Reactivity of the Mo(O)(S) functional group in the [(L)Mo(O)(.mu.-S)2Mo(O)(S)]n- dimeric thiomolybdate complexes, (L = C5H5-, n = 1; S42-, n = 2) and implications regarding the function of xanthine oxidase. Synthesis and structural characterization of [(DMF)3Mo(O)(.mu.-S)2Mo(O)(S2)], [Ph4P][(C5H5)Mo(O)(.mu.-S)2Mo(O)(S2)], [Ph4P]2[(S4)Mo(O)(.mu.-S)2Mo(O)(S)] and (Et4N)4{[(S4)Mo(O)(.mu.-S)2Mo(O)(S)]2}