UC San Diego

An important focus in molecular magnetism is the delicate interplay of single-ion anisotropy and coupling between magnetic centers when designing the magnetic energy landscape to yield intended magnetic properties. Throughout this dissertation, we explore how these two perturbations interplay to create this environment and how dynamic behavior in magnetic systems are affected. In Chapter 1, we explore the current design principles dictating the state-of-the-art in molecular magnetic design and outline the parameter space we seek to optimize. In Chapter 2, we explore the ability of highly charge-dense alkoxide bridging ligands to tightly bind highly anisotropic ErCOT units to couple them via the dipolar interaction and explore how this changes in asymmetric complexes. By introducing such a large perturbation, the beneficial aspects of coupling are tempered by increased mixing in states that are close in energy to each other. In Chapter 3, we describe the angular dependence of the dipolar interaction in a series of alkyl-bound ErCOT units by modulating the number of bridging ligands. By enforcing collinearity, we raise the energy separation within dipolar coupled states to increase the temperature dependence of relaxation mechanisms below the first excited state. In Chapter 4, we extend the model describing the dipolar interaction beyond the ground state to describe long-timescale relaxation in a series of halide-bridged ErCOT complexes. By using first-order perturbation theory, we can describe how magnetic states couple indpedently when well-separated and how magnetic relaxation is affected in turn. As a step in this direction we build from the established premise that the COT2− ligand is consistently able to stabilize uniaxial Ising-type magnetic anisotropy in the Er3+ ion along the metal-centroid vector. This premise allows a tangible method to translate spin-space models into molecule design using classical principals for axial moments. Extending from this, ErCOT-derived polynuclear complexes have a useful structural handle to predict and direct the individual centers’ anisotropies; therefore, they are ideal for tuning the throughspace dipolar coupling mechanism. We have carefully modified the magnetic environment as enforced by the bridging ligands across two series of complexes. In one, we show the lengthened relaxation when moving from an inversion-symmetric arrangement of anisotropy axes to a colinear one. In the other, we maintain an inversion-symmetric bridging motif and modify the crystal field strength of the bridging ligands, noting the effect of both coupling strength and single-ion properties of the individual magnetic centers.