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J Phys Chem Lett. 2016 Dec 15;7(24):5253-5258. Epub 2016 Dec 7.

Tracking Co(I) Intermediate in Operando in Photocatalytic Hydrogen Evolution by X-ray Transient Absorption Spectroscopy and DFT Calculation.

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Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences , Beijing 100190, People's Republic of China.
Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences , Beijing 100049, People's Republic of China.
X-ray Sciences Division, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60430, United States.
Synchrotron SOLEIL, L'Orme des Merisiers , Saint Aubin 91192 GIF-sur-Yvette Cedex, France.


X-ray transient absorption spectroscopy (XTA) and optical transient spectroscopy (OTA) were used to probe the Co(I) intermediate generated in situ from an aqueous photocatalytic hydrogen evolution system, with [RuII(bpy)3]Cl2·6H2O as the photosensitizer, ascorbic acid/ascorbate as the electron donor, and the Co-polypyridyl complex ([CoII(DPA-Bpy)Cl]Cl) as the precatalyst. Upon exposure to light, the XTA measured at Co K-edge visualizes the grow and decay of the Co(I) intermediate, and reveals its Co-N bond contraction of 0.09 ± 0.03 Å. Density functional theory (DFT) calculations support the bond contraction and illustrate that the metal-to-ligand π back-bonding greatly stabilizes the penta-coordinated Co(I) intermediate, which provides easy photon access. To the best of our knowledge, this is the first example of capturing the penta-coordinated Co(I) intermediate in operando with bond contraction by XTA, thereby providing new insights for fundamental understanding of structure-function relationship of cobalt-based molecular catalysts.

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