Co2(CO)8 and Me2P(S)P(S)Me2 react to form the two cluster complexes: Co4(CO)9S(PMe2)2) (1) and Co3(CO)7S(SPMe2) (2). The strucure of1 and of the disubstituted triphenyl phosphine derivative of2. Co3(CO)5(PPh3)2S (SPMe3) (2a) were determined. Compound1 contains a quasi-planar rhomboidal Co4 cluster formed by two Co3 isosceles triangles sharing a Co-Co edge. One triangle is capped by a sulfur atom, the other triangle has two edge-bridging PMe2 moieties. Electron counting gives 64 electrons corresponding to a planar system; the distribution of long Co-Co distances, in particular in the triangle bearing PMe2 bridges, suggests that the excess electrons are located on Co-Co antibonding ortibals. Compound2a contains a Co3S cluster with one side bridged by a SPMe2 unit forming a four-membered Co2SP ring. The substitution of two CO groups with two PPh3 causes a large deformation of the cluster Co-Co bondscis to these two phosphorus atoms. Crystal data for1, space group P1,a = 9.728(2) A,b = 10.288(2) A,c = 11.860(3) A,α = 86.41(2)°,β = 76.20(2)°,γ = 80.37(5)°,Z = 2, 5300 reflections,R = 0.0398; for2a, space group P1,a = 9.78(3) A,b = 13.05(4) A,c = 18.28(6) A,α = 93.23(3)°,β = 99.17(2)°,γ = 97.26(6)°,Z = 2, 2976 reflections,R = 0.0579.