Abstract: Tn this paper, synthesis, structure and properties of a new Mo-Fc-Scluster complex (Et₄N)₃(Mo₂FeS₈O₂)·CH₃CN (Ⅰ) with oxygen coordinated to Mo atom are reported, in which UV-Vis. spectra, IRspectra, Mossbauer spectra, eletrochemical properties and catalytic activity reducing C₂H₃ to C₂H₄ are involved. Our conclusions obtained from contrasting properties of the complex with that of the complex (Et4N)₃(Mo₂FeS₈O₃) (Ⅱ) and (Bu₄N)₃(Mo₂FeS₈O) (Ⅲ) previously reported by us are as follows (1) the electrochemical data show that the order of ability for obtaining electron is Ⅰ<Ⅱ<Ⅲ, (2) the order of stability in air is Ⅰ > Ⅱ>Ⅲ, (3) the order of symmetry is Ⅱ>Ⅰ > Ⅲ, (4) the order of reducing C₂H₃ to C₂H₄ by catalysis is contrary to that of stability.