Salt Ion Pairs Research Articles

Fluorination Promotes Lithium Salt Dissolution in Borate Esters for Lithium Metal Batteries

Lithium metal batteries promise higher energy densities than current lithium-ion batteries but require novel electrolytes to extend their cycle life. To promote electrolyte stability against lithium metal and improve the reversibility of lithium deposition/stripping, several electrolyte design strategies have been pursued. For example, high concentration electrolytes (HCEs) and localized high concentration electrolytes (LHCEs) produce solvation structure rich in salt aggregates and ion pairs, which can increase lithium metal cycling Coulombic efficiency to as high as 99.5%. Recently, molecular design of fluorinated ether solvents also leads to high lithium metal Coulombic efficiency of up to 99.9% in single-solvent-single-salt ~ 1 M electrolytes. In addition, fluorinated acetals, fluorinated carbonates, and fluorinated sulfonamides are also reported to enable efficient lithium metal cycling. Among those novel electrolytes, fluorinated solvents or diluents are frequently used because fluorinated moieties are known to yield LiF as a preferable component in solid electrolyte interphase (SEI). However, fluorinated groups are believed to weaken ion solvation as most fluorinated solvents show poorer solvation ability or lower ionic conductivity compared to their nonfluorinated counterparts. The trade-off between SEI passivation and ion solvation limits further optimization of fluorinated electrolytes.In this work, we synthesize tris(2-fluoroethyl) borate (TFEB) as a new fluorinated borate ester solvent. Interestingly, moderately fluorinated TFEB shows unexpectedly high lithium salt solubility (~1 M LiFSA) while the nonfluorinated triethyl borate (TEB) and heavily fluorinated tris(2,2,2-trifluoroethyl) borate (TTFEB) can hardly dissolve lithium salt. Through density functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations, we show that the partially fluorinated -CH2F group in TFEB acts as primary coordination site that promotes lithium salt dissolution. The electrochemical property of TFEB electrolyte is then compared to the methoxy polyethyleneglycol borate esters reported in literature. Owing to the fluorinated solvent structure, TFEB electrolyte passivates lithium metal with LiF-rich SEI and supports compact lithium deposition morphology, high lithium metal Coulombic efficiency, and stable cycling of lithium metal/LiFePO4 cells. This work ushers in a new electrolyte design paradigm where partially fluorinated moieties enable salt dissolution and can serve as primary ion coordination sites for next-generation electrolytes. Figure 1

Ammonium halide selective ion pair recognition and extraction with a chalcogen bonding heteroditopic receptor.

The first example of a heteroditopic receptor capable of cooperative recognition and extraction of ammonium salt (NH4X) ion-pairs is described. Consisting of a bidentate 3,5-bis-tellurotriazole chalcogen bond donor binding cleft, the appendage of benzo-15-crown-5 (B15C5) substituents to the tellurium centres facilitates binding of the ammonium cation via a co-facial bis-B15C5 sandwich complex, which serves to switch on chalcogen bonding-mediated anion binding potency. Extensive quantitative ion-pair recognition 1H NMR titration studies in CD3CN/CDCl3 (1 : 1, v/v) solvent media reveal impressive ion-pair binding affinities towards a variety of ammonium halide, nitrate and thiocyanate salts, with the heteroditopic receptor displaying notable ammonium halide salt selectivity. The prodigious solution phase NH4X recognition also translates to efficient solid-liquid and liquid-liquid extraction capabilities.

CO2 Adsorption Based on Porphyrin Based Porous Organic Polymers

In order to efficiently catalyze the cycloaddition reaction of CO2 and epoxy alkanes under mild environment and no catalyst, this paper designed and synthesized two kinds of porphyrin based porous organic polymers—porphyrin based porous organic polymer containing carboxyl group (ppop-cooh) and porphyrin based porous organic polymer containing quaternary ammonium salt ion pair. Quaternary ammonium salt cation anion pair nucleophilic groups and metal active centers were introduced into the polymer by pre- and post-modification respectively. The chemical structure and pore structure of the polymer were characterized by infrared spectroscopy and physical adsorption instrument, and its effect as a catalyst on the cycloaddition reaction of CO2 and epoxy alkanes was studied. From the results, it is demonstrated that the two polymers had a multistage pore structure with a specific surface area of 302 m2/g-514 m2/g. The synergistic effect of Lewis acid metal ions, nucleophiles and multistage pore structure in the polymer significantly promotes the cycloaddition reaction between CO2 and epoxy alkanes. Under mild conditions (80°C, 0.3 MPa, 24h), the selectivity and conversion of the reaction reach more than 99%. The polymer is repeated for many times. After use, it still has good catalytic performance.

Synthesis, Crystal Structure, and Conductivity of a Weakly Coordinating Anion/Cation Salt for Electrolyte Application in Next-Generation Batteries.

ConspectusResearch at historically black colleges and universities (HBCUs) started with humble beginnings by G. W. Carver at Tuskegee Institute AL, the nation's first HBCU. He is now remembered as the man who transformed one crop, peanuts to more than 300 useful products such as food, beverages, medicines, cosmetics, and chemicals. However, research was not the focus of most of the newly founded HBCUs to provide, primarily, liberal arts education and training in agriculture for the black minority. HBCUs remained segregated, lacking facilities such as libraries and scientific/research equipment comparable to those at traditionally white institutions. While the Civil Rights Act of 1964 heralded the dawn of "equal opportunity" and progressive desegregation in the South, many public HBCUs had to close or merge with white institutions due to loss of funding and/or students. In order to remain competitive in enrollment and financial support of the best talents, HBCUs have been expanding their research and federal contracts by working in collaboration with research-intensive institutions and/or minority-serving institutions (MSIs). Albany State University (ASU), an HBCU with a great tradition of in-house and extramural undergraduate research, has partnered with the laboratory of Dr. John Miller at Brookhaven National Laboratory (BNL) to offer the best training and mentorship to our undergraduates. Students synthesized and performed conductivity measurements on a new generation of ion-pair salts. One of these constitutes, potentially, a nonaqueous electrolyte for the next generation of high-energy-density batteries owing to its electrochemical properties.The quest for rechargeable batteries with greater energy density and capable of shorter recharge time at the "pump" for electrical vehicles (EVs) is leading the development of electrolytes with higher ionic mobility and greater limiting conductivity. In order to achieve high energy density, it is vital for an electrolyte to be electrochemically stable while operating at high voltages.The development of a weakly coordinating anion/cation electrolyte for energy storage applications offers a challenge of technological significance. This class of electrolytes is advantageous for the investigation of electrode processes in low-polarity solvents. The improvement arises from the optimization of both ionic conductivity and solubility of the ion pair formed between a substituted tetra-arylphosphonium (TAPR) cation and tetrakis-fluoroarylborate (TFAB), a weakly coordinating anion. The chemical "push-pull" between cation and anion affords a highly conducting ion pair in low-polarity solvents such as tetrahydrofuran (THF) and tert-butyl methyl ether (TBME). The limiting conductivity value of the salt, namely, tetra-p-methoxy-phenylphosphonium-tetrakis(pentafluorophenyl)borate or TAPR/TFAB (R = p-OCH3), is in the range of lithium hexafluorophosphate (LiPF6) used in lithium-ion batteries (LIBs). This TAPR/TFAB salt can improve the efficiency and stability of batteries over those of existing and commonly used electrolytes by optimizing the conductivity tailored to the redox-active molecules. LiPF6 dissolved in carbonate solvents is unstable with high-voltage electrodes that are required to achieve greater energy density. In contrast, the TAPOMe/TFAB salt is stable and has a good solubility profile in low-polarity solvents given its relatively great size. And it constitutes a low-cost supporting electrolyte capable of bringing nonaqueous energy storage devices to compete with existing technologies.

Structural and physicochemical characterization of ion-pair salts with dipyridyl cations and [Fe(CN)6]4− and [Fe(CN)5(NO)]2− anions

The series of salts with 2,2′-H2bpy, 2,2′-Hbpy, 4,4′-H2bpy and dq2+ as cations (where bpy – bipyridine, dq - diquat) and, [Fe(CN)6]4- as anions were synthesized and described. Three of them, with the [Fe(CN)5(NO)]2- anion were structurally characterized, and the formulas of other salts were determined on the basis of elemental analysis and IR spectra. In the [Fe(CN)6]4- salts, the ion-pair-charge-transfer bands in the visible range of the reflectance spectra were observed. The relationships between the position of this band, the type of cation, and the oxidation state of these compounds were discussed.

Structural and Physicochemical Characterization of Ion-Pair Salts with Dipyridyl Cations and Cyanido Complexes of Fe(Ii) and Fe(Iii)

Structural and Physicochemical Characterization of Ion-Pair Salts with Dipyridyl Cations and Cyanido Complexes of Fe(Ii) and Fe(Iii)

SPECTROSCOPY STUDY OF MCl2(H2O)n CLUSTER USING AB INITIO CALCULATIONS

The Infrared (IR) spectroscopy of alkali earth halide salt (MX2) complexes with few numbers of water molecules have been investigated for the first time in this work. BeCl2 and MgCl2 are divalent salts and have been incorporated with water as a polar solvent to form complexes of type MX2(H2O)n. The effect of ion size plays a critical rule in the interactions between solvent and solute. Therefore, Beryllium and Magnesium salts with chloride were chosen to explore this difference. The importance of BeCl2 and MgCl2 comes from their several applications in the industry and pharmacy. For instance, BeCl2 is widely used in the industry as a catalysis of Friede-Craft reactions, while the main application of MgCl2 in pharmacy is as hemodialysis and peritoneal dialysis fluids. Three complexes of each BeCl2 and MgCl2 with water, MX2(H2O)n (n=1-3), were studied, and the chemical structures of these complexes have been performed using ab initio calculations. Ab initio calculations were used to predict possible structures, isomers, and their corresponding IR spectra using Second-order Møller-Plesset perturbation theory (MP2) with 6-311++G as a basis sets. The Geometry evaluations, energy searches, vibrational frequency calculations, and the binding energy of each complex were also extracted theoretically. The minimum energy of complexes structures was calculated, and different isomers have been recorded. Ionic hydrogen bonds (IHBs) between the OH in each water molecule and the chloride ion in the MCl2 was proposed to be the main prevalent contribution to the binding between the salt and water. The bond length between the alkaline metal and chlorine showed a significant increase with increasing the attached water molecule as a result of forming the IHB. Also, the infrared vibrational bands of the OH stretching region were recorded for the minimum structures, and dramatic redshift was performed. The formation of contact-ion pair structures in which each solvent molecule forms an ionic hydrogen bond (IHB) to the salt ion-pair (X-M+X-) has been confirmed by the predicted infrared spectra.

Ion Conductance, Walden Product Pressure Coefficient And Hydrodynamic Radii Of Sodium Salt Of Methane Sulphonic Acid In Water-Methanol And Water-Dmf Compositions

Ion-conductance, prfencial solvation by Walden product pressure coefficient pressure coefficient and Hydrodynamic Radii correlated with different electrolytes with in solvents is formed by diverse aspects like cohesive energy density, relative viscosity, solvent dielectric constant values of intermediate, with in duel mixture associations of its solvent adesive solvent measures. Sodium saltion solvent interactions of solute ion with solvent core. Conductance data and physical properties of ion viscosity electrolytes are used by change of the sodium salt ion conductance values, Walden product pressure coefficient and Hydrodynamic radii behavior of the ions and these are measured for derived Sodium salt of Methane Sulphonic acid electrolytein water-MeOH and water-DMF of dissimilar composition in the heat choice of 283K to 313K. A o values KA of electrolyle sodium saltion pair, Association constant values figured out with Shedlovsky Extrapolation method. A°rise with composition of pure water solvent in organic aqueous duel mixture composition in binary sheeth. KA value is more in 80% water-MeOH composition signifying sodium saltion of sodium solvention interactions are more at this binary composition of solvention and thermodynamic properties for the function of specified sodium saltion solvent interaction in composition for structural effects.

Cation Effect of Chloride Salting Agents on Transition Metal Ion Hydration and Solvent Extraction by the Basic Extractant Methyltrioctylammonium Chloride.

The addition of a nonextractable salt has an important influence on the solvent extraction of metal ions, but the underlying principles are not completely understood yet. However, relating solute hydration mechanisms to solvent extraction equilibria is key to understanding the mechanism of solvent extraction of metal ions as a whole. We have studied the speciation of Co(II), Zn(II), and Cu(II) in aqueous solutions containing different chloride salts to understand their extraction to the basic extractant methyltrioctylammonium chloride (TOMAC). This includes the first speciation profile of Zn(II) in chloride media with the three Zn(II) species [Zn(H2O)6]2+, [ZnCl3H2O]−, and [ZnCl4]2–. The observed differences in extraction efficiency for a given transition metal ion can be explained by transition metal ion hydration due to ion–solvent interactions, rather than by ion–solute interactions or by differences in speciation. Chloride salting agents bearing a cation with a larger hydration Gibbs free energy reduce the free water content more, resulting in a lower hydration for the transition metal ion. This destabilizes the transition metal chloro complex in the aqueous phase and increases the extraction efficiency. Salting agents with di- and trivalent cations reduce the transition metal chloro complex hydration less than expected, resulting in a lower extraction efficiency. The cations of these salting agents have a very large hydration Gibbs free energy, but the overall hydration of these salts is reduced due to significant salt ion pair formation. The general order of salting-out strength for the extraction of metal ions from chloride salt solutions is Cs+ < Rb+ < NH4+ ≈ K+ < Al3+ ≈ Mg2+ ≈ Ca2+ ≈ Na+ < Li+. These findings can help in predicting the optimal conditions for metal separation by solvent extraction and also contribute to a broader understanding of the effects of dissolved salts on solutes.

Studies on potential interaction between cinacalcet hydrochloride and diclofenac sodium

Cinacalcet (CT) is an important drug for the treatment hyperparathyroidism. Only few studies havereported thepotential interaction between CT and other potentially coadministered drugs. In this study, the potential of invitro interaction between CT and DF sodium (DF-Na) was investigated. An ion pair salt of CT with DF was obtained by mixing the two compounds in solution; the product was fully characterized by HPLC analysis, UV, FTIR, NMR spectroscopy in addition to DSC. The solubility and partition coefficients were found to significantly decrease and increase, respectively, for the obtained ion pair salt in comparison to the parent compounds. Dissolution studies in phosphate buffer pH 6.8 revealed a significant decrease in the dissolution of an already poorly water soluble drug (decrease to ~20% of the original). Permeation studies, through Caco-2 cells monolayer, revealed a significant decrease in permeation of CT when coexisted with DF (almost to half). Apparent permeability coefficient (Papp) decreased from 3.6 × 10−6 to 1.8 × 10−6 cm/s. Interestingly, a structure for the formed CT-DF salt that could explain the above findings (increase in lipophilicity), could be proposed based on structural modelling, molecular dynamic simulations and NMR proton chemical shifts analysis.

Quaternary ammonium salt ion pair reagent sensitizing for determination of fluorescence whitening agent 85 in paper food packaging.

Fluorescent whitening agents (FWAs) are added to food packaging during manufacture to improve the whiteness and brightness. It is of great significance to develop a fast and sensitive FWAs detection method because their potential hazards to human health. Herein, we found that the quaternary ammonium salt ion pair reagents could enhance the fluorescence of FWAs, and then developed a fluorescent determination method for FWA 85 in paper food packaging. Under the optimized conditions, the linear range for the determination of FWA 85 was 5-200ng/mL (R2=0.9996). The limit of detection was 1.20ng/mL (S/N=3) and the limit of quantitation was 3.99ng/mL. The analytical feasibility was investigated further via determination of FWA 85 in paper food packing, which shows the recoveries were varied from 83.84% to 115.29% with RSDs from 1.64% to 7.22%. The method provides a new quaternary ammonium salt ion pair reagent sensitization for the detection of FWAs in paper food packaging.

Effects of ion specificity on the surface electrical properties of kaolinite and montmorillonite

Clay minerals present a widespread problem in mineral processing and dewatering due to their shrinking and swelling characteristics. These minerals complex surface and interlayer interactions with ions in water play a critical role in governing their behavior. In this paper, the surface electrical properties and suspensions pH of kaolinite (a non-swelling, 1:1 type clay) and montmorillonite (a swelling clay, 2:1 type clay) in the presence of alkaline monovalent salts were investigated to identify the interactions between the ions and the minerals from an ion-pairing perspective. For benchmarking, the two key oxides of SiO2 and Al2O3 constituting the clay minerals were also used in the experiments. It was found that the particle zeta potentials and the suspension pH were strongly related to the type and concentration of the salt ions in water. The results show that ion-pairing and hydration energy being specific to salt ion pairs are the two main driving forces in governing the minerals surface charge and the suspension pH. Ions with weak pairing abilities such as NaI and CsF would have a significant effect on changing the electrical properties of clay surfaces. However, unpaired ions affinity to the surface of the mineral can be minimized because of their high hydration energy. Thus, the interaction with clay minerals surface would be weaker for ions with lower surface charge density (e.g., Cs+ and I−) and smaller hydration energy. Our quantification of the experimental results using the electrical double-layer theory also confirms the ion-pairing and hydration energy theory. The outcome of our investigation would be useful for a better understanding of the dewatering of fine clay-rich tailings.

Interaction of pseudoephedrine and azithromycin with losartan: Spectroscopic, dissolution and permeation studies.

This study aims at investigating the potential effect of selected cationic drugs (azithromycin (AZN) and pseudoephedrine sulfate (PSD) on the dissolution profile and intestinal permeation of losartan potassium (LOS) that might occur due to ion pair salt formation. DSC, FT-IR and 1H NMR indicated the formation of ion pair salts between LOS and each of AZN and PSD. Based on NMR chemical shifts calculations, utilizing specialized software, the most likely structures of the salt were proposed and revealed interesting structural features. The obtained ion pair products were shown to have lower aqueous solubilities (water and phosphate buffer pH 6.8) and higher apparent partition coefficient values compared to the parent compound. Neither of the cations affected the dissolution of LOS tablet (Cozaar® 100 mg) in the studied media (HCl pH 1.2 and phosphate buffer pH 6.8). Interestingly, AZN significantly increased the dissolution of LOS in phosphate buffer pH 4.5 (f2 = 33), and an explanation based on distinguished association pattern between AZN and LOS (CH/π) was offered. Employing permeation test across Caco-2 cells monolayer, the apparent permeability coefficient (Papp) of LOS increased significantly (from 0.9 × 10-5 cm/s to 1.8 × 10-5 cm/s) in the presence of the selected cations. Therefore, while the employed cationic drugs were not shown to form ion pair salts under the in-vitro dissolution conditions, they may still participate in significant in-vivo interaction with LOS.

Cationic Covalent Organic Framework Nanosheets for Fast Li-Ion Conduction.

Covalent organic frameworks (COFs) with their porous structures that are accommodative of Li salts are considered to be potential candidates for solid-state fast Li+ conductors. However, Li salts simply infiltrated in the pores of solid-state COFs tend to be present in closely associate ion pairs, resulting in slow ionic diffusion dynamics. Here we incorporate cationic skeleton into the COF structure to split the Li salt ion pair through stronger dielectric screening. It is observed that the concentration of free Li+ ions in the resulting material is drastically increased, leading to a significantly improved Li+ conductivity in the absence of any solvent (up to 2.09 × 10-4 S cm-1 at 70 °C).

Solubility of Gliclazide and Ion-Molecular Interactions with Aminopropanol in Aqueous Solutions

A new salt of gliclazide (GZD) was prepared and was shown to have a significantly higher aqueous solubility at physiological pH together with superior dissolution profiles in comparison to GZD employing an organic amino-alcohol base. Characterization by NMR, IR, DSC, conductometry and HPLC techniques concluded that an ion pair salt is formed between acidic GZD and basic aminopropanol (AMP). In addition to the presence of about 5% tightly bound water, hydrogen bonds appeared to form extensively between GZD, AMP and water molecules. Unlike many of solubility enhancing approaches, the salt did not hamper the permeability of GZD as shown by transport through Caco-2 cells model. In vivo studies on rats confirmed that the blood glucose lowering effect of GZD-AMP was significantly higher and more rapid compared to parent GZD indicating an enhanced overall performance of the prepared salt.

On the Mesophase Formation of 1,3-Dialkylimidazolium Ionic Liquids

A series of seven different 1,3-dialkylimidazolium-based ion-pair salts with the same molecular weight and size but different symmetries was synthesized. For all salts, bromide was chosen as the counterion, giving the series ([CnIMCm][Br]), where IM = imidazolium and Cn and Cm are varying N-alkyl substituents with n + m = 13. Thus, the effect of symmetry on the physicochemical properties, such as thermal transitions, densities and viscosities and particularly mesophase formation, is investigated herein. All salts are fully characterized by NMR spectroscopy and mass spectrometry, and their physicochemical properties such as thermal transitions, densities, and viscosities are reported. Single crystal X-ray structure analysis is reported for 1-tridecylimidazolium bromide ([C0IMC13][Br]) and 1-ethyl-3-undecylimidazolium bromide ([C2IMC11][Br]). Salts 1-tridecylimidazolium bromide ([C0IMC13][Br]) and 1-dodecyl-3-methylimidazolium bromide ([C1IMC12][Br]) exhibit thermotropic liquid crystal behavior, confirmed by differential scanning calorimetry, polarized optical microscopy, and small-angle X-ray diffraction to be the SmA mesophase. A structure with interdigitation of alkyl chains is observed for all of [C0IMC13][Br], [C1IMC12][Br], and [C2IMC11][Br], despite the absence of thermotropic liquid crystalline behavior for the latter (and all other isomers with an alkyl chain length less than 12 carbon atoms). This allows us to draw the conclusion that for the liquid crystal phase of an ionic liquid to exist, not only are the calamitic shape and integral length of a molecule important but a minimal alkyl chain length of n = 12 is also required. Therefore, a dodecyl group could be considered as the functional group responsible for liquid crystalline behavior.

Near-infrared pigments based on ion-pair charge transfer salts of dicationic and dianionic metal–dithiolene [M(ii) = Pd, Pt] complexes

Mixing [M(Et2dazdt)2](BF4)2 [M = Ni(II), Pd(II), Pt(II); Et2dazdt = N,N'-diethyl-perhydrodiazepine-2,3-dithione] with (Bu4N)2[M(mnt)2] (mnt = maleonitrile-2,3-dithiolate) in CH3CN produces the known mixed ligand dithiolene complex [Ni(Et2dazdt)(mnt)] in the nickel case and ion-pair salts [M(Et2dazdt)2][M(mnt)2] in the palladium (1) and platinum (2) cases. Structural characterization of 2 shows that the anionic (donor) and cationic (acceptor) complexes form an irregular stack that lies in the bc crystallographic plane. The shortest contacts exchanged by the anion and cation molecules within each stack are those occurring through the hydrogen atoms of the CH2 groups of Et2dazdt and the Pt(2)-S(22) segment (d(H(81a)-S(22) = 2.981(3) Å) and the nitrogen atom of the cyano group of mnt and the carbon atom of one of the thione moieties (d(N(12)-C(11) = 3.179(3) Å). The Pt atom of [Pt(mnt)2](2-) is surrounded by two hydrogen atoms of the Et2dazdt ligand, whereas the Pt atom of [Pt(Et2dazdt)2](2+) is surrounded by two carbon atoms of the dithiolate moiety of mnt. Intramolecular interactions are due to contacts exchanged mainly through H-atoms, which are suitable to mediate charge-transfer (CT) interactions. In fact, these salts are characterized by a long wavelength CT peak [λmax = 905 nm (1), 937 nm (2)], which makes them candidates as near-infrared pigments, whose properties are tunable with the redox features of the components, the energy of the NIR absorption being relatable to the driving force of electron transfer from the donor (dianion) to the acceptor (dication). A thorough description of interactions occurring between the complex anions and complex cations has been achieved by investigating the Hirshfeld surface (HS) properties. Computational methods are in agreement with experimental findings and allow us to highlight the electronic features of the components of these CT salts, providing a structure-property relationship, useful in designing new candidates to optimize the desired properties.

Correlations of Ion Motion and Chain Motion in Salt-in-Polysiloxane-g-oligoether Electrolytes

The transport properties of salt and chains in a salt-in-polymer electrolyte consisting of polysiloxane-g-oligoether with different concentrations of lithium triflate, LiSO3CF3, are investigated. Temperature-dependent impedance spectroscopy, viscosity, and multinuclear self-diffusion NMR characterize the mobility of the chains and the different salt species, i.e., ion pairs or single ions. Comparison of different transport parameters allows conclusions about the motions of different species and correlations between them. For example, comparing diffusion coefficients and conductivities via the Nernst–Einstein equation, the fraction of undissociated ion pairs is concluded to be larger than 90%. Macroscopic and microscopic viscosities describe chain and small species motions, respectively. Distinct differences are observed between the temperature-dependence of the transport parameters of ion pairs, which is of Arrhenius-type, and that of the transport of chains or single ions, which deviates from Arrhenius, ...

Application of Tetraphenyl- and Ethyltriphenylphosphonium Salts for Separation of Reactive Dyes from Aqueous Solution

The decolorization efficiency of four anionic dyes dissolved in aqueous solution using two quaternary phosphonium salts, ethyltriphenylphosphonium bromide, and tetraphenylphosphonium bromide, has been investigated by spectroscopic measurements in neutral, acidic and basic media. The NMR studies suggest possible formation of ion pairs of tetrasubstituted phosphonium salts with the reactive dyes. According to the results, the tetraphenylphosphonium bromide, which contains a more hydrophobic and bulky cation, exhibited a stronger tendency to associate with the dyes.

Neutral species from “non-protic” N-heterocyclic ionic liquids

Possible isomerisation of 1,2,3-trialkylimidazolium and 1-alkylpyridinium ion pairs by proton transfer and by the nucleophilic addition of the anion to the cation have been investigated at the B3LYP/6-31+G* and B3LYP/6-311+G** levels of density functional theory. The deprotonation energies of 1,2,3-trialkylimidazolium and 1-alkylpyridinium cations to diaza-pentafulvene and pyridinium-ylide, respectively, were only slightly larger than that of 1,3-dialkylimidazolium salts yielding N-heterocyclic carbenes. Accordingly, in the case of 1,2,3-dialkylimidazolium salt ion pairs the stability of the H-bonded complex between the fulvene and the corresponding acid can be comparable to that of the ion pair in the presence of sufficiently basic anions, such as acetate. In the case of the pyridinium salts the nucleophilicity of the cation dominates over the acidity, and the formation of 1,2- or 1,4-dihydropyridine derivatives is preferred over proton transfer.