Stability studies on (99m)technetium(III) complexes with tridentate/monodentate thiol ligands and phosphine ('3 + 1 + 1' complexes).

The preparation and characterisation of 3 + 1 + 1 technetium complexes of the general formula [Tc(SES)(RS)(PMe2Ph)] (SES = tridentate dithiol ligand, E = S, O, NMe; RSH = monothiol ligand) at the n.c.a. level is described. The Tc(III) complexes are prepared in a one-step procedure starting from pertechnetate in yields of 85-95% of radiochemical purity. A comparison of their chromatographic data with the fully characterised 99Tc complexes indicate the identity of the investigated compounds. Stability studies show that the 99mTc complexes undergo some alteration in solution. They are oxidised to the 3 + 1 oxotechnetium (V) complexes and/or decompose in aqueous solution. In challenge experiments performed with glutathione, exchange of the monothiolato ligand occurs in the same manner as known for the 3 + 1 complexes.