transThe reaction of NH2NHC(S)OR, (R = Me, Et) with MoO2(acac)2 yields the dimeric complexes MO2O3(MeC(O)CHC(Me)NNC(S)0R)2 (1) with the planar O = Mo - O - Mo = O group. The tetradentate O,N,S-donor ligand is formed through condensation of acetylacetone with the organohydrazine. The reactions of NH2NHC(S)OMe with MoO2(S2CNEt2)2 and MoO2(ONEt2)2 give the diazenido hydrazido complexes Mo(NNC(S)OMe)(NH2NC(S)OMe)(S2CNEt2)2·CH2Cl2(2) and Mo(NNC(S)OMe)(NH2NC(S)OMe)2(ONEt2) (4). The metal atoms in both compounds are seven coordinated and contain the approximately linear diazenido ligand NNC(S)OMe and one (2) or two (4) N,S-chelating hydrazido(1-) ligands NH2NC(S)OMe. 2 has crystallographically imposed mirror symmetry. Recrystallization of 2 from toluene in air gives the asymmetric dinuclear complex (Et2NCS2)(O)Mo(μ-NNC(S)OMe)2Mo(S2CNMe2) (3). The Mo-Mo distance is 267.0(2) pm. One Mo site has square pyramidal MoOS2N2 geometry, the other trigonal prismatic MoN2S4 geometry. The coordination of the bridging N atoms is slightly pyramidal. The compounds 1, 2 and 3 have been further characterized by vibrational spectroscopy.