Abstract
[FeFe]-hydrogenase-active-site models containing larger chalcogens such as Se or Te have exhibited greater electron richness at the metal centers and smaller gas-phase ionization energies and reorganization energies relative to molecules containing S atoms. Diiron complexes related to the much-studied molecule [Fe2(μ-SC3H6S)(CO)6] (1) have been prepared with one S atom replaced either by one Se atom to give [Fe2(μ-SC3H6Se)(CO)6] (2) or by one Te atom to give [Fe2(μ-SC3H6Te)(CO) 6] (3). The molecules have been characterized by use of mass spectrometry and 13C{1H} NMR, 77Se{ 1H} NMR, IR, and photoelectron spectroscopic techniques along with structure determination with single-crystal X-ray diffraction, electrochemical measurements, and DFT calculations. He I photoelectron spectra and DFT computations of 2 and 3 show a lowering of ionization energies relative to those of the all-sulfur complex 1, indicating increased electron richness at the metal centers that favors electrocatalytic reduction of protons from weak acids to produce H2. However, chalcogen substitution from S to Se or Te also causes an increase in the Fe-Fe bond length, which disfavors the formation of a carbonyl-bridged "rotated" structure, as also shown by the photoelectron spectra and computations. This "rotated" structure is believed to be important in the mechanism of H2 production. As a consequence of the competing influences of increased electron richness at the metals with less favorable "rotated" structures, the catalytic efficiency of the Se and Te molecules 2 and 3 is found to be comparable to that of molecule 1.
Original language | English (US) |
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Pages (from-to) | 3976-3985 |
Number of pages | 10 |
Journal | European Journal of Inorganic Chemistry |
Issue number | 25 |
DOIs | |
State | Published - Sep 1 2010 |
Keywords
- Electrocatalysis
- Hydrogenases
- Iron
- Selenium
- Sulfur
- Tellurium
ASJC Scopus subject areas
- Inorganic Chemistry