Computational studies have showed that there are many potential sites of protonation on the FeMoco, including the sulfides, the Mo-coordinated homocitrate, and even the carbide. Studies on multi-site proton-coupled electron transfer (PCET) have demonstrated that various protonation sites can influence the redox potentials and bond dissociation free energies (BDFE). These inspirations motivated us to pursue thermochemical studies on well-characterized (SCS)Fe complexes with proton-responsive ligands to examine the effects of distant protonation events on potentially biologically-relevant iron sites.