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)(2)Cl-2] (2), wherein the bridging sulfides are oxidized to elemental sulfur by four electrons (2S(2-) -> 2S(0) + 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)Cl-3] (3), along with elemental sulfur and hydrogen sulfide (H2S), which are the two-electron-oxidized products of the bridging sulfides (2S(2-) + 2H(+) -> H2S + S-0 + 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.