Symmetric Anion Research Articles

Synthesis and Characterization of New Organoammonium, Thiazolium, and Pyridinium Triiodide Salts: Crystal Structures, Polymorphism, and Thermal Stability

Triiodide salts are of interest for a variety of applications, including but not limited to electrochemical and photochemical devices, as antimicrobials and disinfectants, in supramolecular chemistry and crystal engineering, and in ionic liquids and deep eutectic solvents. Our work has focused on the design of salt–solvate cocrystals and deep eutectic solvents in which the triiodide anion interacts as a halogen bond acceptor with organoiodine molecules. To understand structure–property relationships in these hybrid materials, it is essential to have benchmark structural and physical data for the parent triiodide salt component. Herein, we report the structure and thermal properties of eight new triiodide salts, three of which exhibit polymorphism: tetrapentylammonium triiodide (1a and 1b), tetrahexylammonium triiodide (2), trimethylphenylammonium triiodide (3), trimethylbenzylammonium triiodide (4), triethylbenzylammonium triiodide (5), tri-n-butylbenzylammonium triiodide (6), 3-methylbenzothizolium triiodide (7a and 7b), and 2-chloro-1-methylpyridinium triiodide (8a and 8b). The structural features of the triiodide anion, Raman spectroscopic analysis, and melting and thermal decomposition behavior of the salts, as well as a computational analysis of the polymorphs, are discussed. The polymorphic pairs here are distinguished by symmetric versus asymmetric triiodide anions, as well as different packing patterns. Computational analyses revealed more subtle differences in their isosurface plots. Importantly, this study provides reference data for these new triiodide salts for comparison to hybrid cocrystals and deep eutectic solvents formed from their combination with various organoiodines.

Symmetric Anion Mediated Dynamic Kinetic Asymmetric Knoevenagel Reaction for N-C and N-N Atropisomers Synthesis.

A symmetric anion mediated dynamic kinetic asymmetric Knoevenagel reaction was established as a general and efficient method for accessing both N-C and N-N atropisomers. The resulting highly enantio-pure pyridine-2,6(1H,3H)-diones exhibit diverse structures and functional groups. The key to excellent regio- and remote enantiocontrol could be owed to the hydrogen bond between the enolate anion and triflamide block of the organocatalyst. This connected the enolate anion and iminium cation by a chiral backbone. The mechanism investigation via control experiments, correlation analysis, and density functional theory calculations further revealed how the stereochemical information was transferred from the catalyst into the axially chiral pyridine-2,6(1H,3H)-diones. The synthetic applications also demonstrated the reaction's potential.

Symmetric Anion Mediated Dynamic Kinetic Asymmetric Knoevenagel Reaction for N−C and N−N Atropisomers Synthesis

A symmetric anion mediated dynamic kinetic asymmetric Knoevenagel reaction was established as a general and efficient method for accessing both N−C and N−N atropisomers. The resulting highly enantio‐pure pyridine‐2,6(1H,3H)‐diones exhibit diverse structures and functional groups. The key to excellent regio‐ and remote enantiocontrol could be owed to the hydrogen bond between the enolate anion and triflamide block of the organocatalyst. This connected the enolate anion and iminium cation by a chiral backbone. The mechanism investigation via control experiments, correlation analysis, and density functional theory calculations further revealed how the stereochemical information was transferred from the catalyst into the axially chiral pyridine‐2,6(1H,3H)‐diones. The synthetic applications also demonstrated the reaction's potential.

Demonstrating the Connection between the Nonvalence Correlation-Bound Anions of Polyaromatic Hydrocarbons and the Image Potential States of Graphene Using a One-Electron Model Hamiltonian.

The ground and excited state nonvalence correlation-bound (NVCB) anion states of the hexagonal polycylic aromatic hydrocarbons and of hexagonal graphene nanoflakes are characterized using a one-electron model Hamiltonian which incorporates atomic electrostatic moments up to the quadrupole, coupled inducible charges and dipoles, and atom-centered Gaussians to describe the short-range repulsive interactions. Extrapolation of the calculated electron binding energies of the lowest energy symmetric and antisymmetric (with respect to the molecular plane) NVCB anions of both the polycylic aromatic hydrocarbons and the carbon nanoflakes to the n → ∞ limit yields binding energies that are in good agreement with those of the most stable symmetric and antisymmetric image potential states of freestanding graphene as determined from two-photon photoemission spectroscopy (2PPE) experiments.

The Interactions between Ionic Liquids and Lithium Polysulfides in Lithium-Sulfur Batteries: A Systematic Density Functional Theory Study.

Ionic liquids (ILs) based on hybrid anions have recently garnered attention as beguiling alternative electrolytes for energy storage devices. This attention stems from the potential of these asymmetric anions to reduce the melting point of ILs and impede the crystallization of ILs. Furthermore, they uphold the advantages associated with their more conventional symmetric counterparts. In this study, we employed dispersion-corrected density functional theory (DFT-D) calculations to scrutinize the interplay between two hybrid anions found in ionic liquids [FTFSA]- and [MCTFSA]- and the [C4mpyr]+ cation, as well as in lithium polysulfides in lithium-sulfur batteries. For comparison, we also examined the corresponding ILs containing symmetric anions, [TFSA]- and [FSA]-. We found that the hybrid anion [MCTFSA]- and its ionic liquid exhibited exceptional stability and interaction strength. Additionally, our investigation unveiled a remarkably consistent interaction between ionic liquids (ILs) and anions with lithium polysulfides (and S8) during the transition from octathiocane (S8) to the liquid long-chain Li2Sn (4 ≤ n ≤ 8). This contrasts with the gradual alignment observed between cations and lithium polysulfides during the intermediate state from Li2S4 to the solid short-chain Li2S2 and Li2S1. We thoroughly analyzed the interaction mechanism of ionic liquids composed of different symmetry anions and their interactions with lithium polysulfides.

Asymmetric anion effects of anions in ionic liquids: Crystal polymorphs and magnetic properties

In this study, the phase transitions and magnetic properties of magnetic ionic liquids (mILs) were investigated at low temperatures. The mILs were [Cnmim]2[MnCl4-mBrm] (n = 2, 3, and 4; m = 0, 1, 2, 3, and 4), where [Cnmim]+ is 1-alkyl-3-methylimidazolium. Here, simultaneous X-ray diffraction and differential scanning calorimetry were used to determine the crystal polymorphs in the mILs. The results showed that shorter alkyl chain lengths of cations and symmetric anions aided crystallization. Melting points in [C2mim]2[MnCl4-mBrm] were also found to be strongly dependent on asymmetric anionic configurational and cationic conformational entropies. Furthermore, the asymmetric anion effect contributed slightly to the paramagnetic properties of mILs.

Lithium Solvation and Mobility in Asymmetric Cyano(trifuloromethanesulfonyl)Imide Based Ionic Liquid Electrolyte for Li-Metal Battery

The solvation structure and transport properties of Li+ in ionic liquid (IL) electrolytes based on n-methyl-n-butylpyrrolidinium cyano(trifluoromethanesulfonyl)imide [PYR14][CTFSI] and [Li][CTFSI] (0≤ xLi ≤ 0.7) were studied by Raman and Nuclear Magnetic Resonance (NMR) spectroscopy, and molecular dynamics (MD) simulations. Li+-anion coordination is found to be dominated through the cyano group. Coordination through the sulfonyl group is seen only at higher Li-salt concentrations (xLi > 0.3). Such a trend is not observable in the case of the analogous electrolyte composed of the 1:1 mixture of the symmetric anions bis(trifluoromethanesulfonyl)imide ([TFSI]) and dicyanamide ([DCA]) since the Li-salt concentration was limited by its solubility (xLi < 0.05). The calculated ion pair lifetimes of Li+-cyano coordination for [CTFSI] are found to be shorter than that of [DCA] at xLi = 0.05, indicating the competition from the sulfonyl group on [CTFSI] weakens its solvation with Li+. This translated to the higher Li+ transference estimated for the IL electrolyte with [CTFSI] in comparison to [TFSI]:[DCA]. The NMR diffusivity measurements indicated an increase in Li+ diffusivity compared to [CTFSI] as xLi approached 0.7. These findings suggest the Li+ transport mechanism changes in the asymmetric anion at high salt concentrations. In relation to the utility of these electrolytes in energy storage, the Li-LiFePO4 half cells assembled with IL electrolyte were tested at 363 K. The system with xLi=0.7 demonstrated a capacity retention of 61% at 0.1 C-rate and 363 K after 100 cycles; remarkably higher than those of xLi=0.3 and 0.5. This is attributed to the improved electrochemical stability of the IL electrolyte with the asymmetric anion at higher salt concentrations.

Interfacial structures and decomposition reactions of hybrid anion-based ionic liquids at lithium metal surface from first-principles and ab initio molecular dynamics

Ionic liquids (ILs) based on hybrid anions have recently been investigated as appealing alternative electrolytes for energy storage devices, because such asymmetric anions have the potential to reduce melting point and inhibit crystallization of ILs without losing advantages found for the common symmetric ones. In this work, interfacial structures and decomposition reactions of the ILs consisting of two hybrid anions (FTFSI− and MCTFSI−) with the [BMP] cation at lithium metal surface were intensively studied using the combination of first-principles DFT calculations and ab initio molecular dynamics (AIMD) simulations. The corresponding ILs comprising the symmetric anions (TFSI− and FSI−) were also considered for comparison. The adsorption of the ILs on the surface is governed by the interactions between the anions and the substrate mainly via the Li−O bonds. For [BMP][FTFSI] rapid decomposition of the anion triggered by the S−F and S−N bond cleavage was observed, while the first reaction step for [BMP][MCTFSI] involves the breaking of the C−S and S−N bonds of the anion. Particularly, the differences of adsorption properties and reaction mechanisms for these two classes of ILs on the Li surface were demonstrated in detail.

Unraveling anion effect on lithium ion dynamics and interactions in concentrated ionic liquid electrolyte

The anion chemistry of lithium salts plays a pivotal role in determining the physicochemical and electrochemical performances of ionic liquid (IL) electrolytes. This work explores the effects of anion size and symmetry on coordination and dynamics of lithium ions (Li+) through molecular dynamics simulations. Four types of ILs composed of the same cation N-N-diethyl-N-methyl-N-(2-methoxyethyl)-ammonium (DEME+) and different anions of symmetrical bis(fluorosulfonyl)imide (FSI−) and bis(trifluoromethanesulfonyl)imide (TFSI−), as well as asymmetric (fluorosulfonyl)(trifluoromethylsulfonyl)imide (FTFSI−) and (difluoromethylsulfonyl)-(trifluoromethylsulfonyl)imide (DFTFSI−) are studied for comparison purpose. The calculation results show that the formation of Li+ aggregates in concentrated IL electrolytes could enhance Li+ transport due to the Li+ transport mechanism gradually shifts from vehicle transport to Li+ hopping through the anion ligand layers. Furthermore, it can be seen that the asymmetric anion based electrolytes possess superior performance than that of symmetric anions. In addition, the dual-anion based electrolytes all exhibit faster Li+ diffusion coefficient than mono-anion based electrolytes, which arise from the synergistic effect between mixed anions. As such, this work highlights the role of the anion structures and synergism in the rational design of concentrated IL-based electrolytes.

Ionic-liquid-gated porous graphene membranes for efficient CO2/CH4 separation

Ion-gated graphene membranes coated with monolayer ionic liquids (ILs) on porous graphene have shown good separation performance. However, it is necessary to match the IL with the appropriate pore size of porous graphene for practical applications. In this study, we investigated the effects of different ILs and graphene pore sizes on the CO2/CH4 separation performance using non-equilibrium molecular dynamics simulations. When the same anion was used as a gating ion, the different cation sizes influenced the separation performance of the membrane. The selectivity of [BMIM][BF4] for CO2 reached 104.2, which was the highest among the [EMIM][BF4], [BMIM][BF4], and [HMIM][BF4] systems for 6 Å pores. With increasing pore size, larger anions were required as the gating ions. [EMIM][PF6] was found to be a suitable gating ion for 7 Å pores and led to higher selectivity and CO2 membrane permeability. We also studied the effects of the number of IL molecules and the charges of the pore atoms for [EMIM][PF6] with 7 Å pore systems. The results showed that increasing the charge of the pore atoms could significantly improve the selectivity for CO2, reaching as high as 231.82. Although increasing the amount of IL molecules can enhance selectivity, it may decrease the CO2 membrane permeability. Further, non-spherical symmetric anion gating was studied. When [EMIM][NTF2] was coated on porous graphene with 6 Å pores, neither CO2 nor CH4 could pass through the membrane pores. For 7 Å pores, the CO2 separation selectivity reached 88, and the permeation number of CO2 was 22. [EMIM][PF6] and [EMIM][NTF2] were determined to be unsuitable gating ions for 8.5 Å pores. They showed poor selectivity and significant permeation of both CO2 and CH4 for porous graphene with 8.5 Å pores.

Insight into the nanostructure of “water in salt” solutions: A SAXS/WAXS study on imide-based lithium salts aqueous solutions

“Water-in-salt” electrolyte (WISE) series have been studied for lithium-ion batteries and supercapacitor applications, but so far, most of the focus has been on the LiTFSI salt-based systems. Herein, we used small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) and molecular dynamics (MD) simulation to investigate the solvation structure of a series of lithium salts with four different symmetric anions: (bis(fluoro sulfonyl)imide (FSI), bis(trifluoromethane sulfonyl)imide (TFSI), bis(pentafluoroethane sulfonyl) imide (BETI) and bis(nonafluorobutane sulfonyl)imide (BNTI)), which have similar parent structures but different lengths of the fluorocarbon chains. Two competing structures were found in the four lithium salts aqueous solutions: anion solvated structure and anion network. The anion network plays a crucial role in obtaining a stable and enlarged electrochemical window. The d spacing of the anion solvated structure follows a linear correlation with the number of carbons in the fluorocarbon chains and an exponential correlation with the concentrations. We also observed that the transition from one structure to another is predominantly controlled by the salt volume fraction for all imide-based aqueous solutions. This work provides a systematic study of the atomistic scale structures of a series of imide-based lithium salt aqueous solutions that could extend the knowledge of WIS electrolytes.

Crystal growth and physical properties of an antiferromagnetic molecule: trans-dibromidotetrakis(acetonitrile)chromium(III) tribromide, [CrBr2(NCCH3)4](Br3)

The synthesis, crystal structure determination, magnetic properties and bonding interaction analysis of a novel 3d transition-metal complex, [CrBr2(NCCH3)4](Br3), are reported. Single-crystal X-ray diffraction results show that [CrBr2(NCCH3)4](Br3) crystallizes in space group C2/m (No. 12) with a symmetric tribromide anion and the powder X-ray diffraction results show the high purity of the material specimen. X-ray photoelectron studies with a combination of magnetic measurements demonstrate that Cr adopts the 3+ oxidation state. Based on the Curie–Weiss analysis of magnetic susceptibility data, the Néel temperature is found to be around 2.2 K and the effective moment (μeff) of Cr3+ in [CrBr2(NCCH3)4](Br3) is ∼3.8 µB, which agrees with the theoretical value for Cr3+. The direct current magnetic susceptibility of the molecule shows a broad maximum at ∼2.3 K, which is consistent with the theoretical Néel temperature. The maximum temperature, however, shows no clear frequency dependence. Combined with the observed upturn in heat capacity below 2.3 K and the corresponding field dependence, it is speculated that the low-temperature magnetic feature of a broad transition in [CrBr2(NCCH3)4](Br3) could originate from a crossover from high spin to low spin for the split d orbital level low-lying states rather than a short-range ordering solely; this is also supported by the molecular orbital diagram obtained from theoretical calculations.

Unexpected Formation of the Highly Symmetric Borate Ion [B(SiCl3)4]−

AbstractDisproportionation reactions of chlorosilane compounds in the presence of boron trichloride yield the compound H[B(SiCl3)4]. Spectroscopic analyses of the yellow‐whitish solid with IR‐, Raman‐, and NMR‐spectroscopy (29Si, 11B) show the presence of a highly symmetric anion containing boron, which is fourfold coordinated with silicon. Due to the high symmetry 1J(11B,29Si) and even 1J (10B, 29Si) couplings can be observed in the NMR spectra of the dissolved compound. The crystal structure analysis with a crystal obtained from toluene solution proves the existence of a highly symmetric borate anion, which is stabilized by four trichlorosilyl groups. The molecular structure consists of a para‐protonated toluene cation and the weakly coordinating borate anion [B(SiCl3)4]−. Quantum chemical analysis of the tetrakis(trichlorosilyl)borate ion shows a negatively charged boron atom and the presence of polar Si−Cl and Si−B bonds. Highly reactive compounds [E(SiCl3)n]− which are stabilized solely by trichlorosilyl groups have been prepared with E=C, Si, Ge, P, S in recent years. The superacid H[B(SiCl3)4] represents a new member in this elusive compound family.

Structure-Property Relation of Trimethyl Ammonium Ionic Liquids for Battery Applications

Ionic liquids are attractive and safe electrolytes for diverse electrochemical applications such as advanced rechargeable batteries with high energy densities. Their properties that are beneficial for energy storage and conversion include negligible vapor-pressure, intrinsic conductivity as well as high stability. To explore the suitability of a series of ionic liquids with small ammonium cations for potential battery applications, we investigated their thermal and transport properties. We studied the influence of the symmetrical imide-type anions bis(trifluoromethanesulfonyl)imide ([TFSI]−) and bis(fluorosulfonyl)imide ([FSI]−), side chain length and functionalization, as well as lithium salt content on the properties of the electrolytes. Many of the samples are liquid at ambient temperature, but their solidification temperatures show disparate behavior. The transport properties showed clear trends: the dynamics are accelerated for samples with the [FSI]− anion, shorter side chains, ether functionalization and lower amounts of lithium salts. Detailed insight was obtained from the diffusion coefficients of the different ions in the electrolytes, which revealed the formation of aggregates of lithium cations coordinated by anions. The ionic liquid electrolytes exhibit sufficient stability in NMC/Li half-cells at elevated temperatures with small current rates without the need of additional liquid electrolytes, although Li-plating was observed. Electrolytes containing [TFSI]− anions showed superior stability compared to those with [FSI]− anions in battery tests.

Small dissymmetry, yet large effects on the transport properties of electrolytes based on imide salts: Consequences on performance in Li-ion batteries

To gain better insight into the influence of the anion size and symmetry on the transport properties and thermal stability of an electrolyte based on lithium (fluorosulfonyl)(trifluoromethanesulfonyl)-imide (FTFSI) salt, we performed the physical and electrochemical characterization of an electrolyte based on FTFSI incorporated in standard binary (3EC/7EMC) and ternary (EC/PC/3DMC) alkylcarbonate mixtures. By applying the Jones-Dole-Kaminsky (JDK), Eyring and Arrhenius empirical models to the electrolyte viscosity we show that the activation enthalpy and entropy energy barriers (ΔH≠,ΔS≠) for viscous flow are between 12 and 15 kJ·mol−1. They are strongly dependent on the solvent nature and are significantly lower than their symmetric anions LiFSI and LiTFSI (19–20 kJ·mol−1) in the binary mixture. Furthermore, the hydrodynamic radius, rs, calculated by JDK, and the ionicity behavior illustrated by the Walden role, showed that the FTFSI anion is outside the solvation sphere (rs > 0.6 nm) which is smaller in the case of an EC/EMC solvent base. In the 3EC/7EMC solvent mixture, LiFTFSI is less conductive than in the ternary mixture i.e., σmax = 8.9 mS cm−1 at Cmax = 1.1 mol L−1 for 3EC/7EMC and, σmax = 10.5 mS cm−1 at max = 0.7 mol L−1 for EC/PC/3DMC, due to a strong solvation and a greater association of FTFSI ions in the binary solvent mixture. The thermal stability of FTFSI based electrolytes was determined by the shift of the evaporation temperature of the volatile solvents (DMC, EMC) in the presence of salt, towards the higher temperatures. This feature is visible on the thermograms obtained by DSC both with the liquid electrolyte and with charged LMO cathodes in presence of electrolytes. The consequences of these properties on the electrochemical behavior of a graphite (Gr) half-cell, a lithium metal (Li) anode and a manganese lithium oxide (LMO) cathode demonstrated on the one hand the formation of a thick solid electrolyte interphase (SEI) on graphite that consumed a significant amount of lithium i.e., 18% of total capacity of the first charge. Furthermore, LiFTFSI delivered 95% of the initial capacity C = 360 mAh g−1 at C/10 with EC/PC/3DMC versus 91% when it was combined with 3EC/7EMC C = 348 mAh g−1, while the capacities obtained for LiTFSI in EC/PC/3DMC were the lowest (C = 275 mAh g−1) compared to those of the other salts. After 10 cycles, the capacity loss at C/20 is <2% for LiFSI and LiFTFSI with the two solvent mixtures. On the other hand, manganese dissolution from LMO as well as current collector corrosion were confirmed by post-mortem examination of opened coin cells. The incompatibility of the LMO cathode with an electrolyte based on FTFSI was confirmed by the position of the decomposition peak of charged LMO in contact with this electrolyte observed by DSC. These results demonstrate that the nature of the anion as well as the composition of the solvent considerably influence the performance of imide-based lithium salts both on the anode, but especially on the high voltage cathode.

Реакции пентафенилсурьмы и пента-пара-толилсурьмы с каликсареном [4-t-BuC6H2OH(S-2)

Pentaphenylantimony and penta-para-tolylantimony react with calixarene [4-t-BuC6H2OH(S-2)]4 (СArH) by way of arene elimination and formation of the [Ph4Sb]+[СAr]- × TolH (1), [p-Tol4Sb]+[CAr]- × H2O (2) ionic products with a yield up to 96%. The compound has been identified by IR spectroscopy and X-ray diffraction analysis. According to the X-ray diffraction data, compounds 1 and 2 are ionic complexes with solvate molecules of toluene (1) and water (2). The cation has a tetrahedral coordination of the antimony atom with aryl ligands at the polyhedron vertices; the anion is represented by the deprotonated form of p-tert-butylthiacalix[4]arene. The three tert-butyl groups, the phenyl ring and solvated toluene in the structure of compound 1, and two tert-butyl fragments in the structure of compound 2 are disordered over two positions. The tetrahedral coordination of antimony atoms in the cations of compounds 1 and 2 is slightly distorted. The CSbC angles deviate from the theoretical value and vary within 106.0(4)−117.7(4)° (1), 105.75(15)−112.84(15)° (2). The average Sb–C bond lengths are 2.101(3) and 2.106(4) Å in structures 1 and 2, respectively. The [СAr]- anion is in the cone conformation, the upper rim of which is represented by the tert-butyl groups in the para-position, while the lower one is represented by hydroxy groups, one of which is deprotonated. The СAr–O– bond length (1.318(4) (1) and 1.326(4) (2) Å) is less than the average value of the СAr–OH bond lengths (1.338(4) (1) and 1.343(4) (2) Å), which indicates increasing multiplicity of the bond and localization of a negative charge on the oxygen atom. Intramolecular hydrogen bonds with the neiboring O atom are observed. The H∙∙∙O distances are 2.16, 1.69, 1.77 Å in 1 and 1.92, 1.79, 1.76 Å in 2. Dihedral angles between opposite phenoxide rings are 60.64° and 87.07° (1) and 83.85° and 80.42° (2), which indicates somewhat less symmetric anion in structure 1 than in structure 2. The formation of the crystal spatial structure is due to the formation of hydrogen bonds between ions with participation of oxygen and sulfur atoms, as well as СН∙∙∙π–interactions, while the ions form chains in the crystal of compound 1, and layers in the crystal of compound 2. Complete tables of atom coordinates, bond lengths and valence angles are deposited at the Cambridge Crystallographic Data Center (No. 1850118 (1); No. 2013220 (2); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk/data_request/cif).

Structural transitions at electrodes, immersed in simple ionic liquid models.

We used a recently developed classical Density Functional Theory (DFT) method to study the structures, phase transitions, and electrochemical behaviours of two coarse-grained ionic fluid models, in the presence of a perfectly conducting model electrode. Common to both is that the charge of the cationic component is able to approach the electrode interface more closely than the anion charge. This means that the cations are specifically attracted to the electrode, due to surface polarization effects. Hence, for a positively charged electrode, there is competition at the surface between cations and anions, where the latter are attracted by the positive electrode charge. This generates demixing, for a range of positive voltages, where the two phases are structurally quite different. The surface charge density is also different between the two phases, even at the same potential. The DFT formulation contains an approximate treatment of ion correlations, and surface polarization, where the latter is modelled via screened image interactions. Using a mean-field DFT, where ion correlations are neglected, causes the phase transition to vanish for both models, but there is still a dramatic drop in the differential capacitance as proximal cations are replaced by anions, for increasing surface potentials. While these findings were obtained for relatively crude coarse-grained models, we argue that the findings can also be relevant in "real" systems, where we note that many ionic liquids are composed of a spherically symmetric anion, and a cation that is asymmetric both from a steric and a charge distribution point of view.

Impact of Anion Asymmetry on Local Structure and Supercooling Behavior of Water-in-Salt Electrolytes

Salts with asymmetric (fluorosulfonyl)(trifluoromethanesulfonyl)imide (FTFSI) anions have recently been shown to suppress crystallization of water-in-salt electrolytes, enabling low-temperature operation of high-voltage aqueous rechargeable batteries. To clarify the underlying mechanism for the kinetic suppression of crystallization, we investigate the local solution structures and dynamic behaviors of water-in-salt electrolytes based on the asymmetric FTFSI anion and its symmetric anion analogues by Raman spectroscopy and molecular dynamics simulations. We find that monodentate coordination of FTFSI to cations leads to high rotational mobility of the uncoordinated SO2CF3 group. We conclude that the peculiar, coordination-dependent, local dynamics in the asymmetric FTFSI anion, manifested by enhanced intramolecular bond rotation, enables the strong supercooling behavior.

Asymmetric effects of anions in magnetic ionic liquids

Phase behaviors and magnetic properties of magnetic ionic liquids (mILs) were investigated at low temperature. The mILs were [C4mim][FeCl4], [C4mim][FeCl3Br], [C4mim][FeCl2Br2], [C4mim][FeClBr3], and [C4mim] [FeBr4], where [C4mim]+ is 1-butyl-3-methylimidazolium. The formation of symmetric and asymmetric anions was identified using Raman spectroscopy. In addition, [C4mim][FeCl4], [C4mim][FeCl3Br], and [C4mim][FeCl2Br2] indicated a paramagnetic behavior of magnetic susceptibility, which obeyed the Curie-Weiss law. In [FeClBr3]−-, and [FeBr4]−-based mILs, crystallization was induced at a low temperature upon cooling. Moreover, nonparamagnetic magnetic susceptibility was observed in [C4mim][FeClBr3], and [C4mim][FeBr4].

"Smart" Triiodide Compounds: Does Halogen Bonding Influence Antimicrobial Activities?

Antimicrobial agents containing symmetrical triiodides complexes with halogen bonding may release free iodine molecules in a controlled manner. This happens due to interactions with the plasma membrane of microorganisms which lead to changes in the structure of the triiodide anion. To verify this hypothesis, the triiodide complex [Na(12-crown-4)2]I3 was prepared by an optimized one-pot synthesis and tested against 18 clinical isolates, 10 reference strains of pathogens and five antibiotics. The antimicrobial activities of this symmetrical triiodide complex were determined by zone of inhibition plate studies through disc- and agar-well-diffusion methods. The triiodide complex proved to be a broad spectrum microbicidal agent. The biological activities were related to the calculated partition coefficient (octanol/water). The microstructural analysis of SEM and EDS undermined the purity of the triiodide complex. The anionic structure consists of isolated, symmetrical triiodide anions [I-I-I]− with halogen bonding. Computational methods were used to calculate the energy required to release iodine from [I-I-I]− and [I-I···I]−. The halogen bonding in the triiodide ion reduces the antibacterial activities in comparison to the inhibitory actions of pure iodine but increases the long term stability of [Na(12-crown-4)2]I3.