Two new dioxomolybdenum(VI) complexes, [MoO2 (Cinh)(CH3OH)] (1) and [MoO2(Minh)(CH3OH)] (2), with the isonicotinohydrazone ligands H2Cinh and H2Minh derived from isonicotinohydrazide with 5-chlorosalicylaldehyde and 3-methoxysalicylaldehyde, respectively, have been synthesized and structurally characterized by physico-chemical methods and single crystal X-ray determination. The crystal of (1) crystallizes in triclinic space group P-1, with a = 6.553(2), b = 10.737(4), c = 12.907(4) Å, α = 68.021(2), β = 83.788(3), γ = 75.072(3)°, V = 813.6(5) Å3, Z = 2, R1 = 0.0291, wR2 = 0.0617, S = 1.044. The crystal of (2) crystallizes in monoclinic space group P21/n, with a = 6.792(2), b = 30.259(4), c = 7.920(3) Å, β = 93.703(3)°, V = 1624.3(8) Å3, Z = 4, R1 = 0.0501, wR2 = 0.1250, S = 1.087. X-ray analysis indicates that the structures of both complexes are similar to each other. The molybdenum atom in each complex is in an octahedral coordination environment, constructed by two oxo groups and NO2 donor set of the isonicotinohydrazone ligand, and one methanol O atom. [ABSTRACT FROM AUTHOR]