Compound ½Cp à 2 Mo 2 O 5 reacts with thioglycolic acid, HSCH 2 COOH, in an acidic (CF 3 COOH) mixed water-methanol solvent, to yield compound [{Cp*Mo(l-SCH 2 CO 2 )} 2 (l-S)]. During this reaction, the thioglycolic acid acts as a reducing agent, as a ligand, and provides a sulfide ion for the Mo-S-Mo bridge. The molecular structure of the product can be described as containing two four-legged piano stools that share three legs. The Mo-Mo distance of 2.792(7) Å indicates metal-metal bonding, in agreement with the compound diamagnetism.