Abstract
The complexes of 18-crown-6 with alkali-earth metal halides were synthesized to simulate the macrocyclic component of crown-containing extractants selective for radionuclide 90Sr and to investigate the effect of cationic and anionic factors on its radiation destruction at low-temperature (77 K) irradiation. The halide anion was found to protect the complexes from ring opening at the initial stages of radiolysis due to positive charge transfer from the primary macrocyclic radical cation to anion. This effect was found in 18-crown-6 complexes with SrCl2, SrBr2 and BaCl2, where the macrocycle had D3d symmetry. In contrast, the anionic protection was less efficient when the 18-crown-6 conformation was measurably distorted, as illustrated by the examples of complexes with SrI2, CaCl2 and, especially, MgCl2 with folded C2 and D2 symmetries. Based on the results obtained, it was concluded that preliminary conformational analysis of a macrocyclic complex could be a useful way to predict its resistance to radiation-induced polyether ring cleavage.
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