A novel small-molecular europium(III) complex with quinoline derivative has been designed and prepared for anion recognition. This Eu3+ complex displays striking emission changes at 616 nm in response to NO3− and Cl−. What's more, the anion-selective luminescence enhancement is easily detected by the naked eye. UV, luminescence titration experiments and the Job plot analysis revealed that the ligand can form stable 1
:1 complexes with Eu(NO3)3 or EuCl3 in CH3CN; log K = 7.10 and 6.76 (295 K), respectively. The crystal structure shows that three oxygen atoms and one nitrogen atom of the ligand are approximately coplanar and wrap around the Eu3+ ion through a semicircle-shaped coordination structure and some unoccupied sites of the central europium ions are available for guest anions in the complexes. Thus, three nitrate ions are located in the gap of the semicircle. It is supposed that the mechanism of luminescence enhancement is of NO3− or Cl− anions squeezing out solvent molecules from the inner coordination sphere.
Dalton Transactions
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