The new μ4-S heterometallic cluster (η5-C5H4-CH3)Fe 3Co(μ4-S)(CO)11 was synthesized in high yield by the addition of (η5-C5H4CH3)Fe(CO)2 (derived from (η5-C5H4CH3)Fe(CO) 2Cl) to HFe2Co(μ3-S)(CO)9 at room temperature. The cluster was characterized by elemental analyses, IR, and NMR as well as X-ray diffraction analysis. It crystallizes in the monoclinic space group P1121/n, a = 8.255(1) Å, b = 12.832(2) Å, c = 21.408(3) Å, γ = 90.81(1)°, V = 2268.4(6) Å3, Z = 4, and Dc = 1.89 g•cm-3. Structure solution and refinement were based on 2367 independent reflections with I ≥ 3.0σ(I) (Mo Kα, λ = 0.710 73 Å) and converged at R = 0.0447 (Rw = 0.0399). The μ4-S cluster is proposed as an example of intermediates in electrophilic addition-substituent elimination, and the existence of its isoelectronic analogues (η5-C5H5)MoFe2Co(μ 4-S)(CO)12and (η5-C5H4CH3)MoFe 2Co-(μ4-S)(CO)12 also is proposed.