Investigating reactive intermediates formed in the [ru(bpy)(tpy)(oh2)]2+ catalyzed water oxidation reaction

Nickson, Kathleen Ann

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https://hdl.handle.net/2142/107687 Copy

Description

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

Issue Date

2020-06-25

Keyword(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.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

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http://hdl.handle.net/2142/107687

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Copyright 2020 is held by the Author(s)

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