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Title:INVESTIGATING REACTIVE INTERMEDIATES FORMED IN THE [RU(BPY)(TPY)(OH2)]2+ CATALYZED WATER OXIDATION REACTION
Author(s):Nickson, Kathleen Ann
Contributor(s):Garand, Etienne ; Sherman, Summer Lee
Subject(s):Dynamics and kinetics
Abstract:In an effort to find alternative energy sources to fossil fuels, there is much interest in coupling water oxidation and CO$_{2}$ reduction reactions to create ``solar fuels". Through water oxidation, the following reaction occurs: 2H$_{2}$O $\rightarrow$ 4H$^{+}$ + 4e$^{-}$ + O$_{2}$. The de facto representative of homogenous mononuclear water oxidation catalysts is [Ru$^{II}$(bpy)(tpy)(H$_{2}$O)]$^{2+}$, or more simply [Ru$^{II}$H$_{2}$O]$^{2+}$. For this catalyst, the rate limiting step and reaction bottleneck is the O-O bond formation step, which proceeds through a water nucleophilic attack of the electrophilic Ru=O bond. The two intermediates that can potentially undergo this water nucleophilic attack to form the O-O bond are [Ru$^{IV}$=O]$^{2+}$ and [Ru$^{V}$=O]$^{3+}$. Kinetic evidence and our calculations suggest that the [Ru$^{IV}$=O]$^{2+}$ intermediate is significantly less reactive with H$_{2}$O than the [Ru$^{V}$=O]$^{3+}$ species, which may be due to the Ru=O bond being less electrophilic in the [Ru$^{IV}$=O]$^{2+}$ species than the [Ru$^{V}$=O]$^{3+}$ species. Experimentally, we form these highly reactive intermediates in an octopole ion trap by introducing a buffer gas mix of O$_{3}$/O$_{2}$ to [Ru$^{II}$]$^{2+}$ or [Ru$^{III}$]$^{3+}$, and then capture them by evaporative quenching of collision complexes. This has allowed us to isolate the [Ru$^{IV}$=O]$^{2+}$ species and will allow us to later focus on isolating and probing [Ru$^{V}$=O]$^{3+}$ using cryogenic ion IR predissociation spectroscopy. These predissociation spectra allow us to determine the Ru=O stretching frequencies of these two intermediates, which can be confirmed through isotopically labeled $^{18}$O substitution. In particular, the frequency of the Ru=O stretching mode is likely sensitive to the electronic structure of the Ru=O bond. Also, with the addition of our dual reaction traps, we will cluster water on [Ru$^{IV}$=O]$^{2+}$ and [Ru$^{V}$=O]$^{3+}$ in order to elucidate the water bonding orientation and arrangement, which will reveal if the water acts as a nucleophile, or if it is the Ru=O that is the electrophile in the water addition step.
Issue Date:25-Jun-20
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:CONFERENCE PAPER/PRESENTATION
Type:Text
Language:English
URI:http://hdl.handle.net/2142/107687
Date Available in IDEALS:2020-06-26


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