Dual effects of dimethylsulfoxide on cellulose solvating ability of 1-allyl-3-methylimidazolium chloride

Polar aprotic solvents are considered to act as cosolvents with ionic liquids (ILs) for cellulose, strengthening the solvating ability of ILs by improving their cellulose solvating kinetics without influencing the solubility of cellulose in ILs. In this work, it was found that dimethylsulfoxide (DMSO) at low concentration improves the cellulose solvating ability of [AMIM][Cl], but weakens it at high concentration. To clarify the mechanism of these dual effects of DMSO on the cellulose solvating ability of [AMIM][Cl], the [AMIM][Cl]/DMSO system was investigated using excess infrared spectroscopy, nuclear magnetic resonance (NMR) T ₂ relaxometry, ¹H NMR, ³⁵Cl NMR, and dynamic light scattering. The results indicate that the tight association between the cation and anion in the [AMIM][Cl] network is loosened at low DMSO concentration. As a result, mass transport is accelerated due to the enhanced dynamics of [AMIM][Cl], promoting the cellulose solvating kinetics of [AMIM][Cl]. However, ion clusters of [AMIM][Cl] start to form when the molar fraction of DMSO (x _DMSO) exceeds 0.5. The hydrogen bonds between cations and anions in the ion clusters become much stronger than in pure [AMIM][Cl], leading to decreased ability of [AMIM][Cl] to form hydrogen bonds with cellulose and thus decreased cellulose solubility in the [AMIM][Cl]/DMSO mixture.     

Aqueous interfaces with hydrophobic room-temperature ionic liquids: a molecular dynamics study

We report a molecular dynamics study of the interface between water and (macroscopically) water-immiscible room-temperature ionic liquids "ILs", composed of PF6(-) anions and butyl- versus octyl-substituted methylimidazolium+ cations (noted BMI+ and OMI+). Because the parameters used to simulate the pure ILs were found to exaggerate the water/IL mixing, they have been modified by scaling down the atomic charges, leading to better agreement with the experiment. The comparison of [OMI][PF6] versus [BMI][PF6] ILs demonstrates the importance of the N-alkyl substituent on the extent of solvent mixing and on the nature of the interface. With the most hydrophobic [OMI][PF6] liquid, the "bulk" IL phase is dryer than with the [BMI][PF6] liquid. At the interface, the OMI+ cations retain direct contacts with the bulk IL, whereas the more hydrophilic PF6(-) anions gradually dilute in the local water micro-environment and are thus isolated from the "bulk" IL. The interfacial OMI+ cations are ordered with their imidazolium moiety pointing toward the aqueous side and their octyl chains toward the IL side of the interface. With the [BMI][PF6] liquid, the system gradually evolves from an IL-rich to a water-rich medium, leading to an ill-defined interfacial domain with high intersolvent mixing. As a result, the BMI+ cations are isotropically oriented "at the interface". Because the imidazolium cations are more hydrophobic than the PF6(-) anions, the charge distribution at the interface is heterogeneous, leading to a positive electrostatic potential at the interface with the two studied ILs. Mixing-demixing simulations on [BMI][PF6]/water mixtures are also reported, comparing Ewald versus reaction field treatments of electrostatics. Phase separation is very slow (at least 30 ns), in marked contrast with mixtures involving classical organic liquids, which separate in less than 0.5 ns at the microscopic level. The results allow us to better understand the specificity of the aqueous interfaces with hydrophobic ionic liquids, compared with classical organic solvents, which has important implications as far as the mechanism of liquid-liquid ion extraction is concerned.     

Thermodynamic studies of ionic interactions in aqueous solutions of imidazolium-based ionic liquids [Emim][Br] and [Bmim][Cl

Experimental measurements of density at different temperatures ranging from 293.15 to 313.15 K, the speed of sound and osmotic coefficients at 298.15 K for aqueous solution of 1-ethyl-3-methylimidazolium bromide ([Emim][Br]), and osmotic coefficients at 298.15 K for aqueous solutions of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) in the dilute concentration region are taken. The data are used to obtain compressibilities, expansivity, apparent and limiting molar properties, internal pressure, activity, and activity coefficients for [Emim][Br] in aqueous solutions. Experimental activity coefficient data are compared with that obtained from Debye-Hückel and Pitzer models. The activity data are further used to obtain the hydration number and the osmotic second virial coefficients of ionic liquids. Partial molar entropies of [Bmim][Cl] are also obtained using the free-energy and enthalpy data. The distance of the closest approach of ions is estimated using the activity data for ILs in aqueous solutions and is compared with that of X-ray data analysis in the solid phase. The measured data show that the concentration dependence for aqueous solutions of [Emim][Br] can be accounted for in terms of the hydrophobic hydration of ions and that this IL exhibits Coulombic interactions as well as hydrophobic hydration for both the cations and anions. The small hydration numbers for the studied ILs indicate that the low charge density of cations and their hydrophobic nature is responsible for the formation of the water-structure-enforced ion pairs.     

Dissecting the Vaporization Enthalpies of Ionic Liquids by Exclusively Experimental Methods: Coulomb Interaction,Hydrogen Bonding,and Dispersion Forces

The quantification of hydrogen bonding and dispersion energies from vaporization enthalpies is a great challenge. Dissecting interaction energies is particularly difficult for ionic liquids (ILs), for which the composition of the different types of interactions is known neither for the liquid nor for the gas phase. In this study, we demonstrate the existence of ion pairs in the gas phase and dissect the interaction energies exclusively from measured vaporization enthalpies of different alkylated protic ILs (PILs) and aprotic ILs (AILs) and the molecular analogues of their cations. We demonstrate that the evaporated ion pairs are characterized by H‐bond‐enhanced Coulomb interaction. The overall interaction energy for the ILs in the bulk phase is composed of Coulomb interaction (76 kJ mol^?1), hydrogen bonding (38 kJ mol^?1), and minor dispersion interaction (10 kJ mol^?1). Thus, hydrogen bonding prominently contributes to the overall interaction energy of PILs, which is reflected in the properties of this class of liquids.     

Vibrational spectroscopy and dynamics of small anions in ionic liquid solutions

Fourier-transform infrared (FTIR) and time-resolved IR spectroscopies have been used to study vibrational band positions, vibrational energy relaxation (VER) rates, and reorientation times of anions in several ionic liquid (IL) solutions. The ILs primarily investigated are based on the 1-butyl-2,3-dimethylimidazolium ([BM(2)IM]) cation with thiocyanate (NCS-), dicyanamide (N(CN)2-), and tetrafluoroborate (BF4-) anions. Spectroscopic studies are carried out near 2000 cm-1 for the C[Triple Bond]N stretching bands of NCS- and N(CN)2- as the IL anion as well as for NCS-, N(CN)2-, and azide (N3-) anions dissolved in [BM2IM][BF4]. The VER studies of N(CN)2- are reported for the first time. VER of N3-, NCS-, and N(CN)2- is measured in normal solvents, such as N-methylformamide, to compare with the IL solutions. The spectral shifts and VER rates of the anions in IL solution are quite similar to those in polar aprotic, conventional organic solvents, i.e., dimethylsulfoxide, and significantly different than those in methanol, in which there is hydrogen bonding. Similar studies were also carried out for the anions in another IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), in which the C2 hydrogen is present. The results for the anions are similar to those in the [BM2IM] containing ILs, in which the C2 hydrogen is methyl substituted. This suggests that substituting this hydrogen has, at most, a minor effect on the degree of hydrogen bonding in the anion-IL solvation interaction based on the infrared spectra and dynamics.     

Photoinduced electron transfer reaction in room temperature ionic liquids: a combined laser flash photolysis and fluorescence study

A detailed study of the photoinduced electron transfer (PET) reaction between pyrene and N,N-dimethylaniline has been made in four different room temperature ionic liquids (ILs) using steady state and time-resolved fluorescence and laser flash photolysis techniques. Unlike that in the conventional media, no exciplex emission for this well-known system could be observed in ILs. The rate constants for the PET induced quenching of the fluorescent state of pyrene, which lie between 6.9 and 37 x 107 M-1 s-1 depending on the viscosity, are found to be 2-4 times higher than the diffusion-controlled rates in ILs. The primary photoproducts of the PET process have been characterized by transient absorption spectroscopy, and the yields of the solvent-separated PET products have been determined. Even in the least viscous IL, [emim][Tf2N], the yield of the solvent-separated radical ion is estimated to be only 0.015 +/- 0.005. In more viscous ILs such as [bmim][PF6], the yield is found to be so low that absorption due to these species could not be observed. The rate constant for the escape of the ionic products from the geminate ion pair in ILs has been estimated to be nearly 2-3 orders of magnitude lower than the back electron transfer rate. However, the small fraction of the PET products, which manage to escape geminate recombination, have been found to survive much longer compared to those in less viscous conventional solvents.     

离子液体对木瓜蛋白酶催化特性的影响

研究了以1-丁基-3-甲基咪唑、四乙基铵及N-乙基吡啶为阳离子, 配以多种阴离子(H₂PO₄^-, ClO₄^-, HSO₄^-, CH₃COO^-, Cl^-, Br^-, NO₃^-, SCN^-, BF₄^-, PF₆^-)的离子液体对木瓜蛋白酶催化N-苯甲酰-L-精氨酸乙酯(BAEE)水解的活性及热稳定性的影响. 通过分析含离子液体体系中木瓜蛋白酶的水解活性和热力学失活参数, 发现该酶活性及稳定性与离子液体的Kosmotropicity性质无关. 因此, 离子的Hofmeister效应并不适合解释离子液体对木瓜蛋白酶催化特性的影响规律. 当以BF₄^-为阴离子, 改变阳离子结构时, 仅[BMIm][BF₄]可提高酶活性, 其它含官能团的咪唑类离子液体则降低酶活性, 但大部分离子液体明显提高木瓜蛋白酶的热稳定性. 在所研究的离子液体中, 基于PF₆^-或BF₄^-阴离子的离子液体可提高木瓜蛋白酶的活性及其热稳定性. 在含[BMIm][PF₆]介质中, 木瓜蛋白酶的水解活性最高; 在含[HOEtMIm][BF₄]介质中其热稳定性最好.     

Crystal Structures,Thermal Analysis and Electrochemical Behaviors of Functionalized Pyridinium Ionic Liquids Comprising One 1-Ethyl Acetate Group

Pyridinium ionic liquids(ILs, 1-ethyl acetate pyridinium hexfluorophosphate[EAPy][PF₆] and 1-ethyl acetate-3-methyl pyridinium hexfluorophosphate[EAMPy][PF₆]), were synthesized by a two-step process involving introduction of one ethyl acetate group and anion metathesis. Colorless single crystals of the two ILs were initially obtained using the solvent-evaporation method in mixed solvents. Single-crystal X-ray diffraction was used to determine the crystal structures.[EAPy][PF₆] crystallizes in the monoclinic space group C2/c with a=2.2748(16) nm, b=0.6204(4) nm, c=1.8552(12) nm and Z=8, whereas[EAMPy][PF₆] crystallizes in the orthorhombic space group P2₁2₁2₁ with a=0.7126(17) nm, b=1.2792(3) nm, c=1.5327(3) nm and Z=4. The structure of[EAPy][PF₆] contains double zigzag chains formed by alternately pairing large organic cations with the octahedral anions of[P1F₆]^- or[P2F₆]^-. The[P1F₆]^- and[P2F₆]^- anions occupy respectively two distinct crystallographic sites in crystal packing models. The structure of[EAMPy][PF₆] includes ladder-type chains constructed through pairing pyridinium cations with inorganic anions of[PF₆]^-. The[PF₆]^- anion in[EAMPy][PF₆] shows a distorted octahedron structure and is sandwiched by ethyl acetate groups in crystallographic stacking. This study reveals the influence of chemical mo-dification involving the methyl group(CH₃) onto crystallographic structure of pyridinium ILs. Thermal analysis indicates that the difficult crystallization of the two ILs is related to the low void filling of ion pairs in crystal structure, leading to relatively low melting point and evident supercooling during the cooling process. Additionally, the experimental results indicate that the two ILs have electrochemical activity. The ethyl acetate group also allows downward shifting of electrochemical windows to less negative positions and the ionic conductivities of the two ILs follow an Arrhenius-type behavior.     

Alkali cation extraction by calix[4]crown-6 to room-temperature ionic liquids. The effect of solvent anion and humidity investigated by molecular dynamics simulations

We report a molecular dynamics study on the solvation of M+ (Na+ to Cs+) alkali cations and of their LM+ complexes with a calix[4]arene host (L = 1,3-dimethoxy-calix[4]arene-crown-6 in the 1,3-alternate conformation) in the [BMI][PF6] and [BMI][Tf2N] room-temperature ionic liquids "ILs" based on the BMI+ (1-butyl-3-methylimidazolium) cation. The comparison of the two liquids and the dry versus humid form of the former one (with a 1:1 ratio of H2O and BMI+PF6- species) reveals the importance of humidity: in [BMI][PF6]-dry as in the [BMI][Tf2N] liquid, the first solvation shell of the "naked" M+ ions is composed of solvent anions only (four PF6- anions, and from four to five Tf2N- anions, respectively, quasi-neutralized by a surrounding cage of BMI+ cations), while in the [BMI][PF6]-humid IL, it comprises from one to three solvent anions and about four H2O molecules. In the LM+ complexes, the cation is shielded from solvent, but still somewhat interacts with a solvent anion in the dry ILs and with water in the humid IL. We also report tests on M+ interactions with solvent anions PF6- and Tf2N- in the gas phase, showing that the AMBER results are in satisfactory agreement with QM results obtained at different levels of theory. The question of ion recognition by L is then examined by free energy perturbation studies in the three liquids, predicting a high Cs+/Na+ selectivity upon liquid extraction from an aqueous phase, in agreement with experimental results on a parent calixarene host. A similar Cs+/Na+ selectivity is predicted upon complexation in a homogeneous IL phase, mainly due to the desolvation energy of the free cations. Thus, despite their polar character, ionic liquids qualitatively behave as classical weakly polar organic liquids (e.g., choroform) as far as liquid-liquid extraction is concerned but more like polar liquids (water, alcohols) as far as complexation in a single phase is concerned.     

Kinetic study of the addition of trihalides to unsaturated compounds in ionic liquids. Evidence of a remarkable solvent effect in the reaction of ICl2-

The kinetic constants and activation parameters for the reactions of Br(3)(-) and ICl(2)(-) with some alkenes and alkynes have been determined in the ionic liquids [bmim][PF(6)], [emim][Tf(2)N], [bmim][Tf(2)N], [hmim][TF(2)N], [bm(2)im][Tf(2)N], and [bpy][TF(2)N] (where emim = 1-ethyl-3-methylimidazolium, bmim = 1-butyl-3-methylimidazolium, hmim = 1-hexyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bpy = butylpyridinium, PF(6) = hexafluorophosphate, and Tf(2)N = bis(trifluoromethylsulfonyl)imide) and in 1,2-dichloroethane. The rates of both reactions increase on going from 1,2-dichloroethane to ILs. Evidence suggests that, while the hydrogen bonding ability of the imidazolium cation is probably the main factor able to increase the rate of the addition of ICl(2)(-) to double and triple bonds, this property has no effect on the electrophilic addition of Br(3)(-) to alkenes and alkynes. Furthermore, in the case of the ICl(2)(-) reaction, the hydrogen bonding ability of ILs can be exploited to suppress the unwanted nucleophilic substitution reaction on the products by the Cl(-) anion.     

Fourier transform infrared spectroscopy of azide and cyanate ion pairs in AOT reverse micelles

Evidence for ion pair formation in aqueous bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles (RMs) was obtained from infrared spectra of azide and cyanate with Li(+), Na(+), K(+), and NH(4)(+) counterions. The anions' antisymmetric stretching bands near 2000 cm(-1) are shifted to higher frequency (blueshifted) in LiAOT and to a lesser extent in NaAOT, but they are very similar to those in bulk water with K(+) and NH(4)(+) as the counterions. The shifts are largest for low values of w(o) = [water]/[AOT] and approach the bulk value with increasing w(o). The blueshifts are attributed to ion pairing between the anions and the counterions. This interpretation is reinforced by the similar trend (Li(+)>Na(+)>K(+)) for producing contact ion pairs with the metal cations in bulk dimethyl sulfoxide (DMSO) solutions. We find no evidence of ion pairs being formed in NH(4)AOT RMs, whereas ammonium does form ion pairs with azide and cyanate in bulk DMSO. Studies are also reported for the anions in formamide-containing AOT RMs, in which blueshifts and ion pair formation are observed more than in the aqueous RMs. Ion pairs are preferentially formed in confined RM systems, consistent with the well established ideas that RMs exhibit reduced polarity and a disrupted hydrogen bonding network compared to bulk water and that ion-specific effects are involved in mediating the structure of species at interfaces.     

Structure formation features of water and concentrated aqueous lithium halide solutions at low temperatures from the data of integral equation method

The structure of water and the influence of halide ions on the structure formation of concentrated LiX : H₂O (1 : 5; X = Cl, Br, I) solutions at low temperatures were studied by the method of integral equations. Based on the results obtained, supercooling of pure water is expected to significantly enhance the tetrahedral ordering of its molecules, strengthen hydrogen bonding in the system, and decrease the number of the nearest-neighbor water molecules. The effects for the solutions on lowering the temperature include a partial restoration of the tetrahedral network of H-bonds of the solvent molecules, insignificant increase in the number of the nearest-neighbor water molecules, enhancement of the coordination ability of Li⁺ cation, strengthening of hydrogen bonding between anions and water molecules in the first hydration shell, increase in the number of solvent-separated ion pairs, and weakening of the temperature effect on these structural parameters in the following order of solutions: LiCl > LiBr > LiI. The probability of contact ion pair formation in the systems studied should appreciably decrease. The temperature should to a greater extent influence the associative ability of larger anions.     

"Alkaline-earth metals in a box": structures of solvent-separated ion pairs

During our research on homoleptic organocalcium compounds, we found that fluorenylcalcium complexes show unusual solution behavior and precipitate from nonpolar solvents after addition of THF. Their solid-state structures reveal the unexpected rupture of both metal-carbanion bonds by the polar solvent THF. The crystal structures of five new Mg and Ca solvent-separated ion pairs are described. The compound [Ca(2+)(thf)(6)][Me(3)Si(fluorenyl(-))](2) is the first organometallic complex of a Group 2 element that crystallizes as a completely solvent-separated ion pair. The driving forces for its formation are: 1) the strong Ca-THF bond; 2) the stability of the free [Me(3)Si(fluorenyl)](-) ion; 3) encapsulation of [Ca(2+)(thf)(6)] in a "box", the walls of which consist of anionic fluorenyl ligands and benzene molecules; and 4) the presence of numerous (THF)C- H...pi interactions. The magnesium analogue [Mg(2+)(thf)(6)][Me(3)Si(fluorenyl(-))](2) is isostructural. Bis(7,9-diphenylcyclopenta[a]acenaphthadienyl)calcium also crystallizes as a completely solvent-separated ion pair and can likewise be described as a [Ca(2+)(thf)(6)] species in a box of delocalized anions and benzene molecules. In addition, the structures of two Ph(4)B(-) complexes of Mg and Ca are described. [Mg(2+)(thf)(6)][Ph(4)B(-)](2) crystallizes as a completely solvent-separated ion pair and also shows a solvated metal cation bonded via C-H.pi interactions in a cavity formed by Ph(4)B(-) ions. [(thf)(4)CaBr(+)][Ph(4)B(-)] has a structure in which one of the anionic ligands is still bonded to the Ca atom. Bridging bromide ligands result in the formation of the dimer [(thf)(4)CaBr(+)](2).     

A convenient route to lanthanide triiodide THF solvates. Crystal structures of LnI(3)(THF)(4) [Ln = Pr] and LnI(3)(THF)(3.5) [Ln = Nd, Gd, Y

The reaction between 1.5 equiv of elemental iodine and rare earth metals in powder form in THF at room temperature gives the rare earth triiodides LnI(3)(THF)(n)() in good yields. Purification by Soxhlet extraction of the crude solids with THF reliably gives the THF adducts LnI(3)(THF)(4) [Ln = La, Pr] and LnI(3)(THF)(3.5) [Ln = Nd, Sm, Gd, Dy, Er, Tm, Y] as microcrystalline solids. X-ray crystallography reveals that the early, larger lanthanide iodide PrI(3)(THF)(4) crystallizes as discrete molecules having a pentagonal bipyramidal structure, whereas the later, smaller lanthanide iodides LnI(3)(THF)(3.5) [Ln = Nd, Gd, Y] crystallize as solvent-separated ion pairs [LnI(2)(THF)(5)][LnI(4)(THF)(2)] in which the cations adopt a pentagonal bipyramidal geometry and the anions adopt an octahedral geometry in the solid state.     

Aqueous divalent metal-nitrate interactions: hydration versus ion pairing

Nitrate aqueous solutions, Mg(NO(3))(2), Ca(NO(3))(2), Sr(NO(3))(2), and Pb(NO(3))(2), are investigated using Raman spectroscopy and free energy profiles from molecular dynamics (MD) simulations. Analysis of the in-plane deformation, symmetric stretch, and asymmetric stretch vibrational modes of the nitrate ions reveal perturbation caused by the metal cations and hydrating water molecules. Results show that Pb(2+) has a strong tendency to form contact ion pairs with nitrate relative to Sr(2+), Ca(2+), and Mg(2+), and contact ion pair formation decreases with decreasing cation size and increasing cation charge density: Pb(2+) > Sr(2+) > Ca(2+) > Mg(2+). In the case of Mg(2+), the Mg(2+)-OH(2) intermolecular modes indicate strong hydration by water molecules and no contact ion pairing with nitrate. Free energy profiles provide evidence for the experimentally observed trend and clarification between solvent-separated, solvent-shared, and contact ion pairs, particularly for Mg(2+) relative to other cations.     

Hydrogen bonding in the crystal structures of the ionic liquid compounds butyldimethylimidazolium hydrogen sulfate, chloride, and chloroferrate(II,III)

Four ionic liquid (IL) salts containing the 1-butyl-2,3-dimethylimidazolium (BDMIM) and 1-allyl-2,3-dimethylimidazolium (ADMIM) cations have been prepared; the characterization was based on IR spectroscopy and single-crystal structure determination. The compounds BDMIM[HSO4], BDMIMCl, ADMIMBr, and (BDMIM)4[FeIICl4][FeIIICl4]2 were chosen to incorporate anions significantly differing in hydrogen-bond-acceptor strength in order to elucidate the influence of directional bonding on crystal packing. The cations adopt different arrangements with respect to the counterions. The role of hydrogen bonding in these compounds is discussed with respect to its general significance for lattice energies of IL salts.     

Effect of ionic solutes on the hydrogen bond network dynamics of water: power spectral analysis of aqueous NaCl solutions

To understand the modifications of the hydrogen bond network of water by ionic solutes, power spectra as well as static distributions of the potential energies of tagged solvent molecules and solute ions have been computed from molecular dynamics simulations of aqueous NaCl solutions. The key power spectral features of interest are the presence of high-frequency peaks due to localized vibrational modes, the existence of a multiple time scale or 1/falpha frequency regime characteristic of networked liquids, and the frequency of crossover from 1/falpha type behavior to white noise. Hydrophilic solutes, such as the sodium cation and the chloride anion, are shown to mirror the multiple time scale behavior of the hydrogen bond network fluctuations, unlike hydrophobic solutes which display essentially white noise spectra. While the power spectra associated with tagged H2O molecules are not very sensitive to concentration in the intermediate frequency 1/falpha regime, the crossover to white noise is shifted to lower frequencies on going from pure solvent to aqueous alkali halide solutions. This suggests that new and relatively slow time scales enter the picture, possibly associated with processes such as migration of water molecules from the hydration shell to the bulk or conversion of contact ion pairs into solvent-separated ion pairs which translate into variations in equilibrium transport properties of salt solutions with concentration. For anions, cations, and solvent molecules, the trends in the alpha exponents of the multiple time scale region and the self-diffusivities are found to be strongly correlated.     

Extraction separation of rare-earth ions via competitive ligand complexations between aqueous and ionic-liquid phases

The extraction separation of rare earth elements is one of the most challenging separation processes in hydrometallurgy and advanced nuclear fuel cycles. The TALSPEAK process (trivalent actinide lanthanide separations by phosphorus-reagent extraction from aqueous komplexes) is a prime example of these separation processes. The objective of this paper is to explore the use of ionic liquids (ILs) for the TALSPEAK-like process, to further enhance its extraction efficiencies for lanthanides, and to investigate the potential of using this modified TALSPEAK process for separation of lanthanides among themselves. Eight imidazolium ILs ([C(n)mim][NTf(2)] and [C(n)mim][BETI], n = 4,6,8,10) and one pyrrolidinium IL ([C(4)mPy][NTf(2)]) were investigated as diluents using di(2-ethylhexyl)phosphoric acid (HDEHP) as an extractant for the separation of lanthanide ions from aqueous solutions of 50 mM glycolic acid or citric acid and 5 mM diethylenetriamine pentaacetic acid (DTPA). The extraction efficiencies were studied in comparison with diisopropylbenzene (DIPB), an organic solvent used as a diluent for the conventional TALSPEAK extraction system. Excellent extraction efficiencies and selectivities were found for a number of lanthanide ions using HDEHP as an extractant in these ILs. The effects of different alkyl chain lengths in the cations of ILs and of different anions on extraction efficiencies and selectivities of lanthanide ions are also presented in this paper.     

Liquid/solid interface of ultrathin ionic liquid films: [C1C1Im][Tf2N] and [C8C1Im][Tf2N] on Au(111)

Ultrathin films of two imidazolium-based ionic liquids (IL), [C(1)C(1)Im][Tf(2)N] (= 1,3-dimethylimidazolium bis(trifluoromethyl)imide) and [C(8)C(1)Im][Tf(2)N] (= 1-methyl-3-octylimidazolium bis(trifluoromethyl)imide) were prepared on a Au(111) single-crystal surface by physical vapor deposition in ultrahigh vacuum. The adsorption behavior, orientation, and growth were monitored via angle-resolved X-ray photoelectron spectroscopy (ARXPS). Coverage-dependent chemical shifts of the IL-derived core levels indicate that for both ILs the first layer is formed from anions and cations directly in contact with the Au surface in a checkerboard arrangement and that for [C(8)C(1)Im][Tf(2)N] a reorientation of the alkyl chain with increasing coverage is found. For both ILs, geometry models of the first adsorption layer are proposed. For higher coverages, both ILs grow in a layer-by-layer fashion up to thicknesses of at least 9 nm (>10 ML). Moreover, beam damage effects are discussed, which are mainly related to the decomposition of [Tf(2)N](-) anions directly adsorbed at the gold surface.