Autocatalytic Synthesis of Bifluoride Ionic Liquids by SuFEx Click Chemistry.

Ionic liquids with bifluoride anions possess properties such as high conductivity, wide electrochemical windows, and low viscosity that make them attractive materials for various electrochemical devices. However, owing to the lack of reliable synthetic routes, bifluoride-based ionic liquids have seldom been explored. Herein, an autocatalytic strategy for the HF-free synthesis of bifluoride-based sulfonamide ionic liquids based on the sulfur(VI) fluoride exchange (SuFEx) reaction is reported. This reaction requires no chromatographic purification, and yields are quantitative. The thermophysical properties (phase transition behavior and decomposition temperature) and electrochemical stabilities of the resulting products were studied. The products with alkyl, aryl, and perfluoroalkyl side chains exhibited extraordinarily wide electrochemical windows (up to 6.0 V) with reproducible results among multiple replicate measurements.

CO2 capture in ionic liquid 1-alkyl-3-methylimidazolium acetate: a concerted mechanism without carbene.

Ionic liquids (ILs) provide a promising medium for CO2 capture. Recently, the family of ILs comprising imidazolium-based cations and acetate anions, such as 1-ethyl-3-methylimidazolium acetate (EMI+OAc-), has been found to react with CO2 and form carboxylate compounds. N-Heterocyclic carbene (NHC) is widely assumed to be responsible by directly reacting with CO2 though NHC has not been detected in these ILs. Herein, a computational analysis of CO2 capture in EMI+OAc- is presented. Quantum chemistry calculations predict that NHC is unstable in a polar environment, suggesting that NHC is not formed in EMI+OAc-. Ab initio molecular dynamics simulations indicate that an EMI+ ion "activated" by the approach of a CO2 molecule can donate its acidic proton to a neighboring OAc- anion and form a carboxylate compound with the CO2 molecule. Analysis of this termolecular process indicates that the EMI+-to-OAc- proton transfer and the formation of 1-ethyl-3-methylimidazolium-2-carboxylate occur essentially concurrently. Based on these findings, a novel concerted mechanism that does not involve NHC is proposed for CO2 capture.

Theoretical study of interactions of a Li(+)(CF3SO2)2N(-) ion pair with CR3(OCR2CR2)nOCR3 (R = H or F).

Interactions of a lithium bis(trifluoromethane sulfonyl)imide (Li(+)Tf2N(-)) ion pair with oligoethers are investigated via density functional theory (DFT). As a model for polymer electrolytes polyethyleneoxide (PEO) and perfluoropolyether (PFPE), CR3(OCR2CR2)n=1-5OCR3 (R = H or F) is considered. Topographical analysis of the molecular electrostatic potential (MESP) is performed to determine preferential binding sites of Li(+). Our study shows that the MESP value near the oxygen sites of the polymer backbone is more negative for PEO than for PFPE. This result indicates that substitution of hydrogen by fluorine in polyethers leads to reduction in Li(+)-polymer interactions, in concert with the experimental ionic conductivity results. S-O stretching vibrations of Tf2N(-) are calculated for the lithium salt in the presence and absence of electrolytes. The blue and red shifts predicted for S-O stretching are further explained by natural bond orbital analysis and molecular electron density topography. The S-O stretching vibrations can be used as a useful tool to understand the ion pair interactions and thus ion transport phenomena in polymer electrolytes.

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.

Ionic Association in CH3-(CH2-CF2) n -CH3(PVDF)-Li+-(CF3SO2)2N- for n = 1, 4: A Computational Approach.

The ionic conductivity of solid polymer electrolytes is governed by the ionic association caused by the polymer···Li+ and the anion···Li+ interactions. We performed the density functional calculation to analyze the molecular interactions in the CH3-(CH2-CF2) n -CH3-Li+-(CF3SO2)2N- for n = 1,4 systems. The gauche conformation is predicted in the lowest energy conformer of pure polymer except for n = 1. The lithium coordination number with the polymer is changed from 3 to 2 in the presence of anion for n = 2, 4 systems. The consequences of the Li+ ion and Li+-(CF3SO2)2N- to the vibrational spectrum are studied to understand the ionic association at the molecular level.

Electronic structure and normal vibrations of the 1-ethyl-3-methylimidazolium ethyl sulfate ion pair.

Electronic and structural properties of the ion pair 1-ethyl-3-methylimidazolium ethyl sulfate are studied using density functional methods. Three locally stable conformers of the ion pair complex are considered to analyze molecular interactions between its cation and anion. Manifestations of these interactions in the vibrational spectra are discussed and compared with experimental IR and Raman spectroscopy data. NBO analysis and difference electron density coupled with molecular electron density topography are used to interpret the frequency shifts of the normal vibrations of the ion pair, compared to the free anion and cation. Excitation energies of low-lying singlet excited states of the conformers are also studied. The density functional theory results are found to be in a reasonable agreement with experimental UV/vis absorption spectra.

Effect of Bulky Anion around the Dication on the Electronic Structure and Normal Frequencies in 1,3-Bis(3-methylimidazolium-1-yl)propane Bis(trifluoromethanesulfonyl)imide Ionic Liquid.

A manifestation of hydrogen bonding between the dication and anions attributed to their relative position of the anions around the cation can influence both the conformational equilibrium and the physical properties of ionic liquids. With this view, we studied the electronic structure and normal frequencies using density functional theory calculations to analyze the hydrogen-bonding interactions in dicationic ionic liquids. The conformers are distinguished based on the hydrogen-bonding sites of the cation and anion. The weak hydrogen bonding between the dication and anions in dication ionic liquids can lead to greater conformational equilibrium compared to the monocation system. Consequences of these interactions for the vibrational spectrum are analyzed to provide an insight into the conformational equilibrium in dicationic ionic liquids at the molecular level.

Molecular interactions in 1-ethyl-3-methylimidazolium acetate ion pair: a density functional study.

The density functional method is used to obtain the molecular structure, electron density topography, and vibrational frequencies of the ion pair 1-ethyl-3-methylimidazolium acetate. Different conformers are simulated on the basis of molecular interactions between the 1-ethyl-3-methylimidazolium cation and acetate anion. The lowest energy conformers exhibit strong C-H...O interionic interactions compared with other conformers. Characteristic vibrational frequencies of the ion pair and their shifts with respect to free ions are analyzed via the natural bond orbitals and difference electron density maps coupled with molecular electron density topology. Theoretically scaled vibrational frequencies are also compared with the spontaneous Raman scattering and attenuated total reflection infrared absorption measurements.

Theoretical Study of Alkylsulfonic Acids: Force-Field Development and Molecular Dynamics Simulations.

Potential model descriptions for alkylsulfonic acids, methanesulfonic, ethanesulfonic, and propanesulfonic acids, are developed based on CHARMM and OPLS parameters and protocols. Thermodynamic, structural, and transport properties of these alkylsulfonic acids, including density, heat of vaporization, radial and spatial distribution functions, hydrogen bond structure, shear viscosity, and translational diffusion coefficients, are examined via molecular dynamics simulations using these potential models. The results are compared with the predictions of ab initio molecular dynamics simulations as well as with available experimental information. A good overall agreement indicates that the force-field descriptions developed here provide a reliable framework to study liquid systems containing alkylsulfonic acids.

Theoretical studies on NMR chemical shifts in azacubanes.

Successive substitution of CH groups of cubane (CH)(8), by isoelectronic nitrogen atoms leads to a class of energy-rich azacubanes (CH)(8-alpha)N(alpha) (with alpha=1-8). In the present work, we systematically investigate how substitution of nitrogen in a cubanoid influence deshielding of carbon and manifest in the chemical shift in NMR spectra calculated using the second order Møller-Plesset (MP2) perturbation level of theory. PMR spectra predict a large downshift of delta(H)=7.9 ppm in heptaazacubane owing to the more number of nitrogen and the stronger C-H...N interactions. These chemical shifts are explained by the net atomic charges derived from the population analysis based on Hirshfeld partitioning scheme.

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.

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.

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.

Electronic structure, molecular electrostatic potential and hydrogen bonding in DMSO-X complexes (X = ethanol, methanol and water).

In the present work, we have studied the electronic structure, molecular electrostatic potential (MEP) and hydrogen bonding in DMSO-ethanol, DMSO-methanol and DMSO-water complexes by employing the MP2 method. Different conformers were simulated on the basis of possible binding sites guided by molecular electrostatic potential topology. The stronger hydrogen bonded interaction lowers the energy of the conformer. Molecular electron density topology and natural bond orbital analysis were used to explain the strength of interactions. Experimental vibrations are also compared with the calculated normal vibrations. Blue shift is predicted for SC vibration in experimental and theoretical spectra as well. Molecular electrostatic potential and topology are used to understand the interaction strength of the conformer.

Theoretical studies on blue versus red shifts in diglyme-M+-X- (M=Li, Na, and K and X=CF3SO3, PF6, and (CF3SO2)2N)).

Ab initio Hartree-Fock calculations have been used to obtain the electronic structure and the frequencies of normal vibrations in the 1:1:1 solid polymer electrolytes CH3(OCH2CH2)2OCH3-M+-X- (M=Li, Na, and K and X=CF3SO3, PF6, (CF3SO2)2N). These calculations predict stronger binding for the lithium ion toward the ether oxygens of diglyme in these electrolytes. Consequences of diglyme-MX interactions to the infrared spectra have been presented. Natural bond analysis and the electron density topography have been used to explain the direction of the frequency shifts of the normal vibrations of the anions in these electrolytes.

Electronic structure and normal vibrations of CH3(OCH2CH2)nOCH3-M+-CF3SO3- (n = 2-4, M = Li, Na, and K).

Electronic structure and the vibrational frequencies of CH(3)(OCH(2)CH(2))(n)OCH(3)-M(+)-CF(3)SO(3)(-) (n = 2-4, M = Li, Na, and K) complexes have been derived from ab initio Hartree-Fock calculations. The metal ion shows varying coordination from 5 to 7 in these complexes. In tetraglyme-lithium triflate, Li(+) binds to one of the oxygens of CF(3)SO(3)(-) (triflate or Tf(-)) unlike for potassium or sodium ions, which possess bidentate coordination. Structures of glyme-MTf complexes thus derived agree well with those determined from X-ray diffraction experiments. The metal ion binds more strongly to ether oxygens of tetraglyme than its di- or triglyme analogues and engenders contraction of SO (for oxygens binding to metal ion) bonds with consequent frequency upshift for the corresponding vibration in the complex relative to those in the free MTf ion pairs. Complexation of the diglyme with LiTf engenders the largest downshift (91 cm(-1)) for the SO(2) stretching vibration of the free anion, which suggests stronger binding of lithium to the diglyme than the tri- (79 cm(-1)) or tetraglyme (70 cm(-1)). A frequency shift in the opposite direction for the SO (where oxygens do not coordinate to the metal) and CF(3) stretchings, which stems from the ion-polymer and anion-ion interactions, has been noticed. These frequency shifts have been analyzed using natural bond orbital analysis and difference electron density maps coupled with molecular electron density topography.

Molecular electrostatic potentials and electron densities in nitroazacubanes.

Successive introduction of nitrogen atoms in the cubyl corners instead of C-NO2 groups of octanitrocubane (CNO2)8, the most powerful explosives known to date, leads to a class of energy-rich compounds known as nitroazacubanes. In present work the ab initio Hartree-Fock and hybrid density functional calculations have been carried out on the possible conformers of (CNO2)(8-alpha)Nalpha (with alpha=0-8), nitroazacubanes. The charge distributions in these systems have been derived using the topography of the molecular electrostatic potential and electron density. Molecular electrostatic potential investigations reveal that of different nitroazacubane conformers, the electron-rich regions around nitro oxygens of the lowest energy conformer having face opposite nitrogen atoms within a cube are more delocalized. These conformers are predicted to have the largest difference of the energies of the highest occupied molecular orbital and lowest unoccupied molecular orbital relative to the other conformers. The dipole moments of nitroazacubanes are dependent on the nitrogen sites within a cube, caused by the resultant of C-N bond moments and nearly insensitive to position of the NO2 groups. The lowest frequency vibration (522 cm(-1)) suggests octa-azacubane having robust structure in the nitroazacubane series. Substitution of nitrogen atom instead of C-NO2 group leads to increase in electron density at the bond critical point of the X-N (X=C or N) bonds in a cube. The heats of formation of different nitroazacubanes were calculated by using the isodesmic reaction approach. The present calculation has shown that for the di- though hexanitroazacubanes the most destabilized conformer possess largest dipole moment and the heat of formation as well. A linear correlation of the electron density at the bond critical point of X-N bonds and the heat of formation has been obtained.