Dielectric relaxation of the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate: microwave and far-IR properties

Dielectric relaxation of the ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate (EMI+ETS–), is studied using molecular dynamics (MD) simulations. The collective dynamics of polarization arising from cations and anions are examined. Characteristics of the rovibrational and translational components of polarization dynamics are analyzed to understand their respective roles in the microwave and terahertz regions of dielectric relaxation. The MD results are compared with the experimental low-frequency spectrum of EMI+ETS–, obtained via ultrafast optical Kerr effect (OKE) measurements

Removal of Confined Ionic Liquid from a Metal Organic Framework by Extraction with Molecular Solvents

This work was supported in part by NSF Grant No. CHE-1223988 and by EPSRC Grant No. EP/K00090X/1.Peer reviewedPostprin

Molecular Interactions of a Cu-Based Metal-Organic Framework with a Confined Imidazolium-Based Ionic Liquid : A Combined Density Functional Theory and Experimental Vibrational Spectroscopy Study

This work was supported in part by NSF Grant CHE-1223988 and by EPSRC Grant EP/K00090X/1.Peer reviewedPublisher PD

Molecular Structure and Interactions in the Ionic Liquid 1‑Ethyl-3-methylimidazolium Bis(Trifluoromethylsulfonyl)imide

Electronic structure theory (density functional and Møller–Plesset perturbation theory) and vibrational spectroscopy (FT-IR and Raman) are employed to study molecular interactions in the room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide. Different conformers of a cation–anion pair based on their molecular interactions are simulated in the gas phase and in a dielectric continuum solvent environment. Although the ordering of conformers in energy varies with theoretical methods, their predictions for three lowest energy conformers in the gas phase are similar. Strong C–H---N interactions between the acidic hydrogen atom of the cation imidazole ring and the nitrogen atom of the anion are predicted for either the lowest or second lowest energy conformer. In a continuum solvent, different theoretical methods yield the same ion-pair conformation for the lowest energy state. In both phases, the density functional method predicts that the anion is in a trans conformation in the lowest energy ion pair state. The theoretical results are compared with experimental observations from Raman scattering and IR absorption spectroscopies and manifestations of the molecular interactions in the vibrational spectra are discussed. The directions of the frequency shifts of the characteristic vibrations relative to the free anion and cation are explained by calculating the difference electron density coupled with electron density topography

Influence of Water on the Chemistry and Structure of the Metal–Organic Framework Cu₃(btc)₂

The structural stability of a Cu-based metal–organic framework (MOF), subject to different conditions including exposure to ambient air and liquid water, was investigated. A detailed characterization of the substrate was performed using FTIR, XRD, SEM, N₂ adsorption, and TGA. Cu₃(btc)₂ was found to be stable after exposure to ambient air for short periods but undergoes irreversible changes during long-term exposure. These changes are not only manifested in terms of structural modifications as determined by XRD and FTIR data but also suggested by an altered morphology as observed by electron microscopy. Slow hydrolysis reactions initially involving a weakening of the metal–ligand bonds are identified as the main mechanism for the irreversible degradation of the Cu₃(btc)₂. The length of exposure and the amount of water were found to be the key parameters that determine the stability of the MOF

Revisiting the Aqueous Solutions of Dimethyl Sulfoxide by Spectroscopy in the Mid- and Near-Infrared: Experiments and Car–Parrinello Simulations

The infrared and near-infrared spectra of the aqueous solutions of dimethyl sulfoxide are revisited. Experimental and computational vibrational spectra are analyzed and compared. The latter are determined as the Fourier transformation of the velocity autocorrelation function of data obtained from Car–Parrinello molecular dynamics simulations. The experimental absorption spectra are deconvolved, and the excess spectra are determined. The two-dimensional excess contour plot provides a means of visualizing and identifying spectral regions and concentration ranges exhibiting nonideal behavior. In the binary mixtures, the analysis of the SO stretching band provides a semiquantitative picture of the formation and dissociation of hydrogen-bonded DMSO–water complexes. A maximum concentration of these clusters is found in the equimolar mixture. At high DMSO concentration, the formation of rather stable 3DMSO:1water complexes is suggested. The formation of 1DMSO:2water clusters, in which the water oxygen atoms interact with the sulfoxide methyl groups, is proposed as a possible reason for the marked depression of the freezing temperature at the eutectic point

Graphene Oxide Supercapacitors: A Computer Simulation Study

Supercapacitors with graphene oxide (GO) electrodes in a parallel plate configuration are studied with molecular dynamics (MD) simulations. The full range of electrode oxidation from 0% (pure graphene) to 100% (fully oxidized GO) is investigated by decorating the graphene surface with hydroxyl groups. The ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI⁺BF₄⁻) is examined as an electrolyte. Capacitance tends to decrease with increasing electrode oxidation, in agreement with several recent measurements. This trend is attributed to the decreasing reorganization ability of ions near the electrode and a widening gap in the double layer structures as the density of hydroxyl groups on the electrode surface increases

Computer Simulation Study of Graphene Oxide Supercapacitors: Charge Screening Mechanism

Graphene oxide supercapacitors in the parallel plate configuration are studied via molecular dynamics (MD) simulations. The full range of electrode oxidation from 0 to 100% is examined by oxidizing the graphene surface with hydroxyl groups. Two different electrolytes, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI⁺BF₄^–) as an ionic liquid and its 1.3 M solution in acetonitrile as an organic electrolyte, are considered. While the area-specific capacitance tends to decrease with increasing electrode oxidation for both electrolytes, its details show interesting differences between the organic electrolyte and ionic liquid, including the extent of decrease. For detailed insight into these differences, the screening mechanisms of electrode charges by electrolytes and their variations with electrode oxidation are analyzed with special attention paid to the aspects shared by and the contrasts between the organic electrolyte and ionic liquid