A novel C-S bond formation has been found in the reaction of [{Ru(AN)(3)(TMP)(2)}(2)(mu-S-2)](4+) with acetone (AN is acetonitrile, and TMP is P(OMe)(3)). The crystal structure of the resulting compound, [{Ru-III(AN)(2)(TMP)(2))}(mu-S2CH2COCH3){Ru-III(AN)(3)(TMP(2)}](CF3SO3)(3).0.5(CH3)(2)CO, has been solved by single-crystal X-ray diffraction analysis. The crystal data are as follows : triclinic, space group P (1) over bar, a 12.238(4) Angstrom, b = 22.148(7) Angstrom, c = 12.344(4) Angstrom, alpha = 93.29(3)degrees, beta 112.69(2)degrees, gamma = 78.54(3)degrees, V = 3074(2) Angstrom(3), and Z = 2. The two ruthenium atoms originally bridged by a S-2(2-) bridging Ligand in the starting material are bridged by a S2CH2COCH33- ligand in the product with the two sulfur-coordinating atoms. In the new bridging ligand, deprotonated acetone, CH3COCH2-, is bonded to the S-2(2-) bridge, forming a C-S bond. The carbonyl oxygen atom of the new bridge coordinates to one of the ruthenium atoms to form a RuOCCS five-membered ring. The S-S distance is 2.067(6). Angstrom, the two Ru-S distances are 2.339(5) and 2.380(5) Angstrom, and the two Ru atoms are attached to the S-S bridging Ligand in a trans mode.