The present invention provides an improved method for preparing compounds of the formula Mo.sub.4 S.sub.4 L.sub.6 comprising:contacting a compound having the formula Mo.sub.2 S.sub.4 L.sub.2, wherein L is a 1,1-dithioacid ligand, with a reducing agent having a reduction potential sufficient to reduce Mo(V) to lower oxidation states, especially to Mo(III) and Mo(IV), at a temperature and for a time sufficient to form the Mo.sub.4 S.sub.4 L.sub.6 compound. Preferably, the Mo.sub.2 S.sub.4 L.sub.2 compound is dissolved in an organic solvent along with the reducing agent and the solution is heated at temperatures above 25.degree. C., up to the boiling point of the solvent and, more preferably, at temperatures in the range of from about 50.degree. C. to about 250.degree. C.