DFT calculation and experimental validation on the interactions of bis(trifluoromethylsulfonyl)imide and hexafluorophosphate with cesium

Bis(trifluoromethylsulfonyl)imide (NTf 2 − ) and hexafluorophosphate (PF 6 − ) are the most frequently used anions for hydrophobic ionic liquids (ILs) which have been considered as promising solvents in the extraction of cesium ions. The interactions of NTf 2 − and PF 6 − with Cs + were explored in this work. The results of DFT calculation indicated that both Cs + and Cs(18C6) + prefer to interact with two NTf 2 − or PF 6 − anions in gas phase, where 18C6 is 18-crown-6. The complex of Cs(NTf 2 ) 2 − was observed in electrospray ionization mass spectrometry (ESI-MS), and the complexes of [Cs(18C6)NTf 2 ] 2 and [Cs(18C6)PF 6 ] 2 were crystallized in which Cs(18C6) + interacted with two anions. The interactions of NTf 2 − with cesium resulted in a synergistic effect between dicyclohexano-18-crown-6 (DCH18C6) and NTf 2 − in the extraction of Cs + using n -octanol as diluent. However, DFT calculation revealed that the complex Cs(DCH18C6) + interacted with one NTf 2 − anion was more thermodynamically stable than that with two anions in organic phase, different from that in gas phase.