Master of Science
Gilroy, Joseph B.
This thesis describes the synthesis and characterization of various three- and four-coordinate cationic and dicationic boron complexes supported by formazanate ([R1-N-N=C(Ph)-N=N-R5]− ligands. The first chapter provides a review of various three-coordinate and cationic boron complexes and related applications. Chapter two examines the effect of several variations (i.e., charge, coordination number and boron-bound substituents) on the electronic structure of cationic boron formazanate complexes. Absorption spectroscopy measurements reveal that the wavelengths, intensities, and type of the first electronic transitions in cationic boron complexes can be modulated by these structural variations. Chapter three exploits the electron deficiency of a borenium cation supported by a N2O2– formazanate ligand. Excellent Lewis acidity is demonstrated using the Gutmann-Beckett method. Further, a drastic decrease in the LUMO energy is observed upon introduction of cationic boron, compared to related neutral complexes. Together, this work demonstrates the utility of these cationic boron formazanates in the design of molecular materials.
Summary for Lay Audience
Designing boron-containing molecules can be challenging, especially if the boron atom has fewer than four bonds with other atoms. This violates a fundamental bonding principle in chemistry, the octet rule, which requires atoms to make a net total of four bonds, containing a total of eight electrons. Boron is often used in its three-coordinate mode (three bonds) as it is in a state of electron deficiency, meaning it can act as an acceptor of electrons. This property is exploited in the design of materials such as organic light emitting diodes (OLEDs), which can be found in your LED TV, providing a vivid and attractive display. The electron acceptor property can also be used in sensing, where the electron deficient boron atom can make a bond with anions (e.g., fluoride ions), which can be detected using different spectroscopic techniques. This work presents a set of cationic (‘positively charged’) boron complexes, supported by a nitrogen-rich ligand (formazanate). Imposing a positive charge increases the electron deficiency and allows for a wider use of applications with an increased performance. The challenge when using cationic boron is their propensity to bind with water and other electron donating molecules because of the electron deficiency. Cationic boron can be difficult to successfully make in a lab, but is typically done by removing a weakly bound halogen (i.e., fluorine or chlorine) from boron. The research performed in this thesis examines how changing the chemical environment around boron will affect its properties. We also examine a strongly electron deficient boron complex (very reactive) and gain a qualitative and quantitative understanding of its properties. The work provides a platform and guidelines for the design of electron deficient cationic boron complexes with desired properties for use in material applications.
Katzman, Benjamin D., "Cationic Boron Formazanate Complexes" (2021). Electronic Thesis and Dissertation Repository. 7838.
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