New Molybdenum(VI) Complexes with Thiosemicarbazone Ligands Containing 4-hydroxy-2-pyrone Ring

New molybdenum(VI) complexes have been prepared by the reaction of {MoO2(acac)2}(acac = acetylacetonate ion) with the thiosemicarbazone ligands derived from dehydroacetic acid and thiosemicarbazide (H2L1) or 4-phenylthiosemicarbazide (H2L2). All complexes consist of the MoO2 2+ core with molybdenum coordinated by ligand L via three donor atoms: pyran-4-ol-oxygen, imine-nitrogen and thiol-sulphur. Unlike the monomeric complexes {MoO2L2D}, where the octahedral coordination around the molybdenum atom is achieved by additional coordination of one neutral solvent molecule D (methanol in 2a or ethanol in 2b), in the polymeric complexes {MoO2L}n (1 and 2) the octahedral coordination is accomplished by an intermolecular metaloxygen interaction (metal...oxygen//Mo=O•••Mo=O). All compounds were characterized by means of elemental analyses, IR spectra, thermal analysis and some of them by X-ray crystallography (ligand HL1 and complex 2b).