Synthesis and Thermophysical Properties of Ether‐Functionalized Sulfonium Ionic Liquids as Potential Electrolytes for Electrochemical Applications

During this work, a novel series of hydrophobic room temperature ionic liquids (ILs) based on five ether functionalized sulfonium cations bearing the bis{(trifluoromethyl)sulfonyl}imide, [NTf₂]^? anion were synthesized and characterized. Their physicochemical properties, such as density, viscosity and ionic conductivity, electrochemical window, along with thermal properties including phase transition behavior and decomposition temperature, have been measured. All of these ILs showed large liquid range temperature, low viscosity, and good conductivity. Additionally, by combining DFT calculations along with electrochemical characterization it appears that these novel ILs show good electrochemical stability windows, suitable for the potential application as electrolyte materials in electrochemical energy storage devices.     

新型磺酸功能化离子液体理化性质的研究

合成了三类磺酸功能化离子液体,通过STA、DSC-TG、UV-Vis、运动粘度/密度计等手段考察了离子液体的热力学性质、酸度、粘度和密度等理化性质,发现离子液体阴阳离子的结构对这些理化性质有不同程度的影响,并对离子液体的结构与理化性质变化关系进行初步探讨.     

Alkylimidazolium Protic Ionic Liquids: Structural Features and Physicochemical Properties

We focus on a series of protic ionic liquids (PILs) with imidazolium and alkylimidazolium (1R3HIm, R=methyl, ethyl, propyl, and butyl) cations. Using the literature data and our experimental results on the thermal and transport properties, we analyze the effects of the anion nature and the alkyl radical length in the cation structure on the above properties. DFT calculations in gas and solvent phase provide further microscopic insights into the structure and cation-anion binding in these PILs. We show that the higher thermodynamic stability of an ion pair raises the PIL decomposition temperature. The melting points of the salts with the same cation decrease as the hydrocarbon radical in the cation becomes longer, which correlates with the weaker ion-ion interaction inthe ion pairs. A comparative analysis of the protic ILs and corresponding ILs (1R3MeIm) with the same radical (R) in the cation structure and the same anion has been performed. The lower melting points of the ILs with 1R3MeIm cations are assumed to result from the weakening of both the ion-ion interaction and the hydrogen bond.     

Ether-Functionalized Pyrrolidinium-Based Room Temperature Ionic Liquids: Physicochemical Properties,Molecular Dynamics,and the Lithium Ion Coordination Environment

The physicochemical properties of room temperature ionic liquids (RTILs) consisting of bis(trifluoromethanesulfonyl)amide (TFSA⁻) combined with 1-hexyl-1-methylpyrrolidinium (Pyr_1,6⁺), 1-(butoxymethyl)-1-methylpyrrolidinium (Pyr_1,1O4⁺), 1-(4-methoxybutyl)-1-methyl pyrrolidinium (Pyr_1,4O1⁺), and 1-((2-methoxyethoxy)methyl)-1-methylpyrrolidinium (Pyr_1,1O2O1⁺) were investigated using both experimental and computational approaches. Pyr_1,1O2O1TFSA, which contains two ether oxygen atoms, showed the lowest viscosity, and the relationship between its physicochemical properties and the position and number of the ether oxygen atoms was discussed by a careful comparison with Pyr_1,1O4TFSA and Pyr_1,4O1TFSA. Ab initio calculations revealed the conformational flexibility of the side chain containing the ether oxygen atoms. In addition, molecular dynamics (MD) calculations suggested that the ion distributions have a significant impact on the transport properties. Furthermore, the coordination environments of the Li ions in the RTILs were evaluated using Raman spectroscopy, which was supported by MD calculations using 1000 ion pairs. The presented results will be valuable for the design of functionalized RTILs for various applications.     

Transport,Electrochemical and Thermophysical Properties of Two N‐Donor‐Functionalised Ionic Liquids

Two N‐donor‐functionalised ionic liquids (ILs), 1‐ethyl‐1,4‐dimethylpiperazinium bis(trifluoromethylsulfonyl)amide ( 1 ) and 1‐(2‐dimethylaminoethyl)‐dimethylethylammonium bis(trifluoromethylsulfonyl)amide ( 2 ), were synthesised and their electrochemical and transport properties measured. The data were compared with the benchmark system, N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ( 3 ). Marked differences in thermal and electrochemical stability were observed between the two tertiary‐amine‐functionalised salts and the non‐functionalised benchmark. The former are up to 170 K and 2 V less stable than the structural counterpart lacking a tertiary amine function. The ion self‐diffusion coefficients (D_i) and molar conductivities (Λ) are higher for the IL with an open‐chain cation ( 2 ) than that with a cyclic cation ( 1 ), but less than that with a non‐functionalised, heterocyclic cation ( 3 ). The viscosities (η) show the opposite behaviour. The Walden [Λ∝(1/η)^t] and Stokes–Einstein [D_i/T)∝(1/η)^t] exponents, t, are very similar for the three salts, 0.93–0.98 (±0.05); that is, the self‐diffusion coefficients and conductivity are set by η. The D_i for 1 and 2 are the same, within experimental error, at the same viscosity, whereas Λ for 1 is approximately 13 % higher than that of 2 . The diffusion and molar conductivity data are consistent, with a slope of 0.98±0.05 for a plot of ln(ΛT) against ln(D₊+D_?). The Nernst–Einstein deviation parameters (Δ) are such that the mean of the two like‐ion VCCs is greater than that of the unlike ions. The values of Δ are 0.31, 0.36 and 0.42 for 3 , 1 and 2 , respectively, as is typical for ILs, but there is some subtlety in the ion interactions given 2 has the largest value. The distinct diffusion coefficients (DDC) follow the order ${D{{{\rm d}\hfill \atop - - \hfill}}}$ <${D{{{\rm d}\hfill \atop ++\hfill}}}$ <${D{{{\rm d}\hfill \atop +- \hfill}}}$ , as is common for [Tf₂N]^? salts. The ion motions are not correlated as in an electrolyte solution: instead, there is greater anti‐correlation between the velocities of a given anion and the overall ensemble of anions in comparison to those for the cationic analogue, the anti‐correlation for the velocities of which is in turn greater than that for a given ion and the ensemble of oppositely charged ions, an observation that is due to the requirement for the conservation of momentum in the system. The DDC also show fractional SE behaviour with t～0.95.     

Synthesis and Characterization of 5‐Cyanotetrazolide‐Based Ionic Liquids

New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C₂N₅]^? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm^?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C₂N₅]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries.     

Synthesis and Improved Properties of Hypergolic Boronium‐Based Ionic Liquids

A series of asymmetric monoimidazolium dihydroboronium‐based ionic liquids (ILs) were synthesized from amine‐boranes. All the resulting ILs were fully characterized by ¹H and ¹³C NMR, IR spectroscopy, elemental analysis or high resolution mass spectrum. Compared with the symmetric bisimidazolium dihydroboronium‐based ILs, these new ILs exhibited improved properties with shorter ignition delay times (IDs), higher densities, and lower phase transition temperature showing the promising application potential as green propellants.     

Synthesis and Properties of Alkoxy‐ and Alkenyl‐Substituted Peralkylated Imidazolium Ionic Liquids

Novel peralkylated imidazolium ionic liquids bearing alkoxy and/or alkenyl side chains have been synthesized and studied. Different synthetic routes towards the imidazoles and the ionic liquids comprising bromide, iodide, methanesulfonate, bis(trifluoromethylsulfonyl)imide ([NTf₂]^?), and dicyanamide {[N(CN)₂]^?} as the anion were evaluated, and this led to a library of analogues, for which the melting points, viscosities, and electrochemical windows were determined. Incorporation of alkenyl moieties hindered solidification, except for cations with high symmetry. The alkoxy‐derivatized ionic liquids are often crystalline; however, room‐temperature ionic liquids (RTILs) were obtained with the weakly coordinating anions [NTf₂]^? and [N(CN)₂]^?. For the viscosities of the peralkylated RTILs, an opposite trend was found, that is, the alkoxy derivatives are less viscous than their alkenyl‐substituted analogues. Of the crystalline compounds, X‐ray diffraction data were recorded and related to their molecular properties. Upon alkoxy substitution, the electrochemical cathodic limit potential was found to be more positive, whereas the complete electrochemical window of the alkenyl‐substituted imidazolium salts was shifted to somewhat more positive potentials.     

Dual Amino‐Functionalised Phosphonium Ionic Liquids for CO2 Capture

CO ₂ is locked up : Dual amino‐functionalised phosphonium ionic liquids (ILs; see figure) have been prepared. The ILs have excellent thermal properties, such as low glass transition temperatures and high thermal decomposition temperatures. The supported CO₂ absorption of four of the ILs on porous SiO₂ was found to approach one mol CO₂ per mol IL, a factor of two greater than that reported before.

     

Synthesis,Structure, and Physico‐optical Properties of Manganate(II)‐Based Ionic Liquids

Several ionic liquids (ILs) based on complex manganate(II) anions with chloro, bromo, and bis(trifluoromethanesulfonyl)amido (Tf₂N) ligands have been synthesized. As counterions, n‐alkyl‐methylimidazolium (C_nmim) cations of different chain length (alkyl=ethyl (C₂), propyl (C₃), butyl (C₄), hexyl (C₆)) were chosen. Except for the 1‐hexyl‐3‐methylimidazolium ILs, all of the prepared compounds could be obtained in a crystalline state at room temperature. However, each of the compounds displayed a strong tendency to form a supercooled liquid. Generally, solidification via a glass transition took place below ?40 °C. Consequently, all of these compounds can be regarded as ionic liquids. Depending on the local coordination environment of Mn²⁺, green (tetrahedrally coordinated Mn²⁺) or red (octahedrally coordinated Mn²⁺) luminescence emission from the ⁴T(G) level is observed. 1 The local coordination of the luminescent Mn²⁺ centre has been unequivocally established by UV/Vis as well as Raman and IR vibrational spectroscopies. Emission decay times measured at room temperature in the solid state (crystalline or powder) were generally a few ms, although, depending on the ligand, values of up to 25 ms were obtained. For the bromo compounds, the luminescence decay times proved to be almost independent of the physical state and the temperature. However, for the chloro‐ and bis(trifluoromethanesulfonyl)amido ILs, the emission decay times were found to be dependent on the temperature even in the solid state, indicating that the measured values are strongly influenced by nuclear motion and the vibration of the atoms. In the liquid state, the luminescence of tetrahedrally coordinated Mn²⁺ could only be observed when the tetrachloromanganate ILs were diluted with the respective halide ILs. However, for [C₃mim][Mn(Tf₂N)₃], in which Mn²⁺ is in an octahedral coordination environment, a weak red emission from the pure compound was found even in the liquid state at elevated temperatures.     

Task‐Specific Ionic Liquids

In recent years, ionic liquids have attracted the attention of many chemists as a result of their unique properties as solvents for chemical transformations. The focus of this Minireview is on applications of so‐called “task‐specific” ionic liquids, whereby the role of the ionic liquid goes beyond that of a solvent. Such ionic liquids find application in a wide range of areas, including catalysis, synthesis, gas absorption, and analysis.     

Electrochemical Study of Dialcarb “Distillable” Room‐Temperature Ionic Liquids

Electrode‐dependent potential windows (see picture, GC=glassy carbon) are determined for five dialkylammonium carbamate (dialcarb) room‐temperature ionic liquids in a systematic study of their physical and electrochemical properties. The viscosity and conductivity of the dialcarb ionic liquids, which are “distillable” at low temperature, are comparable to those of some conventional room‐temperature ionic liquids.

     

Terpenes to Ionic Liquids: Synthesis and Characterization of Citronellal-Based Chiral Ionic Liquids

A series of new chiral ionic liquids have been prepared and characterized starting from a simple, economical, and commercially available monoterpene, citronellal. The aldehyde functionality in citronellal is converted into a Schiff base using an amine, followed by reduction with Raney nickel to give the desired quaternary amine. Most of the ionic liquids generated using this procedure are found to be liquids at room temperature.     

Electrodeposition of Metals and Semiconductors in Air‐ and Water‐Stable Ionic Liquids

In addition to their stability, the advantages of air‐ and water‐stable ionic liquids over chloroaluminate ionic liquids, which were intensively investigated in the past, are that they are easy to dry, purify, and handle. Moreover, some of these ionic liquids have an extremely large electrochemical window of more than 5 V, and hence they give access to the electrodeposition of many metals and semiconductors, such as Ta, Ti, Si, and Ge. The results to date for the electrodeposition of metals and semiconductors in the most popular air‐ and water‐stable ionic liquids are presented.     

Ionic Liquids with More than One Metal: Optical and Electrochemical Properties versus d-Block Metal Combinations

Thirteen N-butylpyridinium salts, including three monometallic [C₄Py]₂[MCl₄], nine bimetallic [C₄Py]₂[M_1−x^aM_x^bCl₄] and one trimetallic compound [C₄Py]₂[M_1−y-z^aM_y^bM_z^cCl₄] (M=Co, Cu, Mn; x=0.25, 0.50 or 0.75 and y=z=0.33), were synthesized and their structure and thermal and electrochemical properties were studied. All compounds are ionic liquids (ILs) with melting points between 69 and 93 °C. X-ray diffraction proves that all ILs are isostructural. The conductivity at room temperature is between 10⁻⁴ and 10⁻⁸ S cm⁻¹. Some Cu-based ILs reach conductivities of 10⁻² S cm⁻¹, which is, however, probably due to IL dec. This correlates with the optical bandgap measurements indicating the formation of large bandgap semiconductors. At elevated temperatures approaching the melting points, the conductivities reach up to 1.47×10⁻¹ S cm⁻¹ at 70 °C. The electrochemical stability windows of the ILs are between 2.5 and 3.0 V.     

Lanthanoid‐Based Ionic Liquids Incorporating the Dicyanonitrosomethanide Anion

A series of low‐melting‐point salts with hexakisdicyanonitrosomethanidolanthanoidate anions has been synthesised and characterised: (C₂mim)₃[Ln(dcnm)₆] ( 1 Ln ; 1 Ln = 1 La , 1 Ce , 1 Pr , 1 Nd ), (C₂C₁mim)₃[Pr(dcnm)₆] ( 2 Pr ), (C₄C₁pyr)₃[Ce(dcnm)₆] ( 3 Ce ), (N₁₁₁₄)₃[Ln(dcnm)₆] ( 4 Ln ; 4 Ln = 4 La , 4 Ce , 4 Pr , 4 Nd , 4 Sm , 4 Gd ), and (N_1112OH)₃[Ce(dcnm)₆] ( 5 Ce ) (C₂mim=1‐ethyl‐3‐methylimidazolium, C₂C₁mim=1‐ethyl‐2,3‐dimethylimidazolium, C₄C₁py=N‐butyl‐4‐methylpyridinium, N₁₁₁₄=butyltrimethylammonium, N_1112OH=2‐(hydroxyethyl)trimethylammonium=choline). X‐ray crystallography was used to determine the structures of complexes 1 La , 2 Pr , and 5 Ce , all of which contain [Ln(dcnm)₆]^3? ions. Complexes 1 Ln and 2 Pr were all ionic liquids (ILs), with complex 3 Ce melting at 38.1 °C, the lowest melting point of any known complex containing the [Ln(dcnm)₆]^3? trianion. The ammonium‐based cations proved to be less suitable for forming ILs, with complexes 4 Sm and 4 Gd being the only salts with the N₁₁₁₄ cation to have melting points below 100 °C. The choline‐containing complex 5 Ce did not melt up to 160 °C, with the increase in melting point possibly being due to extensive hydrogen bonding, which could be inferred from the crystal structure of the complex.     

Halide‐Free Synthesis of Hydrochalcogenide Ionic Liquids of the Type [Cation][HE] (E=S,Se, Te)

We present the synthesis and thorough characterization of ionic liquids and organic salts based on hydrochalcogenide HE^? (E=S, Se, Te) anions. Our approach is based on halide‐, metal‐, and water‐free decarboxylation of methylcarbonate precursors under acidic conditions, resulting from the easily dissociating reagents H₂E. The compounds were characterized by elemental analysis, multinuclear NMR spectroscopy, thermal and single‐crystal XRD analyses. The hydrosulfide salts were investigated with respect to their ability to dissolve elemental sulfur in varying stoichiometry. Thus‐prepared polysulfide ILs were also analyzed by UV/Vis spectroscopy and cyclic voltammetry.     

Novel Bipyridinium Ionic Liquids as Liquid Electrochromic Devices

Novel mono and dialkylbipyridinium (viologens) cations combined with iodide, bromide, or bis(trifluoromethanesulfonyl)imide [NTf₂] as anions were developed. Selective alkylation synthetic methodologies were optimized in order to obtain the desired salts in moderate to high yields and higher purities. All prepared mono‐ and dialkylbipyridinium salts were completely characterized by ¹H, ¹³C, and ¹⁹F NMR spectroscopy, Fourier‐transform IR spectroscopy, and elemental analysis (in the case of NTf₂ salts). Melting points, glass transition temperatures by differential scanning calorimetry (DSC) studies, and decomposition temperatures were also checked for different prepared organic salts. Viscosities at specific temperatures and activation energies were determined by rheological studies (including viscosity dependence with temperature in heating and cooling processes). Electrochemical studies based on cyclic voltammetry (CV), differential pulsed voltammetry (DPV), and square‐wave voltammetry (SWV) were performed in order to determine the redox potential as well as evaluate reversibility behavior of the novel bipyridinium salts. As proof of concept, we developed a reversible liquid electrochromic device in the form of a U‐tube system, the most promising dialkylbipyridinium‐NTf₂ ionic liquid being used as the electrochromic material and the room‐temperature ionic liquid (RTIL), 1‐ethyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)‐imide [EMIM][NTf₂], as a stable and efficient electrolyte.     

离子液体的分类、合成与应用

离子液体易于循环利用从而减少对环境的污染,作为绿色溶剂可用于分离过程、化学反应,特别是催化反应、以及电化学等方面,并已取得许多良好的实验结果。本文简要介绍离子液体的分类、合成、物理化学特性及应用。