Ion-pair Research Articles

Structure and intermolecular interactions in ionic liquid 1-ethyl-3-methylimidazolium bromide and its aqueous solutions investigated by vibrational spectroscopy and quantum chemical computations.

The recently developed efficient protocol to explicit quantum mechanical modeling of structure and IR spectra of liquids and solutions (S. A. Katsyuba, S. Spicher, T. P. Gerasimova, S. Grimme, J. Phys. Chem. B 2020, 124, 6664) is applied to ionic liquid (IL) 1-ethyl-3-methylimidazolium bromide (EmimBr), its C2-deuterated analog [Emim-d]Br and its aqueous solutions. It is shown that the solvation strongly modifies frequencies and IR intensities of the CH/CD stretching vibrations (νCH/νCD) of the imidazolium ring. The main vibrational spectroscopic features of the neat IL are reproduced by the simulations for a cluster (EmimBr)9, in which all three imidazolium CH moieties of the solvated cation form short contacts with three Br- anions, and another two Br- anions are located on top and bottom of imidazolium ring. Cluster models of aqueous solutions reproduce the experimental vibrational frequencies of actual solutions, provided that the Br- anion of solvated contact ion pair (CIP) is situated on top of imidazolium ring, and CH/CD moieties of the latter participate in short contacts with surrounding water molecules. Both structural and spectroscopic analysis allow to interpret the short contacts CH/CD⋯Br- and CH/CD⋯OH2 as hydrogen bonds of approximately equal strength. Enthalpies of bonding of these liquid-state H-bonds, estimated with the use of empirical correlations, amount to ca. 1.4 kcal⋅mol-1, while the analogous estimates obtained for the gas-phase charged species [Emim]2Br+ increase to 5.6 kcal⋅mol-1. It is shown that formation of solvent-shared ion pair (SIP) in aqueous solution, where the counterions of IL are separated by two water molecules H-bonded to a Br- anion, produces frequency shifts ΔνCH/CD, strongly different from the case of CIP formation. This difference can be used for IR/Raman spectroscopic differentiation of the type of solvated ion pairs of EmimBr or other related ILs.

Designing ester-ether hybrid electrolytes for aldehyde-based organic anode to achieve superior K-storage

Electrolyte engineering strategy has attracted high expectations for addressing the universally existed serious dynamics and thermodynamics issues in potassium-ion batteries (PIBs), especially for the batteries adopted with organic electrode materials. Herein, a new kind of ester-ether hybrid electrolytes (EEHEs) was developed with widely manipulatable solvation structures from solvent-separated ion pair (SSIP) to aggregate (AGG)-dominated states for PIBs. The optimized EEHEs of 5 M KFSI/EC+DME enabled high Coulombic efficiency and ultra-stable K plating/stripping stability in K||Cu cells and K||K symmetric cells, respectively. When the developed novel organic anode material of 2-Bromobenzene-1,3-dialdehyde/carbon nanotube (BBD/CNT) was matched with the 5 M KFSI/EC+DME electrolyte, it delivered a reversible capacity of about 288 mAh g−1 at 50 mA g−1 and approximately 244 mAh g−1 at 200 mA g−1 with negligible capacity fade. The excellent performance should be attributed to the surface capacitive-dominated mechanism with fast K-storage kinetics guaranteed by the AGG-dominated solvation structures.

Chirality in Singlet Fission: Controlling Singlet Fission in Aqueous Nanoparticles of Tetracenedicarboxylic Acid Ion Pairs.

The singlet fission characteristics of aqueous nanoparticles, self-assembled from ion pairs of tetracene dicarboxylic acid and various amines with or without chirality, are thoroughly investigated. The structure of the ammonium molecule, the counterion, is found to play a decisive role in determining the molecular orientation of the ion pairs and its regularity, spectroscopic properties, the strength of the intermolecular coupling between the tetracene chromophores, and the consequent singlet fission process. Using chiral amines has led to the formation of crystalline nanosheets and efficient singlet fission with a triplet quantum yield as high as 133% ±20% and a rate constant of 6.99×109s-1. The chiral ion pairs also provide a separation channel to free triplets with yields as high as 33% ±10%. In contrast, nanoparticles with achiral counterions do not show singlet fission, which gave low or high fluorescence quantum yields depending on the size of the counterions. The racemic ion pair produces a correlated triplet pair intermediate by singlet fission, but no decorrelation into two free triplets is observed, as triplet-triplet annihilation dominates. The introduction of chirality enables higher control over orientation and singlet fission in self-assembled chromophores. It provides new design guidelines for singlet fission materials.

Theoretical Study of an Authentic Hydrocarbon Ion Pair.

For many years researchers believed that hydrocarbons only contain covalent bonds. However, since 1985 Okamoto et al. demonstrated the formation of hydrocarbon salts in several systems, demolishing the structural principle that hydrocarbons only contain covalent bonds. Despite the great importance of this outcome to the study of chemical bonds, quantum chemical calculations on these systems are essentially nonexistent. The stability of the hydrocarbon ions along with the steric hindrance associated with the formation of the covalent bond contribute to their occurrence either in solution (dissociated) or in the solid state. These facts along with the common formation of ion pairs in solvents of low polarity motivated us to search for hydrocarbon ion pairs in the gas phase. Its energetics has also been studied in four nonprotic solvents, through a continuum solvation model (CPCM). DFT and CASSCF calculations indicate a metastable and highly polar ion pair between the tricyclopropylcyclopropenylium cation and a simplified Kuhn's anion. The barrier to the covalent structure varies from ∼4.8 to 14.4 kcal/mol, while the energy difference between the ion pair and the covalent form varies from ∼4.3 to 25.4 kcal/mol. The obtained theoretical results along with previous experimental results suggest the following strategy to obtain kinetically and thermodynamically stable hydrocarbon ion pairs: choose very stable hydrocarbon ions and systematically increase the steric hindrance between them.

Crystal structure of (1,4,7,10,13,16-hexa-oxa-cycloocta-decane-κ6 O)potassium-μ-oxalato-tri-phenylstannate(IV), the first reported 18-crown-6-stabilized potassium salt of tri-phenyl-oxalatostannate.

The title complex, (1,4,7,10,13,16-hexa-oxa-cyclo-octa-decane-1κ6 O)(μ-oxalato-1κ2 O 1,O 2:2κ2 O 1',O 2')triphenyl-2κ3 C-potassium(I)tin(IV), [KSn(C6H5)3(C2O4)(C12H24O6)] or K[18-Crown-6][(C6H5)3SnO4C2], was synthesized. The complex consists of a potassium cation coordinated to the six oxygen atoms of a crown ether mol-ecule and the two oxygen atoms of the oxalatotri-phenyl-stannate anion. It crystallizes in the monoclinic crystal system within the space group P21. The tin atom is coordinated by one chelating oxalate ligand and three phenyl groups, forming a cis-trigonal-bipyramidal geometry around the tin atom. The cations and anions form ion pairs, linked through carbonyl coordination to the potassium atoms. The crystal structure features C-H⋯O hydrogen bonds between the oxygen atoms of the oxalate group and the hydrogen atoms of the phenyl groups, resulting in an infinite chain structure extending along a-axis direction. The primary inter-chain inter-actions are van der Waals forces.

The solvation shell probed by resonant intermolecular Coulombic decay

Molecules involved in solvation shells have properties differing from those of the bulk solvent, which can in turn affect reactivity. Among key properties of these molecules are their nature and electronic structure. Widely used tools to characterize this type of property are X-ray-based spectroscopies, which, however, usually lack the capability to selectively probe the solvation-shell molecules. A class of X-ray triggered “non-local” processes has the recognized potential to provide this selectivity. Intermolecular Coulombic decay (ICD) and related processes involve neighbouring molecules in the decay of the X-ray-excited target, and are thus naturally sensitive to its immediate environment. Applying electron spectroscopy to aqueous solutions, we explore the resonant flavours of ICD and demonstrate how it can inform on the first solvation shell of excited solvated cations. One particular ICD process turns out to be a potent marker of the formation of ion pairs. Another gives a direct access to the electron binding energies of the water molecules in the first solvation shell, a quantity previously elusive to direct measurements. The resonant nature of the processes makes them readily measurable, providing powerful new spectroscopic tools.

Investigation of ion pairs in electrochemical hexacyanoferrate(II)– hexacyanoferrate(III) system in presence of supporting electrolyte

The study of ion pair formation involving redox couples and the cation or anion of supporting electrolytes in solutions is a fundamental question in the field of fluid mechanics and electrochemistry. In this research, density functional theory (DFT) calculations were performed to investigate the ion pair reactions of hexacyanoferrate(III) and hexacyanoferrate(II) with varying numbers of potassium ions from the supporting electrolyte KCl. The binding energy and Gibbs free energy for the ion pair reactions were evaluated. The DFT results revealed a non-monotonic behavior in the binding energy and Gibbs free energy for the ion pair reaction of hexacyanoferrate(III) with different numbers of K ions.Further exploration of the chemical structures of ion pair compounds of hexacyanoferrate(III) and hexacyanoferrate(II) with varying numbers of K ions was conducted using DFT methods. Notably, in the first step of the ion pair reaction with K ions, the iron-potassium chemical bond length in hexacyanoferrate(III) was observed to be smaller than in subsequent steps.The DFT results also provided insights into the capacity of hexacyanoferrate(III) and hexacyanoferrate(II) to accept potassium ions for forming ion pair structures, showing that the former has a lower acceptance capacity than the latter. Furthermore, DFT calculations of equilibrium constants confirmed experimental results based on reduction electrical conductivity data obtained from ion pair formation in the solution.

Bionic repair protective coatings with high toughness and bond strength based on anionic waterborne polyurethane-modified cement

Protection and repair of surface cracks play pivotal roles in enhancing their effective service life. Inspired by the bionic shell principle, an anionic waterborne polyurethane (WPU) was designed. The Synthetic WPU was applied to sulphoaluminate (SAC) and ordinary Portland (OPC) cements to prepare composite coatings. The results showed that with the increase in polymer-to-cement ratio (P/C), attributable to the electrostatic adsorption and complexation of R-COO-, the content of CH, AH3 and AFm increased, while the content of AFt decreased due to the inhibitory effect of WPU on hydration reactions. The molecular dynamics model indicated that the oxygen atoms in WPU can not only form ion pairs with Ca2+ in AFt but also form strong hydrogen bonds with the H in the hydroxyl group of AFt and the H in water molecules. Hence, for P/C exceeding 10 %, combined with Flory-Huggins theory, a continuous interpenetration polymer network (IPN) comprising multiphase composites was successfully demonstrated, bolstered by the macromolecular structure composed of —OH, —COOH, Ca2+ and Al3+ serving as a bridge. The network was more pronounced in coatings with SAC than in those with OPC due to synergistic effects caused by rapid hydration reactions. Due to the presence of IPN and the Si-O-Si bonds caused by the hydrolysis condensation reaction of silane coupling agent, the tensile and bond strengths exhibited an upward trend with increasing P/C, surging by up to 326 % and 180 %, respectively. The value reached 6.81 MPa and 2.2 MPa. And the addition of WPU enhanced crack resistance.

Charged Porphyrins That Form Electronically Functional Ion Pairs and Assemblies Via I π– I π Interactions

π-Electronic ions with appropriate geometries and peripheral substituents provide assemblies through the interactions between charged building subunits, resulting in fascinating electronic properties. Structures and properties of the assemblies can be controlled by the combined positively and negatively charged species in the assemblies.[1–3] In fact, π-electronic ion pairs comprising porphyrin-based π-electronic anions have exhibited characteristic assembling modes via i π– i π interactions and resulting electronic properties such as solid-state absorption, which was correlated with the arrangement of constituent charged π-systems, and photoinduced electron transfer.[4] Among various combinations of the porphyrin anions with porphyrin–AuIIIcomplexes as π-electronic cations,[5] the “activated” ion pair of meso-EWG (electron-withdrawing group)-substituted cation and meso-EDG (electron-donating group)-substituted anion exhibited the electron transfer in the ground state, resulting in the production of the heterodiradical in a close stacking structure as revealed by the ESR.[6] Further modifications of charged porphyrins and analogs have been examined for the electronic properties that are derived from ion pairing.[1] Recent reviews: (a) Haketa, Y.; Yamasumi, K. et al. Chem. Soc. Rev. 2023, 52, 7170; (b) Haketa, Y. et al. Responsive Mater. 2023, 1, e20230018. [2] Recent reports on ion pairs and assemblies: (a) Yamasumi, K. et al. Angew. Chem. Int. Ed. 2023, 62, e202216013; (b)Sugiura, S. et al. J. Am. Chem. Soc. 2023, 144, 8122; (c) Haketa, Y. et al. Chem. Sci. 2024, 15, in press (DOI: 10.1039/d3sc04564a). [3] Selected reports on pyrrole-based π-electronic molecules: (a) Haketa, Y. et al. J. Am. Chem. Soc. 2020, 142, 16420; (b) Ishikawa, S. et al. under revision. [4] Sasano, Y.; Tanaka, H. et al. Chem. Sci. 2021, 12, 9645. [5](a) Haketa, Y. et al. iScience 2019, 14, 241; (b) Nakajima, R. et al. to be submitted; (c) Maruyama, Y. et al. to be submitted. [6](a) Tanaka, H. et al. J. Am. Chem. Soc. 2022, 144, 21710; (b) Tanaka, H. et al. Chem. Eur. J. 2023, 29, e202203957.

Exploration of Synthesis and Coordination Chemistry of Thiazole-Containing Calix[3]Pyrroles

Calix[n]pyrroles have been used as powerful and specific receptors and as extractants for anions and ion pairs over the past 20 years. In the recent past, calix[4]pyrroles have been used as systems that can move ions and ion pairs over lipophilic membranes [1]. Unfortunately, the coordination chemistry of calix[n]pyrroles hardly explored. The ring-contracted analog of calix[n]pyrrole, calix[3]pyrrole, was synthesized and recently published [2]. The structure of calix[3]pyrrole and its analogues is strained, and they show an appealing strain-induced ring expansion response. On the other hand, the synthesis of calix[3]pyrrole requires multistep reactions including cyclization of hexaketone precursor and Paar–Knorr synthesis with the total yield of 4%. Extended use of calix[3]pyrrole analogues necessitates further refinement of the synthesis process.Here, we demonstrate the synthesis of new calix[3]pyrroles analogue, calix[1]pyrrole[2]thiazole (3). Direct macrocyclization between bis(α-bromoketone) and 2,2-dimethylpropane (bis-thioamide) produced the calix[1]furan[2]thiazole (1), with 60% yield. The furan unit of 1 was converted into pyrrole to give calix[1]pyrrole[2]thiazole 3 (Figure 1).Single-crystal X-ray analysis revealed a cone-shaped conformation of calix[1]pyrrole[2]thiazole 3, with all three heterocycles pointing in the same direction through strong intramolecular hydrogen bonding. However, unlike calix[3]pyrrole, calix[1]pyrrole[2]thiazole was completely stable under acidic conditions, which may be due to the basic nature of the thiazolimine units.Metal coordination of calix[1]pyrrole[2]thiazole was attempted and its Zn(II), Ag(I) and Pd(II) complexes were obtained by appropriate metalation procedures. The central metal ion of the Zn(II) complex is coordinated by a conical 3 and an axial ethyl group to behave as a monoanionic tridentate ligand. In contrast, it acts as a bidentate neutral ligand for Pd(II) or Ag(I) complexation. The synthesis of meso-aza calix[1]pyrrole[2]thiazole is in progress. Figure 1

(Invited) Core-Multi-Shell Design: Unlocking Multimodal Capabilities in Lanthanide-Based Nanoparticles

The remarkable optomagnetic properties of the lanthanides (Ln) make Ln-based materials ideal for biomedical applications, including diagnostic (e.g., imaging, nanothermometry) and therapeutic (e.g., drug delivery, photodynamic therapy) approaches. This is due the unique electronic properties of the f-elements allowing for upconversion and near-infrared emission under near-infrared excitation as well as high magnetic moments. Yet, challenges remain, including low emission intensity and efficiency of small nanoparticles (NPs), and reliable, fast synthesis routes. As material chemists, we tackle these challenges with new designs of Ln-NPs by chemically controlled synthesis, application-oriented surface chemistry, and understanding of structure-property-relationships. We developed a straightforward and rapid microwave-assisted synthesis approach towards core-multi-shell Ln-NPs. Careful architecture design and choice of RE3+ dopant ions allow to tune the optical properties of the resultant nanoparticles, i.e., upconversion and near-infrared emission. This presentation will shed light on recent results with respect to microwave-assisted synthesis of Ln-NPs as well as structural and optomagnetic properties, seeking biomedical application.For instance, multimodal bioimaging probes merging optical imaging, magnetic resonance imaging (MRI), and X-ray computed tomography (CT) capabilities have attracted considerable attention due to their potential biomedical applications. This includes nanoparticles that combine upconverting Er3+/Yb3+ and magnetic NaDyF4 for optical/T2-weighted MRI/CT multimodal capabilities. A known drawback of multimodal probes that merge the upconverting Er3+/Yb3+ ion pair with magnetic Dy3+ ions for T2-weighted MRI is the loss of upconversion emission due to Dy3+ poisoning. The synthesis of controlled nanoparticle architectures with tuned inner NaGdF4 shell thicknesses separating Dy3+ and Er3+/Yb3+ allow to shed light on this distance-dependent loss of upconversion due to Yb3+ → Dy3+ energy transfer. As a result, the Ln-NP architecture was tuned to not only restore but enhanced the upconversion emission. In addition to multimodal imaging, Ln-NPs are promising candidates for application in nanothermometry due to the distinct, temperature-induced changes in their spectral features. We seek the development of novel Ln-NP nanothermometers for new opportunities in the near-infrared biological transparency windows (1000 to 2000 nm), by doping RE3+ ions, such as Er3+ and Tm3+ as well as unconventional Pr3+, into core-multi-shell lanthanide-based nanoparticles.

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

(Invited) Modeling of the Electric Double Layer (EDL) Structures of Localized High-Concentration Electrolytes (LHCE)

Various electrical double layer (EDL) models have been proposed but mainly for homogenous solutions. Recently, the so-called Localized high-concentration electrolytes (LHCE) have shown many benefits to high-capacity electrodes. Recently, we have proposed micelle-like structures to enable a complete understanding of microstructures in LHCE, which contains a salt, solvent, and non-ion-solvating diluent, analogical to the roles of oil, surfactant, and water as in micelles. [1] As the solid electrolyte interphase (SEI) formation is sensitive to the EDL structure, [2] it is critical to understand the EDL structures for LHCE with heterogeneous structures.Molecular dynamics simulations were performed in several electrolytes with heterogeneous structures on negatively charged surfaces. It was found the Stern model with an absorbed cation layer adsorption layer and a more diffused layer with cation, anion, solvent, and diluents, should be used to describe the EDL of this type of electrolyte.For the system consisting of LiFSI salt, DME solvent, and TFEO diluent at a concentration of LiFSI-1.2DME-2TFEO, the heterogeneous micelle-like structures in LHCE are maintained in the EDL, with the Li+-rich salt-solvent clusters and the Li+-poor diluent regions. The diluent region contains Li+ near the negatively charged surface but does not have any ions in the bulk of LHCE. This is because TFEO cannot form a complete solvation shell in the bulk electrolyte due to the steric effect, however, only a partial solvation shell is needed in the Stern layer in the EDL. The appearance of Li+ in the diluent is also necessary for the EDL, as TFEO alone cannot screen the charge.The chemical and concentration design space for the three components is very large. To obtain a more general picture, we also explored different salt-solvent ratios and different diluent-salt interactions. As the salt solvent ratio increases from low (LCE), to medium (MCE) to high concentration electrolytes (HCE), where all solvents are coordinated with ions, the salt-solvent structures evolve from fully solvated ions or ion pairs in LCE, 3D branched networks in MCE, to fully connected salt aggregates in HCE. The salt-diluent interactions and diluent concentration further modify the micelle-like structures. The EDL for both LHCE and LMCE are heterogenous. [1] Nature Materials 22, 1531–1539 (2023)[2] J. Am. Chem. Soc. 145, 4, 2473–2484 (2023)

Modified Liquid Electrolyte with Porous Liquid Type-II for Lithium-Metal Batteries

Liquid electrolytes modified by adding type-II porous liquid (PL) were designed and prepared to study its effect on the performance of lithium-metal batteries. Porous liquids provide internal, permanent, and empty porosity which are capable of coordinating and transporting Li+. The potential of the porous liquid to capture and transport ions with high mobility leads to enhancement in battery performance. In this study, the physicochemical properties of electrolytes, mechanism of solvation, transport, and electrical conductivity of lithium ions through the new electrolytes will be presented, and the potential of the liquid electrolyte based on the type-II porous liquid to develop the battery performance was investigated. This modification effectively improved the Li ionic conductivity of the electrolyte because of the Li+ ion solvation by type-II PL. The dissociation of Li+-TFSI− ion pairs and the formation of complexes with Li+ ions (Li-PL) were improved by using the type-II PL, resulting in an increase in the ionic conductivity of the electrolyte. Our findings suggest that the use of PL electrolytes can be a good candidate for improvement in physicochemical properties of electrolytes leading to an enhancement in Lithium-Metal Batteries.

Refractive Laser Beam Measuring Diffusion Coefficient of Concentrated Battery Electrolytes

A thorough understanding of electrolyte transport properties is crucial in the development of alternative battery technology. As a key parameter, the diffusion coefficient offers important insights into the behavior of electrolytes, especially for fast charge of high-energy batteries. Existing methods of measurement are often limited by redox species or offer questionable accuracy due to side reactions and/or disruption of the diffusion profile. A highly sensitive optical method was developed using a refractive laser beam through triangular diffusion column to measure the diffusion coefficient of concentrated battery electrolytes. The method based on Snell’s law can be applied to all liquid phase electrolytes since the refractive index is concentration dependent for all liquid electrolytes. This universal method relies on the deflection of a refractive laser beam passing through an electrolyte of a minor concentration gradient in a triangular diffusion column (Figure 1). A polarized HeNe laser was arranged to pass the beam through a right-angled triangular quartz precision cell, slightly rotated to the normal. The exact position of the refracted beam was located by a silicon photodiode-based position detector. Deflection calibration curves made simple conversion of beam position to concentration, and during the diffusion of two layered solutions, data points were collected every minute to produce a concentration profile descriptive of the 48-hour diffusion. Diffusion coefficients were calculated using a model based on OSM theory, accounting for multi-component concentrated systems in a restricted diffusion column.1 The measured diffusion coefficients are between 4.12x10-10 m2/s for 0.15 mol/kg ZnSO4 and 0.681x10-10 m2/s for 2.5 mol/kg ZnSO4 at 22.4 °C. The profile of concentration-dependent diffusion coefficients follows a non-linear inverse relationship described by the function D=4.943(1+m)-1.564 (Figure 2).Several other physicochemical properties of the same electrolytes were studied to correlate to the concentration-dependent diffusion coefficients, including refractive index, viscosity, conductivity, and microstructure analysis based on vibrational spectroscopy (Infrared and Raman). High concentration electrolytes with more ion pairs show increased viscosity which ultimately leads to smaller diffusion coefficients. A QCM-I instrument standard flow cell were used to determine the viscosity of ZnSO4 electrolyte and the concentration-dependent viscosity was fitted to the function η=1.06-0.476m+2.13m2-1.01m3+0.204m4. Interionic interactions also led to reduced conductivity at concentrations beyond 1.5mol/kg, despite the increased charge density of concentrated solutions. FT-IR spectrums allowed analyzation of increased charge density, which increased intensity of the O-H stretching peak in concentrated electrolytes, despite the decrease in the ratio of water. Competition between charge density and viscosity continues to challenge the efficiency of concentrated electrolytes.Lastly, we demonstrate the prototype in situ triangular cell to characterize the electrolyte in working batteries. The cell responds to short, low-voltage pulses with beam deflection and relaxation, and offers an opportunity as a novel in situ spectroscopic tool to characterize the battery electrolyte. Acknowledgments This work is supported by a grant from NSF (CBET-2243098).

Designing Interphases in Zn and Al Aqueous Electrolytes

This talk will cover two recent studies led by the Army Research Laboratory investigating interphase formation and cation solvation in zinc and aluminum aqueous electrolytes, respectively. In the former, two co-cations were carefully designed to offer distinct, complementary improvements in aqueous Zn electrolytes: a partially fluorinated pyrrolidinium cation effectively suppresses parasitic reactions such as hydrogen evolution (< 6 µA cm-2), and an ether-functionalized ammonium cation inhibits dendrite formation (almost 10 Ah cm-2 cumulative capacity, > 1 year, Zn||Zn). In the later, transient electrostatic hydrolysis of Al-OH2 ligands, without Al-OTf contact ion pairs, leads to insufficient reductive stability for rechargeable metal anodes. These contrasting systems provide helpful guidance for designing aqueous electrolytes with energy-dense multivalent metal anodes.

Role of ion pairs in model glycosylation reactions of permethylated glucosyl and xylosyl triflates

Elucidating the molecular mechanisms of chemical O-glycosylation remains a significant challenge in glycochemistry. This study examines the mechanism of the nucleophilic substitution reaction between glycosyl triflates, which are extensively used in studies of glycosylation mechanisms, and several acceptor alcohols. The investigation was conducted through a comparative analysis of permethylated glucosyl triflate GTf and its xylosyl counterpart XTf. The glycosylation reactions, conducted in dichloromethane using GTf and XTf with EtOH, tBuOH, and CF3CH2OH, exhibited diverse α/β selectivities depending on the types of donor and acceptor molecules used. Identifying a unified mechanism to explain this range of selectivities proved challenging. Notably, we observed a distinct trend wherein the addition of excess triflate salt (Bu4NOTf) had a more pronounced effect on the α/β selectivity in glycosylation reactions utilizing XTf compared to those using GTf. Quantum chemical calculations performed at the SCS-MP2//DFT(M06-2X) level, with explicit inclusion of five solvent molecules, showed that contact ion pairs arising from XTf were significantly more stable than those from GTf. These experimental and computational results strongly suggest that ion pairs play a more crucial role in the glycosylation process involving XTf than GTf. Additionally, our quantum chemical analyses clarified that the enhanced stability of the ion pairs from XTf was attributed not to the strength of the C-1−OTf bond within XTf but to the flexibility in the conformational changes of XTf's pyranosyl ring.

Spinel-Type Structured Phosphor Near-Infrared-II Emission: Intervalence Charge Transfer and Hetero-Valent Chromium Pairs.

Near-infrared (NIR) emitting phosphors draw much attention because they show great applicability and development prospects in many fields. Herein, a series of inverse spinel-type structured LiGa5O8 phosphors with a high concentration of Cr3+ activators is reported with a dual emission band covering NIR-I and II regions. Except for strong ionic exchange interactions such as Cr3+-Cr3+ and Cr3+ clusters, an intervalence charge transfer (IVCT) process between aggregated Cr ion pairs is proposed as the mechanism for the ~1210 nm NIR-II emission. Comprehensive structural and luminescence characterization points to IVCT between two Cr3+ being induced by structural distortion and further enhanced by irradiation. Construction of the configurational energy level diagram enabled elucidation of this transition within the IVCT process. Therefore, this work provides insight into the emission mechanism within the high Cr3+ concentration system, revealing a new design strategy for NIR-II emitting phosphors to promote its response.

Response to "Comment on 'Binding Debye-Hückel theory for associative electrolyte solutions'" [J. Chem. Phys. 159, 154503 (2023)

This Response addresses critiques raised about the Binding Debye-Hückel (BiDH) theory [Naseri Boroujeni et al., J. Chem. Phys. 159, 154503 (2023)] by Simonin and Bernard [J.-P. Simonin and O. Bernard, J. Chem. Phys. (2024)]. The critiques questioned the foundational framework of the Debye-Hückel (DH) theory, the relevance of ion pairing in primitive model fluids, and the accuracy of the BiDH model compared to mean spherical approximation model. Through a systematic rebuttal, supported by extensive literature review and comparison with Monte Carlo simulation data, this Response addresses these concerns. It demonstrates the efficacy of DH theory in describing real electrolyte solutions, validates the relevance of ion pairing in primitive model fluids, and establishes the BiDH model's accuracy in describing electrolyte properties.

Ion Pair Solvent Bar Microextraction of Paraquat from Soil Samples Prior to Determination by UV–Vis Spectrophotometry

Ion Pair Solvent Bar Microextraction of Paraquat from Soil Samples Prior to Determination by UV–Vis Spectrophotometry