Electronic Structures of Perfunctionalized Dodecaborate Clusters

Citation

Schwan, Lars Josef (2020) Electronic Structures of Perfunctionalized Dodecaborate Clusters. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jf75-8k37. https://resolver.caltech.edu/CaltechTHESIS:04062020-155127311

Abstract

Dodecahydro-closo-dodecaborate is only stable as a dianionic closed-shell species, however, some alkyloxy- and aryloxy-perfunctionalized dodecaborate clusters ([B₁₂(OR)₁₂], R = alkyl or aryl) can be isolated in hypoelectronic hypocloso-dodecaborate(1-) and hypercloso-dodecaborate(0) states. These hypoelectronic clusters display strong visible absorption bands and highly reversible redox behavior, which have inspired applications in photochemistry, charge-storage and as dopants in conducting polymers. Chapter 1 provides a historic overview of dodecaborate research with particular focus on the development and applications of hypoelectronic clusters. Chapter 2 summarizes our spectroscopic investigtion of the photochemistry and photophysical properties of aryloxy-perfunctionalized hypercloso-dodecaborate(0) clusters. Obtaining reliable photophysical data proved exceedingly difficult due to formation of reduced hypocloso-dodecaborate(1-) species through solvent photooxidation, disproportionation and solvent-cluster interactions. A detailed discussion on these issues is presented, along with the final luminescence data collected for hypercloso-dodecaborate(0) and hypocloso-dodecaborate(1-) clusters. In Chapter 3, we present evidence indicating that certain alkyloxy-perfunctionalized dodecaborate clusters can be further oxidized to a cationic state. Electrochemical and spectroelectrochemical characterization indicate reversible conversion between the dodecaborate(0) and dodecaborate(1+) state. The results are further corroborated by EPR studies on dodecaborate(1+) clusters in-situ generated using the strong oxidant tris(2,4-dibromophenyl)ammoniumyl hexachloroantimonate. In chapter 4, we present Q-band pulsed EPR results that give a quantitative measure of the spin distribution of both hypercloso-dodecaborate(1-) and super-oxidized dodecaborate(1+) clusters. This is to our knowledge the first time pulsed EPR techniques have been applied to hypoelectronic dodecaborate clusters. The EPR data indicate that the frontier orbitals of hypoelectronic dodecaborate clusters are confined to the cluster core and delocalized evenly across the B₁₂ pseudo-icosahedron. Furthermore, we provide UV–vis–NIR evidence indicating that the visible and NIR electronic transitions of these clusters occur between orbitals that are largely confined to the cluster core. Chapter 5 summarizes our results and discusses future directions.

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