Charge transfer rhenium complexes analogue to pertechnetate removal

Technetium (99Tc) mobility in the environment increases when 99Tc(IV) is combined with certain organic ligands under reducing environment. Therefore, it is important to detect and characterize 99Tc-organic ligand complex species to understand 99Tc mobility in various environmental conditions. Rhenium (Re) was used as a 99Tc surrogate with ethylenediaminetetracetic acid (EDTA) to produce Re–EDTA complexes, with perrhenate (ReO4−) reduced in the presence of EDTA with tin ion (Sn2+) in an anoxic glove box. Liquid–liquid and vapor–liquid diffusion methods were applied to isolate the Re complexes from the reaction mixture, and they were characterized using ultraviolet–visible, Raman, Fourier-transform infrared spectroscopy, and matrix-assisted laser desorption/ionization-time of flight mass spectroscopy. Bi-metallic base complex [(Sn)(EDTA)(ReO)(OH)(OH2)] was discovered, which transformed to a charge transfer (CT) complex, [CT complex1]=[(OH)2(H2O)2Re2(μ-O2)(EDTA)2·Sn2)] and [CT complex2]=[Re2(μ-O2)(EDTA)2Na4] over a period of 1 month. These CT complexes and a base complex were detected by matrix-assisted laser desorption/ionization-time of flight in black and yellow products, respectively. Oxidation states of +5 and +4 were assigned to Re in [CT complex1] and [CT complex2], respectively, based on Warner’s structure model. These CT complexes were neither broken apart to form ReO2(s) nor reversely transformed to form a base complex during a dissolution experiment, even in oxic conditions. These results suggest that the CT complexes of Re(IV/V) are highly stable and environmentally persistent with mobility higher than immobile 99Tc(IV) oxide.