Interaction of Water Highly Diluted in 1-Alkyl-3-methyl Imidazolium Ionic Liquids with the PF6− and BF4− Anions

Flipping Water Orientation at the Surface of Water-in-Salt and Salt-in-Water Solutions

Salt-in-water and water-in-salt mixtures are promising for battery applications and fine-tuning of room-temperature ionic liquid (RTIL) properties. Although critical processes take place at interfaces of these systems, including charge transfer and heterogeneous catalytic reactions, the microscopic interfacial structures remain unclear. Here, we apply heterodyne-detected sum-frequency generation spectroscopy to aqueous solutions of imidazolium-based RTILs to unveil the microscopic structure of the interfaces of these solutions with air. Our results show that, under salt-in-water conditions, the orientation of the OH group hydrogen-bonded to the other water molecules flips from the OH group pointing down into the liquid for pure water to up due to the accumulation of anions in the cation-rich interfacial region. However, under the water-in-salt condition, the interfacial water molecules are confined by RTIL, and their orientation is down. Details of the water organization depend critically on the alkyl chain length of the imidazolium cation. Our results demonstrate that the surface structure can be tuned by altering the molecular structure and concentration of the RTIL.

Probing the Effects of Size and Charge on the Monohydration and Dihydration of SiF5- and SiF62- via Comparisons with BF4- and PF6. J Phys Chem A 2024;128:5637-5645. [PMID: 38976798 DOI: 10.1021/acs.jpca.4c03430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

This study systematically examines the interactions of the trigonal bipyramidal silicon pentafluoride and octahedral silicon hexafluoride anions with either one or two water molecules, (SiF5-(H2O)n and SiF62-(H2O)n, respectively, where n = 1, 2). Full geometry optimizations and subsequent harmonic vibrational frequency computations are performed using the CCSD(T) ab initio method with a triple-ζ correlation consistent basis set augmented with diffuse functions on all non-hydrogen atoms (cc-pVTZ for H and aug-cc-pVTZ for Si, O, and F; denoted as haTZ). Two monohydrate and six dihydrate minima have been identified for the SiF5-(H2O)n systems, whereas one monohydrate and five dihydrate minima have been identified for the SiF62-(H2O)n systems. Both monohydrated anions have a minimum in which the water molecule adopts a symmetric double ionic hydrogen bond (DIHB) motif with C2v symmetry. However, a second unique monohydrate minimum has been identified for SiF5- in which the water molecule adopts an asymmetric DIHB motif along the edge of the trigonal bipyramidal anion between one axial and one equatorial F atom. This Cs structure is more than 2 kcal mol-1 lower in energy than the C2v local minimum at the CCSD(T)/haTZ level of theory. While the interactions between the solvent and ionic solute are quite strong for the monohydrated anions (electronic dissociation energies of ≈12 and ≈24 kcal mol-1 for the SiF5-(H2O)1 and SiF62-(H2O)1 global minima, respectively), these values are nearly perfectly doubled for the dihydrates, with the lowest-energy SiF5-(H2O)2 and SiF62-(H2O)2 minima exhibiting dissociation energies of ≈24 and ≈47 kcal mol-1, respectively. Structures that form hydrogen bonds between the solvating water molecules also exhibit the largest shifts in the harmonic OH stretching frequencies for the waters of hydration. These shifts can exceed -100 cm-1 for the SiF5-(H2O)2 minimum and -300 cm-1 for the SiF62-(H2O)2 minimum relative to an isolated H2O molecule at the CCSD(T)/haTZ level of theory. This work also corrects the OH stretching frequency shifts for two dihydrate minima of PF6- that were previously erroneously reported ( J. Phys. Chem. A 2020, 124, 8744-8752, DOI: 10.1021/acs.jpca.0c06466).

Competition between Solvent···Solvent and Solvent···Solute Interactions in the Microhydration of the Tetrafluoroborate Anion, BF4-(H2O)n=1,2,3,4

This study systematically examines the interactions of the tetrafluoroborate anion (BF4-) with up to four water molecules (BF4-(H2O)n=1,2,3,4). Full geometry optimizations and subsequent harmonic vibrational frequency computations are performed using a variety of density functional theory (DFT) methods (B3LYP, B3LYP-D3BJ, and M06-2X) and the MP2 ab initio method with a triple-ζ correlation consistent basis set augmented with diffuse functions on all non-hydrogen atoms (cc-pVTZ for H and aug-cc-pVTZ for B, O, and F; denoted as haTZ). Optimized structures and harmonic vibrational frequencies were also obtained with the CCSD(T) ab initio method and the haTZ basis set for the mono- and dihydrate (n = 1, 2) structures. The 2-body:Many-body (2b:Mb) technique, in which CCSD(T) computations capture the 1- and 2-body contributions to the interactions and MP2 computations recover all higher-order contributions, was used to extend these demanding computations to the tri- and tetrahydrate (n = 3, 4) systems. Four, five, and eight new stationary points have been identified for the di-, tri-, and tetrahydrate systems, respectively. The global minimum of the monohydrate adopts a symmetric double ionic hydrogen bond motif with C2v symmetry and an electronic dissociation energy of 13.17 kcal mol-1 at the CCSD(T)/haTZ level of theory. This strong solvent···solute interaction, however, competes with solute···solute interactions in the lowest-energy BF4-(H2O)n=2,3,4 minima that are not seen in the other di-, tri-, or tetrahydrate minima. The latter interactions help increase the 2b:Mb dissociation energies to more than 26, 41, and 51 kcal mol-1 for n = 2, 3, and 4, respectively. Structures that form hydrogen bonds between the solvating water molecules also exhibit the largest shifts in the harmonic OH stretching frequencies for the waters of hydration. These shifts can exceed -280 cm-1 relative to an isolated H2O molecule at the 2b:Mb/haTZ level of theory.

Density Functional Method Study on the Cooperativity of Intermolecular H-bonding and π-π+ Stacking Interactions in Thymine-[Cnmim]Br (n = 2, 4, 6, 8, 10) Microhydrates

The exploration of the ionic liquids’ mechanism of action on nucleobase’s structure and properties is still limited. In this work, the binding model of the 1-alkyl-3-methylimidazolium bromide ([Cnmim]Br, n = 2, 4, 6, 8, 10) ionic liquids to the thymine (T) was studied in a water environment (PCM) and a microhydrated surroundings (PCM + wH2O). Geometries of the mono-, di-, tri-, and tetra-ionic thymine (T-wH2O-y[Cnmim]+-xBr−, w = 5~1 and x + y = 0~4) complexes were optimized at the M06-2X/6-311++G(2d, p) level. The IR and UV-Vis spectra, QTAIM, and NBO analysis for the most stable T-4H2O-Br−-1, T-3H2O-[Cnmim]+-Br−-1, T-2H2O-[Cnmim]+-2Br−-1, and T-1H2O-2[Cnmim]+-2Br−-1 hydrates were presented in great detail. The results show that the order of the arrangement stability of thymine with the cations (T-[Cnmim]+) by PCM is stacking > perpendicular > coplanar, and with the anion (T-Br−) is front > top. The stability order for the different microhydrates is following T-5H2O-1 < T-4H2O-Br−-1 < T-3H2O-[Cnmim]+-Br−-1 < T-2H2O-[Cnmim]+-2Br−-1 < T-1H2O-2[Cnmim]+-2Br−-1. A good linear relationship between binding EB values and the increasing number (x + y) of ions has been found, which indicates that the cooperativity of interactions for the H-bonding and π-π+ stacking is varying incrementally in the growing ionic clusters. The stacking model between thymine and [Cnmim]+ cations is accompanied by weaker hydrogen bonds which are always much less favorable than those in T-xBr− complexes; the same trend holds when the clusters in size grow and the length of alkyl chains in the imidazolium cations increase. QTAIM and NBO analytical methods support the existence of mutually reinforcing hydrogen bonds and π-π cooperativity in the systems.

OH Stretching and Libration Bands of Solitary Water in Ionic Liquids and Dipolar Solvents Share a Single Dependence on Solvent Polarity

Ionic liquids are an emerging class of materials which are finding application in a variety of technologically important areas. Because of their hydrophilic character, at least a small concentration of water is often present when ionic liquids are used in practical applications. This study employs infrared spectroscopy in the OH stretching and libration regions together with DFT calculations to better characterize the state of dilute water in ionic liquids. Water mole fractions (x_w ∼ 0.1) are chosen such that nearly all water occurs in monomeric form and spectra probe the solvation structure and dynamics of solitary water molecules. New data are reported for a series of 1-ethyl-3-methylimidazolium liquids [Im₂₁][X] with X^- = (C₂F₅)₃F₃P^-, (CF₃SO₂)₂N^-, BF₄^-, B(CN)₄^-, CF₃SO₃^-, C₂H₅SO₄^-, NO₃^-, SCN^-, and CH₃CO₂^-, as well as for the two 1-hexyl-3-methylimidazolium liquids [Im₆₁][Cl] and [Im₆₁][I]. For comparison, spectra are also recorded in a variety of dipolar solvents, and much of the available literature data are summarized, providing a comprehensive perspective on monomeric water in homogeneous solution. Most prior studies of dilute water in ionic liquids interpreted OH stretching spectra only in terms of water being specifically bonded to two anions in A^-···H-O-H···A^- type solvates. The more detailed analysis presented here indicates the additional presence of asymmetrically solvated water, which in some cases includes both singly solvated (A^-···H-O-H) and more subtle forms of asymmetric solvation. The same pattern of solvation also pertains to dipolar solvents capable of accepting hydrogen bonds from water. No clear distinction is found between OH spectra in high-polarity conventional solvents and ionic liquids. In all solvents, OH frequencies are strongly correlated to measures of solvent basicity or hydrogen bond accepting ability. Far-infrared spectra of the water libration band also show common trends in ionic and dipolar solvents. Despite the different character of the libration and OH modes, the frequencies of these vibrations show virtually the same solvent dependence (apart from sign) except in weakly polar or nonpolar solvents.

Interfacial Water and Microheterogeneity in Aqueous Solutions of Ionic Liquids

In this work, aqueous solutions of two prototypical ionic liquids (ILs), [BMIM][BF4] and [BMIM][TfO], were investigated by UV Raman spectroscopy and small-angle neutron scattering (SANS) in the water-rich domain, where strong heterogeneities at mesoscopic length scales (microheterogeneity) were expected. Analyzing Raman data by a differential method, the solute-correlated (SC) spectrum was extracted from the OH stretching profiles, emphasizing specific hydration features of the anions. SC-UV Raman spectra pointed out the molecular structuring of the interfacial water in these microheterogeneous IL/water mixtures, in which IL aggregates coexist with bulk water domains. The organization of the interfacial water differs for the [BMIM][BF4] and [BMIM][TfO] solutions, being affected by specific anion-water interactions. In particular, in the case of [BMIM][BF4], which forms weaker H-bonds with water, the aggregation properties clearly depend on concentration, as reflected by local changes in the interfacial water. On the other hand, stronger water-anion hydrogen bonds and more persistent hydration layers were observed for [BMIM][TfO], which likely prevent changes in IL aggregates. The modeling of SANS profiles, extended to [BPy][BF4] and [BPy][TfO], evidences the occurrence of significant concentration fluctuations for all of the systems: this appears as a rather general phenomenon that can be ascribed to the presence of IL aggregation, mainly induced by (cation-driven) hydrophobic interactions. Nevertheless, larger concentration fluctuations were observed for [BMIM][BF4], suggesting that anion-water interactions are relevant in modulating the microheterogeneity of the mixture.

A mechanical, electrical dual autonomous self-healing multifunctional composite hydrogel

The versatile properties make hydrogels a potential multipurpose material that finds wide applications. However, the preparation of multipurpose hydrogels is very challenging. Here, we report a method based on free radical reaction and composite mechanisms to prepare mechanical and electrical self-healing multifunctional hydrogels. In this study, the introduction of imidazolium salt ionic liquids and glycerol in the hydrogel system endows the gels with good antibacterial, conductive, and adhesive properties and excellent antifreeze properties. The testing results show that the as-prepared hydrogel has stable mechanical and electrical properties even under the extremely cold condition of -50°C after self-healing. Moreover, the active esters formed in the dynamic radical reaction have better reducibility, thus further investing the as-prepared hydrogel with high antioxidant activity. The application results show that these comprehensive properties make such hydrogel system very useful in wound repair and wearable strain sensors.

Targeted modifications in ionic liquids - from understanding to design

Ionic liquids are extremely versatile and continue to find new applications in academia as well as industry. This versatility is rooted in the manifold of possible ion types, ion combinations, and ion variations. However, to fully exploit this versatility, it is imperative to understand how the properties of ionic liquids arise from their constituents. In this work, we discuss targeted modifications as a powerful tool to provide understanding and to enable design. A 'targeted modification' is a deliberate change in the structure of an ionic liquid. This includes chemical changes in an experiment as well as changes to the parameterisation in a computer simulation. In any case, such a change must be purposeful to isolate what is of interest, studying, as far as is possible, only one concept at a time. The concepts can then be used as design elements. However, it is often found that several design elements interact with each other - sometimes synergistically, and other times antagonistically. Targeted modifications are a systematic way of navigating these overlaps. We hope this paper shows that understanding ionic liquids requires experimentalists and theoreticians to join forces and provides a tool to tackle the difficult transition from understanding to design.

Competition between Solvent-Solvent and Solvent-Solute Interactions in the Microhydration of the Hexafluorophosphate Anion, PF6-(H2O)n=1,2

This study systematically examines the interactions of the hexafluorophosphate anion (PF₆^-) with one or two solvent water molecules (PF₆^-(H₂O)_n where n = 1, 2). Full geometry optimizations and subsequent harmonic vibrational frequency computations are performed on each stationary point using a variety of common density functional theory methods (B3LYP, B3LYP-D3, M06-2X, and ωB97XD) and the MP2 and CCSD(T) ab initio methods with a triple-ζ correlation consistent basis set augmented with diffuse functions on all non-hydrogen atoms (cc-pVTZ for H and aug-cc-pVTZ for P, O, and F; denoted as haTZ). Five new stationary points of PF₆^-(H₂O)₂ have been identified, one of which has an electronic energy of approximately 2 kcal mol^-1 lower than the only other dihydrate structure reported for this system. The CCSD(T) computations also reveal that the detailed interactions between PF₆^- and H₂O can be quite difficult to model reliably, with some methods struggling to correctly characterize stationary points for n = 1 or accurately reproduce the vibrational frequency shifts induced by the formation of the hydrated complex. Although the interactions between the solvent and ionic solute are quite strong (CCSD(T) electronic dissociation energy ≈10 kcal mol^-1 for the monohydrate minimum), the solvent-solvent interactions in the lowest-energy PF₆^-(H₂O)₂ minimum give rise to appreciable cooperative effects not observed in the other dihydrate minima. In addition, this newly identified structure exhibits the largest frequency shifts in the OH stretching vibrations for the waters of hydration (with Δω exceeding -100 cm^-1 relative to the values for an isolated H₂O molecule).

Microstructural and Dynamical Heterogeneities in Ionic Liquids

Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.

Distance Angle Descriptors of the Interionic and Ion-Solvent Interactions in Imidazolium-Based Ionic Liquid Mixtures with Aprotic Solvents: A Molecular Dynamics Simulation Study

The aim of this paper is to quantify the changes of the interionic and ion-solvent interactions in mixtures of imidazolium-based ionic liquids, having tetrafluoroborate (BmimBF₄), hexafluorophosphate (BmimPF₆), trifluoromethylsulfonate (BmimTFO), or bis(trifluoromethanesulfonyl)imide (BmimTFSI), anions, and polar aprotic molecular solvents, such as acetonitrile (AN), γ-butyrolactone (GBL), and propylene carbonate (PC). For this purpose, we calculate, using the nearest-neighbor approach, the average distance between the imidazolium ring H atom in positions 2, 4, and 5 (H^2,4,5) and the nearest high-electronegativity atom of the solvent or anion (X) as distance descriptors, and the mean angle formed by the C^2,4,5-H^2,4,5 bond and the H^2,4,5···X axis around the H^2,4,5 atom as angular descriptors of the cation-anion and cation-solvent interactions around the ring C-H groups. The behavior of these descriptors as a function of the ionic liquid mole fraction is analyzed in detail. The obtained results show that the extent of the change of these descriptors with respect to their values in the neat ionic liquid depends both on the nature of the anion and on the mixture composition. Thus, in the case of the mixtures of the molecular solvents with BmimBF₄ and BmimTFO, a small change of the distance and a drastic increase of the angular descriptor corresponding to the cation-anion interactions are observed with decreasing mole fraction of the ionic liquid, indicating that the anion moves from the above/below position (with respect to the imidazolium ring plane) to a position that is nearly linearly aligned with the C²-H² bond and hinders the possible interaction between the C²-H² group and the solvent molecules. On the other hand, in the case of mixtures of BmimTFSI and BmimPF₆ with the molecular solvents, both the observed increase of the distance descriptor and the slight change of the angular descriptor with decreasing ionic liquid mole fraction are compatible with the direct interactions of the solvent with the C²-H² group. The behavior of these descriptors is correlated with the experimentally observed ¹H chemical shift of the C²-H² group and the red shift of the C²-H² vibrational mode, particularly at low ionic liquid mole fractions. The present results are thus of great help in interpreting these experimental observations.

Vibration Spectral Dynamics of Weakly Coordinating Water Molecules near an Anion: FPMD Simulations of an Aqueous Solution of Tetrafluoroborate

The extent to which the ions affect the nearby water molecules will decide the structure-making or breaking nature of those ions in aqueous solutions. The effects of a weakly coordinating anion on the structure, dynamics, and vibrational properties of water molecules are not so significant as compared to an anion capable of making strong ion-water hydrogen bonds. The present work deals with the first-principles molecular dynamics study of an aqueous solution of such a weakly coordinating anion, tetrafluoroborate (BF₄^-), using dispersion-corrected DFT-based first-principles molecular dynamics (FPMD) simulations. Various structural, dynamical, and spectral properties, such as radial distribution functions (RDFs), rotational dynamics, vibrational density of states (VDOS), hydrogen bond as well as dangling OH autocorrelation functions, and residence dynamics, were calculated to investigate the effects of the anion on nearby water molecules. The process of spectral diffusion was assessed through a time series wavelet transformation of trajectories obtained from FPMD simulations. The first ion-water solvation shell extends up to 5.5 Å, containing around 20 water molecules. The lifetime of the ion-water hydrogen bond is found to be 1.19 ps, whereas the water-water hydrogen bond lifetime is found to be 1.13 ps. Inside the solvation shell, the persistence time of dangling OH chromophores and the average frequency of OH modes inside the solvation shell are found to be more compared to bulk. Three time scales are found for solvation shell OH modes from the frequency-frequency correlation function. A very short time scale is found for the intact ion-water interaction; the short time scale is for the ion-water hydrogen bond, and the long time scale is for escape dynamics of water molecules from the ion solvation shell. From the mean squared displacement, it is found that solvation water molecules diffuse slower than the bulk. However, solvation shell water molecules show faster relaxation from the analysis of rotational anisotropy. Within the longer time scale of spectral diffusion, this process (which is related to various dynamics of the molecules) is not yet complete, as compared to fast anisotropic decay. This fact is similar to the experimental finding of spectral diffusion and anisotropy time scales in the aqueous solution of borohydride anion. The calculated results are also compared with available experimental data wherever possible.

How Meaningful Is the Halogen Bonding in 1-Ethyl-3-methyl Imidazolium-Based Ionic Liquids for CO2 Capture?

We report on several parameters that can be used to describe the 1-ethyl-3-methyl-4,5-(X₂)imidazolium cations (where X = H, Br, and I) within the Canongia-Lopez and Padua Force Field (CL&P) framework. Geometrical parameters like intramolecular distances and radial distribution functions are close to the experimental structure. Density values obtained with our force field are within the expected ones from CL&P calculations in related systems. This information is used to simulate through molecular dynamics the solubilization of CO₂ by these ILs. For pure ILs, the addition of halides in position 4 and 5 promotes an enhanced hydrogen bond interaction at position 2 with the oxygen atoms in the anion. It is found that CO₂ should be in the interstices of the anion-cation 3D network with longer distances than those found in other reports at ab initio levels, suggesting that halogen bond, if present, may be not the driving force interaction in these systems. Therefore, it seems that CO₂ interacts linearly via an oxygen atom with the cation and with the anion through a π-stacking or hydrogen-bonded fashions. Solvation enthalpies compare well with the experimental data, thereby suggesting that halogenated ILs dissolve more efficiently in CO₂ than C₂C₁Im⁺ derivatives. This result suggests that halogenated ILs can be considered as reliable candidates for CO₂ capture.

Ion pair and solvation dynamics of [Bmim][BF4 ] + water system

In this work, 1-butyl-3-methylimidazolium tetrafluoroborate/water mixtures were analysed over the whole water composition (x_w ) in order to study the rotational and translational behaviour of the ions. We employed a multinuclear NMR approach to determine anion/cation/water diffusion coefficients and longitudinal relaxation rates at different water content. In neat ionic liquids (IL), the cation diffuses faster than the anion, and at low x_w , anions and cations share almost the same diffusion coefficient, but above a critical water concentration, the anion begins to diffuse faster than the cation. We identified this composition as approximately 10% x_w where the ions share the same diffusion coefficient. We found that the water at this composition seems to have a much more dramatic effect in the rotational diffusion of the anion that decreases substantially and approaches that of the anion in the diluted IL. Translational and rotational dynamics of the ions suggest that water is first incorporated in pockets in the nanostructure of the IL allowing the ions to maintain most of the cation/anion interactions present in neat IL but already disrupting some anion/cation interactions due to preferential interaction with the anion. HOESY and NOESY data show that water displays contacts both with the cation and the anion in a positive NOE regime in contrary to the negative regime found for the cation/anion and cation/cation cross-relaxation. This is in accordance with the high relative diffusion coefficient of water and suggests that water molecules can exchange between preferential location sites that allow water to maintain contacts both with the anion and cation.

The local structure in the BmimPF6/acetonitrile mixture: the charge distribution effect

The effect of the charge distribution on the local structure in the binary mixture of 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆) ionic liquid and acetonitrile is investigated over the entire composition range.

Vibrational Spectroscopy of Ionic Liquids

Vibrational spectroscopy has continued use as a powerful tool to characterize ionic liquids since the literature on room temperature molten salts experienced the rapid increase in number of publications in the 1990's. In the past years, infrared (IR) and Raman spectroscopies have provided insights on ionic interactions and the resulting liquid structure in ionic liquids. A large body of information is now available concerning vibrational spectra of ionic liquids made of many different combinations of anions and cations, but reviews on this literature are scarce. This review is an attempt at filling this gap. Some basic care needed while recording IR or Raman spectra of ionic liquids is explained. We have reviewed the conceptual basis of theoretical frameworks which have been used to interpret vibrational spectra of ionic liquids, helping the reader to distinguish the scope of application of different methods of calculation. Vibrational frequencies observed in IR and Raman spectra of ionic liquids based on different anions and cations are discussed and eventual disagreements between different sources are critically reviewed. The aim is that the reader can use this information while assigning vibrational spectra of an ionic liquid containing another particular combination of anions and cations. Different applications of IR and Raman spectroscopies are given for both pure ionic liquids and solutions. Further issues addressed in this review are the intermolecular vibrations that are more directly probed by the low-frequency range of IR and Raman spectra and the applications of vibrational spectroscopy in studying phase transitions of ionic liquids.

Electrochemistry of single droplets of inverse (water-in-oil) emulsions

Single water droplet electrochemistry investigated for the first time, reveals the biphasic kinetics of ion transfer within water-in-oil emulsions.

Non-covalent interactions in ionic liquid ion pairs and ion pair dimers: a quantum chemical calculation analysis

Weak non-covalent interactions were studied by means of QTAIM and NCI approaches in ion pairs and ion pair dimers of 1-alkyl-3-methylimidazolium cations coupled with perfluorinated anions.

Residual water in ionic liquids: clustered or dissociated?

A rigorous statistical thermodynamic theory clarifies how residual water molecules interact in three dialkylimidazolium ionic liquids.

Ionic Liquid Doped β Lactoglobulin as Template for Nanoclusters of Nickel Oxide

In this work, Langmuir films of organized assemblies of β-lactoglobulin (βLG) with 1-ethyl-3-methyl imidazolium ethyl sulfate (IL-emes) have been characterized at air/water interface using surface pressure-specific area isotherms and dilational rheology. The protein in the IL-mediated assembly shows excellent packing at the interface and is stable as seen in circular dichroic spectroscopy. These spread films on nickel chloride were transferred as Langmuir–Schaffer films of βLG and βLG+IL-emes and used as template for designing nanoclusters of nickel oxide. The nanoclusters have been characterized using transmission electron microscopy (TEM) and powder XRD. While pure protein template gives needle-shaped structures, the IL-mediated template gives spherical shapes of hexagonal nickel oxide in the range 30 nm to 40 nm. Presence of ionic liquid seems to slow down the growth of the cluster and also prevents aggregation of the clusters.

Molecular dynamics investigation of the vibrational spectroscopy of isolated water in an ionic liquid

Experimental studies examining the structure and dynamics of water in ionic liquids (ILs) have revealed local ion rearrangements that occur an order of magnitude faster than complete randomization of the liquid structure. Simulations of an isolated water molecule embedded in 1-butyl-3-methyl imidazolium hexafluorophosphate, [bmim][PF6], were performed to shed insight into the nature of these coupled water-ion dynamics. The theoretical calculations of the spectral diffusion dynamics and the infrared absorption spectra of the OD stretch of isolated HOD in [bmim][PF6] agree well with experiment. The infrared absorption line shape of the OD stretch is narrower and blue-shifted in the IL compared to those in aqueous solution. Decomposition of the OD frequency time correlation function revealed that translational motions of the anions dominate the spectral diffusion dynamics.