Binuclear oxidative addition of Sb–Cl bonds with the clusters Os3(CO)11(NCCH3), 1, or Os3(CO)10(NCCH3)2, 2, was found to be an effective synthetic route to organometallic clusters and rings containing μ2-SbPh2 or μ3-SbPh moieties. Thus, the reaction of SbPh2Cl with 1 afforded the tetranuclear ring Os3(CO)11(Cl)(μ-SbPh2), 3, while its reaction with 2 afforded the pentanuclear ring Os3(CO)10(Cl)2(μ-SbPh2)2, 6. In each case, two or three isomeric products were isolated depending on the reaction conditions. The analogous reaction of SbPhCl2 with 1, on the other hand, afforded the spiked triangular cluster Os3(CO)11(Cl)2(μ3-SbPh), 7, which also existed as two isomers. Pathways for these reactions have been proposed, and the experimental and computational evidence presented. ; MOE (Min. of Education, S’pore)