UC Berkeley

Solar energy storage is critical to combatting anthropogenic climate change and transitioning to renewable sources of energy. Billions of years ago, plants evolved the ability to harvest and store energy from the sun in a process initiated by Photosystems I and II, wherein the oxygen evolving complex oxidizes water to produce dioxygen. This heterocubane CaMn4O5 cluster serves as a source of inspiration for the Tilley group’s investigations into the chemistry of water oxidation by cobalt oxo cubanes. Chapter 1 briefly describes the current understanding of the mechanism for water oxidation by the oxygen evolving complex, and the challenges posed to synthetic inorganic chemists by this system. Chapter 2 details the first approach attempted to synthesize new heterometallic cobalt oxo cubanes starting from simple tricobalt precursors. While the primary aim of this study was to find rational synthetic routes to a wide library of MCo3O4 clusters, the electronic structure of the Co3O4 fragment provides insight into the role of the fourth cobalt in the parent cluster. Chapter 3 presents a near complete investigation into the metal-metal exchange reaction between the Co4O4 cubane and MnII/III complexes to give the MnCo3O4 cubane. This study provides mechanistic evidence for a pendant metal intermediate during the exchange process, details reactions with CoIII and CoIV materials, and also reports an array of substituted benzoate and pyridine ligated cobalt oxo cubanes. This manuscript is available publicly on ChemRxiv. Chapter 4 details the synthesis and properties of a vanadium-cobalt oxo cubane through the principles outlined in the metal-metal exchange study. The isostructural vanadium and ruthenium cobalt oxo cubanes allow for interrogation of the role of the tricobalt framework. This chapter continues to describe the oxidative reactivity of the vanadium-cobalt oxo system and attempts to observe the oxidized intermediate spectroscopically with in situ methods. Theory and experiment suggest a more localized hole compared to the all-cobalt system, which may have implications for vanadium-cobalt oxide materials.