Molecules and materials featuring unpaired electrons are fundamental elements of modern energy, device, and imaging technologies. The high sensitivity of electronic spins to their surroundings renders these compounds further attractive as environmental sensors. In order to successfully realize these applications, the electronic spins must be precisely controlled. One promising strategy toward generating compounds with improved performances and emerging properties involves spin control using the chemical design of coordination compounds. Transition metal-based compounds are especially well suited to this end owing to their exceptional synthetic tunability, high environmental responsiveness, and ease of manipulating their spin state and electronic structure. Nevertheless, the employment of molecule-based transition metal compounds in practical settings is scarce and further investigations are necessary to develop design principles that allow for the rational synthesis of such compounds that meet society’s expectations. In this dissertation, I report efforts to manipulating the electronic structure and spin state of series of transition metal complexes to design responsive magnetic resonance imaging (MRI) probes and to elucidate design principles for molecule-based magnets with high operating temperatures. I have focused on compounds featuring FeII and CoII metal centers due to their favorable magnetic and nuclear magnetic resonance (NMR) properties. Chapter 1 describes the need for new bioresponsive MRI probes and metal-organic magnets and outlines our synthetic strategies to these ends. Chapter 2 details the first example of a spin-crossover FeII complex for sensing temperature using 19F NMR chemical shift and illustrates that a temperature-dependent change in electronic spin state can significantly improve the sensitivity of 19F MR thermometers. Chapter 3 describes a novel proof-of-principle study for the ratiometric quantitation of pH using CoII2 paramagnetic chemical exchange saturation transfer (PARACEST) probes. Building on the strategy developed in Chapter 3, Chapters 4 and 5 are complementary in describing our thorough investigation of how ligand modifications can enhance the performance of this family of CoII2 PARACEST pH probes. These studies lead to the discovery of a probe that exhibits one of the highest pH sensitivity yet reported for a ratiometric MRI probe in the physiological pH range. Chapter 6 illustrates that changes in the magnetic anisotropy at CoII can be employed to distinguish between Ca2+ and Na+ ions in solution, providing the first example of a ratiometric quantitation of Ca2+ concentration using PARACEST. Finally, Chapter 7 examines the effects of bridging ligand substituents on magnetic exchange coupling in two series of benzoquinoid-bridged FeII2 complexes and Chapter 8 provides a thorough survey of structurally characterized metal-organic framework magnets. Together, these results demonstrate that the high chemical and magnetic tunability of transition metals enables the realization of compounds with unprecedented properties.

Creator

• Thorarinsdottir, Agnes Eva E

DOI

• https://doi.org/10.21985/n2-rmdr-2481

Subject

• Inorganic chemistry

Language

• en

Alternate Identifier

• etdadmin_upload_705667
• http://dissertations.umi.com/northwestern:14946

Keyword

• bioresponsive probes
• transition metal compounds
• metal-organic magnets
• electronic spin
• magnetic resonance imaging

Date created

• 2019-01-01

Resource type

• Dissertation

Rights statement

• In Copyright