Described is the preparation of the first iron carbide-sulfides. The cluster [Fe6C(CO)(15)(SO2)](2) ([2](2)), which is generated quantitatively from [Fe6C(CO)(16)](2) ([1](2)), was O-methylated to give the sulfinite [2Me](-). Demethoxylation of [2Me](-) with BF3 gave the face-capped octahedral cluster Fe6C(CO)(15)(SO) (3). In solution, 3 spontaneously converted to the sulfide Fe6C(CO)(16)(S) (4), an edge-fused double cluster with Fe5C and Fe3S subunits. Although 4 undergoes 1e reduction reversibly, 2e reduction (or base hydrolysis) of 4 gives closo-[Fe6C(CO)(14)(S)](2) ([5](2-)). The synthetic entries into the Fe6CS(x) manifold may underpin the preparation of active-site analogues of the FeMoco and FeVco cofactors.