Several new mixed-metal clusters of the Fe-Ru-Os triad have been prepared through the addition of carbonylmetalates to closed metal trimers. Addition of Na2[Fe(CO)4] to Ru2Os(CO)12and RuOs2(CO)12, followed by acidification, yielded H2FeRu2Os(CO)13and H2FeRuOs2(CO)13, the first examples of clusters comprised of three different transition metals. H2Fe2Ru2(CO)13was prepared by allowing Na2[Fe(CO)4] to react with Fe2Ru(CO)12or by addition of [Ru(CO)4]2- to Fe3(CO)12. Addition of [Ru(CO)4]2-to Os3(CO)12or [Os(CO)4]2-to Ru3(CO)12gave an inseparable mixture of H4Ru4(CO)12, H3Ru3Os(CO)12, H4Ru2Os2(CO)12, H4RuOs3(CO)12, and H4Os4(CO)12. An improved synthesis of H2Fe-Ru3(CO)13is reported and an alternative route to H2FeOs3(CO)13is described. The new clusters have been characterized by their NMR, infrared, electronic absorption, and mass spectra and the spectral evidence suggests tetrahedral structures similar to the known structures of H2FeRu3(CO)13and H2Ru4(CO)13.