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Which metal atom grabs the nitrogen and what the cluster looks like at that moment are uncertain.","posed_since":"","precise":"For the E4 (Janus) state of FeMoco, determine the positions of the four added hydrogens (bridging hydrides, protonated sulfides), the site of $\\mathrm{N_2}$ binding (Fe2/Fe6 face, Mo, or after sulfide displacement), and the energetics of reductive elimination of $\\mathrm{H_2}$ coupled to $\\mathrm{N_2}$ binding. 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