Photoelectron spectroscopy of dithiolatodiironhexacarbonyl models for the active site of [Fe–Fe] hydrogenases: Insight into the reorganization energy of the “rotated” structure in the enzyme

Synthesis and Characterization of [FeFe]‐Hydrogenase Models with Bridging Moieties Containing (S, Se) and (S, Te)

“…The spectra suggest that the expected lowering of the adiabatic ionization due to the increased electron richness at the metals from 1 through 2 to 3, as evidenced by the decrease in carbonyl stretching frequencies, is counterbalanced somewhat by a decrease in the molecular reorganization energies. This suggestion is consistent with previous studies [33,36,54] and is examined further in the following section.…”

“…The DFT computational methodology utilized in this study has previously been shown to give good quantitative agreement with the structures, carbonyl stretching frequencies, oxidation potentials, reduction potentials, bond energies, and pKa values of a variety of [FeFe]-hydrogenase model compounds. [33,36,[54][55][56] It is important to re-examine the validity of a method for each new class of molecules.…”

“…The chalcogen-based valence p-orbital ionizations, S through Te, are expected to be observed in the higher-energy-ionization side of this region, on the basis of previously reported photoelectron spectra of chalcogencontaining [FeFe]-hydrogenase model compounds. [33,36,54] The second and third distinct ionization bands, above 9.0 eV, are assigned as having a mixture of chalcogen character and Fe d orbitals from previous studies. [33,36,54] These ionization energies decrease substantially with substitution from S through Se to Te, as expected from the decreasing electronegativity of the atoms and the decreasing inherent stability of the atomic orbitals.…”

“…The general assignments of the ionizations are based on previously reported analogous compounds. [33,36,54] The energy region displayed in the spectra contains the valence ionizations from the Fe-based 3d orbitals and the chalcogen-based p orbitals. The first broad ionization profile of each molecule, from about 7.5 to 8.8 eV ionization energy, arises predominantly from combinations of the Fe d-based orbitals with a weak shoulder on the low-ionization-energy side corresponding to ionization from the HOMO of the molecule.…”

Diiron Dichalcogenolato (Se and Te) Complexes: Models for the Active Site of [FeFe] Hydrogenase

“…The computational methodology utilized by Weigand and co-workers to investigate these catalysts (12, 13, 23-27) has previously been shown to give good quantitative agreement with the structures, CO stretching frequencies (νCO), oxidation and reduction potentials, bond energies, and pK a values of a variety of catalysts inspired by [FeFe] hydrogenase active sites. [56,59,60,[101][102][103] The optimized geometries and computed νCO values agree very well with the experimental values, suggesting that the computations are able to yield sufficiently reasonable electron distributions and energies for catalysts 12, 14, and 23-27.…”