An intramolecular cooperative extraction system for the removal of strontium cations (Sr2+) from water by use of a novel macrocyclic receptor (H-2 beta DA18C6) composed of diaza-18-crown-6 and two beta-diketone fragments in ionic liquid (IL) is reported, together with X-ray spectroscopic characterization of the resulting extracted complexes in the IL and chloroform phases. The covalent attachment of two beta-diketone fragments to a diazacrown ether resulted in a cooperative interaction within the receptor for Sr2+ transfer, which remarkably enhanced the efficiency of Sr2+ transfer relative to a mixed beta-diketone and diazacrown system. The intramolecular cooperative effect was observed only in the IL extraction system, providing a 500 fold increase in extraction performance for Sr2+ over chloroform. Slope analysis and potentiometric,titration confirmed that identical extraction mechanisms operated in both the IL and chloroform systems. Extended X-ray absorption fine structure spectroscopy revealed that the average distance between Sr2+ and O atoms in the Sr2+ complex was shorter in IL than in chloroform. Consequently, Sr2+ was held by H-2 beta DA18C6 more rigidly in IL than M chloroform, representing an important factor dominating the magnitude of the intramolecular cooperative effect of H-2 beta DA18C6 for Sr2+. Furthermore, competitive extraction studies with alkaline earth metal ions revealed that the magnitude of the intramolecular cooperative effect depended on the suitability between metal ion size and the cavity size of H-2 beta DA18C6. Sr2+ was successfully recovered from IL by controlling the pH in the receiving phase, and the extraction performance of H-2 beta DA18C6 in IL was maintained after five repeated uses.