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Molecular Reorientational Dynamics of the Neat Ionic Liquid 1‐Butyl‐3‐methylimidazolium Hexafluorophosphate by Measurement of 13 C Nuclear Magnetic Relaxation Data
Author(s) -
Antony Jürgen H.,
Mertens Dirk,
Dölle Andreas,
Wasserscheid Peter,
Carper William R.
Publication year - 2003
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200200603
Subject(s) - hexafluorophosphate , chemistry , ionic liquid , relaxation (psychology) , molecular dynamics , arrhenius equation , rotational diffusion , ionic bonding , chemical physics , nuclear magnetic resonance , computational chemistry , ion , molecule , activation energy , organic chemistry , psychology , social psychology , physics , catalysis
The reorientational dynamics of the ionic liquid 1butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM]PF 6 ) were studied over a wide range of temperatures by measurement of 13 C spin–lattice relaxation rates and NOE factors. The reorientational dynamics were evaluated by performing fits to the experimental relaxation data. Thus, the overall reorientational motion was described by a Cole–Davidson spectral density with a Vogel–Fulcher–Tammann temperature dependence of the correlation times. The reorientational motion of the butyl chain was modelled by a combination of the latter model for the overall motion with a Bloembergen–Purcell–Pound spectral density and an Arrhenius temperature dependence for the internal motion. Except for C2 in the aromatic ring, an additional reduction of the spectral density by the Lipari–Szabo model had to be employed. This reduction is a consequence of fast molecular motions before the rotational diffusion process becomes effective. The C2 atom did not exhibit this reduction, because the librational motion of the corresponding C2H vector is severely hindered due to hydrogen bonding with the hexafluorophosphate anion. The observed dynamic features of the [BMIM] + cation confirm quantum‐chemical structures obtained in a former study.