In acetonitrile, bis(acetylacetonato)dioxomolybdenum(VI), [MoO2(acac)2], reacts with disubstituted hydrazine hydrohalides (RR’NNH3+X- : R = R’ = Ph; R = Ph, R’ = Me; X = Cl, Br, I) to yield a new series of complexes, which have been characterized by elemental analysis, electrochemistry and spectroscopy (IR, UV-visible, and H-1 NMR) and formulated as [Mo(NHNPh2)(NNPh2)(acac)X2] (X = Cl (1), Br (2), I (3)) and [Mo(NHNMePh)-(NNMePh)2 (NNMePh)(acaC)X2] (X = Cl (4), Br (5), I (6)). The X-ray crystal structures of 1 and 4 are reported. Crystals of 1 are monoclinic, space group P2(1)/a, with a = 9.352(1) angstrom, b = 31.320(2) angstrom, c = 9.612(1) angstrom, beta = 95.35(1)degrees, and Z = 4. The structure was solved using 3833 unique reflections, and refinement gave final R and R(w) values of 0.037 and 0.052, respectively. Crystals of 4 are triclinic, space group P1BAR, with a = 7.765(1) angstrom, b = 7.715(2) angstrom, c = 17.910(2) angstrom, alpha = 89.18(1)degrees, beta = 91.35(1)degrees, gamma = 92.64(1)degrees, and Z = 2. The structure was solved using 4515 unique reflections, and refinement gave final R and R(w) values of 0.032 and 0.033, respectively. Both complexes display similar distorted octahedral geometries. The coordination sphere consists of two mutually cis organohydrazido ligands, two mutually trans chloro ligands and one chelated acetylacetonato ligand. The organohydrazido(2-) and organohydrazido(1-) ligands adopt the linear and bent ’end-on’ conformations, respectively.