Ion-pair Interactions Research Articles

Cation-Specific interfacial behavior in organic electrolytes for enhanced energy storage

Energy storage systems such as electrical double-layer capacitors have achieved significant attention due to their high power density and cyclability, attained through charge accumulation at the electrode interfaces. Organic electrolytes are widely investigated for energy storage applications owing to their broad potential windows and high specific energy. In this study, we employed constant potential molecular dynamics simulations at various applied potential differences from 0.0 V to 4.0 V to investigate the interfacial structure between organic electrolytes and graphene electrodes. The electrolytes consisted of propylene carbonate (PC) as the solvent, various cations (Li+, Na+, and K+), and bis(trifluoromethanesulfonyl)imide (TFSI−) as the anion. We observed significant structural reorientation of the PC solvent near the electrode surface under high applied potentials, which altered the K+ layer position near the cathode surface and influenced the capacitive behavior of the system. Additionally, K+ ions exhibited a high desolvation rate, lower ion pair interactions, and faster diffusion capabilities compared to Li+ and Na+ ions. These insights are crucial for advancing the understanding and development of organic electrolyte-based metal ion energy storage systems.

Synergistic effect of ceramic filler in polymer salt complex for improved ion dissociation and migration mechanism

Abstract Use of Ceramic filler is one of the most common approaches to improve the conductivity and stability properties of a solid polymer electrolyte (SPE) cum separator. Among them, active fillers like Garnet have been extensively used to enhance the stability and conductivity of SPE. However, SPE suffers from limited ion migration at room temperature acting as a bottleneck for their application in all solid-state batteries. An extensive study on these fillers' role in ion dissociation and migration can be a stepping stone for advanced SPE. In the present work, an FTIR analysis has primarily been used to identify and evaluate cation coordinate site-cation, and ion pair interactions in a Li6.5La3Zr1.75Te0.25O12 loaded polyethylene oxide-LiCF3SO3 matrix with varying ceramic concentrations. Further, the Trukhan model has been used to calculate diffusion coefficient, mobility, and charge carrier density to interpret relaxation parameters, conductivity, and FTIR results in the SPE samples. Finally, an ion migration model has been proposed based on the results obtained in experimental studies.

Quaternized poly(aryl imidazolium) containing bulky binaphthyl group as proton exchange membrane for high-temperature fuel cells

The low power output and high phosphoric acid (PA) leakage are the main constraints restricting the commercialization of PA-doped high-temperature proton exchange membranes (HT-PEMs). Ionized imidazoles have been shown to be an effective strategy to improve PA retention, however, less research has been conducted on the fractional free volume (FFV) of the backbone of the main chain on PA loss. Herein, novel imidazolium ions polymer (PQBN-4-IM) material with bulky binaphthyl (BN) group was prepared as PA-doped HT-PEM using a one-step superoxid acid catalyzed polycondensation and subsequent methylation process. The rigidity and hydrophobicity of the BN group promote PQBN-4-IM PEM to produce more obvious microphase separation morphology and large FFV, which is beneficial for forming better ion transport channels and excellent PA interaction. Notably, the PA-doped PQBN-4-IM (PQBN-4-IM/PA) membrane has the highest proton conductivity (90.26 mS cm−1, 180 ℃) and peak power density (PPD) (802.5 mW cm−2, 180 ℃) than PQTP-4-IM/PA and m-PBI/PA HT-PEMs. Moreover, the PQBN-4-IM/PA membrane has higher PA retention at 80 ℃/40 % relative humidity (RH), 40 ℃/60 % RH, or immersed in water due to enhancement on ion-pair interactions by microstructure. Under the accelerated stress test (AST) of the fuel cell (FC), the PQBN-4-IM/PA membrane loses only 12.22 % of PPD after 200 cycles at 80 ℃, which exhibits higher PPD retention than that of the PQBP-4-IM/PA (70.23 %), PQTP-4-IM/PA (74.36 %) and m-PBI/PA (65.25 %) membranes, and shows excellent durability of cell performance for more than 1000 h without significant voltage decay at 160 °C. Thus, the outstanding performance suggests that the microstructure and morphology of imidazolium ions polymer membranes significantly influence proton conductivity, performance, and the durability of a cell.

Exploiting Ion-Pairing Interactions for Fast and Controlled Ring-Opening Polymerization of rac-β-Butyrolactone at Room Temperature with Dinuclear Sodium and Potassium Catalysts

Exploiting Ion-Pairing Interactions for Fast and Controlled Ring-Opening Polymerization of <i>rac</i>-β-Butyrolactone at Room Temperature with Dinuclear Sodium and Potassium Catalysts

Ion-Pairing Stereodynamic Probes for Circular Dichroism Chiral Sensing of Amines.

Tris(2-pyridylmethyl)amine (TPMA) and tris(2-phenolmethyl)amine (TPA) metal complexes have been extensively used for catalysis and molecular recognition applications. In particular, due to their ability to form stereodynamic complexes through the helical arrangement of the ligand around the metal in a propeller shape, chiroptical sensing has been extensively investigated. In particular, the capability of the analyte, usually a Lewis base, to bind the metal complex has been the predominant recognition motif. Herein, we report the synthesis and application of a zinc TPA-based stereodynamic probe for the sensing of chiral amines and amino-alcohols in which an ion-pair interaction between the anionic metal complexes and the ammonium ions is responsible for the recognition.

Benchtop-Stable Carbyl Iminopyridyl NiII Complexes for Olefin Polymerization.

Design of catalysts for Ni-catalyzed olefin polymerization predominantly focuses on ligand design rather than the activation process when attempting to achieve a broader scope of polyolefin micro- and macrostructures. Air-stable alkyl-or aryl-functionalized NiII precatalysts were designed which eliminate the need of in situ alkylating processes and are activated solely by halide abstraction to generate the cationic complex for olefin polymerization. These complexes represent an emerging class of olefin polymerization catalysts, enabling the study of various cocatalysts forming either inner- or outer-sphere ion pairs. It is demonstrated that an organoboron cocatalyst activation produces a well-defined ion pair, which in contrast to ill-defined organoaluminum cocatalysts, can directly activate the complex by halide abstraction to yield comparatively higher molecular weight homo/copolymers. Under high ethylene pressure, broader branching densities and the gradual incorporation of short-chain branches were achieved, circumventing the need for elaborate ligand design and copolymerization with α-olefins. The underlying chain-walking mechanism and ion pair interactions were further elucidated by DFT calculations. A phenyl group on the bridging carbon functioned as a rotational barrier, producing higher molecular weight polymers compared to methyl-substituted analogs. Here, we provide a perspective to manipulate the iminopyridyl NiII system, leveraging ion pair interactions and ligand design to govern polyolefin molecular weights and microstructures.

Simulating the Competitive Ion Pairing of Hydrated Electrons with Chaotropic Cations.

Experiments show that the absorption spectrum of the hydrated electron (ehyd-) blue-shifts in electrolyte solutions compared with what is seen in pure water. This shift has been assigned to the ehyd-'s competitive ion-pairing interactions with the salt cation relative to the salt anion based on the ions' positions on the Hofmeister series. Remarkably, little work has been done investigating the ehyd-'s behavior when the salts have chaotropic cations, which should greatly change the ion-pairing interactions given that the ehyd- is a champion chaotrope. In this work, we remedy this by using mixed quantum/classical simulations to analyze the behavior of two different models of the ehyd- in aqueous RbF and RbI electrolyte solutions as a function of salt concentration. We find that the magnitude of the salt-induced spectral blue-shift is determined by a combination of the number of chaotropic Rb+ cations near the ehyd- and the number of salt anions near those cations so that the spectrum of the ehyd- directly reflects its local environment. We also find that the use of a soft-cavity ehyd- model predicts stronger competitive interactions with Rb+ relative to I- than a more traditional hard cavity model, leading to different predicted spectral shifts that should provide a way to distinguish between the two models experimentally. Our simulations predict that at the same concentration, salts with chaotropic cations should produce larger spectral blue-shifts than salts with kosmotropic cations. We also found that at high salt concentrations with chaotropic cations, the predicted blue-shift is greater when the salt anion is kosmotropic instead of chaotropic. Our goal is for this work to inspire experimentalists to make such measurements, which will help provide a spectroscopic means to distinguish between simulations models that predict different hydration structures for the ehyd-.

Unveiling Charge-Pair Salt-Bridge Interaction Between GAGs and Collagen Protein in Cartilage: Atomic Evidence from DNP-Enhanced ssNMR at Natural Isotopic Abundance.

The interactions between glycosaminoglycans (GAGs) and proteins are essential in numerous biochemical processes that involve ion-pair interactions. However, there is no evidence of direct and specific interactions between GAGs and collagen proteins in native cartilage. The resolution of solid-state NMR (ssNMR) can offer such information but the detection of GAG interactions in cartilage is limited by the sensitivity of the experiments when 13C and 15N isotopes are at natural abundance. In this communication, this limitation is overcome by taking advantage of dynamic nuclear polarization (DNP)-enhanced magic-angle spinning (MAS) experiments to obtain two-dimensional (2D) 15N-13C and 13C-13C correlations on native samples at natural abundance. These experiments unveiled inter-residue correlations in the aliphatic regions of the collagen protein previously unobserved. Additionally, our findings provide direct evidence of charge-pair salt-bridge interactions between negatively charged GAGs and positively charged arginine (Arg) residues of collagen protein. We also identified potential hydrogen bonding interactions between hydroxyproline (Hyp) and GAGs, offering atomic insights into the biochemical interactions within the extracellular matrix of native cartilage. Our approach may provide a new avenue for the structural characterization of other native systems.

Pnictogen-Bonding Enzymes.

The objective of this study was to create artificial enzymes that capitalize on pnictogen bonding, a s-hole interaction that is essentially absent in biocatalysis. For this purpose, stibine catalysts were equipped with a biotin derivative and combined with streptavidin mutants to identify an efficient transfer hydrogenation catalyst for the reduction of a fluorogenic quinoline substrate. Increased catalytic activity from wild-type streptavidin to the best mutants coincides with the depth of the s hole on the Sb(V) center, and the emergence of saturation kinetic behavior. Michaelis-Menten analysis reveals transition-state recognition in the low micromolar range, more than three orders of magnitude stronger than the millimolar substrate recognition. Carboxylates preferred by the best mutants contribute to transition-state recognition by hydrogen-bonded ion pairing and anion-π interactions with the emerging pyridinium product. The emergence of challenging stereoselectivity in aqueous systems further emphasizes compatibility of pnictogen bonding with higher order systems catalysis.

Organocatalyzed Asymmetric Conjugate Addition of Alcohols to β-Fluoroalkyl Vinylsulfones by Bifunctional Phosphonium Salt Catalyst.

Chiral secondary alcohols, serving as essential structural motifs, hold significant potential for diverse applications. The exploration of effective synthetic strategies toward these compounds is both attractive and challenging. Herein, we present an asymmetric oxa-Michael reaction involving aliphatic alcohols as nucleophiles and β-fluoroalkyl vinylsulfones catalyzed by bifunctional phosphonium salt (BPS), achieving high yields and excellent enantioselectivities (up to 98 % yield and 98 % ee). Additionally, a sequential process including asymmetric oxa-Michael and debenzylation, facilitated by BPS/Lewis acid cooperation, was revealed for synthesizing diverse chiral secondary alcohol compounds in high yields (81-88 %) with consistent stereoselectivities. Furthermore, mechanistic explorations and subsequent results unveiled that the enantioselectivity originates from hydrogen-bonding and ion-pair interactions between the BPS catalyst and the substrates.

Experimental and theoretical study on the interaction of an ionic resorcin[4]arene and some pollutants in aqueous solution

The complexation process between an ionic resorcinarene, C-ethyl-tetraminomethylated-resorcin[4]arene hydrochloride, with resorcinol, phenol and potassium cyanide has been studied in aqueous solution using spectroscopic, calorimetric, and computational techniques. The results show the formation of resorcinarene-phenol and resorcinarene-resorcinol inclusion complexes stabilized by means of π-π interactions. On the other hand, the interaction between the macrocycle and the cyanide ions is principally mediated by ion pairing and electrostatic interactions. A turn-on effect on the fluorescence intensity is found when resorcinol or phenol is added to the macrocycle. The quantification and detection limits have been calculated and the obtained values are comparable to other sensors reported in the literature. These results extend the use of this type of macrocycles as chemosensors.

Combined DFT and ionic model computational study of the effect of alkali metal cations on the structure, bonding and properties of molten cryolites, M3AlF6 (M = li, Na, K, Rb, and Cs)

ABSTRACT Ionic melts, in the form of ionic liquids and molten salts, are important in many technological aspects such as metal production and energy applications. Cryolite melts constitute an important family especially for the industrial production of Al. The present computational study aims to analyse the effect of different cations on the structure and properties of Al (III) fluorocomplexes in cryolite melts. Cation effects are discussed as the ion pair interactions due to alkali metal cations of cryolite compounds M3AlF6 with M= Li, Na, K, Rb, or Cs for various microclusters using ionic interaction model (IM) and DFT calculations. DFT results for different ion complexes are compared with the energy calculations using a pseudoclassical model for isolated clusters. QTAIM and ELF analyses were performed to understand the nature of interactions in detail. A link between open-shell interactions and decreased ionic conductivity is proposed within the series of K, Rb, and Cs. Environmental effects, such as temperature and presence of other ions, are investigated in detail by DFT analysis.

Cadmium pollution exacerbated by drought: Insights from the nanoscale interaction at the clay mineral surface

Drought is a global environmental problem, while the effect of drought-induced unsaturation on the fate of heavy metal ions is still poorly understood, particularly the lack of mechanistic information at the molecular level. This study used molecular dynamics simulations to investigate nanoscale interactions at the montmorillonite surface under different moisture conditions. Compared to the saturated condition, drought increased the amounts and strength of Cd2+ ions adsorbed on the montmorillonite (MMT) surface while decreased the diffusivity, which was especially obvious in extreme drought conditions (θv=21%−7%). This is closely related to the compressed electric double layer, overcompensation of surface charge, and increased ion pair interactions, resulting from the confinement of water films under drought stress. Further analysis showed that the decrease of hydration effect was responsible for the exacerbated cadmium pollution. Therefore, this study may break the stereotypes about the interactions between heavy metal ions and soil minerals. The results suggest that water management (e.g., irrigation) may be prioritized before beginning heavy metal remediation.

A Conserved Intramolecular Ion-Pair Plays a Critical but Divergent Role in Regulation of Dimerization and Transport Function among the Monoamine Transporters.

The monoamine transporters, including the serotonin transporter (SERT), dopamine transporter (DAT), and norepinephrine transporter (NET), are the therapeutic targets for the treatment of many neuropsychiatric disorders. Despite significant progress in characterizing the structures and transport mechanisms of these transporters, the regulation of their transport functions through dimerization or oligomerization remains to be understood. In the present study, we identified a conserved intramolecular ion-pair at the third extracellular loop (EL3) connecting TM5 and TM6 that plays a critical but divergent role in the modulation of dimerization and transport functions among the monoamine transporters. The disruption of the ion-pair interactions by mutations induced a significant spontaneous cross-linking of a cysteine mutant of SERT and an increase in cell surface expression but with an impaired specific transport activity. On the other hand, similar mutations of the corresponding ion-pair residues in both DAT and NET resulted in an opposite effect on their oxidation-induced dimerization, cell surface expression, and transport function. Reversible biotinylation experiments indicated that the ion-pair mutations slowed down the internalization of SERT but stimulated the internalization of DAT. In addition, cysteine accessibility measurements for monitoring SERT conformational changes indicated that substitution of the ion-pair residues resulted in profound effects on the rate constants for cysteine modification in both the extracellular and cytoplasmatic substrate permeation pathways. Furthermore, molecular dynamics simulations showed that the ion-pair mutations increased the interfacial interactions in a SERT dimer but decreased it in a DAT dimer. Taken together, we propose that the transport function is modulated by the equilibrium between monomers and dimers on the cell surface, which is regulated by a potential compensatory mechanism but with different molecular solutions among the monoamine transporters. The present study provided new insights into the structural elements regulating the transport function of the monoamine transporters through their dimerization.

Multitype Electronic Interactions in Precursor Solutions of Molecular Doped P3HT Polymer.

Spin-casting of molecularly doped polymer solution mixtures is one of the commonly used methods to obtain conductive organic semiconductor films. In spin-casted films, electronic interaction between the dopant and polymer is one of the crucial factors that dictates the doping efficiency. Here, we investigate excitonic couplings using ultrafast two-dimensional electronic spectroscopy to examine the different types of electronic interactions in ion pairs of the prototype F4TCNQ-doped P3HT polymer system in a precursor solution mixture for spin-casting. Off-diagonal peaks in the 2D spectra clearly establish the excitonic coupling between P3HT+ and F4TCNQ- ions in solution. The observed excitonic coupling is the direct manifestation of a Coulombic interaction between the ion pair. The excited-state lifetime of F4TCNQ- in ion pairs shows biexponential decay at 30 and 200 fs, which hints toward the presence of a heterogeneous population with different interaction strengths. To examine the nature of these different types of interactions in solution mixtures, we study the system using molecular dynamics simulations on a fully solvated model employing the generalized Amber force field. We retrieve three dominant interaction modes of F4TCNQ anions with P3HT: side chain, π-stack, and slipped stack. To quantify these interactions, we complement our studies with electronic structure calculations, which reveal the excitonic coupling strengths of ∼ 75 cm-1 for side chain, ∼ 150 cm-1 for π-π-stack, and ∼69 cm-1 for slipped stack. These various interaction modes provide information about the key geometries of the seed structures in precursor solution mixtures, which may determine the final structures in spin-casted films. The insights gained from our study may guide new strategies to control and ultimately tune Coulomb interactions in polymer-dopant solutions.

Exploiting the Strained Ion-Pair Interactions of Sterically Hindered Pyridinium Salts Toward SN2 Glycosylation of Glycosyl Trichloroacetimidates.

We demonstrate here that strained and sterically hindered protonated 2,4,6-tri-tert-butylpyridinium (TTBPy) tetrafluoroborate, a crystalline, bench stable salt serves as a mild and efficient organocatalyst for the SN2 type displacement of glycosyl trichloroacetimidates toward the stereoselective synthesis of both α- and β-glycosides. The strained ion-pair interactions between the sterically hindered pyridinium cation and the tetrafluoroborate anion infuse unusual reactivity to the ions resulting in the unique anion assisted activation of alcohol. This mild activation of alcohol facilitates the SN2 type displacement of glycosyl α-trichloroacetimidates into β-glycosides in a highly diastereoselective manner. These unique interactions were established based on extensive infrared and 1H, 19F, 11B NMR studies and theoretical studies.

Low-Valent Transition Metalate Anions in Synthesis, Small Molecule Activation, and Catalysis.

This review surveys the synthesis and reactivity of low-oxidation state metalate anions of the d-block elements, with an emphasis on contributions reported between 2006 and 2022. Although the field has a long and rich history, the chemistry of transition metalate anions has been greatly enhanced in the last 15 years by the application of advanced concepts in complex synthesis and ligand design. In recent years, the potential of highly reactive metalate complexes in the fields of small molecule activation and homogeneous catalysis has become increasingly evident. Consequently, exciting applications in small molecule activation have been developed, including in catalytic transformations. This article intends to guide the reader through the fascinating world of low-valent transition metalates. The first part of the review describes the synthesis and reactivity of d-block metalates stabilized by an assortment of ligand frameworks, including carbonyls, isocyanides, alkenes and polyarenes, phosphines and phosphorus heterocycles, amides, and redox-active nitrogen-based ligands. Thereby, the reader will be familiarized with the impact of different ligand types on the physical and chemical properties of metalates. In addition, ion-pairing interactions and metal-metal bonding may have a dramatic influence on metalate structures and reactivities. The complex ramifications of these effects are examined in a separate section. The second part of the review is devoted to the reactivity of the metalates toward small inorganic molecules such as H2, N2, CO, CO2, P4 and related species. It is shown that the use of highly electron-rich and reactive metalates in small molecule activation translates into impressive catalytic properties in the hydrogenation of organic molecules and the reduction of N2, CO, and CO2. The results discussed in this review illustrate that the potential of transition metalate anions is increasingly being tapped for challenging catalytic processes with relevance to organic synthesis and energy conversion. Therefore, it is hoped that this review will serve as a useful resource to inspire further developments in this dynamic research field.

High-performance and robust high-temperature polymer electrolyte membranes with moderate microphase separation by implementation of terphenyl-based polymers

Acid loss and plasticization of phosphoric acid (PA)-doped high-temperature polymer electrolyte membranes (HT-PEMs) are critical limitations to their practical application in fuel cells. To overcome these barriers, poly(terphenyl piperidinium)s constructed from the m- and p-isomers of terphenyl were synthesized to regulate the microstructure of the membrane. Highly rigid p-terphenyl units prompt the formation of moderate PA aggregates, where the ion-pair interaction between piperidinium and biphosphate is reinforced, leading to a reduction in the plasticizing effect. As a result, there are trade-offs between the proton conductivity, mechanical strength, and PA retention of the membranes with varied m/p-isomer ratios. The designed PA-doped PTP-20m membrane exhibits superior ionic conductivity, good mechanical strength, and excellent PA retention over a wide range of temperature (80–160 °C) as well as satisfactory resistance to harsh accelerated aging tests. As a result, the membrane presents a desirable combination of performance (1.462 W cm−2 under the H2/O2 condition, which is 1.5 times higher than that of PBI-based membrane) and durability (300 h at 160 °C and 0.2 A cm−2) in the fuel cell. The results of this study provide new insights that will guide molecular design from the perspective of microstructure to improve the performance and robustness of HT-PEMs.

Perrhenate and pertechnetate complexes of dicationic pyridinium-fused 1,2,4-selenodiazoles featuring Se⋯O chalcogen bonding and anion⋯anion interactions

Coupling between 2-pyridylselenyl chloride and various cyanopyridinium salts resulted in the formation of dicationic pyridinium-fused 1,2,4-selenodiazoles. Novel bicyclic heterocycles are highly soluble in water and readily precipitate pertechnetate and perrhenate anions from aqueous media. All the novel compounds were comprehensively characterized using 1H and 13CNMR techniques, ESI-MS, and X-ray diffraction analysis (for eight compounds). Theoretical calculations have shown the intricate nature of chalcogen bonding (ChBs) and anion-π interactions across a series of compounds, each exhibiting unique bonding patterns and interaction energies. Compounds [1]H(ReO4)2, [2]H(ReO4)2, [3](ReO4), [2]H(TcO4)2 and [3](TcO4) displayed complex assemblies, highlighting the role of ion-pair interactions, bifurcated ChBs, and directional mater bonds.

Modelling structure and ionic diffusion in a class of ionic liquid crystal-based solid electrolytes.

Next-generation high-efficiency Li-ion batteries require an electrolyte that is both safe and thermally stable. A possible choice for high performance all-solid-state Li-ion batteries is a liquid crystal, which possesses properties in-between crystalline solids and isotropic liquids. By employing molecular dynamics simulations together with various experimental techniques, we have designed and analyzed a novel liquid crystal electrolyte composed of rigid naphthalene-based moieties as mesogenic units, grafted to flexible alkyl chains of different lengths. We have synthesized novel highly ordered lamellar phase liquid crystal electrolytes at 99% purity and have evaluated the effect of alkyl chain length variation on ionic conduction. We find that the conductivity of the liquid crystal electrolytes is directly dependent on the extent of the nanochannels formed by molecule self-organization, which itself depends non-monotonously on the size of the alkyl chains. In addition, we show that the ion pair interaction between the anionic center of the liquid crystal molecules and the Li+ ions plays a crucial role in the overall conductivity. Based on our results, we suggest that further improvement of the ionic conductivity performance is possible, making this novel family of liquid crystal electrolytes a promising option for the design of entirely solid-state Li+ ion batteries.