Four polydentate thiosemicarbazones have been synthesised and characterised by melting point measurements and infrared spectroscopy: 2,6-diacetylpyridine bis(thiosemicarbazone) (Hadaptsc); 2,6-diacetylpyridine monothiosemicarbazone (Hdapmtsc); 2-hydroxypropiophenone thiosemicarbazone (Hzhptsc); and salicylaldehyde thiosemicarbazone (H2satsc). The former two ligands were isolated following published procedures with some modifications. Reactions of these four thiosemicarbazones with selected bioactive first-row transition metal ions, namely VO2+, Mn, Fest, Co2+ and Cu2+, have produced several interesting complexes. Much attention has been devoted to the reaction of 2,6 diacetylpyridine bis(thiosemicarbazone) with oxovanadium(IV) in the presence of excess NaC104.H20. The product of this reaction, [{V(daptsc)(MeOH)2(u-0)](CIO4)2, is unusual and was unexpected. The structure of this compound has been determined by single-crystal X-ray crystallography. The compound [{V(daptsc) (MeOH)2(L 0)](CIO4)2 crystallises in the monoclinic system, space group P21/c. The X-ray crystal structure reveals a centrosymmetric u-oxo-bridged dimeric complex cation. Each of the vanadium(IV) ions adopts a distorted pentagonal bipyramidal geometry with the quinquedentate thiosemicarbazonato ligand occupying the equatorial plane and a methanol solvent molecule together with the bridging oxygen atom at the axial positions. Commonly, u-oxo-bridges arise from hydrolysis of high-valent metal ions. However, the structural analysis of[{V(daptsc)(MeOH)}2(u-O)la provides evidence for breakage of the strong V=O bond in the vanadyl cation Vo-t. Unsurprisingly, the electron spins of the vanadium atoms are strongly coupled as shown by the effective magnetic moment of 1.42 MB for each V atom. Further support of this coupling of spins is provided by electron paramagnetic resonance (EPR) spectroscopy which showed the compound to be EPR-inactive at 77 K. Several other complexes of oxovanadium(IV) with Hadaptsc and Hdapmtsc have been synthesised utilising various inorganic anions (e.g. SCN,SO42- and N3) as additional ligands or counter ions. The formulations of these complexes have been proposed only tentatively based solely on IR spectroscopy pending characterisation by elemental analysis and mass spectrometry. One of the most interesting compounds of Co(II) with the thiosemicarbazones is [Co(H2daptsc)(SCN)2]-nCH3CN. The cobalt(II) ion is high-spin and, as expected, the complex shows a large orbital contribution to the effective magnetic moment. Due to time constraints, only preliminary studies have been performed on the complexation of 2-hydroxypropiophenone thiosemicarbazone and salicylaldehyde thiosemicarbazone with some first-row transition metal ions.