Abstract：The hexanuclear cobalt carbonyl cluster compounds, disubstituted derivative Co_6(μ_6-P)(μ-SCH_2CH_2CH_2S)(μ-PSCH_2CH_2CH_2S)(μ-CO) (CO)_9[P(OC_2H_5)_3]_2 (I), and two monosubstituted derivatives Co_6(μ _6-P)(μ-SCH_2CH_2CH_2S)(μ-PSCH_2CH_2CH_2S)(CO)_(11)[P(OC_2H_5)_3] (II a and II b), were synthesized from the parent, Co_6(μ_6-P)(μ- SCH_2CH_2CH_2S)(μ-PSCH_2CH_2CH_2S)(CO)_(12), by substituting P(OC_2H_5) _3 for two or one carbonyl groups, and the cluster derivatives were characterized by elemental analysis, IR, ~1H NMR, ~(31)P NMR and MS spectroscopies, respectively. Obviously, II b is an isomer of II a with different spectra data. The molecular structure of compound I was determined by using single crystal X-ray diffraction analysis, and the crystal is monoclinic, space group P2_1/n, with a = 1.1170(2)nm, b = 2. 3554(5) nm, c = 1.7997(4) nm, β = 99.50(3)°, V = 4.6649(17) nm~3, Z = 4, D_c = 1.763 g/cm~3, F(000) = 2488, μ = 24.64 cm~(-1). The structural analysis of compound I by X-ray diffraction identified the site of P(OC_2H_5)_3 substitution at the two apical Co atoms. The structure was solved by direct methods, and refined by full-matrix least-squares method. Finally, the departure factors are R_1 = 0.0497, wR_2 = 0.1386.