The complexes of thiobarbituric acid and adenine with Mn (II), Mo(VI) and Cr(III) were prepared. The structures, mode of bonding and the geometry of the prepared complexes were characterized by the elemental analysis, IR and electronic spectroscopy. Thermal studies were carried for the prepared complexes. The mechanisms of the thermal decomposition for the prepared complexes were studied by TGA. Thermodynamic and kinetic studies of the complexes were determined by DTA, and DSC techniques. The influences of the structural properties of the chelating agent and the type of the metal on the thermal behavior of the complexes, the order (n) , the heat of activation (E) , The collisions number (Z) and The change of entropy values (S#) of the various decomposition stages were determined from the TG and DTA. The reaction of some of the prepared complexes with 18F-in different media was studied. Characterization of the 18F-complexes and the determination of the extent of radiolabeling was done by thin layer chromatography using (95:5) acetonitrile to water solution as a solvent.