Acid-Dependent Degradation of a [2Fe–2S] Cluster by Nitric Oxide

New types of degradation products of iron–sulfur clusters by nitric oxide (NO) have been identified in the acidic environment. In the absence of acid, NO reacts with (Et4N)2[Fe2S2Cl4] (1) to form a {Fe(NO)2}9 dinitrosyliron complex, (Et4N)[Fe(NO)2Cl2] (2), wherein the bridging sulfides are oxidized to elemental sulfur by four electrons (2S2– → 2S0 + 4e–). In contrast, the successive additions of NO and HCl to 1 result in the formation of a {Fe(NO)}7 mononitrosyliron complex, (Et4N)[Fe(NO)Cl3] (3), along with elemental sulfur and hydrogen sulfide (H2S), which are the two-electron-oxidized products of the bridging sulfides (2S2– + 2H+ → H2S + S0 + 2e–). The results demonstrate that the acidic environment plays a significant role in controlling the chemistry of an iron–sulfur cluster with NO and imply how two important gaseous molecules, NO and H2S, can be interconnected through iron–sulfur clusters.