Publications
Experiences with an Inquiry-Based Ionic Liquid Module in an Undergraduate Physical Chemistry Laboratory
J. Chem. Educ. 2024, Accepted
The topic of ionic liquids is typically not taught at the undergraduate level. Many properties, such as conductivity, vapor pressure, and viscosity, of these so-called “green solvents” are unique compared to traditional molecular solvents. Using active learning techniques, we introduced an ionic liquid module in the physical chemistry laboratory where their structures and physical properties, namely, viscosity, conductivity, and vapor pressure, were explored in relation to molecular solvents. Summative and formative assessments show that a majority of the participants were able to grasp the key concepts of ionic liquids. We envision that our methods and strategies can be one of the building blocks of introducing ionic liquids into the undergraduate chemistry curriculum.
Hydrogen-bonded complexes in binary mixture imidazolium-based ionic liquids with organic solvents
J. Phys. Chem. B 2023, Accepted
Though local structures in ionic liquids are dominated by strong Coulomb forces, directional hydrogen bonds also can influence the physiochemical properties of imidazolium-based ionic liquids. In particular, the C-2 position of imidazolium cation is acidic and can bind with suitable hydrogen bond acceptor sites of molecular solvents dissolved in imidazolium-based ionic liquid. In this report, we identify hydrogen-bonded microenvironments of the model ionic liquid, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate, and the changes that occur when molecular solvents are dissolved in it by using a C-D infrared reporter at C-2 position of the cation. Our linear and nonlinear infrared experiments, along with computational studies, indicate that the molecular solvent dimethyl sulfoxide can form strong hydrogen-bonded dimers with the cation of the ionic liquid at the C-2 position. In contrast acetone, which is also a hydrogen bond acceptor similar to dimethyl sulfoxide, does not show evidence of cation-solvent hydrogen-bonded conformers at the C-2 position. The outcome of our study, on a broad scale, strengthens the importance of cation-solute interactions in ionic liquids. .
C–D Vibration at C2 Position of Imidazolium Cation as a Probe of the Ionic Liquid Microenvironment
J. Phys. Chem. A 2019, 123, 29, 6342–6349
Unlike molecular solvents, imidazolium-based ionic liquids are entirely made of ions with spatial heterogeneity. There is a need for spectroscopic probes that can assess the microenvironment near the cations of these complex liquids. In this manuscript, we describe simple chemical procedures to label the C2 position of imidazolium cation with a C–D vibrational probe and show, through linear and nonlinear vibrational spectroscopies, that this C–D stretching mode can be a useful analytical tool to assess both the solvent microenvironment and solute–solvent interactions in imidazolium-based ionic liquids from the cation point of view. It is expected that this C–D vibration probe on the cation will lead to the development of innovative experimental strategies that can provide a better understanding of such ionic liquids.
Striking temperature-dependent molecular reorganization at the C-2 position of [EMIM][BF4]
Chemical Physics Letters 783(13):138956
Understanding the temperature-dependent structural evolution of imidazolium-based ionic liquids can facilitate their high-temperature applications. In this manuscript, we report an anomalous redshift and line-narrowing of the C-D vibration at the C-2 position of the imidazolium cation of the ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), when compared to other investigated ionic liquids upon heating suggesting the possibility of structural ordering of this ionic liquid upon heating. Computational studies show that this ordering could arise due to the formation of strong hydrogen bonding conformers. Further infrared studies indicate the existence of a possible hidden transition in this liquid which was subsequently confirmed by calorimetric measurement.
Our group is funded by NSF, NIH, and NASA