EPR Studies ofMagnetic Properties of Coordination Complexes in Solid Host Matrices

Abstract

EPR studies of the magnetic properties of coordination complexes in solid state matrices: a thesis submitted to The University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science and Engineering. This thesis presents a collection of projects directed towards the study of metal complexes in the solid state by Electron Paramagnetic Resonance (EPR) spectroscopy. The properties investigated are related to relaxation of magnetic states of metal complexes of interest in the field of molecular magnetism and quantum information processing. The first chapter introduces magnetic relaxation and how to measure and fit the relaxation time constants T1 and Tm experimentally and how to model the temperature dependence of T1 to extract information on the mechanisms of relaxation. In the second and third chapter these methods are applied, in the former to a chromium nitrido complex in order to ascertain whether its similarities to vanadyl complexes lead to similar properties, and in the latter to Gd(trensal) to understand its relaxation behaviour observed in a previous high field EPR experiment. The chromium nitrido complex is found to have the same desirable relaxation properties possessed by vanadyl: long phase memory time and room temperature quantum coherence. This could make chromium nitrido complexes a system of interest for further qubit research. The spin-lattice relaxation of Gd(trensal) is measured and linked to the direct relaxation mechanism at liquid helium temperature, the Raman mechanism below liquid nitrogen temperature and local mode processes at high temperature. In addition, the long phase memory time from high field EPR is explained by the spin polarization of the lattice making the phase memory time field dependent. The fourth chapter focuses on cw EPR measurements of the zero field splitting (ZFS) in a series of Gd(III) complexes with near pentagonal bipyramidal coordination spheres, to understand how ZFS relates to geometry and crystal field (CF) strength in this seldom encountered symmetry. An inverse relationship between size of the ZFS and the CF strength of the axial ligands is established and this is extended to a correlation with the barrier for reversal of the magnetic moment (Ueff) of the analogous Dy(III) single molecule magnets. Jonatan Birch Petersen December 2022

Date of Award	31 Dec 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Eric Mcinnes (Supervisor), Richard Winpenny (Supervisor) & Floriana Tuna (Supervisor)