Probing the Electron Accepting Orbitals of Ni-Centered Hydrogen Evolution Catalysts with Noninnocent Ligands by Ni L-Edge and S K-Edge X-ray Absorption
| Autor: | Kristjan Kunnus, Kiryong Hong, Das Amit, Kasper S. Kjær, Marco Reinhard, Kelly J. Gaffney, C. Das Pemmaraju, Lin Li, Sergey Koroidov, Richard Eisenberg, Robert W. Hartsock, Amy A. Cordones |
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| Rok vydání: | 2018 |
| Předmět: |
Valence (chemistry)
Absorption spectroscopy Chemistry Ligand 02 engineering and technology Electronic structure Reaction intermediate 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Catalysis Inorganic Chemistry Crystallography Delocalized electron K-edge Physical and Theoretical Chemistry 0210 nano-technology |
| Zdroj: | Inorganic Chemistry. 57:13167-13175 |
| ISSN: | 1520-510X 0020-1669 |
| Popis: | The valence electronic structure of several square planar Ni-centered complexes, previously shown to catalyze the hydrogen evolution reaction, are characterized using S K-edge and Ni L-edge X-ray absorption spectroscopy and electronic structure calculations. Measurement of the atomic Ni 3d and S 3p contributions enables assessment of the metal-ligand covalency of the electron accepting valence orbitals and yields insight into the ligand-dependent reaction mechanisms proposed for the catalysts. The electron accepting orbital of the Ni(abt)2 (abt = 2-aminobenzenethiolate) catalyst is found to have large ligand character (80%), with only 9% S 3p (per S) character, indicating delocalization over the entire abt ligand. Upon two proton-coupled reductions to form the Ni(abt-H)2 intermediate, the catalyst stores 1.8 electrons on the abt ligand, and the ligand N atoms are protonated, thus supporting its role as an electron and proton reservoir. The electron accepting orbitals of the Ni(abt-H)2 intermediate and Ni(mpo)2 (mpo = 2-mercaptopyridyl- N-oxide) catalyst are found to have considerably larger Ni 3d (46-47%) and S 3p (17-18% per S) character, consistent with an orbital localized on the metal-ligand bonds. This finding supports the possibility of metal-based chemistry, resulting in Ni-H bond formation for the reduced Ni(abt-H)2 intermediate and Ni(mpo)2 catalyst, a critical reaction intermediate in H2 generation. |
| Databáze: | OpenAIRE |
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