Liquid Structure of CO2-Reactive Aprotic Heterocyclic Anion Ionic Liquids from X-ray Scattering and Molecular Dynamics

Quintin R. Sheridan, Seungmin Oh, Oscar Morales-Collazo, Ed Castner, Joan F. Brennecke, Edward J. Maginn

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

A combination of X-ray scattering experiments and molecular dynamics simulations were conducted to investigate the structure of ionic liquids (ILs) which chemically bind CO2. The structure functions were measured and computed for four different ILs consisting of two different phosphonium cations, triethyloctylphosphonium ([P2228]+) and trihexyltetradecylphosphonium ([P66614]+), paired with two different aprotic heterocyclic anions which chemically react with CO2, 2-cyanopyrrolide, and 1,2,4-triazolide. Simulations were able to reproduce the experimental structure functions, and by deconstructing the simulated structure functions, further information on the liquid structure was obtained. All structure functions of the ILs studied had three primary features which have been seen before in other ILs: a prepeak near 0.3-0.4 Å-1 corresponding to polar/nonpolar domain alternation, a charge alternation peak near 0.8 Å-1, and a peak near 1.5 Å-1 due to interactions of adjacent molecules. The liquid structure functions were only mildly sensitive to the specific anion and whether or not they were reacted with CO2. Upon reacting with CO2, small changes were observed in the structure functions of the [P2228]+ ILs, whereas virtually no change was observed upon reacting with CO2 in the corresponding [P66614]+ ILs. When the [P2228]+ cation was replaced with the [P66614]+ cation, there was a significant increase in the intensities of the prepeak and adjacency interaction peak. While many of the liquid structure functions are similar, the actual liquid structures differ as demonstrated by computed spatial distribution functions. (Graph Presented).

Original languageEnglish
Pages (from-to)11951-11960
Number of pages10
JournalJournal of Physical Chemistry B
Volume120
Issue number46
DOIs
Publication statusPublished - Nov 23 2016

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Ionic Liquids
X ray scattering
Ionic liquids
Anions
Molecular dynamics
Negative ions
molecular dynamics
anions
Liquids
liquids
scattering
x rays
Cations
Positive ions
alternations
cations
Spatial distribution
Distribution functions
Molecules
spatial distribution

ASJC Scopus subject areas

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

Cite this

Liquid Structure of CO2-Reactive Aprotic Heterocyclic Anion Ionic Liquids from X-ray Scattering and Molecular Dynamics. / Sheridan, Quintin R.; Oh, Seungmin; Morales-Collazo, Oscar; Castner, Ed; Brennecke, Joan F.; Maginn, Edward J.

In: Journal of Physical Chemistry B, Vol. 120, No. 46, 23.11.2016, p. 11951-11960.

Research output: Contribution to journalArticle

Sheridan, Quintin R. ; Oh, Seungmin ; Morales-Collazo, Oscar ; Castner, Ed ; Brennecke, Joan F. ; Maginn, Edward J. / Liquid Structure of CO2-Reactive Aprotic Heterocyclic Anion Ionic Liquids from X-ray Scattering and Molecular Dynamics. In: Journal of Physical Chemistry B. 2016 ; Vol. 120, No. 46. pp. 11951-11960.
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AB - A combination of X-ray scattering experiments and molecular dynamics simulations were conducted to investigate the structure of ionic liquids (ILs) which chemically bind CO2. The structure functions were measured and computed for four different ILs consisting of two different phosphonium cations, triethyloctylphosphonium ([P2228]+) and trihexyltetradecylphosphonium ([P66614]+), paired with two different aprotic heterocyclic anions which chemically react with CO2, 2-cyanopyrrolide, and 1,2,4-triazolide. Simulations were able to reproduce the experimental structure functions, and by deconstructing the simulated structure functions, further information on the liquid structure was obtained. All structure functions of the ILs studied had three primary features which have been seen before in other ILs: a prepeak near 0.3-0.4 Å-1 corresponding to polar/nonpolar domain alternation, a charge alternation peak near 0.8 Å-1, and a peak near 1.5 Å-1 due to interactions of adjacent molecules. The liquid structure functions were only mildly sensitive to the specific anion and whether or not they were reacted with CO2. Upon reacting with CO2, small changes were observed in the structure functions of the [P2228]+ ILs, whereas virtually no change was observed upon reacting with CO2 in the corresponding [P66614]+ ILs. When the [P2228]+ cation was replaced with the [P66614]+ cation, there was a significant increase in the intensities of the prepeak and adjacency interaction peak. While many of the liquid structure functions are similar, the actual liquid structures differ as demonstrated by computed spatial distribution functions. (Graph Presented).

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