Role of anions in radiation-induced transformations of 18-crown-6 complexes with barium salts: simulating the effects of extraction mechanism on radiation stability of macrocyclic extractants

Complexes of 18-crown-6 with BaCl2, Ba(NO3)2 and Ba(NTf2)2 salts were synthesized and irradiated with X-rays to simulate the radiation degradation of a macrocyclic component of extractants based on crown ether solutions in commonly used solvents. Structures and post-irradiation transformations of radical products stabilized in these complexes at 77 K were studied using EPR spectroscopy, and the mechanism of their formation and decay was proposed. Differences in ionization potentials of the macrocycle and the anions and reactivity of the intermediates generated from the anions are of importance for radiation stability of the studied compounds. The nitrate-anions was demonstrated to protect 18C6 from destruction whereas Cl− and bis(trifluoromethylsulfonyl)imide-anions can impair the radiation stability of the macrocycle. The results of the present study offer an opportunity to predict the radiation stability of the crown ether extractants and their applicability for liquid radioactive waste reprocessing.