Carbon-sulfur bond formation through the reaction of sulfur-bridged molybdenum clusters with acetylene. X-ray structures of Mo3(.mu.3-S)(.mu.-O)(.mu.-S)2(H2O)9(CH3C6H4SO3)4.cntdot.7H2O and Mo3(.mu.3-S)(.mu.-O)(.mu.3-S2C2H2)(H2O)9(CH3C6H4SO3)4.cntdot.7H2O