Despite being in an intermediate spin state, these bond distances are closer to those in resting state FeMoco than the two previously-reported (SCS)iron complexes, which were in lower oxidation states and thus had longer Fe-C/S bonds. The final state of the enzyme during catalysis is an iron-ammonia adduct (E8). Because turnover from E8 to E0 is redox neutral, ammonia would be expected to bind to either the iron(II)