Nine potentially S,N,N-tridentate thiosemicarbazones (HL) derived from pyridine-2-carbaldehyde or 1-(2-pyridyl)ethanone have been prepared and fully characterized. The X-ray crystal structures of six of them and two hydrochlorides were determined and analyzed. The reaction of the [ReX(CHCN)(CO)]/[ReX(CO)] (X = Cl and Br) precursors with these ligands yielded different kinds of compounds: the adducts [ReX(HL)(CO)], in which the ligands were S,N-bidentate; the trinuclear species and the thiosemicarbazonate compounds [Re(L)(CO)], where the ligand is S,N,N-tridentate. Besides, the reaction in methanol or ethanol of the thiosemicarbazones derived from aldehydes yielded S,N,N-tridentate hemiaminal cationic [Re(HL)(CO)]X and neutral [Re(L)(CO)] complexes after the coordinated ligand underwent addition of the alcohol group to the imine bond. The reactivity of the complex [ReX(HL)(CO)] in MeOH and NEt led to the formation of dinuclear [Re(L)(CO)], where the thiosemicarbazonate is again S,N-bidentate. The influence that the substituents on the thiosemicarbazone ligands have on the stability of the complexes and the effect of the reaction medium on the resulting compounds have been analyzed.