed to explore magnetic anisotropy and exchange interactions in low-lying states. Electron Paramagnetic Resonance (EPR) spectroscopy was employed to probe the local crystal field environments and magnetic anisotropy. A asymmetric [GdIII2] dimer was synthesized and the doping experiments into yttrium(III) and lutetium(III) analogues were conducted. Magnetometry and EPR spectroscopy revealed weak antiferromagnetic exchange interactions. Doping experiments allowed for the determination of local magnetic properties and zero-field splitting parameters. A series of monometallic lanthanide compounds were synthesized, and their electronic structures were investigated through EPR and XMCD spectroscopies. The accuracy of different theoretical approaches in simulating XMCD spectra was evaluated, with NEVPT2 calculations showing excellent agreement with experimental data for erbium complexes. These studies contribute to the understanding of magnetic interactions, anisotropy, and electronic structures in heterometallic and lanthanide complexes, offering insights into their potential applications in molecular magnetism.

Date of Award	6 Feb 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Richard Winpenny (Main Supervisor), Michael Baker (Co Supervisor), Nicholas Chilton (Co Supervisor) & David Mills (Co Supervisor)