A complete biomimetic iron-sulfur cubane redox series

Synthetic iron-sulfur cubanes are essential models for biological cofactors in the more complex enzymatic environments. However, a complete series of [Fe4S4]n complexes spanning all biorelevant oxidation states (n = 0-3+) has never been prepared. Here, we demonstrate that the use of a bulky arylthiolate ligand promoting the encapsulation of alkali-metal cations in the vicinity of the cubane enables the synthesis of such a series. Characterization by EPR, 57Fe Mössbauer spectroscopy, UV-Vis electronic absorption and variable-temperature X-ray diffraction analysis reveals key trends for the Fe4S4 core’s geometry as well as for the Mössbauer isomer shift, which both correlate systematically with oxidation state. Furthermore, we confirm the S=4 electronic ground state of the most reduced member, [Fe4S4]0, in agreement with that proposed for the all-ferrous cubanes in Nature.

A complete biomimetic iron-sulfur cubane redox series

Synthetic iron-sulfur cubanes are essential models for biological cofactors in the more complex enzymatic environments. However, a complete series of [Fe4S4]n complexes spanning all biorelevant oxidation states (n = 0-3+) has never been prepared. Here, we demonstrate that the use of a bulky arylthiolate ligand promoting the encapsulation of alkali-metal cations in the vicinity of the cubane enables the synthesis of such a series. Characterization by EPR, 57Fe Mössbauer spectroscopy, UV-Vis electronic absorption and variable-temperature X-ray diffraction analysis reveals key trends for the Fe4S4 core’s geometry as well as for the Mössbauer isomer shift, which both correlate systematically with oxidation state. Furthermore, we confirm the S=4 electronic ground state of the most reduced member, [Fe4S4]0, in agreement with that proposed for the all-ferrous cubanes in Nature.

Comment on “Calibration of 57Fe Mössbauer constants by first principles” Phys. Chem. Chem. Phys., 2016, 18, 10201–10206

The proportionality constant between the iron-57 Mössbauer isomer shift and the electron probablility density at the nucleus is reevaluated from the correct experimental isomer shifts.

Calibration of 57Fe Mössbauer constants by first principles

Ab initio periodic esimate of Mössbauer isomer shift and quadrupolar moment for iron: hybrid functional approach in a GTO basis set.

Effect of chemical bond parmeters on hardness, isomer shift, and dielectric constant of rare earth ferroborates

The ionicity, average band gaps, and bond polarization of the rare earth iron ferroborates were calculated using the chemical bond dielectric theory of complex structural crystals. The environment factor defined by electron polarizabilities and covalency was employed to calculate Mössbauer isomer shift of the rare earth iron ferroborates. The calculated isomer shifts of EuFe3(BO3)4 and GdFe3(BO3)4 are in agreement with their experimental values. The hardnesses of rare earth iron ferroborates were predicted using Gao's model, which are also in agreement with the experimental values.