Synthesis and characterisation of thiosemicarbazonato molybdenum(VI) complexes and their in vitro antitumor activity

New dioxomolybdenum(VI) complexes were obtained by the reaction of [MoO2(acac)2] with thiosemicarbazone ligands derived from 3-thiosemicarbazide and 4-(diethylamino)salicylaldehyde (H2L1), 2-hydroxy-3-methoxybenzaldehyde (H2L2) or 2-hydroxy-1-naphthaldehyde (H2L3). In all complexes thiosemicarbazonato ligands are coordinated to molybdenum as tridentate ONS-donors. Octahedral coordination of each molybdenum atom is completed by methanol molecule (in 1a-3a) or by oxygen atom of Mo=O unit from the neighbouring molecule (in 1-3). All complexes were characterized by means of chemical analyses, IR spectroscopy, TG and NMR measurements. The molecular structures of the ligand H2L2 and complex [MoO2L2(CH3OH)].CH3OH (2a) have been determined by single crystal X-ray crystallography. The characterisation of thiosemicarbazonato molybdenum(VI) complexes (1-4) as well as of the 4-phenylthisemicarbazonato molybdenum(VI) complexes (5-8) in aqueous medium revealed that upon dissolving complexes in water, most likely to some extent dissociation took place, although experimental data didn't allow exact quantification of dissociation. The antiproliferative effects of studied molybdenum(VI) complexes (1-8) on the human cell lines were identical to the activity of their corresponding ligands.