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.     

Structure and properties of high stability geminal dicationic ionic liquids

Thirty-nine geminal dicationic ILs were synthesized and characterized in terms of their surface tensions, densities, melting points, refractive indices, viscosities, and miscibilities with a polar and nonpolar solvent. Two imidazolium or pyrrolidinium cations were joined via different length hydrocarbon linkage chains (from 3 to 12 carbons long). The various geminal dications were paired with up to four different anions. The effect of the dication type, linkage chain, alkyl substituents, and anion type on the physicochemical properties of these compounds was examined. Among the more interesting findings for this class of compounds was that their liquid and thermal stability ranges generally exceeded those of the more conventional, better known ILs. Indeed, this range was from -4 to >400 degrees C for one of the pyrrolidinium-based geminal dicationic liquids. X-ray crystallography of the smaller solid ionic compounds indicated that there may be a correlation between the configurational degrees of freedom of the ILs and their melting points/glass transition temperatures. In one case, the crystal structure showed that a dicationic moiety had three distinct conformations in an asymmetric unit cell. The solvation properties of the geminal dicationic ILs tend to be similar to those of their monocationic analogues.     

Geometrical and electronic structures of the dication and ion pair in the geminal dicationic ionic liquid 1,3-bis[3-methylimidazolium-yl]propane bromide

Geminal dicationic ionic liquids (ILs), a new category of IL family, have been developed recently and found to possess unique properties compared to conventional monocationic ILs. To establish a basis for understanding their novel properties, we studied the geometrical and electronic structures of the dication ([(mim)C₃(mim)]²⁺) and the ion pair ([(mim)C₃(mim)]²⁺-2Br⁻) in the geminal dicationic IL 1,3-bis[3-methylimidazolium-yl]propane bromide by performing density functional theory calculations. The geometrical structures and relative stabilities for the dication and the ion pair are discussed, and their electronic properties are analyzed in detail. The intrinsic interaction between the dication and Br anions in the most stable conformer was investigated by performing the natural bond orbital analyses. Results for the dication and the ion pair are compared with those of the corresponding monocation ([C₄mim]⁺) and ion pair ([C₄mim]⁺-Br⁻). ¹H NMR spectroscopy for the most stable ion pair has been calculated and the general trend is found to be in fairly agreement with the experimental data.     

Synthesis and properties of new (μ-oxo)bis[trichloroferrate(III)] dianion salts incorporated with dicationic moiety

New (μ-oxo)bis[trichloroferrate(III)] dianions-based ionic compounds that contain various counterdications were synthesized and characterized with regards to their crystal structures, thermal properties, and magnetic susceptibility. These salts are soluble in polar solvents such as methanol and water. The melting point of these compounds is affected by the dication following the order of triphenylphosphinium > pyridinium > imidazolium dications, and symmetrical dicationic salts > unsymmetrical ones. In these compounds, the trichloroferrate dianion exists in either a linear or a bent form, which is affected by the dications. Interestingly, the dicationic diferrate compounds show magnetic coupling constants fairly smaller than those reported in literature for diferrate salts in which monocations are the counterion. Furthermore, unlike the diferrate salts associated with separate monocations, the linear diferrate dicationic compounds show magnetic coupling constant lower than that of bent diferrate dicationic salts.     

低聚离子液体的体相与界面及其电化学储能应用

近年来,随着单阳离子液体的发展,新型低聚物离子液体被合成并应用。这类离子液体可看作是由几个重复的单阳离子组合而成,可以通过改变阳离子带电基团、间隔连接的长度或种类、末端链的长度以及阴离子种类来获得更多不同的结构。因此,低聚离子液体有更复杂的微观结构和内部相互作用,决定了其多特征的物化性质和电化学特性,有望满足更多对溶剂性能有特定要求的应用。例如,与单阳离子液体相比,低聚离子液体具有更大的可调节性、更宽的液态温度范围、更高的热稳定性等优点,使其在电化学储能设备中得到越来越多的应用,如用作超级电容器和锂离子电池的电解液。在本综述中,我们系统地总结并详细解释了低聚离子液体的性质和结构（包括单个离子的结构和本体液内部的纳米组织）之间的关联,主要是双阳离子液体和三阳离子液体;概括了低聚离子液体作为超级电容器和锂离子电池的电解液的相关研究,重点阐述了由低聚离子液体和不同类型电极组成的双电层的结构和性能,以及与相应单阳离子液体电解液的比较结果;提供了降低低聚离子液体粘度和加速离子扩散的优化措施,提出了低聚离子液体电解液未来可能面临的主要问题和发展前景。     

Synthesis and properties of dicationic ionic liquids with pentasiloxane linker

New dicationic ionic liquids with pentasiloxane linker between two imidazolium moieties and bis(trifluoromethyl-sulfonyl)imide anions were synthesized; their melting points, glass transition temperatures and viscosities were measured, and thermal and hydrolytic stabilities were investigated. The dependence of the properties of these ionic liquids on the length of the siloxane linker in the cation part is revealed.     

Hydrogen bonds in imidazolium ionic liquids

It is critically important to understand the structural properties of ionic liquids. In this work, the structures of cations, anions, and cation-anion ion-pairs of 1,3-dialkylimidazolium based ionic liquids were optimized systematically at the B3LYP/6-31+G level of DFT theory, and their most stable geometries were obtained. It was found that there exist only one-hydrogen-bonded ion-pairs in single-atomic anion ionic liquids such as [emim]Cl and [emim]Br, while one- and two-hydrogen-bonded ion-pairs in multiple atomic anion ionic liquids such as [emim]BF(4) and [emim]PF(6) exist. Further studies showed that the cations and anions connect each other to form a hydrogen-bonded network in 1,3-dialkylimidazolium halides, which has been proven by experimental measurement. Furthermore, the correlation of melting points and the interaction energies was discussed for both the single atomic anion and multiple atomic anion ionic liquids.     

Solvents effects in the photodegradation and reactivity of the various ionic forms of haematoporphyrin

The dependence of the ionic forms of haematoporphyrin(LX) dihydrochloride (HpdiCl) on solvent composition was investigated. In 2.8 x 10(-4) M solutions of HpdiCl in apolar (C6H6) and polar (CH3CN) solvents, HpdiCl exists in dicationic form. In hydrogen-bonding solvents, such as CH3OH, HpdiCl can exist in neutral, monocationic and dicationic forms. In C6H6-CH3OH solvent mixtures, the ionic forms in which HpdiCl is present depend on the composition of the solvent and on the acidity of the solution. The rate of oxidative photodegradation of HpdiCl excitation in its Q bands (WBI) and the ability to produce free radicals are different for the different ionic species. The highest values correspond to the dicationic form of HpdiCl and the lowest values correspond to the neutral species. In the absence of oxygen, the formation of free radicals due to the reaction of 3(Hp dication) is detected in the following solvent mixtures: CH3OH-toluene, CH3OH-ethylbenzene, CH3OH-hexane. The data obtained indicate that interaction of 3(Hp dication) with methine groups is an intermediate step in the formation of free radicals. In the HpdiCl concentration range studied, the presence of a phenolic antioxidant, such as beta-naphtol, inhibits the oxidative photodegradation of the dicationic form in a treated solution, but has little effect on the oxidative photobleaching of the monocation. The rate of oxidative photodegradation of the monocationic form increases with the addition of propionic acid to the solution.     

Synthesis of dicationic ionic liquids and their application in the preparation of hierarchical zeolite Beta

Piperidine- and imidazole-based dicatoinic ionic liquids have been developed for the synthesis of zeolite Beta. Hierarchical Beta has a larger surface area and pore volume than conventional Beta. Beta derived from a dicationic ionic liquid exhibited remarkably higher catalytic activity than the conventional Beta. Experimental evidence and DFT calculations suggest that only a suitable conformation of such dicationic ionic liquids is able to form zeolite Beta (see scheme).     

From dysfunction to bis-function: on the design and applications of functionalised ionic liquids

Some of the recent developments concerning the synthesis, properties and applications of functionalised ionic liquids are highlighted. Various strategies are presented, including functionalisation of the cation, anion or both cation and anion in the same ionic liquid, leading to what has been termed dual-functionalised ionic liquids. Particular attention is given to the application of functionalised ionic liquids as reaction media, to stabilise nanoparticles/modify surfaces and to generate porous materials.     

A redox-active ionic liquid manifesting charge-transfer interaction between a viologen and carbazole and its effect on the viscosity,ionic conductivity,and redox process of the viologen

Redox-active ionic liquids (RAILs) are gaining attention as a material that can create a wide range of functions. We herein propose a charge-transfer (CT) RAIL by mixing two RAILs, specifically a carbazole-based ionic liquid ([CzC₄ImC₁][TFSI]) as a donor and a viologen-based ionic liquid ([C₄VC₇][TFSI]₂) as an acceptor. We investigated the effect of CT interaction on the physicochemical properties of the CT ionic liquid (CT-IL) using the results of temperature-dependent measurements of UV-vis absorption, viscosity, and ionic conductivity as well as cyclic voltammograms. We employed the Walden analysis and the Grunberg–Nissan model to elucidate the effect of the CT interaction on the viscosity and ionic conductivity. The CT interaction reduces the viscosity by reducing the electrostatic attraction between the dicationic viologen and TFSI anion. It also reduces the ionic conductivity by the CT association of the dicationic viologen and carbazole. The electrochemically reversible responses of the viologens in [C₄VC₇][TFSI]₂ and CT-IL are consistent with the Nernstian and the interacting two-redox site models. Notably, the transport and electrochemical properties are modulated by CT interaction, leading to unique features that are not present in individual component ILs. The inclusion of CT interaction in RAILs thus provides a powerful means to expand the scope of functionalized ionic liquids.

A redox-active ionic liquid (RAIL) consisting of a carbazole and viologen shows charge transfer (CT) interaction. The physicochemical properties are modulated by the CT interaction by comparison with the individual RAILs.     

Tuning the physicochemical properties of diverse phenolic ionic liquids for equimolar CO2 capture by the substituent on the anion

Phenolic ionic liquids for the efficient and reversible capture of CO(2) were designed and prepared from phosphonium hydroxide and substituted phenols. The electron-withdrawing or electron-donating ability, position, and number of the substituents on the anion of these ionic liquids were correlated with the physicochemical properties of the ionic liquids. The results show that the stability, viscosity, and CO(2)-capturing ability of these ionic liquids were significantly affected by the substituents. Furthermore, the relationship between the decomposition temperature, the CO(2)-absorption capacity, and the basicity of these ionic liquids was quantitatively correlated and further rationalized by theoretical calculation. Indeed, these ionic liquids showed good stability, high absorption capacity, and low absorption enthalpy for CO(2) capture. This method, which tunes the physicochemical properties by making use of substituent effects in the anion of the ionic liquid, is important for the design of highly efficient and reversible methods for CO(2)-capture. This CO(2) capture process using diverse phenolic ionic liquids is a promising potential method for CO(2) absorption with both high absorption capacity and good reversibility.     

Evaluation of dicationic reagents for their use in detection of anions using positive ion mode ESI-MS via gas phase ion association

Twenty-three different dications were investigated for their effectiveness in pairing with singly charged anions, thereby allowing the electrospray ionization mass spectrometry (ESI-MS) detection of anions as positively charged complexes. Nitrate, iodide, cyanate, monochloroacetate, benzenesulfonate, and perfluoro-octanoate were chosen as representative test anions as they differ in mass, size-to-charge ratio, chaotropic nature, and overall complexity. Detection limits were found using direct injection of the anion into a carrier liquid containing the dication. Detection limits are given for all six anions with each of the 23 dications. Each anion was easily detected at the ppb (microg/L) and often the ppt (ng/L) levels using certain dicationic reagents. The ability of dicationic reagents to pair with anions and produce ESI-MS signals varied tremendously. Indeed, only a few dications can be considered broadly useful and able to produce sensitive results. Liquid chromatography (LC)-ESI-MS also was investigated and used to show how varying the dicationic reagent produced significantly different peak intensities. Also, the use of tandem mass spectrometry can lead to even greater sensitivity when using imidazolium based dications.     

The effect of the anion on the physical properties of trihalide-based N,N-dialkylimidazolium ionic liquids

Low viscosity, high density trihalide-based 1-n-butyl-3-methylimidazolium ionic liquids have been prepared and characterised. Key physical properties (density, conductivity, melting point, refractive index, surface tension and diffusion coefficient) of the ionic liquids have been determined and are compared with those of other 1,3-dialkylimidazolium molten salts. The relationship between anion identity and the physical properties of the ionic liquids under investigation is discussed.     

X-ray photoelectron spectroscopy of pyrrolidinium-based ionic liquids: cation-anion interactions and a comparison to imidazolium-based analogues

We investigate seven 1-alkyl-1-methylpyrrolidinium-based ionic liquids, [C(n)C(1)Pyrr][X], using X-ray photoelectron spectroscopy (XPS). The electronic environment for each element is analysed and a robust fitting model is developed for the C 1s region that applies to each of the ionic liquids studied. This model allows accurate charge correction and the determination of reliable and reproducible binding energies for each ionic liquid studied. The electronic interaction between the cation and anion is investigated for ionic liquids with one and also two anions. i.e., mixtures. Comparisons are made to imidazolium-based ionic liquids; in particular, a detailed comparison is made between [C(8)C(1)Pyrr][X] and [C(8)C(1)Im][X](-), where X(?) is common to both ionic liquids.     

Describing the unsuspected advantage of redox ionic liquids applied to electrochemical energy storage

Ionic liquids are a class of solvents widely studied in the literature for various applications. As a subclass of ionic liquids, redox ionic liquids can endow charge exchange properties (electrons transfer) to these electrolytes for electrochemical energy storage. In this review article, we propose to study this family of ionic liquids and suggest a chronological classification. We introduce five generations of redox ionic liquids with different basic compounds such as polyethylene glycol, ferrocene, different linker lengths, TFSI anion, and biredox ionic liquids. The versatility of the redox ionic liquids synthesis will be discussed as well as the fundamental and applied aspects of their use as electrolytes, which have high charge densities. The impact of the redox ionic liquids on the electrochemical mechanisms will be described. We also present how the redox shuttle effect, detrimental to supercapacitors, can be prevented while it can be used to improve lithium-ion batteries.     

Synthesis and characterization of novel chiral imidazolium and pyridinium ionic liquids derived from tartaric acid and 2-oxazolidinone

Abstract

Novel chiral imidazolium and pyridinium ionic liquids based on tartaric acid and 2-oxazolidinone were designed. Symmetrical dicationic ionic liquids based on tartaric acid have been synthesized and characterized. These chiral ionic liquids were designed by employing very short and simple methods. Incorporation of alkyl halide over tartaric acid and 2-oxazolidinone is an important step. N-methyl imidazole and pyridine were used for preparation of quaternary salts. These ionic liquids have been evaluated for the asymmetric sulfide oxidation. Chiral ionic liquids based on tartaric acid showed superior chiral inducing property as compare to 2-oxazolidinone based chiral ionic liquids.     

Synthesis and optical properties of ZnO nanostructures in imidazolium-based ionic liquids

Different morphologies of ZnO nanostructures have been synthesized by a simple reflux method, in imidazolium-based ionic liquids and water as a solvent. The effects of ionic liquid as a template with different concentrations and the amount of sodium hydroxide on the morphology and size of nanostructures were investigated. The structural and optical properties of these ZnO particles were studied by using XRD, SEM and UV–Visible. The characteristic results revealed that using different ionic liquids in water not only prevent a drastic increase in the crystallite size of the zinc oxide species but also provide suitable conditions for the oriented growth of primary nanoparticles with nano sheet and nano hallow block. The results show that the longer alkyl chain at position-1 of imidazole ring or using dicationic ionic liquid with a definite concentration cause the more width of nano sheet. A possible mechanism was proposed to explain the formation of ZnO nanostructures with different morphology.     

A comparative electrochemical study of diffusion in room temperature ionic liquid solvents versus acetonitrile.

Measurements on the diffusion coefficient of the neutral molecule N,N,N',N'-tetramethyl-para-phenylenediamine and the radical cation and dication generated by its one- and two-electron oxidation, respectively, are reported over the range 298-348 K in both acetonitrile and four room temperature ionic liquids (RTILs). Data were collected using single and double potential step chronoamperometry at a gold disk electrode of micrometer dimension, and analysed via fitting to the appropriate analytical expression or, where necessary, to simulation. The variation of diffusion coefficient with temperature was found to occur in an Arrhenius-type manner for all combinations of solute and solvent. For a given ionic liquid, the diffusional activation energies of each species were not only closely equivalent to each other, but also to the RTIL's activation energy of viscous flow. In acetonitrile supported with 0.1 M tetrabutylammonium perchlorate, the ratio in diffusion coefficients of the radical cation and dication to the neutral molecule were calculated as 0.89 +/- 0.05 and 0.51 +/- 0.03, respectively. In contrast, amongst the ionic liquids the same ratios were determined to be on average 0.53 +/- 0.04 and 0.33 +/- 0.03. The consequences of this dissimilarity are considered in terms of the modelling of voltammetric data gathered within ionic liquid solvents.     

Isothiouronium salts as useful and odorless intermediates for the synthesis of thiaalkylimidazolium ionic liquids

A simple and odorless route for the synthesis of monocationic and dicationic thiaalkylimidazolium ionic liquids (ILs) is reported. Our approach starts with the selective monoalkylation of dihalogenated substrates by methylimidazole derivatives, followed by the synthesis of odorless isothiouronium salts via reaction with thiourea. The target ILs are obtained after sequential hydrolysis-alkylation of the isothiouronium salts followed by anion metathesis in water. After extraction, the novel thiaalkylimidazolium ILs are obtained with high purity, without the requirement of additional purification steps. In order to demonstrate their applicability, two of these task-specific ILs were employed as ligands in Ullmann and Suzuki couplings and also as charged probes to detect copper intermediates via ESI(+)-MS.