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Multiple points of view of heteronuclear NOE: Long range vs short range contacts in pyrrolidinium based ionic liquids in the presence of Li salts

  • Authors: Castiglione, F.; Appetecchi, G.; Passerini, S.; Panzeri, W.; Indelicato, S.; Mele, A.
  • Publication year: 2015
  • Type: Articolo in rivista (Articolo in rivista)
  • Key words: Fluorosulfonylimide; Heteronuclear NOE; Intermolecular NOE; Ionic liquids; Lithium; NMR; Pyrrolidinium; Trifluoromethanesulfonimide; Electronic, Optical and Magnetic Materials; Atomic and Molecular Physics, and Optics; Condensed Matter Physics; Spectroscopy; Physical and Theoretical Chemistry; Materials Chemistry2506 Metals and Alloys
  • OA Link: http://hdl.handle.net/10447/243619

Abstract

The nuclear Overhauser enhancement (NOE) is a powerful tool of NMR spectroscopy extensively used to gain structural information in ionic liquids (ILs). A general model for the distance dependence of intermolecular NOE in ILs was recently proposed showing that NOE spots beyond the first solvation shell and accounts for long-range effects. This conclusion prompted for a deep rethinking of the NOE data interpretation in ILs. In this paper we present an extensive and quantitative study of N-propyl-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI), the homologue with bis(fluorosulfonyl)imide (PYR13FSI), and their mixtures with LiTFSI based on 1H-19F and 1H-7LiNOE correlation experiments (HOESY). The former is mainly tuned on long-range interactions, the latter on short-range ones, due to the small and large Larmor frequency differences of the involved nuclei. The collected data are discussed in two different way: long-range 1H-19FNOEs spot on the polar/apolar domains within the ILs, whereas short-range (e.g. regarding the first coordination shell) 1H-7LiNOEs describe the contacts between first neighbors, with interesting correlation with the distances' statistics derived by crystallographic data of related systems.