Studies on the translational and rotational motions of ionic liquids composed of N-methyl-N-propyl-pyrrolidinium (P13) cation and bis(trifluoromethanesulfonyl)amide and bis(fluorosulfonyl)amide anions and their binary systems including lithium salts

Room-temperature ionic liquids (RTIL, IL) are stable liquids composed of anions and cations. N-methyl-N-propyl-pyrrolidinium (P(13), Py(13), PYR(13), or mppy) is an important cation and produces stable ILs with various anions. In this study two amide-type anions, bis(trifluoromethanesulfonyl)amide [N(SO(2)CF(3))(2), TFSA, TFSI, NTf(2), or Tf(2)N] and bis(fluorosulfonyl)amide [N(SO(2)F)(2), FSA, or FSI], were investigated. In addition to P(13)-TFSA and P(13)-FSA, lithium salt doped samples were prepared (P(13)-TFSA-Li and P(13)-FSA-Li). The individual ion diffusion coefficients (D) and spin-lattice relaxation times (T(1)) were measured by (1)H, (19)F, and (7)Li NMR. At the same time, the ionic conductivity (σ), viscosity (η), and density (ρ) were measured over a wide temperature range. The van der Waals volumes of P(13), TFSA, FSA, Li(TFSA)(2), and Li(FSA)(3) were estimated by molecular orbital calculations. The experimental values obtained in this study were analyzed by the classical Stokes-Einstein, Nernst-Einstein (NE), and Stokes-Einstein-Debye equations and Walden plots were also made for the neat and binary ILs to clarify physical and mobile properties of individual ions. From the temperature-dependent velocity correlation coefficients for neat P(13)-TFSA and P(13)-FSA, the NE parameter 1-ξ was evaluated. The ionicity (electrochemical molar conductivity divided by the NE conductivity from NMR) and the 1-ξ had exactly the same values. The rotational and translational motions of P(13) and jump of a lithium ion are also discussed.     

Nuclear magnetic resonance spectroscopic study on ionic liquids of 1-alkyl-3-methylimidazolium salts

Chemical shifts of ¹H and ¹³C NMR of series of methylimidazolium salts (MIM⁺, X=Br⁻, BF₄⁻ and PF₆⁻) function on the length of alkyl groups on the ring, type of solvents and the concentration. The bromides series demonstrate more chemical shift variation on H2 upon the change of solvents and concentration. Unexpected H-D exchange reactions were also observed in the MIM⁺Br⁻ by using CD₃OD and D₂O. The exchange rates strongly depend on the length of the alkyl group, which could cause more steric factor to reduce the interaction between deuterium atom from solvent and C2 of the ring.     

Anion conformation of low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide

Anion conformation of a low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMI+FSI-) has been studied by Raman spectra and theoretical DFT calculations. Three strong Raman bands were found at 293, 328, and 360 cm(-1), which are ascribed to the FSI- ion. These Raman bands show significant temperature dependence, implying that two FSI- conformers coexist in equilibrium. This is supported by theoretical calculations that the FSI- ion is present as either C2 (trans) or C1 (cis) conformer; the former gives the global minimum, and the latter has a higher SCF energy of about 4 kJ mol(-1). Full geometry optimizations followed by normal frequency analyses show that the observed bands at 293, 328, and 360 cm(-1) are ascribed to the C2 conformer. The corresponding vibrations at 305, 320, and 353 cm(-1) were extracted according to deconvolution of the observed Raman bands in the range280-400 cm(-1 )and are ascribed to the C1 conformer. The enthalpy DeltaH degrees of conformational change from C2 to C1 was experimentally evaluated to be ca. 4.5 kJ mol(-1), which is in good agreement with the predicted value by theoretical calculations. The bis(trifluoromethanesulfonyl) imide anion (TFSI-) shows a conformational equilibrium between C1 and C2 analogues (DeltaH degrees = 3.5 kJ mol(-1)). However, the profile of the potential energy surface of the conformational change for FSI- (the F-S-N-S dihedral angle) is significantly different from that for TFSI- (the C-S-N-S dihedral angle).     

Electrodeposition of Al in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquids: in situ STM and EQCM studies

In the present paper, the electrodeposition of Al on flame-annealed Au(111) and polycrystalline Au substrates in two air- and water-stable ionic liquids namely, 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]Tf(2)N, and 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide, [EMIm]Tf(2)N, has been investigated by in situ scanning tunneling microscopy (STM), electrochemical quartz crystal microbalance (EQCM), and cyclic voltammetry. The cyclic voltammogram of aluminum deposition and stripping on Au(111) in the upper phase of the biphasic mixture of AlCl(3)/[EMIm]Tf(2)N at room temperature (25 degrees C) shows that the electrodeposition process is completely reversible as also evidenced by in situ STM and EQCM studies. Additionally, a cathodic peak at an electrode potential of about 0.55 V vs Al/Al(III) is correlated to the aluminum UPD process that was evidenced by in situ STM. A surface alloying of Al with Au at the early stage of deposition occurs. It has been found that the Au(111) surface is subject to a restructuring/reconstruction in the upper phase of the biphasic mixture of AlCl(3)/[Py(1,4)]Tf(2)N at room temperature (25 degrees C) and that the deposition is not fully reversible. Furthermore, the underpotential deposition of Al in [Py(1,4)]Tf(2)N is not as clear as in [EMIm]Tf(2)N. The frequency shift in the EQCM experiments in [Py(1,4)]Tf(2)N shows a surprising result as an increase in frequency and a decrease in damping with bulk aluminum deposition at potentials more negative than -1.8 V was observed at room temperature. However, at 100 degrees C there is a frequency decrease with ongoing Al deposition. At -2.0 V vs Al/Al(III), a bulk aluminum deposition sets in.     

Nuclear magnetic relaxation and diffusion study of the ionic liquids 1-ethyl- and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide confined in porous glass

The molecular dynamics of the room-temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Bmim Tf2N) confined in porous glass is studied by nuclear magnetic resonance (NMR) relaxometry and diffusometry and is compared with the bulk dynamics over a wide temperature range. The molecular reorientation processes for anions and cations alike are found to be significantly affected by the presence of the glass interface at high temperatures. In this respect, the ionic liquid behaves similarly to polar liquids where proton NMR relaxation is governed by reorientations mediated by translational displacements (RMTDs). This process becomes less significant towards lower temperatures when the characteristic translational correlation times of the ions approach a timescale comparable with those of the RMTD process, and the relaxation dispersions in bulk and in confinement become similar below a temperature corresponding to about 1.2T_g, a value where the onset of dynamic heterogeneity has been observed before. The self-diffusion coefficient, on the other hand, is found to be strongly reduced than the bulk within the accessible temperature range of 248 K and above and is significantly slower than expected from the tortuosity effect, suggesting that ion–surface interactions affect the macroscopic properties.     

Experimental evidences for molecular origin of low-Q peak in neutron/x-ray scattering of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquids

Short- and long-range liquid structures of [C(n)mIm(+)][TFSA(-)] with n = 2, 4, 6, 8, 10, and 12 have been studied by high-energy x-ray diffraction (HEXRD) and small-angle neutron scattering (SANS) experiments with the aid of MD simulations. Observed x-ray structure factor, S(Q), for the ionic liquids with the alkyl-chain length n > 6 exhibited a characteristic peak in the low-Q range of 0.2-0.4 A?(-1), indicating the heterogeneity of their ionic liquids. SANS profiles I(H)(Q) and I(D)(Q) for the normal and the alkyl group deuterated ionic liquids, respectively, showed significant peaks for n = 10 and 12 without no form factor component for large spherical or spheroidal aggregates like micelles in solution. The peaks for n = 10 and 12 evidently disappeared in the difference SANS profiles ΔI(Q) [=I(D)(Q) - I(H)(Q)], although that for n = 12 slightly remained. This suggests that the long-range correlations originated from the alkyl groups hardly contribute to the low-Q peak intensity in SANS. To reveal molecular origin of the low-Q peak, we introduce here a new function; x-ray structure factor intensity at a given Q as a function of r, S(Q) (peak)(r). The S(Q) (peak)(r) function suggests that the observed low-Q peak intensity depending on n is originated from liquid structures at two r-region of 5-8 and 8-15 A? for all ionic liquids examined except for n = 12. Atomistic MD simulations are consistent with the HEXRD and SANS experiments, and then we discussed the relationship between both variations of low-Q peak and real-space structure with lengthening the alkyl group of the C(n)mIm.     

Preparation, properties, and crystal structures of organometallic ionic liquids comprising 1-ferrocenyl-3-alkylimidazolium-based salts of bis(trifluoromethanesulfonyl)amide and hexafluorophosphate

Bis(trifluoromethanesulfonyl)amide (TFSA), hexafluorophosphate (PF(6)(-)), and iodide salts of 1-ferrocenyl-3-alkylimidazolium were prepared and their thermal and physical properties, including the dependence on alkyl chain length (methyl-hexadecyl), were investigated. The TFSA salts were highly viscous ionic liquids with melting points around room temperature. 1-Ferrocenyl-4-methyltriazolium salts were also prepared for comparison. The ferrocenylimidazolium and ferrocenyltriazolium cations showed redox waves for both the ferrocenyl moiety and the azolium moiety and exhibited corresponding charge-transfer bands at around 330 nm, which were analyzed using the Marcus-Hush model. Crystal structure determinations at low temperature revealed that the PF(6) and iodide salts form layerlike structures composed of ionic layers of the charged moieties. The TFSA salt exhibited short hydrogen-bond-like intermolecular contacts between the hydrogen atoms of the cation and oxygen atoms of the anion.     

Properties of ionic liquids containing silver(I) or protic alkylethylenediamine cations with a bis(trifluoromethanesulfonyl)amide anion

Ionic liquids of an N-alkylethylenediamine-silver(I) complex cation (alkyl=hexyl, 2-ethylhexyl, and octyl) or a protic N-alkylethylenediaminium cation (alkyl=butyl, hexyl, 2-ethylhexyl, octyl, decyl, and dodecyl) with a bis(trifluoromethanesulfonyl)amide counter anion (Ag-ILs and PILs, respectively) were prepared and their physicochemical properties were investigated. The trend of solidification decreased in the order octyl?hexyl>2-ethylhexyl for the Ag-ILs, and butyl>dodecyl>decyl>octyl>hexyl?2-ethylhexyl for the PILs. The diffusion coefficients of the cations indicated stronger intermolecular interactions in PILs than in the Ag-ILs because of hydrogen-bonding networks, and it has been revealed that the intermolecular interactions increase in the order, hexyl相似文献   

Role of water in complexation of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) with Li+ and K+ in hydrophobic 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquid

Complexation characteristics of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6, 18C6) with Li⁺ and K⁺ in a hydrophobic ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide under dry and humid conditions at 298.2 K were studied by ¹H and ¹³C NMR chemical shifts. The comparison of the ¹H and ¹³C chemical shifts of 18C6 molecule between the dry and humid IL solutions without the alkali metal ions showed that uncomplexed 18C6 molecules are solvated by water molecules in the humid ionic liquid solution. The changes in the ¹H and ¹³C chemical shifts of 18C6 ligand molecule with the increases in the Li⁺ and K⁺ concentrations revealed that in both dry and humid ionic liquid solutions 18C6 molecule forms 1:1 complexes with Li⁺ and K⁺. The ¹H NMR data of water molecules in the humid ionic liquid solutions demonstrated that water molecules interact with Li⁺-18C6 complexes and free Li⁺, but do not with K⁺-18C6 complexes and free K⁺. The mechanisms of the formation of the Li⁺ and K⁺ complexes in the humid ionic liquid solution are different from each other due to the differences in the complex-water interactions.     

Effect of the pressure on the viscosities of ionic liquids: Experimental values for 1-ethyl-3-methylimidazolium ethylsulfate and two bis(trifluoromethyl-sulfonyl)imide salts

A new falling-body viscometer has been implemented to measure viscosity of liquids in a temperature range from (313.15 to 363.15) K at pressures up to 150 MPa. The accuracy of the viscometer was verified after comparing experimental results of squalane with previous literature data finding an average absolute deviation lower than 1.5%. With this device, we have measured viscosity values for three ionic liquids: 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-1-methylpyrrolidinium bis(trifluoro-methylsulfonyl)imide and 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide within the temperature and pressure ranges noted above. The experimental values were correlated as a function of temperature and pressure with four different equations. In addition, we have analysed the pressure–viscosity derived properties for these fluids and for other five ionic liquids using literature values.     

Physical properties of ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various anions and the bis(trifluoromethylsulfonyl)imide anion with various cations

Physical properties of 4 room-temperature ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various perfluorinated anions and the bis(trifluoromethylsulfonyl)imide (Tf2N-) anion with 12 pyrrolidinium-, ammonium-, and hydroxyl-containing cations are reported. Electronic structure methods are used to calculate properties related to the size, shape, and dipole moment of individual ions. Experimental measurements of phase-transition temperatures, densities, refractive indices, surface tensions, solvatochromic polarities based on absorption of Nile Red, 19F chemical shifts of the Tf2N- anion, temperature-dependent viscosities, conductivities, and cation diffusion coefficients are reported. Correlations among the measured quantities as well as the use of surface tension and molar volume for estimating Hildebrand solubility parameters of ionic liquids are also discussed.     

Infrared spectra of bis(trifluoromethanesulfonyl)imide based ionic liquids: Experiments and DFT simulations

We measured the far- and mid-infrared spectra of three ionic liquids having bis(trifluoromethanesulfonyl)imide anions and three different cations of the families of pyrrolidinium and ammmonium ions. The molecular vibrations of the individual ions were calculated by means of DFT theory at the B3LYP/6-31G** level: we found good agreement between the experimental and the computed frequencies. The infrared lines are ascribable to molecular vibrations of the single ions, suggesting an extremely weak interaction between anions and cations. The spectral lines found experimentally between 760 and 1050 cm⁻¹ are fingerprints for different cations. The comparison with the calculated frequencies allows the assignment of the experimental spectral lines to specific molecular vibrations of anions and for the first time of the specific cations of the measured ionic liquids.     

(Liquid + liquid) equilibrium of aqueous biphasic systems composed of 1-benzyl or 1-hexyl-3-methylimidazolium chloride ionic liquids and inorganic salts

(Liquid + liquid) equilibria for {1-benzyl-3-methylimidazolium chloride ([BzMIM]Cl) or 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl) + inorganic salts (potassium phosphate K₃PO₄, potassium carbonate K₂CO₃, or dipotassium hydrogen phosphate K₂HPO₄) + H₂O} aqueous biphasic systems (ABSs) are presented at T = 298.15 K. An empirical equation was used to correlate the binodal data. The experimental tie lines were appropriately correlated by the Othmer–Tobias and Brancroft empirical equations. The influence of the selected inorganic salts in the phase segregation was investigated by means the calculated effective excluded volume (EEV) and Setschenow-type equation. The salting-out ability of salts was also evaluated in terms of the Gibbs energy of hydration of salt (ΔG_hyd) and assessed with EEV values.     

Effect of temperature and water content on the shear viscosity of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide as studied by atomistic simulations

Atomistic simulations are conducted to examine the dependence of the viscosity of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide on temperature and water content. A nonequilibrium molecular dynamics procedure is utilized along with an established fixed charge force field. It is found that the simulations quantitatively capture the temperature dependence of the viscosity as well as the drop in viscosity that occurs with increasing water content. Using mixture viscosity models, we show that the relative drop in viscosity with water content is actually less than that that would be predicted for an ideal system. This finding is at odds with the popular notion that small amounts of water cause an unusually large drop in the viscosity of ionic liquids. The simulations suggest that, due to preferential association of water with anions and the formation of water clusters, the excess molar volume is negative. This means that dissolved water is actually less effective at lowering the viscosity of these mixtures when compared to a solute obeying ideal mixing behavior. The use of a nonequilibrium simulation technique enables diffusive behavior to be observed on the time scale of the simulations, and standard equilibrium molecular dynamics resulted in sub-diffusive behavior even over 2 ns of simulation time.     

(Liquid + liquid) equilibria in the binary systems (aliphatic,or aromatic hydrocarbons + 1-ethyl-3-methylimidazolium ethylsulfate,or 1-butyl-3-methylimidazolium methylsulfate ionic liquids)

(Liquid + liquid) equilibria of 14 binary systems composed of n-hexane, n-heptane, benzene, toluene, o-xylene, m-xylene, or p-xylene and 1-ethyl-3-methylimidazolium ethylsulfate, [emim]EtSO₄, or 1-butyl-3-methylimidazolium methylsulfate, [bmim]MeSO₄, ionic liquids have been done in the temperature range from (293.2 to 333.2) K. The solubility of aliphatic is less than those of the aromatic hydrocarbons. In particular, the solubility of hydrocarbons in both ionic liquids increases with the temperature in the order n-heptane < n-hexane < m-xylene < p-xylene < o-xylene < toluene < benzene. Considering the high solubility of aromatics and the low solubility of aliphatic hydrocarbons as well as totally immiscibility of the ionic liquids in all hydrocarbons, these new green solvents may be used as potentials extracting solvents for the separation of aromatic and aliphatic hydrocarbons.     

Prediction of the vapor pressure and vaporization enthalpy of 1-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids

The vapor pressures and vaporization enthalpies of a series of 1-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids have been predicted with two different approaches using the COSMO-RS method and quantum chemical gas phase calculations. While the calculated enthalpies are in good agreement with the experimental data, COSMO-RS seems to underestimate the vapor pressures by roughly 0.5-4 log units dependent on the IL and approach used.     

Design and synthesis of spiro bis(1,2,3-triazolium) salts as chiral ionic liquids

Room temperature chiral spiro ionic liquids 1 and 2 based on 1,2,3-triazolium salts, were synthesized via an intramolecular double Huisgen reaction. The preparation of the enantiomerically pure spiro triazolium salts was achieved by resolution by HPLC using a chiral stationary phase column and subsequent N-dialkylations of spiro triazoles 6 and 10.     

Physical and electrochemical properties of N-alkyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquids: PY13FSI and PY14FSI

Two ionic liquids based upon N-alkyl-N-methylpyrrolidinium cations (PY(1R)(+)) (R=3 for propyl or 4 for butyl) and the bis(fluorosulfonyl)imide (FSI(-)), N(SO2F)2(-), anion have been extensively characterized. The ionic conductivity and viscosity of these materials are found to be among the highest and lowest, respectively, reported for aprotic ionic liquids. Both ionic liquids crystallize readily on cooling and undergo several solid-solid phase transitions on heating prior to melting. PY13FSI and PY14FSI are found to melt at -9 and -18 degrees C, respectively. The thermal stability of PY13FSI and PY14FSI is notably lower than for the analogous salts with the bis(trifluoromethanesulfonyl)imide (TFSI(-)), N(SO2CF3)2(-), anion. Both ionic liquids have a relatively wide electrochemical stability window of approximately 5 V.     

A molecular dynamics investigation of the structural and dynamic properties of the ionic liquid 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

Molecular dynamics simulations have been performed to investigate the structure and dynamics of the ionic liquid, 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C(4)mim][Tf(2)N]) in the temperature range of 283-460 K. Extensive analysis was carried out to characterize a number of structural and dynamic features. Transport properties were computed using a variety of equilibrium methods that employed the Green-Kubo and Einstein formulations. Nonequilibrium techniques were also used. In general, different methods mostly yielded consistent results, although some differences were observed. Computed self-diffusivities and ionic conductivities tended to be slightly lower than experimental values, while computed viscosities were significantly higher than experiment. Computed thermal conductivities agreed reasonably well with experimental data. Despite these discrepancies, the simulations capture the experimental temperature-dependent trends for all these transport properties. Single ion dynamics were studied by examining diffusional anisotropy, the self-part of the van Hove function, non-Gaussian parameters, and incoherent intermediate scattering functions. It is found that cations diffuse faster than anions and are more dynamically heterogeneous. A clear anisotropy is revealed in cation displacement, with the motion normal to the imidazolium ring plane being the most hindered and the motion along the alkyl chain in the plane of the ring being the most facile. Cations structurally relax faster than anions but they rotationally relax slower than anions. There is a pronounced temperature dependence to the rotational anisotropy of the cations, but only a weak temperature dependence for the anions. The ionic conductivity deviates from the Nernst-Einstein relation due to the correlated motion of cations and anions. The results suggest that the dynamical behavior of this and related ionic liquids is extremely complex and consists of many different modes with widely varying timescales, making the prediction of dynamical trends extremely difficult.