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4Fe-4S ferredoxin model complexes, [NEt4]2[Fe4S4(Z-cys-Ile-Ala-OMe)4], [N(n-Bu)4]2[Fe4S4(2,4,6-trimethylbenezenethiolato)4], and [NMe4]2[Fe4S4(2,4,6-triisopropylbenzenethiolato)4] having highly sterically hindered ligands exhibit an electrochemically quasi-reversible redox couple of 2-/1- at +0.12 V, +0.02 V, and −0.03 V vs. SCE, respectively, but an irreversible redox couple of 3-/2-. The results suggest that [Fe4S4(SR)4]1− is stabilized with protection by hydrophobic bulkiness, but that [Fe4S4(SR)4]3− is destabilized by the bulkiness.

The crystal structure of [Et4N]2[Fe4S4(2,4,6-trimethylbenzenethiolato)4] was determined by X-ray diffraction. The complex crystallizes in orthorhombic space group (Pcnb). The Fe4S42+ core of the anion approaches C2 symmetry. The complex has relatively long Fe–S(Ph) bond lengths and small Fe–S–C angles. The results suggest the prevention of π-overlap between Fe(d)-SPh(p) orbitals by the steric hindrance of two methyl groups at o-positions of phenyl group.

Die Fe(II)‐l(omplexe der Peptide (I) und (II), die den Bausteinen 6‐9 und 39‐42 in der Aminosäuresequenz von Clostridium pasteurianum Rubredoxin entsprechen, werden zusammen mit den Fe(II)‐Komplexen von (III)‐(V) mittels sichtbarer, CD‐ und MCD‐Spektren untersucht.