Lanthanoid (III) Diphthalocyanines and Goblet-Shaped Complexes: Old and New Architectures for Molecular Qubit Candidates
Open AccessAs quantum computing becomes more popular, research groups from all over the world are focusing on synthesizing usable quantum bits, or qubits, the essential building blocks of a quantum computer. Specifically, significant research has focused on single‑molecule magnets, which are molecules with high magnetic blocking temperatures and large spin-relaxation barriers, as these properties are a direct measure of information storage. Lanthanoid (III) diphthalocyanine double-decker complexes are one class of molecules that have been intensely studied, especially since terbium (III) diphthalocyanine, in particular, has been shown to be an effective single-molecule magnet. Presented in this dissertation is an investigation of the structure-property relationships of four distinct lanthanoid (III) diphthalocyanine polymorphs, which can be selectively and reproducibly prepared with different metal centers. It will be shown how controlled crystallization allows for fine-tuning the molecular geometry, intermolecular interactions, and their impact on the resulting magnetism (specifically in the case of neodymium (III) diphthalocyanine). Halogenated complexes, which have been largely unexplored thus far, were synthesized and characterized to investigate how the position of the halogen substituent affects the electronic and structural properties. Despite their unique electronic and magnetic properties, lanthanoid (III) diphthalocyanines are not without their shortcomings, including low yields and a lengthy purification process. In an effort to overcome these shortcomings, a new goblet-shaped complex was investigated. This complex consists of three parts: a flat aromatic foot which will allow for the complex to be deposited on a surface, and a carbon chain linker, which connects the base to a triscyclopentadienyl lanthanoid (III) bowl, which will provide the anisotropy and bistability that should ideally give the desirable magnetic properties. Presented in this dissertation is the convergent synthesis of these complexes, a complex task due to the coexistence of several active functional groups, with a focus on the reaction of ethylene carbonate with the flat foot of the goblet complex. Chapter 1 focuses on the introduction of quantum computers and their importance, followed by an introduction to qubits and why we are choosing to focus on molecular qubits over other systems. A discussion of lanthanoid single-molecule magnets and the reasoning behind investigating lanthanoid (III) diphthalocyanines and triscyclopentadienyl complexes will conclude this chapter. Chapter 2 introduces the unique properties of lanthanoid (III) diphthalocyanines and focuses on the polymorphism of neodymium diphthalocyanine, ending with a discussion of the preliminary magnetic data obtained for two polymorphs. Chapter 3 continues the discussion of structure-property relationships with the remaining lanthanoids, highlighting how oxidation state and solvent influence the resulting polymorph. Density functional theory calculations were performed to examine why certain polymorphs form over others. Trends across the lanthanoids for each polymorph will be discussed in detail. This chapter concludes with a discussion of the crystal structures of the anionic lanthanoid (III) diphthalocyanine and the zirconium (IV) diphthalocyanine complexes. Chapter 4 focuses on the efforts made in fully characterizing halogenated diphthalocyanine complexes, concluding the discussion of these complexes. Chapter 5 introduces the goblet-shaped complex with a detailed description of each piece of the goblet and continues with a discussion of the structural and electronic properties of the triscyclopentadienyl lanthanoid (III) complexes. These complexes will be studied in-depth, not only because their magnetic data has not previously been published, but because they can aid in understanding the magnetic behavior of the desired goblet-shaped complexes. Chapter 6 introduces the feet chosen for the base of the goblet, followed by a discussion of the development of a universal synthetic route to build the goblet-shaped complexes.
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