From Salt in Solution to Solely Ions: Solvation of Methyl Viologen in Deep Eutectic Solvents and Ionic Liquids

Jeffrey M Klein; Henry Squire; William Dean; Burcu E Gurkan

doi:10.1021/acs.jpcb.0c03296

From Salt in Solution to Solely Ions: Solvation of Methyl Viologen in Deep Eutectic Solvents and Ionic Liquids

J Phys Chem B. 2020 Jul 23;124(29):6348-6357. doi: 10.1021/acs.jpcb.0c03296. Epub 2020 Jul 10.

Authors

Jeffrey M Klein¹, Henry Squire¹, William Dean¹, Burcu E Gurkan¹

Affiliation

¹ Department of Chemical Engineering Biomolecular Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States.

PMID: 32589425
DOI: 10.1021/acs.jpcb.0c03296

Abstract

Solvation and transport properties of methly viologen dichloride (MVCl₂) in 1:2, 1:4, and 1:6 molar mixtures of choline chloride (ChCl) and ethylene glycol (EG), including the deep eutectic solvent (DES) ethaline (1:2 mixture), were studied through the application of the hole theory to measured physical properties, cyclic voltammetry, and Raman spectroscopy. The ChCl:EG mixtures were compared to the ionic liquid (IL) 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([PYR₁₃][TFSI]) and choline bis(trifluoromethylsulfonyl)imide (ChTFSI) EG mixtures with the same molar ratios in order to understand the impact of the anion and hydrogen bond donor on solvation. Exchanging the chloride anion with TFSI is found to increase the fluidity of the solvent and promote stronger solute-solvent interactions. Raman spectroscopy suggests MVCl₂ is strongly solvated by EG in ChTFSI:EG solutions and interstitially accommodated in holes in ChCl:EG mixtures and [PYR₁₃][TFSI]. Complex solvents such as ILs and DESs are regarded as "designer solvents", and it is demonstrated here that the physical properties and solvation characteristics of these fluids strongly depend on the choice of the anion.