Synthetic iron-sulfur cubanes are models for biological cofactors, which are essential to delineate oxidation states in the more complex enzymatic systems. However, a complete series of Fe_4S_4~n complexes spanning all redox states accessible by 1-electron transformations of the individual iron atoms (n = 0-4+) has never been prepared, deterring the methodical comparison of structure and spectroscopic signature. 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, Fe Mossbauer spectroscopy, UV-visible electronic absorption, variable-temperature X-ray diffraction analysis, and cyclic voltammetry reveals key trends for the geometry of the Fe_4S_4 core as well as for the Mossbauer isomer shift, which both correlate systematically with oxidation state. Furthermore, we confirm the 5=4 electronic ground state of the most reduced member of the series, Fe_4S_4~0 , and provide electrochemical evidence that it is accessible within 0.82 V from the Fe_4S_4~(2+) state, highlighting its relevance as a mimic of the nitrogenase iron protein cluster.
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