Determination of Mg<sup>2+</sup> Speciation in a TFSI<sup>-</sup>-Based Ionic Liquid with and Without Chelating Ethers Using Raman Spectroscopy

Tylan Watkins, Daniel Buttry

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32 Citations (Scopus)

Abstract

Raman spectroscopy was employed to assess the complex environment of magnesium salts in the n-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrTFSI) room-temperature ionic liquid (RTIL). At room temperature, Mg(TFSI)<inf>2</inf> was miscible with BMPyrTFSI and formulated by [Mg(TFSI)<inf>2</inf>]<inf>x</inf>[BMPyrTFSI]<inf>1-x</inf> (x ≤ 0.55). Results suggest that at low concentrations of Mg(TFSI)<inf>2</inf>, anionic complexes in which Mg<sup>2+</sup> is surrounded by at least four TFSI<sup>-</sup> were formed. Above x = 0.2 an average of three TFSI<sup>-</sup> surround each Mg<sup>2+</sup>. Below x = 0.12, there is a greater number of monodentate interactions between TFSI<sup>-</sup> oxygens and Mg<sup>2+</sup> cations, whereas above x = 0.12 bidentate ligands dominate. The fraction of TFSI<sup>-</sup> existing in the cis conformation increased with increasing Mg<sup>2+</sup> concentration. Mg(ClO<inf>4</inf>)<inf>2</inf> was also studied as a Mg<sup>2+</sup> source. At equivalent mole fractions to those of the Mg(TFSI)<inf>2</inf> salt, Mg<sup>2+</sup> from Mg(ClO<inf>4</inf>)<inf>2</inf> was surrounded by only two TFSI<sup>-</sup> anions as ClO<inf>4</inf><sup>-</sup> appeared to compete with TFSI<sup>-</sup> for coordination with Mg<sup>2+</sup>. Similar behavior was also observed for the less soluble halide salts MgX<inf>2</inf> (X = Cl, Br, I). Additions of chelating ligands were shown to effectively reduce the average number of TFSI<sup>-</sup> around Mg<sup>2+</sup> in a manner consistent with maintaining a sixfold oxygen coordination number around Mg<sup>2+</sup>. Furthermore, an alternative class of ionic liquids, known as "solvate" ionic liquids, were produced. In this case glymes (Gm, m + 1 ether oxygens) were mixed with Mg(TFSI)<inf>2</inf> so that glymes chelated Mg<sup>2+</sup>, creating Mg(Gm)<inf>y</inf><sup>2+</sup> complexes. The general formula was given by Mg(Gm)<inf>y</inf>(TFSI)<inf>2</inf>. These solvate ILs melt between 40 and 80 °C. Raman spectra clearly showed the glyme chelating ability and stronger coordination with Mg<sup>2+</sup> with respect to TFSI<sup>-</sup>. Finally, linear sweep voltammograms showed the anodic stability of the glymes to improve due to coordination with Mg<sup>2+</sup>. (Graph Presented).

Original languageEnglish (US)
Pages (from-to)7003-7014
Number of pages12
JournalJournal of Physical Chemistry B
Volume119
Issue number23
DOIs
StatePublished - Jun 11 2015

Fingerprint

Imides
Ionic Liquids
Ethers
imides
Chelation
Ionic liquids
Raman spectroscopy
ethers
Salts
Oxygen
salts
oxygen
liquids
Ligands
ligands
room temperature
coordination number
Ether
Magnesium
halides

ASJC Scopus subject areas

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

Cite this

@article{9ec32c3ad8fe45dd98c73ce7cc33c1c1,
title = "Determination of Mg2+ Speciation in a TFSI--Based Ionic Liquid with and Without Chelating Ethers Using Raman Spectroscopy",
abstract = "Raman spectroscopy was employed to assess the complex environment of magnesium salts in the n-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrTFSI) room-temperature ionic liquid (RTIL). At room temperature, Mg(TFSI)2 was miscible with BMPyrTFSI and formulated by [Mg(TFSI)2]x[BMPyrTFSI]1-x (x ≤ 0.55). Results suggest that at low concentrations of Mg(TFSI)2, anionic complexes in which Mg2+ is surrounded by at least four TFSI- were formed. Above x = 0.2 an average of three TFSI- surround each Mg2+. Below x = 0.12, there is a greater number of monodentate interactions between TFSI- oxygens and Mg2+ cations, whereas above x = 0.12 bidentate ligands dominate. The fraction of TFSI- existing in the cis conformation increased with increasing Mg2+ concentration. Mg(ClO4)2 was also studied as a Mg2+ source. At equivalent mole fractions to those of the Mg(TFSI)2 salt, Mg2+ from Mg(ClO4)2 was surrounded by only two TFSI- anions as ClO4- appeared to compete with TFSI- for coordination with Mg2+. Similar behavior was also observed for the less soluble halide salts MgX2 (X = Cl, Br, I). Additions of chelating ligands were shown to effectively reduce the average number of TFSI- around Mg2+ in a manner consistent with maintaining a sixfold oxygen coordination number around Mg2+. Furthermore, an alternative class of ionic liquids, known as {"}solvate{"} ionic liquids, were produced. In this case glymes (Gm, m + 1 ether oxygens) were mixed with Mg(TFSI)2 so that glymes chelated Mg2+, creating Mg(Gm)y2+ complexes. The general formula was given by Mg(Gm)y(TFSI)2. These solvate ILs melt between 40 and 80 °C. Raman spectra clearly showed the glyme chelating ability and stronger coordination with Mg2+ with respect to TFSI-. Finally, linear sweep voltammograms showed the anodic stability of the glymes to improve due to coordination with Mg2+. (Graph Presented).",
author = "Tylan Watkins and Daniel Buttry",
year = "2015",
month = "6",
day = "11",
doi = "10.1021/acs.jpcb.5b00339",
language = "English (US)",
volume = "119",
pages = "7003--7014",
journal = "Journal of Physical Chemistry B Materials",
issn = "1520-6106",
publisher = "American Chemical Society",
number = "23",

}

TY - JOUR

T1 - Determination of Mg2+ Speciation in a TFSI--Based Ionic Liquid with and Without Chelating Ethers Using Raman Spectroscopy

AU - Watkins, Tylan

AU - Buttry, Daniel

PY - 2015/6/11

Y1 - 2015/6/11

N2 - Raman spectroscopy was employed to assess the complex environment of magnesium salts in the n-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrTFSI) room-temperature ionic liquid (RTIL). At room temperature, Mg(TFSI)2 was miscible with BMPyrTFSI and formulated by [Mg(TFSI)2]x[BMPyrTFSI]1-x (x ≤ 0.55). Results suggest that at low concentrations of Mg(TFSI)2, anionic complexes in which Mg2+ is surrounded by at least four TFSI- were formed. Above x = 0.2 an average of three TFSI- surround each Mg2+. Below x = 0.12, there is a greater number of monodentate interactions between TFSI- oxygens and Mg2+ cations, whereas above x = 0.12 bidentate ligands dominate. The fraction of TFSI- existing in the cis conformation increased with increasing Mg2+ concentration. Mg(ClO4)2 was also studied as a Mg2+ source. At equivalent mole fractions to those of the Mg(TFSI)2 salt, Mg2+ from Mg(ClO4)2 was surrounded by only two TFSI- anions as ClO4- appeared to compete with TFSI- for coordination with Mg2+. Similar behavior was also observed for the less soluble halide salts MgX2 (X = Cl, Br, I). Additions of chelating ligands were shown to effectively reduce the average number of TFSI- around Mg2+ in a manner consistent with maintaining a sixfold oxygen coordination number around Mg2+. Furthermore, an alternative class of ionic liquids, known as "solvate" ionic liquids, were produced. In this case glymes (Gm, m + 1 ether oxygens) were mixed with Mg(TFSI)2 so that glymes chelated Mg2+, creating Mg(Gm)y2+ complexes. The general formula was given by Mg(Gm)y(TFSI)2. These solvate ILs melt between 40 and 80 °C. Raman spectra clearly showed the glyme chelating ability and stronger coordination with Mg2+ with respect to TFSI-. Finally, linear sweep voltammograms showed the anodic stability of the glymes to improve due to coordination with Mg2+. (Graph Presented).

AB - Raman spectroscopy was employed to assess the complex environment of magnesium salts in the n-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrTFSI) room-temperature ionic liquid (RTIL). At room temperature, Mg(TFSI)2 was miscible with BMPyrTFSI and formulated by [Mg(TFSI)2]x[BMPyrTFSI]1-x (x ≤ 0.55). Results suggest that at low concentrations of Mg(TFSI)2, anionic complexes in which Mg2+ is surrounded by at least four TFSI- were formed. Above x = 0.2 an average of three TFSI- surround each Mg2+. Below x = 0.12, there is a greater number of monodentate interactions between TFSI- oxygens and Mg2+ cations, whereas above x = 0.12 bidentate ligands dominate. The fraction of TFSI- existing in the cis conformation increased with increasing Mg2+ concentration. Mg(ClO4)2 was also studied as a Mg2+ source. At equivalent mole fractions to those of the Mg(TFSI)2 salt, Mg2+ from Mg(ClO4)2 was surrounded by only two TFSI- anions as ClO4- appeared to compete with TFSI- for coordination with Mg2+. Similar behavior was also observed for the less soluble halide salts MgX2 (X = Cl, Br, I). Additions of chelating ligands were shown to effectively reduce the average number of TFSI- around Mg2+ in a manner consistent with maintaining a sixfold oxygen coordination number around Mg2+. Furthermore, an alternative class of ionic liquids, known as "solvate" ionic liquids, were produced. In this case glymes (Gm, m + 1 ether oxygens) were mixed with Mg(TFSI)2 so that glymes chelated Mg2+, creating Mg(Gm)y2+ complexes. The general formula was given by Mg(Gm)y(TFSI)2. These solvate ILs melt between 40 and 80 °C. Raman spectra clearly showed the glyme chelating ability and stronger coordination with Mg2+ with respect to TFSI-. Finally, linear sweep voltammograms showed the anodic stability of the glymes to improve due to coordination with Mg2+. (Graph Presented).

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