A Bloembergen-Purcell-Pound 13C NMR relaxation study of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

W R Carper; P G Wahlbeck; J H Antony; D Mertens; A Dölle; P Wasserscheid

doi:10.1007/s00216-003-2218-1

A Bloembergen-Purcell-Pound 13C NMR relaxation study of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Anal Bioanal Chem. 2004 Mar;378(6):1548-54. doi: 10.1007/s00216-003-2218-1.

Authors

W R Carper¹, P G Wahlbeck, J H Antony, D Mertens, A Dölle, P Wasserscheid

Affiliation

¹ Department of Chemistry, Wichita State University, Wichita, Kansas 67260-0051, USA. Bob.Carper@wichita.edu

PMID: 15214415
DOI: 10.1007/s00216-003-2218-1

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 (T1) and the rates (R1 = 1/T1) 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.