Abstract
The molecular structure and rotational motion of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) were studied over a wide temperature range using the Bloembergen–Purcell–Pound 13C NMR spin–lattice relaxation method and NOE factors. Examination of the spin–lattice relaxation times (T 1) and the rates (R 1=1/T 1) of the 1-butyl-3-methylimidazolium cation reveals the relative motions of each carbon in the imidazolium cation. The rotational characteristics of the [BMIM] cation are supported by ab-initio molecular structures of [BMIM][PF6] using density functional theory (DFT) and Hartree–Fock (HF) methods. The ab-initio gas phase structures of [BMIM][PF6] indicate that the 1-butyl-3-methylimidazolium C2 hydrogen, the ring methyl group, and the butyl side-chain hydrogen atoms form hydrogen bonds with the hexafluorophosphate anion.
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Acknowledgment
Financial support by the Deutsche Forschungsgemeinschaft (Mercator Visiting Professorship for WRC) is gratefully acknowledged. The authors also thank Professor Dr M.D. Zeidler for his support of this work.
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Carper, W.R., Wahlbeck, P.G., Antony, J.H. et al. A Bloembergen–Purcell–Pound 13C NMR relaxation study of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. Anal Bioanal Chem 378, 1548–1554 (2004). https://doi.org/10.1007/s00216-003-2218-1
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DOI: https://doi.org/10.1007/s00216-003-2218-1