Revisit the classical [Fe4S4(SR)4]2– molecular clusters: The steric effects of ligands and their structural transformations

The synthesized molecular clusters featuring the cubic [4Fe–4S] core have been studied for several decades, as they serve as true analogs of the active components in ferritin within biological systems. Such a model cluster has been extensively investigated in various fields, including structural modulation, catalysis, and self-assembly under laboratory conditions, with the aim of gaining an in-depth understanding of their roles in biological functions. Herein, we revisited three well-known [Fe₄S₄(SR)₄]^2– molecules, namely [Me₄N]₂[Fe₄S₄(SR)₄] (R = o-MBT, m-MBT, p-MBT), and successfully established their single crystal structures that remain unknown prior to this work. Interestingly, it is revealed that the position of the substituent methyl group has an obvious steric effect on the arrangement of the ligand around the [4Fe–4S] core, which further influences their overall packing patterns in single crystals. In addition, this work unveils two new structure transformation behaviors for the [Fe₄S₄(SR)₄]^2– system: i) the monomeric [Fe(SR)₄]^2– and tetrameric [Fe₄S₄(SR)₄]^2– can be interconverted, and ii) [Fe₄S₄(SR)₄]^2– can be transferred into an intriguing iron-oxide complex Na₂Fe₆O(OMe)₁₈·6MeOH in a well-controlled oxidizing environment.