Formation of a single carbon-sulfur bond is described. The reaction of incomplete cubane-type sulfur and oxygen-bridged isothiocyanato tungsten cluster [W-3(mu (3)-S)(mu -O)(mu -S)(2)(NCS)(9)](5-) (7) with acetylene affords (W-3(mu (3)-S)(mu -O)(mu -S)(mu -SCH=CH2)(NCS9)](4-) (8). The cluster 8 has been isolated as K-0.5(Hpy)(3.5) [W-3(mu (3)-S)(mu -O)(mu -S)(mu -SCH=CH2)(NCS)(9)] (8 '), whose structure has been characterized by X-ray crystallography, electronic spectra, and H-1 and C-13 NMR spectroscopy, Crystal data of 8 ': triclinic system, space group P1, a = 14.465(5) Angstrom, b = 17.353(3) Angstrom, c = 10.202(2) Angstrom, alpha = 90.98(1)degrees, beta = 108.59(2)degrees, gamma = 98.13(2)degrees, V = 2397.6(10) Angstrom (3), Z = 2, D-c = 2.096 g cm(-3), D-m = 2.08 g cm(-3), R (R-w) = 3.6 (5.5)% for 8786 reflections (I > 1.50 sigma (I)). The carbon-carbon distance is 1.27(1) Angstrom and is almost equidistant between ethylene (1.339 Angstrom) and acetylene (1.203 Angstrom). The electronic spectrum of 8 ' in 1,0 M HCl containing 1.5 M KSCN has a characteristic broad peak in the near-infrared region [lambda (max), nm (epsilon, M-1 cm(-1)): 840 (650), 575 (1450)]. H-1 NMR and HH correlation spectroscopy (COSY) of 8 ' in CD3CN support the results of the X-ray structural analysis. The H-1 NMR spectrum shows three signals at 2.42 (1H, dd), 4.84 (1H, d, J = 8.8 Hz), and 4.89 (1H, d, J = 16.2 Hz) ppm due to the mu -SCH=CH2 moiety of 8 '. The correlation spectrum shows spin couplings of the signal at 2.42 ppm with the signals at 4.84 and 4.89 ppm. The mechanism of the formation of 8 is suggested to proceed through an intermediate with acetylene bridging two of the sulfur atoms.