The nature of the products of the reactions of [Ru-3(CO)(12)] with diaminogermylenes depends upon the volume and the cyclic or acyclic structure of the latter. Thus, the triruthenium cluster [Ru-3{mu-Ge(NCH2CMe3)(2)C6H4}(3)(CO)(9)], which has a planar Ru3Ge3 core and an overall C-3h symmetry, has been prepared in quantitative yield by treating [Ru-3(CO)(12)] with an excess of the cyclic 1,3-bis(neo-pentyl)-2-germabenzimidazol-2-ylidene in toluene at 100 degrees C, but under analogous reaction conditions, the acyclic and bulkier Ge(HMDS)(2) (HMDS = N(SiMe3)(2)) quantitatively leads to the mononuclear ruthenium(0) derivative [Ru{Ge(HMDS)(2)}(2)(CO)(3)]. Mixtures of products have been obtained from the reactions of [Ru-3(CO)(12)] with the cyclic and very bulky 1,3-bis(tert-butyl)-2-germaimidazol-2-ylidene under various reaction conditions. The Ru3Ge3 and RuGe2 products reported in this paper are the first ruthenium complexes containing diaminogermylene ligands.