Comparisons to the Nitrogenase FeMoco. The C and S-ligated iron complexes have the same donor atoms as the iron sites in the FeMoco, and we briefly explore the comparison of molecular and electronic structures. The most thoroughly-characterized state of FeMoco is the enzyme resting state (E0), and in this structure, the high-spin belt irons are bridged by sulfide ligands and share a central carbide, leading to a 3S/1C environment. Our complex 8 likewise has an iron center ligated exclusively by three S donors and one C donor. Its Fe-C bond length of 2.00 Å is very close to the 2.01 Å Fe-C distance in FeMoco. The Fe-S lengths, which range from 2.24 to 2.25 Å, are also highly similar to Fe-S bond lengths in FeMoco (2.25 to 2.27 Å).