5-Chloro-4-methyl-2-hydroxybenzophenone S-propy1-4-phenyl-thiosemicarbazone (H2L) and its cis-dioxomolybdenum(VI) complexes, in the general formula [MoO2(L)R-OH)] (R: methyl, 1; ethyl, 2; n-pro-pyl, 3; n-butyl, 4; n-pentyl, 5), were synthesized and characterized by micro analysis, electronic, infrared and H-1 and C-13 NMR spectra. The crystal structures of complexes, 1 and 3, have been solved by direct methods (SIR92) and refined to the residual indexes R-1 = 0.098 and R-1 = 0.052 respectively. Complexes 1 and 3 are crystallized in the triclinic space group P-1 with Z = 2. The crystal study of complex 1 showed the first example of intermolecular hydrogen bond for this type of molybdenum-thiosemicarbazone complexes. The hydrogen bond is between the hydroxyl proton of attached alcohol and an oxo oxygen (in MoO22+ unit) of another complex molecule, and its bond distance (1.767(1) angstrom) is shorter than from the sigma-coordination bonds in complex 1. Antioxidant activities of the compounds were determined by using 1,1-dipheny1-2-picryIhydrazyl (DPPH) method. Ligand showed 23.61% DPPH radical scavenging activity at 250 mg/L concentration. Cupric Reducing Antioxidant Capacity (CUPRAC) was also evaluated and trolox-equivalent antioxidant capacity (TEAC) values were found for ligand, 1 and 3 as 0.51, 0.33 and 0.30 respectively. (C) 2015 Elsevier B.V. All rights reserved.