Spectroscopic Studies of Transitional Metal Complexes with Special Electronic Properties

Transition metal complexes have important applications to catalysis, materials science, photochemistry, and biological systems due to their diverse chemical, optical, and
magnetic properties. Such properties are exploited, for example, to create novel complexes that serve as models for intermediates in dioxygen-activated enzymes and
have uncommon electronic and/or magnetic properties. These properties are elucidated in this work by a variety of methods in including ⁵⁷Fe Mössbauer spectroscopy, EPR
spectroscopy, and Density Functional Theory. The results of this work may facilitate advances in the understanding of biological catalytic processes and in the design of new
materials. The mechanism by which proteins perform their chemical functions is assessed by a large number of biologists, chemists, and physicists. A challenge of this assessment is that reactive intermediates along the enzymatic cycle are difficult to trap and isolate. One
approach to solving this problem is mutation of the protein to slow down the catalysis and therefore trap the intermediate. However, this method is time consuming and labor
intensive, hence costly. Such issues can be circumvented by mimicking the fleeting intermediates by use of synthetic transitional metal model complexes. Although this synthetic approach is not new, the model complexes in this work are novel. Their unique spectroscopic characteristics are an important contribution to the literature and provide a
deeper understanding of catalysis by several enzymes. This work provides the first instance of a synthetic non-heme mononuclear Fe^III-superoxo complex, which is important to understanding the dioxygen activation by enzymes such a 2,3-HPCD. A second compound presented in this thesis is a “mysterious,” synthetic high-valent dimer that serves as a possible model of an intermediate in enzymes such as methane monooxygenase (MMO). The trend of moving towards ever smaller devices is driving technology to the molecularscale. This small-scale technology is being approached, in part, from the perspective of transition metal complex-based molecular materials. In an effort to identify complexes with the particular properties required of good candidates for such materials, this work studied two novel Fe- and Ni-based transition metal complexes. The Fe-based compound is the first example of a homoleptically-capped spin crossover (SCO) complex. The homoleptic capping of the Fe-based CN-bridged square complex allows for a one-pot synthesis with good yield. The compound is also a new member of the very small family of polynuclear Fe^II SCO complexes reported in the last two decades. A second complex whose characterization is outlined in this thesis is a Ni^II-based, radical bridged dimer that exhibits remarkably strong ferromagnetic coupling between the Ni^II centers and the radical bridge. The complexes characterized in these studies represent building blocks for future molecule-based devices.