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RISS 인기검색어
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- 저자 : Koroidov, Sergey (검색결과 1 건)
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Koroidov, Sergey,Hong, Kiryong,Kjaer, Kasper S.,Li, Lin,Kunnus, Kristjan,Reinhard, Marco,Hartsock, Robert W.,Amit, Das,Eisenberg, Richard,Pemmaraju, C. Das,Gaffney, Kelly J.,Cordones, Amy A. American Chemical Society 2018 Inorganic Chemistry Vol.57 No.21
<P>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)<SUB>2</SUB> (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)<SUB>2</SUB> 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)<SUB>2</SUB> intermediate and Ni(mpo)<SUB>2</SUB> (mpo = 2-mercaptopyridyl-<I>N</I>-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)<SUB>2</SUB> intermediate and Ni(mpo)<SUB>2</SUB> catalyst, a critical reaction intermediate in H<SUB>2</SUB> generation.</P><P>The electronic structure of Ni-centered hydrogen evolution catalysts with noninnocent ligands was characterized using S and Ni edge X-ray absorption spectroscopies. The electron-accepting valence orbitals involved in catalysis are found to have high (>50%) ligand character. Ligand-dependent differences in electronic structure provide insight into the previously proposed reaction mechanisms of the catalysts.</P> [FIG OMISSION]</BR>
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