title: Electron Paramagnetic Resonance Characterization of Dioxygen-Bridged Cobalt Dimers with Relevance to Water Oxidation.
abstract: A variety of metal oxides can catalyze the oxidation of water to molecular oxygen when polarized by a sufficiently high electrochemical potential. Minimizing the overpotential and increasing the rate of the oxygen-evolving reaction (OER) are key goals in making such materials a component of viable energy storage devices. However, the structural factors that imbue the metal oxides with their catalytic power are difficult to assess as these solids contain many distinct metal-ion sites, have a varying amount of defect sites within the lattice, and can be composed of multiple phases. In the present study, we determined the magnetic properties for a series of dimeric cobalt complexes in which the two metal centers are bridged by a dioxygen moiety. Our spectroscopically validated electronic structure description indicates that each species is best described as two Co(III) ions that are bound to a μ-η1η1superoxide ligand. Intriguingly, we found evidence that the two compounds that possess oxygen-evolving activity coordinate the superoxide ion in an unusual, nonplanar fashion. It appears as if the intermediately long Co···Co distance of 3.9 Å is responsible for the unusual superoxide binding geometry. This structural factor may be an important element in the design of solid-state OER catalysts.
authors.affiliation: Department of Chemistry, University of California , 1 Shields Avenue, Davis, California 95616-0935, United States.
authors.forename: Troy A
authors.initials: TA
authors.lastname: Stich
authors.affiliation: Department of Chemistry, University of California , 1 Shields Avenue, Davis, California 95616-0935, United States.
authors.forename: J Gregory
authors.initials: JG
authors.lastname: McAlpin
authors.affiliation: Department of Chemistry, University of California , 1 Shields Avenue, Davis, California 95616-0935, United States.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Wall
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706-1322, United States.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Rigsby
authors.affiliation: Department of Chemistry, University of California , 1 Shields Avenue, Davis, California 95616-0935, United States.
authors.forename: R David
authors.initials: RD
authors.lastname: Britt