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.