Molecular mobility in several imidazolium‐based ionic liquids according to data of 1H and 13C NMR relaxation

• Published in: Magnetic resonance in chemistry Vol. 56; no. 2; pp. 140 - 143
• Main Authors: Matveev, Vladimir V., Markelov, Denis A., Ievlev, Alexandr V., Brui, Ekaterina A., Tyutyukin, Konstantin V., Lähderanta, Erkki
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.02.2018
• Subjects: emimOAc; Glycerol; Ion pairs; Ionic liquids; Ions; NMR; NMR relaxation; Nuclear magnetic resonance; Shape recognition; Solvents; temperature dependence
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.4681

Temperature dependences are compared for 1H and 13C NMR 1/T1 curves relaxation rates in three imidazolium‐based ionic liquids (ILs), namely, in [bmim]PF6, [bmim]BF4, and [emim]CH3COO. 13C curves show alike behavior for all three ILs and follow a well‐known Bloembergen‐Pound‐Purcell (BPP) equation. On the contrary, an essential part of 1H curves differ strongly from corresponding 13C ones and also have different shapes for different ILs. For the first time, we have detected the specific, two‐maximum shape of 1H relaxation curve for hydrogen atom of C(2)H group of the [emim]CH3COO. Assuming that this maximum reflects the correlated rotation of several adjoining ion pairs, we have tried to destroy this rotation by addition of glycerol to the [emim]CH3COO. The second, high‐temperature maximum has disappeared in the [emim]CH3COO–glycerol mixture, and this fact confirms our assumption. Copyright © 2017 John Wiley & Sons, Ltd. Temperature dependence of 1H NMR spin‐lattice relaxation rate of C(2)H‐group in pure [emim]CH3COO demonstrates unique two‐maximum like shape. The authors connect the second, high‐temperature maximum to formation of the ionic pairs and the subsequent quasi‐parallel package of the pseudo‐molecules. Addition of glycerol prevents the counterions association and destroys the second maximum.