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Synthesis and Characterization of [FeFe]‐Hydrogenase Models with Bridging Moieties Containing (S, Se) and (S, Te)
Author(s) -
Harb Mohammad K.,
Görls Helmar,
Sakamoto Taka,
Felton Greg A. N.,
Evans Dennis H.,
Glass Richard S.,
Lichtenberger Dennis L.,
Elkhateeb Mohammad,
Weigand Wolfgang
Publication year - 2010
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201000278
Subject(s) - chemistry , chalcogen , crystallography , molecule , x ray photoelectron spectroscopy , crystal structure , metal , electrochemistry , density functional theory , atom (system on chip) , computational chemistry , organic chemistry , physics , electrode , nuclear magnetic resonance , computer science , embedded system
[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 [Fe 2 (μ‐SC 3 H 6 S)(CO) 6 ] ( 1 ) have been prepared with one S atom replaced either by one Se atom to give [Fe 2 (μ‐SC 3 H 6 Se)(CO) 6 ] ( 2 ) or by one Te atom to give [Fe 2 (μ‐SC 3 H 6 Te)(CO) 6 ] ( 3 ). The molecules have been characterized by use of mass spectrometry and 13 C{ 1 H} NMR, 77 Se{ 1 H} 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 H 2 . 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 H 2 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 .