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Intramolecular cooperative effect of a macrocyclic receptor bearing $$beta$$-diketone fragments on the extraction of strontium into an ionic liquid

Okamura, Hiroyuki   ; Naganawa, Hirochika  ; Imura, Hisanori*; Shimojo, Kojiro   

The macrocyclic receptor (H$$_{2}$$$$beta$$DA18C6) composed of diaza-18-crown-6 and two molecules of 4-acyl-5-pyrazolone was synthesized for the extraction of Sr(II) into ionic liquids (ILs). The extraction performance of H$$_{2}$$$$beta$$DA18C6 in 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C$$_{n}$$mim][Tf$$_{2}$$N]) was remarkably enhanced by the intramolecular cooperative effect compared with that in chloroform. From the equilibrium analysis, the neutral complex, Sr($$beta$$DA18C6), was extracted into [C$$_{2}$$mim][Tf$$_{2}$$N]. The shortening of the average Sr-O distance in the Sr-$$beta$$DA18C6 complex in the IL was revealed from the extended X-ray absorption fine structure spectroscopy. This is the cause of the intramolecular cooperative effect in the IL.



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