Temperature Dependence of Interactions between Stable Piperidine‐1‐yloxyl Derivatives and an Ionic Liquid

2,2,6,6‐Tetramethylpiperidine‐1‐yloxyl derivatives substituted with either hydrogen bonding [‐OH, ‐OSO₃H] or ionic [‐OSO₃^?Na⁺, ‐OSO₃^?K⁺, N⁺(CH₃)₃I^?, N⁺(CH₃)₃ N^?(SO₂‐CF₃)₂] substituents are investigated in 1‐butyl‐3‐methylimidazolium tetrafluoroborate over a wide temperature range covering both glassy and viscous states. The Vogel–Fulcher–Tammann equation describes the temperature dependence of the ionic liquid viscosity. Quantum chemical calculations of the spin probes at the UB3LYP/6‐311(2d,p++) level are done to describe the dependence of the spin density on nitrogen on the substitution pattern of the 4‐position of the probe. The results of these calculations are also used to understand the experimental results obtained by applying the Spernol–Gierer–Wirtz theory to analyze the viscosity dependence of the rotational correlation time of the spin probes. Significant differences are found between 2,2,6,6‐tetramethylpiperidine‐1‐yloxyl and its derivatives containing substituents that are able to form hydrogen bonds with the ionic liquid. Moreover, derivatives substituted with ionic groups at the 4‐position have a large effect on temperature‐induced solvent viscosity, as this is particularly dependent on the nature of the substituent at the 4‐position. These dependencies include the temperature region that can be used to describe interactions between the spin probes and the ionic liquid, diffusion into the free volume during non‐activated (neutral spin probes) and activated (charged spin probes) processes. Additional parameters are the radii of the ionic liquid and the spin probes, which are calculated and measured approximately. In addition, the temperature dependence of the isotropic hyperfine coupling constants of the spin probes results in information about the micropolarity of the ionic liquid. At room temperature, this is comparable to that of the solvent dimethylsulfoxide.     

Microscopic Diffusion Dynamics of Silver Complex‐Based Room‐Temperature Ionic Liquids Probed by Quasielastic Neutron Scattering

Quasielastic neutron scattering is used to probe the microscopic diffusion dynamics of the hydrogen‐bearing cations of two different silver complex‐derived room‐temperature ionic liquids, [Ag(propylamine)₂⁺][Tf₂N^?] (Tf=trifluoromethanesulfonyl) and [Ag(1‐pentene)⁺][Tf₂N^?]. In the temperature range from 300 to 340 K, analysis of the scattering momentum transfer dependence of the data provides evidence for three distinct diffusion components. The slowest component describes the long‐range cationic translational diffusion. A possible link between the microscopic diffusion parameters and the structural features of the cations comprising these two ionic liquids is discussed.     

Studies on the Solvation Dynamics of Coumarin 153 in 1‐Ethyl‐3‐Methylimidazolium Alkylsulfate Ionic Liquids: Dependence on Alkyl Chain Length

Steady‐state and time‐resolved fluorescence behavior of coumarin 153 (C153) is investigated in a series of 1‐ethyl‐3‐methylimidazolium alkylsulfate ([C₂mim][C_nOSO₃]) ionic liquids differing only in the length of the linear alkyl chain (n=4, 6, and 8) in the anion. The aim of the present study is to understand the role of alkyl chain length in solute rotation and solvation dynamics of C153 in these ionic liquids. The blueshift observed in the steady‐state absorption and emission maxima of C153 on going from the C₄OSO₃ to the C₈OSO₃ system indicates increasing nonpolar character of the microenvironment of the solute with increasing length of the alkyl side chain of the anion of the ionic liquids. The average solvation time is also found to increase on changing the substituent from butyl to octyl, and this is attributed to the increase in the bulk viscosity of the ILs. A steady blueshift of the time‐zero maximum of the fluorescence spectrum with increasing alkyl chain length also indicates that the probe molecule experiences a less polar environment in the early part of the dynamics. Rotational dynamics of C153 are also analyzed by using the Stokes–Einstein–Debye (SED), Gierer–Wirtz (GW), and Dote–Kivelson–Schwartz (DKS) theories. Analyses of the results seem to suggest decoupling of the rotational motion of the probe from solvent viscosity.     

Mass Distribution and Diffusion of [1‐Butyl‐3‐methylimidazolium][Y] Ionic Liquids Adsorbed on the Graphite Surface at 300–800 K

The structure and diffusion behavior of 1‐butyl‐3‐methylimidazolium ([bmim]⁺) ionic liquids with [Cl]^?, [PF₆]^?, and [Tf₂N]^? counterions near a hydrophobic graphite surface are investigated by molecular dynamics simulation over the temperature range of 300–800 K. Near the graphite surface the structure of the ionic liquid differs from that in the bulk and it forms a well‐ordered region extending over 30 Å from the surface. The bottom layer of the ionic liquid is stable over the investigated temperature range due to the inherent slow dynamics of the ionic liquid and the strong Coulombic interactions between cation and anion. In the bottom layer, diffusion is strongly anisotropic and predominantly occurs along the graphite surface. Diffusion perpendicular to the interface (interfacial mass transfer rate k_t) is very slow due to strong ion–substrate interaction. The diffusion behaviors of the three ionic liquids in the two directions all follow an Arrhenius relation, and the activation barrier increases with decreasing anion size. Such an Arrhenius relation is applied to surface‐adsorbed ionic liquids for the first time. The ion size and the surface electrical charge density of the anions are the major factors determining the diffusion behavior of the ionic liquid adjacent to the graphite surface.     

Void‐Assisted Ion‐Paired Proton Transfer at Water–Ionic Liquid Interfaces

At the water–trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate ([P_14,6,6,6][FAP]) ionic liquid interface, the unusual electrochemical transfer behavior of protons (H⁺) and deuterium ions (D⁺) was identified. Alkali metal cations (such as Li⁺, Na⁺, K⁺) did not undergo this transfer. H⁺/D⁺ transfers were assisted by the hydrophobic counter anion of the ionic liquid, [FAP]^?, resulting in the formation of a mixed capacitive layer from the filling of the latent voids within the anisotropic ionic liquid structure. This phenomenon could impact areas such as proton‐coupled electron transfers, fuel cells, and hydrogen storage where ionic liquids are used as aprotic solvents.     

Temperature‐Dependent Prediction of the Liquid Entropy of Ionic Liquids

Modeling of the temperature‐dependent liquid entropy of ionic liquids (ILs) with great accuracy using COSMO‐RS is demonstrated. The minimum structures of eight IL ion pairs are investigated and the entropy, calculated from ion pairs, is found to differ on average only 2 % from the available experimental values (119 data points). For calculations with single ions, the average error amounts to 2.6 % and stronger‐coordinating ions tend to give higher deviations. Additionally, the first parameterization of the standard liquid entropy for ILs is presented in the context of traditional volume‐based thermodynamics (S_l⁰=1.585 kJ mol^?1 K^?1 nm^?3?r_m³+14.09 J mol^?1 K^?1), which sheds light on the statistical treatment of ionic interactions. The findings provide the first direct access to accurate predictions of liquid entropies of ILs, which are tedious and time‐consuming to measure.     

Ionic thermo‐responsive copolymer with multi LCST values: easy and fast LCST‐change through anion exchange

An ionic thermo‐responsive copolymer with multiple lower critical solution temperatures (multi‐LCSTs) has been developed, and the multi‐LCSTs were easily changeable according to the various counter anion types. The multi‐LCST values were achieved by introducing an ionic segment with an imidazolium moiety within the p‐NIPAAm polymer chain to produce poly(NIPAAm‐co‐BVIm) copolymers, [p‐NIBIm]⁺[Br]^?, and changing the counter anion type to produce [p‐NIBIm]⁺[X]^? (X = Cl, AcO, HCO₃, BF₄, CF₃SO₃, PF₆, SbF₆). The as‐prepared temperature‐responsive copolymers were physicochemically characterized via proton nuclear magnetic resonance spectroscopy (¹H‐NMR), Fourier‐transform infrared, X‐ray photoelectron spectroscopy, and thermogravimetric analysis. Their various LCST values, micelle sizes, and surface charges were determined using an Ultraviolet‐visible spectrophotometer and a Zeta (ξ) sizer, which were fitted with temperature and stirring control. The copolymers showed a broad LCST spectrum between 39°C and 52°C. The Zeta (ξ) potential values at a pH = 7 decreased from about +9.7 for [p‐NIBIm]⁺[X]^? (X = Cl ≈ Br) to about +2.0 mV for [p‐NIBIm]⁺[X]^? (X = PF₆ ≈ SbF₆). The micelle size (or volume) of the copolymers with different anionic species gradually increased from 181.2 nm (or 2.49 × 10^?17 cm^?3) for [p‐NIBIm]⁺[Br]^? to 229.2 nm (or 5.04 × 10^?17 cm^?3) for [p‐NIBIm]⁺[CF₃SO₃]^?, showing a clear effect of the anion on the micelle size (or volume) at a constant temperature, such as body temperature. The fact that the most important physicochemical properties for the thermo‐responsive copolymers, such as the LCST value, micelle size (or volume), and surface charge, could be easily controlled only through the anion exchange suggests these are highly applicable as ionic thermo‐responsive copolymers in a drug (or gene, protein) delivery system. Copyright © 2015 John Wiley & Sons, Ltd.     

Molecular Reorientational Dynamics of the Neat Ionic Liquid 1‐Butyl‐3‐methylimidazolium Hexafluorophosphate by Measurement of 13C Nuclear Magnetic Relaxation Data

The reorientational dynamics of the ionic liquid 1butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM]PF₆) were studied over a wide range of temperatures by measurement of ¹³C spin–lattice relaxation rates and NOE factors. The reorientational dynamics were evaluated by performing fits to the experimental relaxation data. Thus, the overall reorientational motion was described by a Cole–Davidson spectral density with a Vogel–Fulcher–Tammann temperature dependence of the correlation times. The reorientational motion of the butyl chain was modelled by a combination of the latter model for the overall motion with a Bloembergen–Purcell–Pound spectral density and an Arrhenius temperature dependence for the internal motion. Except for C2 in the aromatic ring, an additional reduction of the spectral density by the Lipari–Szabo model had to be employed. This reduction is a consequence of fast molecular motions before the rotational diffusion process becomes effective. The C2 atom did not exhibit this reduction, because the librational motion of the corresponding C2? H vector is severely hindered due to hydrogen bonding with the hexafluorophosphate anion. The observed dynamic features of the [BMIM]⁺ cation confirm quantum‐chemical structures obtained in a former study.     

Molecular Structure,Vibrational Spectra,and Hydrogen Bonding of the Ionic Liquid 1‐Ethyl‐3‐methyl‐1H‐imidazolium Tetrafluoroborate

The IR and Raman spectra and conformations of the ionic liquid 1‐ethyl‐3‐methyl‐1H‐imidazolium tetrafluoroborate, [EMIM] [BF₄] ( 6 ), were analyzed within the framework of scaled quantum mechanics (SQM). It was shown that SQM successfully reproduced the spectra of the ionic liquid. The computations revealed that normal modes of the EMIM⁺?BF ion pair closely resemble those of the isolated ions EMIM⁺ and BF , except for the antisymmetric BF stretching vibrations of the anion, and the out‐of‐plane and stretching vibrations of the H? C(2) moiety of the cation. The most plausible explanation for the pronounced changes of the latter vibrations upon ion‐pair formation is the H‐bonding between H? C(2) and BF . However, these weak H‐bonds are of minor importance compared with the Coulomb interactions between the ions that keep them closely associated even in dilute CD₂Cl₂ solutions. According to the ‘gas‐phase’ computations, in these associates, the BF anion is positioned over the imidazolium ring of the EMIM⁺ cation and has short contacts not only with the H? C(2) of the latter, but also with a proton of the Me? N(3) group.     

A uniform and one‐dimensional stacking of 2,5‐di­chloro­tetra­cyano­quinodimethanide mol­ecules in the tetra­methyl­arsonium salt

In the tetra­methyl­arsonium salt of 2,5‐di­chloro‐7,7,8,8‐tetra­cyano­quinodimethanide [systematic name: tetra­methyl­arson­ium 2,2′‐(2,5‐dichlorocyclohexa‐2,5‐diene‐1,4‐diylidene)bis(propanedinitrile)], C₄H₁₂As⁺·C₁₂H₂Cl₂N₄^? or [As(CH₃)₄](C₁₂H₂Cl₂N₄), the cation lies disordered about a twofold axis and the radical ion lies about an inversion center forming a uniform [interplanar distance 3.35 (2) Å] and one‐dimensional stacking without any slip. The electrical conductivity of the single crystal at room temperature was less than 10^?9 S cm^?1, and the temperature dependence of para­magnetic susceptibility obeyed a one‐dimensional antiferromagnetic Heisenberg model with a spin‐exchange integral of 83 K in the temperature range 1.8–320.0 K.     

Highly Efficient Diglycolamide‐Based Task‐Specific Ionic Liquids: Synthesis,Unusual Extraction Behaviour,Irradiation, and Fluorescence Studies

Two new diglycolamide‐based task‐specific ionic liquids (DGA? TSILs) were evaluated for the extraction of actinides and lanthanides from acidic feed solutions. These DGA? TSILs were capable of exceptionally high extraction of trivalent actinide ions, such as Am³⁺, and even higher extraction of the lanthanide ion, Eu³⁺ (about 5–10 fold). Dilution of the DGA? TSILs in an ionic liquid, C₄mim⁺ ? NTf₂^?, afforded reasonably high extraction ability, faster mass transfer, and more efficient stripping of the metal ion. The nature of the extracted species was studied by slope analysis, which showed that the extracted species contained one NO₃^? anion, along with the participation of two DGA? TSIL molecules. Time‐resolved laser fluorescence spectroscopy (TRLFS) analysis showed a strong complexation with no inner‐sphere water molecule in the Eu^III? DGA? TSIL complexes in the presence and absence of C₄mim⁺ ? NTf₂^? as the diluent. The very high radiolytic stability of DGA? TSIL 6 makes it one of the most‐efficient solvent systems for the extraction of actinides under acidic feed conditions.     

DFT Study of the Geometrical and Electronic Structures of Geminal Dicationic Ionic Liquids 1,3‐Bis[3‐methylimidazolium‐1‐yl]hexane Halides

In this work, the geometrical and electronic properties of the mono cationic ionic liquid 1‐hexyl‐3‐methylimidazolium halides ([C₆(mim)]⁺_X^?, X=Cl, Br and I) and dicationic ionic liquid 1,3‐bis[3‐methylimidazolium‐1‐yl]hexane halides ([C₆(mim)₂X₂], X=Cl, Br and I) were studied using the density functional theory (DFT). The most stable conformer of these two types ionic liquids (IL) are determined and compared with each other. Results show that in the most stable conformers, in both monocationic ILs and dicationic ILs, the Cl^? and Br^? anions prefer to locate almost in the plane of the imidazolium ring whereas the I^? anion prefers nearly vertical location respect to the imidazolium ring plan. Comparison of hydrogen bonding and ionic interactions in these two types of ionic liquids reveals that these ionic liquids can be formed hydrogen bond by Cl^? and Br^? anion. The calculated thermodynamic functions show that the interaction of cation — anion pair in the dicationic ionic liquids are more than monocationic ionic liquids and these interactions decrease with increasing the halide anion atomic weight.     

The Role of Ion Pairs in the Second‐Order NLO Response of 4‐X‐1‐Methylpiridinium Salts

A series of 4‐X‐1‐methylpyridinium cationic nonlinear optical (NLO) chromophores (X=(E)‐CH?CHC₆H₅; (E)‐CH?CHC₆H₄‐4′‐C(CH₃)₃; (E)‐CH?CHC₆H₄‐4′‐N(CH₃)₂; (E)‐CH?CHC₆H₄‐4′‐N(C₄H₉)₂; (E,E)‐(CH?CH)₂C₆H₄‐4′‐N(CH₃)₂) with various organic (CF₃SO₃^?, p‐CH₃C₆H₄SO₃^?), inorganic (I^?, ClO₄^?, SCN^?, [Hg₂I₆]^2?) and organometallic (cis‐[Ir(CO)₂I₂]^?) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second‐order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second‐order NLO response, investigated by the electric‐field‐induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10^?3 M , and their dipole moments were determined. Generally, below 5×10^?4 M , ion pairs start to dissociate into ions with parallel increase of the second‐order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10^?3 M , some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second‐order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self‐aggregate.     

Preparation and Application of Cholesteryl‐Benzo‐15‐Crown‐5/Cholesteryl Mixed Liquid Crystals

Various mixed liquid crystals containing crown ether‐cholesteryl liquid crystal, benzo‐15‐crown‐5‐COO‐C₂₇H₄₅ (B15C5‐COOCh), with various common cholesteric liquid crystals, e.g., cholesteryl chloride, cholesteryl benzoate and cholesteryl palmitate, were prepared and studied using polarizing microscopy and differential scanning calorimetry. Investigating the concentration effect of B15C5‐COOCh in mixed liquid crystals revealed that the addition of B15C5‐COOCh resulted in wider phase transition temperature ranges of these cholesteryl liquid crystals. The stability of these B15C5‐COOCh/cholesteryl mixed liquid crystals was studied using comprehensive graphic molecular modeling computer programs (Insight II and Discover) to calculate their molecular energy and stability energy. The effect of salts, e.g. Na⁺, Co³⁺, Y³⁺ and La³⁺, on the transition temperature range of the mixed liquid crystals was also investigated. The crown ether cholesteric liquid crystal B15C5‐COOCh was applied both as a surfactant and an ion transport carrier to transport metal ions through liquid membranes. Cholesteryl benzo‐15‐crown‐5 exhibited distinctive characteristics of a surfactant and the critical micellar concentration (CMC) of the surfactant was investigated by the pyrene fluorescence probe method. Cholesteryl benzo‐15‐crown‐5 was successfully applied as a good ion transport carrier (Ionophore) to transport various metal ions, e.g. Li⁺, Na⁺, La³⁺, Fe³⁺ and Co³⁺, through organic liquid membranes. The transport ability of the cholesteryl benzo‐15‐crown‐5 surfactant for these metal ions was in the order: Co³⁺ ≥ Li⁺ > Fe³⁺ > Na⁺ > La³⁺.     

Imidazolium‐based polymerized ionic liquid crystals containing fluorinated cholesteryl mesogens

A series of polymerized ionic liquid crystals (PILCs) bearing fluorinated cholesteryl mesogens were synthesized in this work, which include polymerized imidazolium bromides (PIBs) and polymerized imidazolium hexafluorophosphates (PIHs). The PIBs were synthesized using alkyl bromine‐containing polysiloxanes and 1‐butyl‐1H‐imidazole, and the PIHs were synthesized by anion metathesis reaction using the corresponding PIBs and KPF₆. The chemical structures, liquid crystalline (LC) properties, and electrorheological (ER) effect of these PILCs were characterized by use of various experimental techniques. All the PILCs showed smectic A mesophase on heating and cooling cycles. The smectic layer structure of these PILCs are originated from the rigid fluorinated cholesteryl mesogens and the flexible moieties in the LC phase, but the ion pairs (imidazolium cations–PF₆^?, Im⁺–PF₆^?; or imidazolium cations–Br^?, Im⁺–Br^?) can disperse in the polysiloxane matrix and expand the d‐spacing in the smectic layers. The PIHs show lower T_g and T_i than the corresponding precursor PIBs, which is due to the larger ion volume of Im⁺–PF₆^? for PIHs than that of Im⁺–Br^? for PIBs. A series of 40 V% ER fluids were prepared by mixing the PILCs with polydimethylsiloxane (PDMS), and the ER behaviors were studied. All the PILC/PDMS fluids showed ER effect, and the PIH/PDMS fluids show a little greater ER effect than the PIB/PDMS fluids. The PILC droplets in the ER fluids become deformed owing to both the orientation of fluorinated cholesteryl mesogens and the suppression of ionic migration when a DC electric field was applied, resulting in the occurrence of ER effect. Copyright © 2015 John Wiley & Sons, Ltd.     

HPLC‐DAD and HPLC‐ESI‐MS separation,determination and identification of the spin‐labeled diastereoisomers of podophyllotoxin

Spin‐labeled nitroxide derivatives of podophyllotoxin had better antitumor activity and less toxicity than that of the parent compounds. However, the 2‐H configurations of these spin‐labeled derivatives cannot be determined by nuclear magnetic resonance (NMR) methods. In the present paper, a high‐performance liquid chromatography‐diode array detection (HPLC‐DAD) and a high‐performance liquid chromatography‐electrospray ionization tandem mass spectrometry (HPLC‐ESI/MS/MS) method were developed and validated for the separation, identification of four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 position. In the HPLC‐ESI/MS spectra, each pair of diastereoisomers of the spin‐labeled derivatives in the mixture was directly confirmed and identified by [M+H]⁺ ions and ion ratios of relative abundance of [M‐ROH+H]⁺ (ion 397) to [M+H]⁺. When the [M‐ROH+H]⁺ ions (at m/z 397) were selected as the precursor ions to perform the MS/MS product ion scan. The product ions at m/z 313, 282, and 229 were the common diagnostic ions. The ion ratios of relative abundance of the [M‐ROH+H]⁺ (ion 397) to [M+H]⁺, [A+H]⁺ (ion 313) to [M‐ROH+H]⁺, [A+H‐OCH₃]⁺ (ion 282) to [M‐ROH+H]⁺ and [M‐ROH‐ArH+H]⁺ (ion 229) to [M‐ROH+H]⁺ of each pair of diastereoisomers of the derivatives specifically exhibited a stereochemical effect. Thus, by using identical chromatographic conditions, the combination of DAD and MS/MS data permitted the separation and identification of the four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 in the mixture.     

A Black Phosphorus–Graphite Composite Anode for Li‐/Na‐/K‐Ion Batteries

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In‐depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP‐based composites for high‐performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li⁺, Na⁺, and K⁺ with BP were performed. Ex situ X‐ray absorption near‐edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K⁺ storage than for Na⁺ and Li⁺, which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K₃P, compared with Li₃P and Na₃P. As a result, restricting the formation of K₃P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g^?1 which retains at 600 mAh g^?1 after 50 cycles at 0.25 A g^?1.     

Quantification of Ion‐Pairing Effects on the Nucleophilic Reactivities of Benzoyl‐ and Phenyl‐Substituted Carbanions in Dimethylsulfoxide

Second‐order rate constants for the reactions of acceptor‐substituted phenacyl (PhCO?CH^??Acc) and benzyl anions (Ph?CH^??Acc) with diarylcarbenium ions and quinone methides (reference electrophiles) have been determined in dimethylsulfoxide (DMSO) solution at 20 °C. By studying the kinetics in the presence of variable concentrations of potassium, sodium and lithium salts (up to 10^?2 mol L^?1), the influence of ion‐pairing on the reaction rates was examined. As the concentration of K⁺ did not have any influence on the rate constants at carbanion concentrations in the range of 10^?4–10^?3 mol L^?1, the acquired rate constants could be assigned to the reactivities of the free carbanions. The counter ion effects increase, however, in the series K⁺<Na⁺<Li⁺, and the sensitivity of the carbanion reactivities toward variation of the counter ion strongly depends on the structure of the carbanions. The reactivity parameters N and s_N of the free carbanions were derived from the linear plots of log k₂ against the electrophilicity parameters E of the reference electrophiles, according to the linear‐free energy relationship log k₂(20 °C)=s_N(N+E). These reactivity parameters can be used to predict absolute rate constants for the reactions of these carbanions with other electrophiles of known E parameters.     

The Effect of Ionic Liquid Covalent Bonding to Sol‐Gel Processed Film on Ion Accumulation and Transfer

Accumulation of electroactive anions into a silicate film with covalently bonded room temperature ionic liquid film deposited on an indium tin oxide electrode was studied and compared with an electrode modified with an unconfined room temperature ionic liquid. A thin film containing imidazolium cationic groups was obtained by sol‐gel processing of the ionic liquid precursor 1‐methyl‐3‐(3‐trimethoxysilylpropyl)imidazolium bis(trifluoromethylsulfonyl)imide together with tetramethylorthosilicate on the electrode surface. Profilometry shows that the obtained film is not smooth and its approximate thickness is above 1 μm. It is to some extent permeable for a neutral redox probe – 1,1′‐ferrocene dimethanol. However, it acts as a sponge for electroactive ions like Fe(CN)₆^3?, Fe(CN)₆^4? and IrCl₆^3?. This effect can be traced by cyclic voltammetry down to a concentration equal to 10^?7 mol dm^?3. Some accumulation of the redox active ions also occurs at the electrode modified with the ionic liquid precursor, but the voltammetric signal is significantly smaller compare with the bare electrode. The electrochemical oxidation of the redox liquid t‐butyloferrocene deposited on silicate confined ionic liquid film is followed by the expulsion of the electrogenerated cation into an aqueous solution. On the other hand, the voltammetry obtained with the electrode modified with t‐butyloferrocene solution in the ionic liquid precursor exhibits anion sensitive voltammetry. This is explained by anion insertion into the unconfined ionic liquid deposit following t‐butylferricinium cation formation.     

Systematic Dielectric and NMR Study of the Ionic Liquid 1‐Alkyl‐3‐Methyl Imidazolium

The dynamic behaviors of ionic liquid samples consisting of a series of 1‐alkyl‐3‐methylimidazolium cations and various counteranionic species are investigated systematically over a wide frequency range from 1 MHz to 20 GHz at room temperature using dielectric relaxation (DR) and nuclear magnetic resonance (NMR) spectroscopies. DR spectra for the ionic liquids are reasonably deconvoluted into two or three relaxation modes. The slowest relaxation times are strongly dependent upon sample viscosity and cation size, whereas the relaxation times of other modes are almost independent of these factors. We attribute the two slower relaxation modes to the rotational relaxation modes of the dipolar cations because the correlation times of the cations evaluated using longitudinal relaxation time (T₁ ¹³C NMR) measurements corresponded to the dielectric relaxation times. On the other hand, the fastest relaxation mode is presumably related to the inter‐ion motions of ion‐pairs formed between cationic and anionic species. In the case of the ionic liquid bis(trifluoromethanesulfonyl)imide, the system shows marked dielectric relaxation behavior due to rotational motion of dipolar anionic species in addition to the relaxation modes attributed to the dipolar cations.