Krämer, Tobias and Tuna, Floriana and Pike, Sebastian D.
(2019)
Photo-redox reactivity of titanium-oxo clusters: Mechanistic insight into a two-electron intramolecular process, and structural characterisation of mixed-valent Ti(iii)/Ti(iv) products.
Chemical Science, 10 (28).
pp. 6886-6898.
ISSN 2041-6539
Abstract
Small titanium-oxo-alkoxide clusters, [TiO(OR)(O2PR0
2)]4, synthesised by the stoichiometric reaction of
Ti(Oi
Pr)4, phosphinic acid and water, undergo a photo-redox transformation under long-wave UV light.
The photo-reaction generates blue coloured, mixed-valence Ti(III)/Ti(IV)-oxo clusters alongside acetone
and isopropanol by-products. This reactivity indicates the ability for photoactivated charge separation to
occur in even the smallest of Ti-oxo clusters. EPR and NMR spectroscopic studies support a photoredox mechanism that occurs via an intramolecular, two-electron pathway, directly relating to current
doubling effects observed at TiO2 photoanodes in the presence of alcohols. The rate of photo-reaction
is solvent dependent, with donor solvents supporting the formation of low coordinate Ti(III) sites. The
nature of the electronic transition is identified by DFT and TDDFT calculations as an oxygen to titanium
charge transfer and it is possible to finetune the UV absorption onset observed by changing the
phosphinate ligand. A two-electron photo-reduced cluster, [Ti4O4(O2PPh2)6], forms spontaneously from
the photo-reaction and its structure is identified by X-ray crystallography with supporting DFT
calculations. These indicate that [Ti4O4(O2PPh2)6] is high-spin and contains two ferromagnetically
coupled electrons delocalised over the Ti4 core. [Ti4O4(O2PPh2)6] undergoes rapid oxidation in air in the
solid-state and performs a remarkable single-crystal to single-crystal transformation, to form a stable
cluster-superoxide salt.
| Item Type: |
Article
|
| Keywords: |
Photo-redox; reactivity; titanium-oxo clusters;
mechanistic; two-electron;
intramolecular; process; structural;
characterisation; mixed-valent; Ti(III); Ti(IV);
products; |
| Academic Unit: |
Faculty of Science and Engineering > Chemistry |
| Item ID: |
13983 |
| Identification Number: |
https://doi.org/10.1039/c9sc01241a |
| Depositing User: |
Tobias Kraemer
|
| Date Deposited: |
09 Feb 2021 17:17 |
| Journal or Publication Title: |
Chemical Science |
| Publisher: |
Royal Society of Chemistry |
| Refereed: |
Yes |
| URI: |
|
| Use Licence: |
This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available
here |
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