Anion Pair Research Articles

Morpholin-4-ium [5-cyano-6-(4-methylphenyl)-4-(morpholin-4-yl)pyrimidin-2-yl](phenylsulfonyl)amide

In the title molecular salt, C4H10NO+·C22H20N5O2S−, pairs of anions are linked by pairs of morpholinium cations through N—H...N and bifurcated N—H...(O,N) hydrogen bonds. Every cation donates two such bonds, one to each of the neighbouring pair of cations, generating centrosymmetric tetramers.

Comparison of Ion Selectivity in Electrodialysis and Capacitive Deionization

Ion-selective removal is an important frontier in water purification technologies. For many emerging applications, removing all ions indiscriminately can lead to excessive energy consumption, high levelized cost of water, poor effluent water quality, and increased waste brine volume. Electrodialysis and capacitive deionization are two electrochemical water purification technologies which are promising toward tunable, ion-selective purification. These technologies have fundamentally different ion removal mechanisms, as electrodialysis leverages electrodiffusion through ion-exchange membranes while capacitive deionization utilizes electrosorption into charged electrodes. We here provide a direct comparison of ion selectivity achieved by these two technologies, focusing on several important ion pairs. We highlight distinct differences in achieved selectivity between these technologies and provide theory results to connect such observations to ion removal mechanisms. Based on the experimental literature, we find that capacitive deionization demonstrates a wider range of achieved ion selectivities than electrodialysis for competing cations such as Na+ vs Ca2+ and Li+ vs Na+, while a wider range is observed for electrodialysis when separating anion pairs such as Cl– vs SO42– and Cl– vs NO3–. We conclude with reviewing “knobs” that can be adjusted to tune the achieved selectivities by both technologies, and emphasize important questions that should be answered in future studies to improve the selectivity of both technologies.

Synthesis, crystal structure and properties of catena-poly[[[bis-(3-methyl-pyridine-κN)nickel(II)]-di-μ-1,3-thio-cyanato] aceto-nitrile monosolvate

In the crystal structure of the title compound, {[Ni(NCS)2(C6H7N)2]·CH3CN} n , the NiII cation is octa-hedrally coordinated by two N-bonding and two S-bonding thio-cyanate anions, as well as two 3-methyl-pyridine coligands, with the thio-cyanate S atoms and the 3-methyl-pyridine N atoms in cis-positions. The metal cations are linked by pairs of thio-cyanate anions into chains that, because of the cis-cis-trans coordination, are corrugated. These chains are arranged in such a way that channels are formed in which disordered aceto-nitrile solvate mol-ecules are located. This overall structural motif is very similar to that observed in Ni(NCS)2[4-(boc-amino)-pyridine]2·CH3CN reported in the literature. At room temperature, the title compound loses its solvent mol-ecules within a few hours, leading to a crystalline phase that is structurally related to that of the pristine material. If the ansolvate is stored in an aceto-nitrile atmosphere, the solvate is formed again. Single-crystal X-ray analysis at room-temperature proves that the crystals decompose immediately, presumably because of the loss of solvent mol-ecules, and from the reciprocal space plots it is obvious that this reaction, in contrast to that in Ni(NCS)2[4-(boc-amino)-pyridine]2·CH3CN, does not proceed via a topotactic reaction.

Roles of Anion–Cation Coupling Transport and Dehydration-Induced Ion–Membrane Interaction in Precise Separation of Ions by Nanofiltration Membranes

Nanofiltration (NF) membranes are playing increasingly crucial roles in addressing emerging environmental challenges by precise separation, yet understanding of the selective transport mechanism is still limited. In this work, the underlying mechanisms governing precise selectivity of the polyamide NF membrane were elucidated using a series of monovalent cations with minor hydrated radius difference. The observed selectivity of a single cation was neither correlated with the hydrated radius nor hydration energy, which could not be explained by the widely accepted NF model or ion dehydration theory. Herein, we employed an Arrhenius approach combined with Monte Carlo simulation to unravel that the transmembrane process of the cation would be dominated by its pairing anion, if the anion has a greater transmembrane energy barrier, due to the constraint of anion-cation coupling transport. Molecular dynamics simulations further revealed that the distinct hydration structure was the primary origin of the energy barrier difference of cations. The cation having a larger incompressible structure after partial dehydration through subnanopores would induce a more significant ion-membrane interaction and consequently a higher energy barrier. Moreover, to validate our proposed mechanisms, a membrane grafting modification toward enlarging the energy barrier difference of dominant ions achieved a 3-fold enhancement in ion separation efficiency. Our work provides insights into the precise separation of ionic species by NF membranes.

Design of novel dual functional ionic liquids and DFT study on their CO2 absorption mechanism

Dual functional ionic liquids with the combinations of diethylenetriamine cation ([DETAH]+) or 1-ethanolamine-ethylenediamine cation([1-AOEt-EDAH]+) and 4-fluorobenzoate anion ([4-F-PhO]−) were explored for efficient CO2 capture in this work, and the absorption mechanisms of isolated ions and ion pairs were investigated using the dispersion corrected density functional theory (DFT) method. Above all, the possible reaction sites and reaction activity of TSILs were inferred by electrostatic potential (ESP) and Frontier molecular orbital analysis, then the reaction pathways for absorbing CO2 were proposed, and the transition state search of each elementary reaction by cation, anion and ion pair absorption was performed. Furthermore, the Gibbs free energy and reaction heat of each path were separately calculated, and the Gibbs free energy barrier and enthalpy barrier diagrams were drawn. In addition, the change of structural parameter, bond order and ADCH charge of reactants (R), transition states (TS), intermediates (IM), and products (P) were compared. The results showed that the absorption reaction of [DETAH]+ was the most likely to occur in kinetics, while that of [1-AOEt-EDAH]+ was favorable in thermodynamics. For the [DETAH][4-F-PhO], ion pair binding competed strongly with the CO2 chemisorption, while for [1-AOEt-EDAH][4-F-PhO], anions improved the stability of the whole structure, leading to the decrease of the Gibbs free energy barrier. Hopefully, the results of this work are helpful to provide a theoretical basis for designing of novel functional ionic liquids.

Effects of substituent and excess electron attachment on proton transfer between the radiosensitizer base pairs in aqueous solution

We investigate the proton transfer reaction of radiosensitizing drugs 5-substituted thymine-adenine (5XT-A, X = Br, OCN) in water solutions through the density functional theory (DFT) computations. The relaxed three-dimension potential energy surfaces (PESs) along the two-hydrogen bond of 5XT-A are constructed to reveal the possible proton transfer pathways. The calculations show that the single proton transfer of 5XT-A undergoes a lower energy barrier than that of normal base pair (5OCNT-A < 5BrT-A < T-A). With considering the excess electron attachment, the anion base pair (T-A)- possesses higher energy barrier associated to the proton transfer process. However, the (5XT-A, X = Br, OCN)- anions could dissociate into T•-A radical, which can promote the intermolecular proton transfer reaction between base pairs. It is found that both the neutral and anionic 5-subsituted base pairs can contribute to DNA mutation through the easier proton transfer reaction, which is qualitatively demonstrated by the substituent-induced hydrogen bond enhancement. Our results are helpful to understand the mechanism of enhanced DNA damage in radiotherapy, and are prospective for the design of radiosensitizing drugs without the biotoxicity.

Hitherto Unknown Solvent and Anion Pairs in Solvation Structures Reveal New Insights into High-Performance Lithium-Ion Batteries.

Solvent‐solvent and solvent‐anion pairings in battery electrolytes have been identified for the first time by nuclear magnetic resonance spectroscopy. These hitherto unknown interactions are enabled by the hydrogen bonding induced by the strong Lewis acid Li+, and exist between the electron‐deficient hydrogen (δ +H) present in the solvent molecules and either other solvent molecules or negatively‐charged anions. Complementary with the well‐established strong but short‐ranged Coulombic interactions between cation and solvent molecules, such weaker but longer‐ranged hydrogen‐bonding casts the formation of an extended liquid structure in electrolytes that is influenced by their components (solvents, additives, salts, and concentration), which in turn dictates the ion transport within bulk electrolytes and across the electrolyte‐electrode interfaces. The discovery of this new inter‐component force completes the picture of how electrolyte components interact and arrange themselves, sets the foundation to design better electrolytes on the fundamental level, and probes battery performances.

Ionic Clathrate Hydrates of Tetraalkylammonium/phosphonium Salts: Structures, Properties, Some Applications, and Perspectives

Ionic clathrate hydrates (ICHs) belong to one of the groups of a wide class of clathrate hydrates. In the crystal structures of ICHs, cation–anion pairs of guest molecules, typically tetraalkylammonium/phosphonium salts, are included into the host framework of hydrogen-bonded water molecules. Because of their suitable phase change temperature and latent heat, ICHs are considered as promising phase change materials for application in cold energy storage and transportation. The presence of vacant cavities in ICHs structures, which can incorporate small gas molecules such as, for example, H2, CH4, CO2, N2, H2S, determines the possibility of their use for the separation and storage of gases. The formation of these double ICHs occurs under much milder pressure and temperature conditions compared to the pure gas hydrates of the same gases. Studying of the structural characteristics and thermophysical properties of ICHs and double ICHs with gases is the necessary basis for their effective applications in different practical ends. This work reviews information related to the new details and features of the structures of ICHs and double ICHs with gases revealed over the last decade or a little more as well as some thermophysical data such as hydrate numbers, temperatures and enthalpies of dissociation. This review focuses only on ICHs of tetrabutyl-, tetraisoamylammonium (TBA, TiAA), and tetrabutylphosphonium (TBP) salts, which are the most common representatives of this class of compounds. One of the sections is devoted to ICHs of TBA and TiAA with polymeric anions such as cross-linked polyacrylates. The purpose of the present paper is to review the studies that have been relatively little addressed in previous works.

Thermal stability limits of imidazolium, piperidinium, pyridinium, and pyrrolidinium ionic liquids immobilized on metal oxides

Twenty-nine different ionic liquids (ILs) consisting of imidazolium, pyridinium, piperidinium, and pyrrolidinium cations and I–, Cl–, Br–, PF6–, BF4–, [DCA]–, and [NTf2]– anions were immobilized on MgO and SiO2. Their short-term thermal stability limits were investigated by thermogravimetric analysis and compared with those of the corresponding bulk ILs. Data showed that the thermal stability limits of ILs change significantly when the ILs are immobilized on metal oxides. These changes were evaluated based on the structural interactions determined by infrared (IR) spectroscopy. Systematic structural differences were considered to investigate the factors affecting the thermal stability of bulk ILs, and their counterparts immobilized on MgO and SiO2. These structural changes were the change in the alkyl chain length, the methylation on C2 site in imidazolium ILs, the change in substituent position in the pyridinium ring, the change in the anion, and the change in the IL family. The strongest factor controlling the thermal stability limits of both bulk ILs and their supported counterparts was determined as the anion type. Accordingly, the basicity of the anion and the surface acidity of the metal oxide and their resulting interactions were found to have a significant effect on the thermal stability limits. Data presented here offer the opportunity to pick a suitable anion and cation pair according to the metal oxide, so that the supported IL can withstand the desired operation conditions in various applications, such as catalysis or gas separation.

High Performance AEM Water Electrolysis with Aemion® Membranes

By 2030 up to 50% of energy is expected to be carried in the bonds of H2. Global electrolysis capacity must increase from the current 240 MW to an anticipated 300 GW in 2030 and 3500 GW in 2050 to enable this transition. Alkaline and PEM electrolyzers are commercially mature with the currently market share of new installations roughly an equal split between these technologies. However, each of these electrolyzers are associated with challenges – alkaline electrolyzers operate at low current density, and require high concentration electrolytes (30 wt% KOH) to conduct hydroxides through the porous electrode separator (I.e., Zirfon). PEM electrolyzers use a proton conductive membrane to enable high current densities, however, running the reaction in acidic electrolyte requires platinum group catalysts and component coatings that hinder scalability at 2050 targets.AEM water electrolyzers address both of these challenges by pairing anion exchange membrane with alkaline electrolyte to enable high current density operation, at high pressure, without noble metal catalysts. These attributes enable the most cost-effective green hydrogen - bringing the DOE hydrogen shot target of $1/kg within reach.Anion exchange membrane chemistries have previously hindered this type of electrolyzer – AEMs based on quaternary amines, or pendant imidazolium groups chemically degrade in concentrated alkaline electrolyte, and mechanically degrade (from swelling) in low concentration alkaline media. Ionomr’s Aemion+ membranes are based on a sterically-protected polybenzimidazole chemistry and are chemically robust (stable in up to 10 M KOH), and exhibit low swelling to enable operation in low concentration electrolytes. These membranes are an enabling technology for long duration water and CO2 electrolysis.This talk highlights how Ionomr’s Aemion+ membranes enable performance in excess of 1 A/cm2 at 1.8 V with non-PGM catalysts and a variety of configurations, and >4000 hours of durability in continuous operation. Figure 1

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

Chemical Characteristics of Surface Water of Sumpil River and Groundwater on its Surroundings

The objective of this study was to know the chemical characteristics of surface water in a segment of Sumpil River and the groundwater on its surrounding. The location of this study was in 3 cross sections, consisting of 1 well on the right of the Sumpil River, 1 well on the left of the Sumpil River flow, and 1 point on the Sumpil River flow. The chemical characteristics of the water were determined by the concentrations of cations and anions in the water sample using the Piper Trilinear Diagram with the GW Chart 1.30 computer program. Based on the results of the study, it was shown that the chemical characteristics of the Sumpil River water and the groundwater at the location of this study were the same, where all water samples had an alkaline earth metals content over the alkali content (zone 1), had a strong acidic content exceeding the weak acidic content (zone 4), have a balanced cation and anion pairs, none of which exceed 50% (zone 9), and shown that all of the water in the location of this study were fresh water.

Strong ion pairing at the origin of modified Li-cation solvation and improved performances of dual-salt electrolytes

Organic phosphates have been widely used as fire-retardant additives/co-solvents to improve the Li-ion electrolyte safety. However, these solvents show poor compatibility with low potential electrodes and cannot work efficiently as sole solvent at low salt concentration. The utilization of high concentration electrolytes was shown to improve the interfacial properties by altering the solvation structure but the drawbacks are low ionic conductivity, high viscosity, and elevated costs. Herein, a dual-salt phosphate-based electrolyte consisting of medium concentration lithium nitrate (LiNO3) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salts in triethyl phosphate (TEP) is analyzed and found to address the above issues. Benefiting from the strong affinity between NO3− and Li+, the use of LiNO3 is found to perturb the solvation structure, with mixed anion (NO3− and TFSI−) pairing with Li+. The detailed environment of Li+ in dual-salt phosphate-based electrolyte is probed through nuclear magnetic resonance and Raman analysis, corroborated by theoretical calculations. The dual-salt formulation is found to lead to the formation of a LiF–Li3N-LiNxOy-rich solid-electrolyte interphase on Li metal surface. The results and analyses not only allow the assembly of LiNi0·5Co0·2Mn0·3O2||Li cells with significantly improved cycling and low-temperature performances but also shine a light on taming strong polarity phosphate electrolytes with fine solvation interplay.

Scaling Up the Simultaneous Production of Clean Electricity and Clean Water

The desalination fuel cell (DFC) is a nascent technology for co-production of clean electricity and water from a single cell, driven by the hydrogen-oxygen redox couple. Previously, DFCs employed a single cation and anion exchange membrane pair, and demonstrated desalination of feedwaters of 30 g l−1 NaCl while generating up to 8.6 kWh per m3 of desalinated water. Here, we propose and demonstrate a scaling strategy for DFCs, by adding additional alternating anion and cation exchange membrane pairs. Such a strategy is supported by previous measurements showing small potential loss across membranes in DFCs relative to that at the electrodes. We characterize and compare three cell configurations, including single, double or triple membrane pairs. We show that adding membrane pairs maintains the desalination performance of our DFC, while only moderately reducing cell power density. In addition, adding membrane pairs enables increased flexibility in the choice of anolyte and catholyte solutions, as these are no longer the primary brine channels. We show that optimizing the anolyte and catholyte enables a record power density of up to 10 mW cm−2 during desalination. We further develop and implement expressions for quantification of the thermodynamic energy efficiency of a multiple-membrane-pair DFC.

Anion π-π Stacking for Improved Lithium Transport in Polymer Electrolytes.

Polymer electrolytes (PEs) with excellent flexibility, processability, and good contact with lithium metal (Li°) anodes have attracted substantial attention in both academic and industrial settings. However, conventional poly(ethylene oxide) (PEO)-based PEs suffer from a low lithium-ion transference number (TLi+), leading to a notorious concentration gradient and internal cell polarization. Here, we report two kinds of highly lithium-ion conductive and solvent-free PEs using the benzene-based lithium salts, lithium (benzenesulfonyl)(trifluoromethanesulfonyl)imide (LiBTFSI) and lithium (2,4,6-triisopropylbenzenesulfonyl)(trifluoromethanesulfonyl)imide (LiTPBTFSI), which show significantly improved TLi+ and selective lithium-ion conductivity. Using molecular dynamics simulations, we pinpoint the strong π-π stacking interaction between pairs of benzene-based anions as the cause of this improvement. In addition, we show that Li°∥Li° and Li°∥LiFePO4 cells with the LiBTFSI/PEO electrolytes present enhanced cycling performance. By considering π-π stacking interactions as a new molecular-level design route of salts for electrolyte, this work provides an efficient and facile novel strategy for attaining highly selective lithium-ion conductive PEs.

Diclofenac Ion Hydration: Experimental and Theoretical Search for Anion Pairs.

Self-assembly of organic ions in aqueous solutions is a hot topic at the present time, and substances that are well-soluble in water are usually studied. In this work, aqueous solutions of sodium diclofenac are investigated, which, like most medicinal compounds, is poorly soluble in water. Classical MD modeling of an aqueous solution of diclofenac sodium showed equilibrium between the hydrated anion and the hydrated dimer of the diclofenac anion. The assignment and interpretation of the bands in the UV, NIR, and IR spectra are based on DFT calculations in the discrete-continuum approximation. It has been shown that the combined use of spectroscopic methods in various frequency ranges with classical MD simulations and DFT calculations provides valuable information on the association processes of medical compounds in aqueous solutions. Additionally, such a combined application of experimental and calculation methods allowed us to put forward a hypothesis about the mechanism of the effect of diclofenac sodium in high dilutions on a solution of diclofenac sodium.

Probing the effect of R-cation radii on structural, vibrational, optical, and dielectric properties of rare earth (R=La, Pr, Nd) aluminates

The present study correlates the effect of R-cation radii on structural, vibrational, optical, and dielectric properties of rhombohedral rare earth aluminates RAlO3 (R = La, Pr, Nd). The polycrystalline samples of RAlO3 have been synthesized using sol-gel synthesis technique. Pure rhombohedral phase of RAlO3 samples has been confirmed with X-ray diffraction. Systematic decrements in the lattice parameter, bond length, and bond angle have been observed, giving rise to structural distortion due to decrease in ionic radii of R-cation. The phononic properties of RAlO3 have been investigated through Raman spectroscopy, where the degree of distortion of AlO6 octahedra can be analyzed with the peak position of Eg and A1g modes. An increase in the energy bandgap with decreasing R-cation radii shows an interconnection with the decrease in Al–O bond length. Interestingly, the decreasing dielectric constant with decreasing ionic radii of R-cation has been correlated with the difference in electronegativity of cation(R3+)-anion(O2−) pair. Also, a positive linear relationship between dielectric constant and energy bandgap has been investigated using Penn model.

Imidazolium ionic liquids as potential persistent pollutants in aqueous environments: Indirect photochemical degradation kinetics and mechanism

Ionic liquids (ILs) with promising application are likely to become ubiquitous contaminants in water environment for their high hydrophilicity, low biodegradability, and especially its potential toxicity. In this work, we have investigated photochemical transformation of six imidazolium ILs for fate prediction and ecological risk assessment. We found that the reaction rates of the ILs with •OH, CO3•─ and 1O2 enhanced with their increasing alkyl chain and varied slightly with the paired anions. Meanwhile, modelled results under different scenarios indicate that the primary contributors to transformation of the ILs are triplet-stated dissolved matter (3CDOM*), •OH and CO3•–. Besides, the overall half-lives of the ILs can reach 670 days, which indicates persistence of these ILs in the environment. Products for ILs in reaction with •OH and triplet-stated sodium anthraquinone-2-sulfonate (3AQ2S*) were probed by UHPLC-Q-TOF-MS/MS and there is a difference between their products: Products by •OH are likely formed by hydrogen abstraction from the side alkyl chain, followed by dehydrogenation, hydroxylation and carbonylation, while one of the products by 3AQ2S* is formed by dihydroxyl-addition of the imidazolium ring. Furthermore, the ILs and its products were estimated to have toxicity and non-readily biodegradability, suggesting potential eco-risk for the environmental water.

The refined determination of the ion pair lifetimes in ionic liquids

Assessing lifetimes of liquid’s local structures could bring impactful output. For example, the key transport properties of ionic liquids are governed by local structure dynamics to a large extent. Due to long-range Coulomb interactions, these systems show pronounced charge ordering. In this case, the local structure breaking rate could be described in terms of cation–anion pair lifetimes. Conventional pair lifetime analysis relies on geometrical criterion, defining the maximum distance from cation to anion in pair. In this study, we argue towards additional restriction to ensure pair stability. Based on vibrational properties, we introduce lower boundary for pair lifetime to exclude false pair recognition in the case of collision-like interaction. Also, we put forward a computational algorithm which allows obtaining both mean lifetime and lifetime distribution. The calculations of mean pair lifetimes in molten alkali halides support our reasoning.

Effect of anion and cation vacancies pairs in conduct of the [formula omitted] and [formula omitted] (x = 0.0033) as a memristor

As a memristor with a memory effect, barium titanate (BT) is an excellent choice for designing a memory circuit. Vacancies control the memory effect, performance, and operating temperature of the BT memristor. However, different anion and cation vacancies pairs as Schottky type defects have diverse effects on memristor conducts. In this research, the influence of oxygen and barium vacancies in Ba1−3xTiO31−x as well as oxygen and titanium vacancies in BaTi(1−3x2)O3(1−x) (x = 0.0033) on memristor manner have been investigated by molecular dynamics (MD) simulation. The obtained results indicate the type of pairs vacancies dramatically influence the diffusion of ions, response to DC voltage, and hysteresis loop area. The barium vacancies trapped fewer oxygen vacancies than titanium vacancies. So, Ba1−3xTiO31−x has more oxygen diffusion ions, better electrical current, and more hysteresis loop area than BaTi(1−3x2)O3(1−x). Therefore, Ba1−3xTiO31−x is an appropriate choice for memristor. Memristor manufacturing companies can use the obtained result from this paper to design memristors with more efficiency and low operation temperature.