Reactions of the dianionic sulfido cluster [Ru3(CO)9(mu3-S)]2- with the lightly stabilized electrophilic cluster-building reagents [M(CO)3(NCCH3)3]+ (M = Mn, Re) produced the mixed-metal sulfido clusters HRu3(CO)9(mu4-S)Mn-(CO)3(NCCH3)2 and HRu3(CO)9(mu4-S)Re(CO)3(NCCH3)2, which contain a pseudotetrahedral mu4-sulfido atom. Analogous reactions of [Ru3(CO)9(mu3-S)]2- with [M(CO)5]+ (M = Mn, Re) yielded clusters identified as HRu3(CO)9(mu4-S)Mn(CO)5 and HRu3(CO)9(mu4-S)Re(CO)5 in solution. The clusters HRU3(CO)9(mu4-S)M(CO)3(NCCH3)2 (M = Mn, Re) were characterized by liquid secondary ionization mass spectroscopy, and the structure of HRu3(CO)9(mu4-S)Mn(CO)3(NCCH3)2 was determined by single-crystal X-ray diffraction. These molecules contain the triangular ruthenium metal array capped by an SM(CO)3(NCCH3)2 moiety. The mu4-sulfido ligand may be viewed as a rive-electron donor to the ruthenium triangle and a one electron donor to the pendant metal. The hydrogen atom, located in the X-ray experiment, resides on the ruthenium framework. Crystal data for HRU3(CO)9(mu4-S)Mn(CO)3(NCCH3)2 : monoclinic (P2(1)/c (No. 14)), a = 16.418(4) angstrom, b = 8.865(1) angstrom, c 17.550(4) angstrom, beta = 96.73(2)-degrees, Z = 4, R (R(w)) = 0.038 (0.042).