2 research outputs found
Ionic Liquid–Solute Interactions Studied by 2D NOE NMR Spectroscopy
Intermolecular interactions between
a Ru<sup>2+</sup>(bpy)<sub>3</sub> solute and the anions and cations
of four different ionic
liquids (ILs) are investigated by 2D NMR nuclear Overhauser effect
(NOE) techniques, including {<sup>1</sup>H–<sup>19</sup>F}
HOESY and {<sup>1</sup>H–<sup>1</sup>H} ROESY. Four ILs are
studied, each having the same bisÂ(trifluoromethylsulfonyl)Âamide anion
in common. Two of the ILs have aliphatic 1-alkyl-1-methylpyrrolidinium
cations, while the other two ILs have aromatic 1-alkyl-3-methylimidazolium
cations. ILs with both shorter (butyl) and longer (octyl or decyl)
cationic alkyl substituents are studied. NOE NMR results suggest that
the local environment of IL anions and cations near the Ru<sup>2+</sup>(bpy)<sub>3</sub> solute is rather different from the bulk IL structure.
The solute–anion and solute–cation interactions are
significantly different both for ILs with short vs long alkyl tails
and for ILs with aliphatic vs aromatic cation polar head groups. In
particular, the solute–anion interactions are observed to be
about 3 times stronger for the cations with shorter alkyl tails relative
to the ILs with longer alkyl tails. The Ru<sup>2+</sup>(bpy)<sub>3</sub> solute interacts with both the polar head and the nonpolar tail
groups of the 1-butyl-1-methylpyrrolidinium cation but only with the
nonpolar tail groups of the 1-decyl-1-methylpyrrolidinium cation
Diffusion Coefficients from <sup>13</sup>C PGSE NMR MeasurementsFluorine-Free Ionic Liquids with the DCTA<sup>–</sup> Anion
Pulsed-field gradient spin–echo (PGSE) NMR is
a widely used
method for the determination of molecular and ionic self-diffusion
coefficients. The analysis has thus far been limited largely to <sup>1</sup>H, <sup>7</sup>Li, <sup>19</sup>F, and <sup>31</sup>P nuclei.
This limitation handicaps the analysis of materials without these
nuclei or for which these nuclei are insufficient for complete characterization.
This is demonstrated with a class of ionic liquids (or ILs) based
on the nonfluorinated anion 4,5-dicarbonitrile-1,2,3-triazole (DCTA<sup>–</sup>). It is demonstrated here that <sup>13</sup>C-PGSE
NMR can be used to both verify the diffusion coefficients obtained
from other nuclei, as well as characterize materials that lack commonly
scrutinized nuclei î—¸ all without the need for specialized NMR
methods