An Insight into the Complexation of Pyrazine‐Functionalized Calix[4]arenes with Am 3+ and Eu 3+ – Solvent Extraction and Luminescence Studies in Room‐Temperature Ionic Liquids

The complexation behaviour of six pyrazine‐functionalized calix[4]arenes, containing substituents such as carbamoyl dioctyl ( L‐1 , L‐2 ), diisopropyl phosphonate ( L‐3 , L‐4 ) and diphenyl phosphoryl ( L‐5 , L‐6 ), with Am 3+ and Eu 3+ ions was investigated by solvent extraction as well as by luminescence spectroscopy (only for Eu 3+ ) in room‐temperature ionic liquids (RTILs), [C n mim][NTf 2 ] (1‐alkyl‐3‐methylimidazolium, n = 4, 6, and 8). The spectacular enhancement in the extraction values of the trivalent metal ions in RTILs, as compared to those reported in a molecular diluent from 3 M HNO 3 , was rather unusual and was further investigated by luminescence studies. Luminescence studies involving Eu 3+ and performed with L ‐ 4 and L ‐ 6 confirmed the 1:1 stoichiometry of the extracted species (Eu 3+  L) with log  β values of 4.42 ± 0.51 and 5.18 ± 0.38 for L‐4 and L‐6 , respectively. Judd–Ofelt parameters, which give information about the nature of bonding as well as the coordinating environment, were computed from the emission spectra of the Eu 3+   L‐4 and Eu 3+   L‐6 complexes.