Time-resolved vibrational spectroscopy of [FeFe]-hydrogenase model compounds

Jamie L. Bingaman, Casey L. Kohnhorst, Glenn A. Van Meter, Brent A. McElroy, Elizabeth A. Rakowski, Benjamin W. Caplins, Tiffany A. Gutowski, Christopher J. Stromberg, Charles Edwin Webster, Edwin J. Heilweil

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

Model compounds have been found to structurally mimic the catalytic hydrogen-producing active site of Fe-Fe hydrogenases and are being explored as functional models. The time-dependent behavior of Fe 2(μ-S 2C 3H 6)(CO) 6 and Fe 2(μ-S 2C 2H 4)(CO) 6 is reviewed and new ultrafast UV- and visible-excitation/IR-probe measurements of the carbonyl stretching region are presented. Ground-state and excited-state electronic and vibrational properties of Fe 2(μ-S 2C 3H 6)(CO) 6 were studied with density functional theory (DFT) calculations. For Fe 2(μ-S 2C 3H 6)(CO) 6 excited with 266 nm, long-lived signals (τ = 3.7 ± 0.26 μs) are assigned to loss of a CO ligand. For 355 and 532 nm excitation, short-lived (τ = 150 ± 17 ps) bands are observed in addition to CO-loss product. Short-lived transient absorption intensities are smaller for 355 nm and much larger for 532 nm excitation and are assigned to a short-lived photoproduct resulting from excited electronic state structural reorganization of the Fe-Fe bond. Because these molecules are tethered by bridging disulfur ligands, this extended di-iron bond relaxes during the excited state decay. Interestingly, and perhaps fortuitously, the time-dependent DFT-optimized exited-state geometry of Fe 2(μ-S 2C 3H 6)(CO) 6 with a semibridging CO is reminiscent of the geometry of the Fe 2S 2 subcluster of the active site observed in Fe-Fe hydrogenase X-ray crystal structures. We suggest these wavelength-dependent excitation dynamics could significantly alter potential mechanisms for light-driven catalysis.

Original languageEnglish (US)
Pages (from-to)7261-7271
Number of pages11
JournalJournal of Physical Chemistry A
Volume116
Issue number27
DOIs
StatePublished - Jul 12 2012

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