Stereoisomeric effect in low temperature radiolysis of dicyclohexano-18-crown-6 complexes with BaCl2

Effect of syn/anti-stereoisomerism of the macrocycle on radiation-chemical transformations of dicyclohexano-18-crown-6 complexes with BaCl2 was studied by EPR spectroscopy. It was found that the stereoisomerism affected the composition of radicals produced under radiolysis at 77 K. In addition, it was demonstrated that the yield of post-radiation macrocycle cleavage after annealing the irradiated complexes at 333 K was also different for the two studied stereoisomers. The radiation-induced destruction of both cis-syn-cis- and cis-anti-cis-complex was predominately localized at the crown ether moiety, and the Cl2- radical anions were not detected in irradiated samples. The last finding was ascribed to a high reactivity of chlorine atoms towards the crown ether. Generally, it may be concluded that the macrocyclic complex with anti-configuration had a lower radiation stability. Thus, it is very important to characterize the stereoisomeric composition of dicyclohexano-18-crown-6 and its complexes in the radiation-chemical tests for practical purposes.