TY - JOUR
T1 - In search of metal hydrides
T2 - an X-ray absorption and emission study of [NiFe] hydrogenase model complexes
AU - Hugenbruch, Stefan
AU - Shafaat, Hannah S.
AU - Krämer, Tobias
AU - Delgado-Jaime, Mario Ulises
AU - Weber, Katharina
AU - Neese, Frank
AU - Lubitz, Wolfgang
AU - DeBeer, Serena
PY - 2016/2/15
Y1 - 2016/2/15
N2 - Metal hydrides are invoked as important intermediates in both chemical and biological H2 production. In the [NiFe] hydrogenase enzymes, pulsed EPR and high-resolution crystallography have argued that the hydride interacts primarily at the Ni site. In contrast, in [NiFe] hydrogenase model complexes, it is observed that the bridging hydride interacts primarily with the Fe. Herein, we utilize a combination of Ni and Fe X-ray absorption (XAS) and emission (XES) spectroscopies to examine the contribution of the bridging hydride to the observed spectral features in [(dppe)Ni(μ-pdt)(μ-H)Fe(CO)3]+. The corresponding data on (dppe)Ni(μ-pdt)Fe(CO)3 are used as a reference for the changes that occur in the absence of a hydride bridge. For further interpretation of the observed spectral features, all experimental spectra were calculated using a density functional theory (DFT) approach, with excellent agreement between theory and experiment. It is found that the iron valence-to-core (VtC) XES spectra reveal clear signatures for the presence of a Fe–H interaction in the hydride bridged model complex. In contrast, the Ni VtC XES spectrum largely reflects changes in the local Ni geometry and shows little contribution from a Ni–H interaction. A stepwise theoretical analysis of the hydride contribution and the Ni site symmetry provides insights into the factors, which govern the different metal–hydride interactions in both the model complexes and the enzyme. Furthermore, these results establish the utility of two-color XES to reveal important insights into the electronic structure of various metal–hydride species.
AB - Metal hydrides are invoked as important intermediates in both chemical and biological H2 production. In the [NiFe] hydrogenase enzymes, pulsed EPR and high-resolution crystallography have argued that the hydride interacts primarily at the Ni site. In contrast, in [NiFe] hydrogenase model complexes, it is observed that the bridging hydride interacts primarily with the Fe. Herein, we utilize a combination of Ni and Fe X-ray absorption (XAS) and emission (XES) spectroscopies to examine the contribution of the bridging hydride to the observed spectral features in [(dppe)Ni(μ-pdt)(μ-H)Fe(CO)3]+. The corresponding data on (dppe)Ni(μ-pdt)Fe(CO)3 are used as a reference for the changes that occur in the absence of a hydride bridge. For further interpretation of the observed spectral features, all experimental spectra were calculated using a density functional theory (DFT) approach, with excellent agreement between theory and experiment. It is found that the iron valence-to-core (VtC) XES spectra reveal clear signatures for the presence of a Fe–H interaction in the hydride bridged model complex. In contrast, the Ni VtC XES spectrum largely reflects changes in the local Ni geometry and shows little contribution from a Ni–H interaction. A stepwise theoretical analysis of the hydride contribution and the Ni site symmetry provides insights into the factors, which govern the different metal–hydride interactions in both the model complexes and the enzyme. Furthermore, these results establish the utility of two-color XES to reveal important insights into the electronic structure of various metal–hydride species.
U2 - 10.1039/C5CP07293J
DO - 10.1039/C5CP07293J
M3 - Article
SN - 1463-9076
VL - 18
SP - 10688
EP - 10699
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 16
ER -