Cage-Like Local Structure of Ionic Liquids Revealed by a (129)Xe Chemical Shift.
The chemical shift of xenon (at natural abundance) dissolved in a variety of 1-butyl-3-methylimidazolium-based ionic liquids (ILs) has been measured with (129)Xe NMR spectroscopy. The large chemical shift differences observed are mainly related to the type of anion; the strongest deshielding effect is observed ILs with I(-), Br(-), and Cl(-) anions, and the strongest shielding is found for the bis(trifluoromethanesulfonyl)imide ([Tf2N](-))-based IL. The measured (129)Xe chemical shift variations correlate well with the IL structure organization imposed by the anions and with the size of the empty voids due to charge alternation patterns. Descriptors taken from literature data on X-ray and neutron scattering, as well as single-crystal structures where available, support this interpretation. The proposed methodology adds a new investigating tool to the elucidation of the short-range order in ILs. The observed chemical shift trend provides information about how these solvents are organized.
†Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. Da Vinci 32, 20133 Milano, Italy.
Franca
F
Castiglione
‡Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, Via Roberto Cozzi 53, 20125 Milano, Italy.
Roberto
R
Simonutti
‡Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, Via Roberto Cozzi 53, 20125 Milano, Italy.
Michele
M
Mauri
†Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. Da Vinci 32, 20133 Milano, Italy.|§CNR - Istituto di Chimica del Riconoscimento Molecolare, Via L. Mancinelli 7, 20131 Milano, Italy.
Andrea
A
Mele
NMR spectroscopy; imidazolium cation; ionic liquids; xenon chemical shift