Preparation and crystal structure of [NEt4]3[Fe6W2S8(SEt)9]; structural and electrochemical comparisons with its molybdenum analogue

[NEt₄]₃[Fe₆M₂S₈(SEt)₉] (M = Mo or W) compounds are isomorphous and contain molybdenum and tungsten atoms in an essentially identical environment. These complexes undergo an irreversible one-electron oxidation at −0.46 V (Mo) and −0.51 V (W) and two one-electron reductions at −1.56 and −1.76 V (Mo) and −1.52 and −1.84 V (W), in DMSO solution versus (0.1 M). The only distinction between the behavior of these molybdenum and tungsten complexes identified thus far is that, for the former the reductions are reversible whereas for the latter they are irreversible. This difference may be relevant to the low activity found for nitrogenases reconstituted with tungsten in place of molybdenum.