Molecular reorientational dynamics of the neat ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate by measurement of 13C nuclear magnetic relaxation data

被引:136
作者
Antony, JH [1 ]
Mertens, D
Dölle, A
Wasserscheid, P
Carper, WR
机构
[1] Rhein Westfal TH Aachen, Inst Phys Chem, D-52056 Aachen, Germany
[2] Rhein Westfal TH Aachen, Inst Tech & Makromol Chem, D-52056 Aachen, Germany
[3] Wichita State Univ, Dept Chem, Wichita, KS 67260 USA
关键词
green chemistry; hydrogen bonds; ionic liquids; molecular dynamics; NMR spectroscopy;
D O I
10.1002/cphc.200200603
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The reorientational dynamics of the ionic liquid 1-butyl-3-methyl-imidazolium hexafluorophosphate ([BMIM]PF6) were studied over a wide range of temperatures of measurement of C-13 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. The 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 C2 H 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.
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页码:588 / 594
页数:7
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