How does the ionic liquid organizational landscape change when nonpolar cationic alkyl groups are replaced by polar isoelectronic diethers?

Hemant K. Kashyap, Cherry S. Santos, Ryan P. Daly, Jeevapani J. Hettige, N. Sanjeeva Murthy, Hideaki Shirota, Ed Castner, Claudio J. Margulis

Research output: Contribution to journalArticle

83 Citations (Scopus)

Abstract

X-ray scattering experiments and molecular dynamics simulations have been performed to investigate the structure of four room temperature ionic liquids (ILs) comprising the bis(trifluoromethylsulfonyl)amide (NTf2-) anion paired with the triethyloctylammonium (N2228+) and triethyloctylphosphonium (P2228+) cations and their isoelectronic diether analogs, the (2-ethoxyethoxy)ethyltriethylammonium (N222(2O2O2) +) and (2-ethoxyethoxy)ethyltriethylphosphonium (P222(2O2O2) +) cations. Agreement between simulations and experiments is good and permits a clear interpretation of the important topological differences between these systems. The first sharp diffraction peak (or prepeak) in the structure function S(q) that is present in the case of the liquids containing the alkyl-substituted cations is absent in the case of the diether substituted analogs. Using different theoretical partitioning schemes for the X-ray structure function, we show that the prepeak present in the alkyl-substituted ILs arises from polarity alternations between charged groups and nonpolar alkyl tails. In the case of the diether substituted ILs, we find considerable curling of tails. Anions can be found with high probability in two different environments: close to the cationic nitrogen (phosphorus) and also close to the two ether groups. For the two diether systems, anions are found in locations from which they are excluded in the alkyl-substituted systems. This removes the longer range (polar/nonpolar) pattern of alternation that gives rise to the prepeak in alkyl-substituted systems.

Original languageEnglish
Pages (from-to)1130-1135
Number of pages6
JournalJournal of Physical Chemistry B
Volume117
Issue number4
DOIs
Publication statusPublished - Jan 31 2013

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Ionic Liquids
Ionic liquids
Anions
Cations
Negative ions
Positive ions
alternations
liquids
anions
cations
analogs
X ray scattering
Amides
Ether
Phosphorus
Molecular dynamics
Ethers
Nitrogen
Diffraction
Experiments

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Chemistry
  • Surfaces, Coatings and Films

Cite this

Kashyap, H. K., Santos, C. S., Daly, R. P., Hettige, J. J., Murthy, N. S., Shirota, H., ... Margulis, C. J. (2013). How does the ionic liquid organizational landscape change when nonpolar cationic alkyl groups are replaced by polar isoelectronic diethers? Journal of Physical Chemistry B, 117(4), 1130-1135. https://doi.org/10.1021/jp311032p

How does the ionic liquid organizational landscape change when nonpolar cationic alkyl groups are replaced by polar isoelectronic diethers? / Kashyap, Hemant K.; Santos, Cherry S.; Daly, Ryan P.; Hettige, Jeevapani J.; Murthy, N. Sanjeeva; Shirota, Hideaki; Castner, Ed; Margulis, Claudio J.

In: Journal of Physical Chemistry B, Vol. 117, No. 4, 31.01.2013, p. 1130-1135.

Research output: Contribution to journalArticle

Kashyap, Hemant K. ; Santos, Cherry S. ; Daly, Ryan P. ; Hettige, Jeevapani J. ; Murthy, N. Sanjeeva ; Shirota, Hideaki ; Castner, Ed ; Margulis, Claudio J. / How does the ionic liquid organizational landscape change when nonpolar cationic alkyl groups are replaced by polar isoelectronic diethers?. In: Journal of Physical Chemistry B. 2013 ; Vol. 117, No. 4. pp. 1130-1135.
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AU - Hettige, Jeevapani J.

AU - Murthy, N. Sanjeeva

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AB - X-ray scattering experiments and molecular dynamics simulations have been performed to investigate the structure of four room temperature ionic liquids (ILs) comprising the bis(trifluoromethylsulfonyl)amide (NTf2-) anion paired with the triethyloctylammonium (N2228+) and triethyloctylphosphonium (P2228+) cations and their isoelectronic diether analogs, the (2-ethoxyethoxy)ethyltriethylammonium (N222(2O2O2) +) and (2-ethoxyethoxy)ethyltriethylphosphonium (P222(2O2O2) +) cations. Agreement between simulations and experiments is good and permits a clear interpretation of the important topological differences between these systems. The first sharp diffraction peak (or prepeak) in the structure function S(q) that is present in the case of the liquids containing the alkyl-substituted cations is absent in the case of the diether substituted analogs. Using different theoretical partitioning schemes for the X-ray structure function, we show that the prepeak present in the alkyl-substituted ILs arises from polarity alternations between charged groups and nonpolar alkyl tails. In the case of the diether substituted ILs, we find considerable curling of tails. Anions can be found with high probability in two different environments: close to the cationic nitrogen (phosphorus) and also close to the two ether groups. For the two diether systems, anions are found in locations from which they are excluded in the alkyl-substituted systems. This removes the longer range (polar/nonpolar) pattern of alternation that gives rise to the prepeak in alkyl-substituted systems.

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