Conformational insight into radiation-chemical transformations of dicyclohexano-18-crown-6 complexes with alkaline earth metal chlorides: Effect of cation size

Abstract Effects of cation size on relative yields of macrocycle cleavage under irradiation of stereoisomeric dicyclohexano-18-crown-6 complexes with alkaline earth metal chlorides were studied to mimic the radiolysis of the macrocyclic components of metal-loaded extractants applicable for radioactive waste reprocessing. Chloride-anions was found to prevent the macrocycle from destruction at early stage of radiolysis. However, radiolytic atomic chlorine was generated as a result of anion decay that promoted radiation-chemical transformations of the crown ether in secondary radical reactions. Interaction of metal cation with donor oxygen atoms of crown ether led to conformational rearrangement of the macrocycle and induced additional channel of C–O bond cleavage at post-radiation stages of radiolysis. Total fraction of acyclic radical products increased as follows: Ca 2+  > Sr 2+  > Ba 2+ . This sequence order is correlated with data of vibrational spectroscopy and implies more radiation sensitivity of the folded, asymmetric conformation of macrocycle in complexes with calcium chloride in contrast to symmetric complexes with barium chloride.