The compound {Ru-3(CO)(9)[mu-P(NPr2i)(2)](3)}{Ru-6(CO)(15)(mu(6)-C)[mu-P(NPr2i)(2)]} (1), Obtained via the addition of PCl-(NPr2i)(2) to K-2[Ru-4(CO)(13)], crystallizes in the monoclinic space group P2(1)/c with a = 15.537(8) Angstrom, b = 36.151(16) Angstrom, c = 19.407(5) Angstrom, beta = 91.14(2)degrees, Z = 4, and R = 0.069 for 8006 observed reflections. The unit cell is unusual in that it contains both a typical octahedral RU6 cluster anion (la), featuring an encapsulated carbide, and a symmetrical phosphido bridge, in addition to a 50-electron trinuclear cluster cation {Ru-3(CO)(9)[mu-P(NPr2i)(2)](3)}(+) (Ic). The latter, with approximate D-3h symmetry, exhibits long Ru-Ru distances (greater than or equal to 3.15 Angstrom). Among the family of clusters with M-3(mu-PR2)(3) cores and different numbers of both electrons (TEC) and terminal ligands (LxLyLz), Ic is unique in that it is a 333 stereotype with 50 valence electrons. MO calculations permit us to predict the existence of redox congeners of Ic clusters and related 48e Re-3 clusters. This work also presents a summary of the relationships between the electronic and the geometric structures for all known M3LxLyLz(mu-PR2)(3) species. The basic stereochemical features are influenced by the total-electron count and, hence, by the degree of M-M bonding, as well as the remarkable flexibility of the phosphido bridging ligands. The mu-PR2 ligands need not necessarily lie in the M-3 plane, and a wide range of M-P-M angles (as small as 72 degrees or as large as 133 degrees) have been observed.