Bridging the crystal and solution structure of a series of lipid-inspired ionic liquids.

A series of 1,2-dimethylimidazolium ionic liquids bearing a hexadecyl alkyl chain are thoroughly examined via X-ray crystallography. The crystal structures reveal several key variations in the non-covalent interactions in the lipid-like salts. Specifically, distinct cation-cation π interactions are observed when comparing the bromide and iodide structures. Changing the anion to bis(trifluoromethane)sulfonimide (Tf2N-) changes these cation-cation π interactions with anion⋯π interactions. Additionally, several well-defined geometries of the cations are noted based on torsion and core-plane angles of the alkyl chains. Hirshfeld surface analysis is used to distinguish the interactions and geometries in the solid state, helping to reveal characteristic structural fingerprints for the compounds. The solid-state structures of the ionic liquids are correlated with the solution-state structures through UV-vis spectroscopic studies, further emphasizing the importance of the π interactions in the formation of aggregates. Finally, we investigated the thermal properties of the ionic liquids, revealing complex phase transitions for the iodide-containing species. These phase transitions are further rationalized via the analysis of the data gathered from the structures of the other crystallized salts.

Ionic Liquids Containing the Sulfonyl Fluoride Moiety: Integrating Chemical Biology with Materials Design.

The persistent achievements of ionic liquids in various fields, including medicine and energy necessitate the efficient development of novel functional ionic liquids that exhibit favorable characteristics, alongside the development of practical and scalable synthetic methodologies. Ionic liquids are fundamentally understood as materials in which structure begets function, and the function and applicability of ILs is of utmost concern. It was recently reported that "full fluorosulfonyl" electrolyte is compatible with both the Li metal anode and the metal-oxide cathode that is crucial for the development of high-voltage rechargeable lithium-metal batteries. Inspired by these results, for the first time, we reported the synthesis of a series of ionic liquids with a sulfonyl fluoride motif using an highly effective and modular fluorosulfonylethylation procedure. Herein, we present a detailed analysis of novel sulfonyl fluoride-based ionic liquids paired with the hexafluorophosphate anion. We employed a combination of computational modeling and X-ray crystallographic studies to gain an in-depth understanding of their structure-property correlations.

Covalently linked hydrogen bond donors: The other side of molecular frustration in deep eutectic solvents.

In this work, we investigated the effects of a single covalent link between hydrogen bond donor species on the behavior of deep eutectic solvents (DESs) and shed light on the resulting interactions at molecular scale that influence the overall physical nature of the DES system. We have compared sugar-based DES mixtures, 1:2 choline chloride/glucose [DES(g)] and 1:1 choline chloride/trehalose [DES(t)]. Trehalose is a disaccharide composed of two glucose units that are connected by an α-1,4-glycosidic bond, thus making it an ideal candidate for comparison with glucose containing DES(g). The differential scanning calorimetric analysis of these chemically close DES systems revealed significant difference in their phase transition behavior. The DES(g) exhibited a glass transition temperature of -58 °C and behaved like a fluid at higher temperatures, whereas DES(t) exhibited marginal phase change behavior at -11 °C and no change in the phase behavior at higher temperatures. The simulations revealed that the presence of the glycosidic bond between sugar units in DES(t) hindered free movement of sugar units in trehalose, thus reducing the number of interactions with choline chloride compared to free glucose molecules in DES(g). This was further confirmed using quantum theory of atoms in molecule analysis that involved determination of bond critical points (BCPs) using Laplacian of electron density. The analysis revealed a significantly higher number of BCPs between choline chloride and sugar in DES(g) compared to DES(t). The DES(g) exhibited a higher amount of charge transfer between the choline cation and sugar, and better interaction energy and enthalpy of formation compared to DES(t). This is a result of the ability of free glucose molecules to completely surround choline chloride in DES(g) and form a higher number of interactions. The entropy of formation for DES(t) was slightly higher than that for DES(g), which is a result of fewer interactions between trehalose and choline chloride. In summary, the presence of the glycosidic bond between the sugar units in trehalose limited their movement, thus resulting in fewer interactions with choline chloride. This limited movement in turn diminishes the ability of the hydrogen bond donor to disrupt the molecular packing within the lattice structure of the hydrogen bond acceptor (and vice versa), a crucial factor that lowers the melting point of DES mixtures. This inability to move due to the presence of the glycosidic bond in trehalose significantly influences the physical state of the DES(t) system, making it behave like a semi-solid material, whereas DES(g) behaves like a liquid material at room temperature.

Autocatalytic Synthesis of Bifluoride Ionic Liquids by SuFEx Click Chemistry.

Ionic liquids with bifluoride anions possess properties such as high conductivity, wide electrochemical windows, and low viscosity that make them attractive materials for various electrochemical devices. However, owing to the lack of reliable synthetic routes, bifluoride-based ionic liquids have seldom been explored. Herein, an autocatalytic strategy for the HF-free synthesis of bifluoride-based sulfonamide ionic liquids based on the sulfur(VI) fluoride exchange (SuFEx) reaction is reported. This reaction requires no chromatographic purification, and yields are quantitative. The thermophysical properties (phase transition behavior and decomposition temperature) and electrochemical stabilities of the resulting products were studied. The products with alkyl, aryl, and perfluoroalkyl side chains exhibited extraordinarily wide electrochemical windows (up to 6.0 V) with reproducible results among multiple replicate measurements.

Synthesis of new lipid-inspired ionic liquids by thiol-ene chemistry: profound solvent effect on reaction pathway.

The synthesis of a series of new lipid-inspired ionic liquids through thiol-ene "click" reaction with a single-step process. This synthesis offers considerable promise as an efficient and orthogonal method to construct structurally diverse imidazolium-type ionic liquids with linear and branched cationic tails, as well as versatility in the placement of the sulfur heteroatom. Profound solvent effect in this ene reaction regioselectivity has been observed.

Crystal structure of tri-phenyl(vinyl)-phospho-nium tetra-phenyl-borate.

The title ionic salt, C21H20P(+)·C24H20B(-), crystallized with two independent vinyl-tri-phenyl-phospho-nium cations and two independent tetra-phenyl-borate anions per asymmetric unit. These four independent moieties contain nearly perfect tetra-hedral symmetry about their respective central C atoms. In the crystal, there are no π-stacking or other inter-molecular inter-actions present.

Are nature's strategies the solutions to the rational design of low-melting, lipophilic ionic liquids?

Ionic liquids (ILs) have emerged as a new class of materials, displaying a unique capability to self-assemble into micelles, liposomes, liquid crystals, and microemulsions. Despite evident interest, advancements in the controlled formation of amphiphilic ILs remain in the early stages. Taking inspiration from nature, we introduced the concept of lipid-like (or lipid-inspired) ILs more than a decade ago, aiming to create very low-melting, highly lipophilic ILs that are potentially bio-innocuous - a combination of attributes that is frequently antithetical but highly desirable from several application-specific standpoints. Lipid-like ILs are a subclass of functional organic liquid salts that include a range of lipidic side chains such as saturated, unsaturated, linear, branched, and thioether while retaining melting points below room temperature. It was observed in several homologous series of [Cnmim] ILs that elongation of N-appended alkyl chains to greater than seven carbons leads to a substantial increase in melting point (Tm) - which is the most characteristic feature of ILs. Accordingly, it is challenging to develop ILs with low Tm values while preserving their hydrophobicity and self-organizing properties. We found that two alternative Tm depressive approaches are useful. One of these is the replacement of the double bonds with thioether moieties in the alkyl chains, as detailed in several published papers detailing the chemistry of these ILs. Employing thiol-ene and thiol-yne click reactions is a facile, robust, and orthogonal method to overcome the challenges associated with the synthesis of alkyl thioether-functionalized ILs. The second approach involves replacing the double bonds with the cisoid cyclopropyl motif, mimicking the strategy used by certain organisms to modulate cell membrane fluidity. This discovery has the potential to greatly impact the utilization of lipid-like ILs in various applications, including gene delivery, lubricants, heat transfer fluids, and haloalkane separations, among others. This feature article presents a concise, historical overview, highlighting key findings from our work while offering speculation about the future trajectory of this de novo class of soft organic-ion materials.

Planting the Seeds of a Decision Tree for Ionic Liquids: Steric and Electronic Impacts on Melting Points of Triarylphosponium Ionic Liquids.

While machine learning and artificial intelligence offer promising avenues in the computer-aided design of materials, the complexity of these computational techniques remains a barrier for scientists outside of the specific fields of study. Leveraging decision tree models, inspired by empirical methodologies, offers a pragmatic solution to the knowledge barrier presented by artificial intelligence (AI). Herein, we present a model allowing for the qualitative prediction of melting points of ionic liquids derived from the crystallographic analysis of a series of phosphonium-based ionic liquids. By carefully tailoring the steric and electronic properties of the cations within these salts, trends in the melting points are observed, pointing toward the critical importance of π interactions to forming the solid state. Quantification of the percentage of these π interactions using modern quantum crystallographic approaches reveals a linear trend in the relationship of C-Hπ and π-π stacking interactions with melting points. These structure-property relationships are further examined by using computational studies, helping to demonstrate the inverse relationship of dipole moments and melting points for ionic liquids. The results provide valuable insights into the features and relationships that are consistent with achieving low Tm values in phosphonium salts, which were not apparent in earlier studies. The data gathered are presented in a simple decision tree format, allowing for visualization of the data and providing guidance toward developing yet unreported compounds.

Alkyl-templated cocrystallization of long-chain 1-bromoalkanes by lipid-like ionic liquids.

The serendipitous discovery of an unorthodox ionic cocrystallization system using 2-mercaptothiazolium-based ionic liquids as a crystallization milieu paves the way for the first report of crystal structures of long-chain 1-bromoalkanes. We used single crystal X-ray diffraction to determine the structures of 1-bromo-hexadecane and 1-octadecane with the aid of ionic liquids with alkyl side chains of equivalent length to the bromoalkane at room temperature. Long alkyl chains in combination with σ-hole interactions from strategically placed sulfur motifs synergistically function to crystallize the 1-bromoalkanes.

A co-crystal of 1,10-phenanthroline with boric acid: a novel aza-aromatic complex.

The title compound, C12H8N2·2B(OH)3, is best described as a host-guest complex in which the B(OH)3 mol-ecules form a hydrogen-bonded cyclic network of layers parallel to the ab plane into which the 1,10-phenanthroline mol-ecules are bound. An extensive network of hydrogen bonds are responsible for the crystal stability. No π-stacking inter-actions occur between the 1,10-phenanthroline mol-ecules.

Ionic Liquids with Benzenesulfonate Anions: Non-Fluorinated, Thermally Stable Anion Options.

Thermally resistant materials have been sought after for use as lubricants, heat transfer fluids, high temperature structural materials, and other applications where thermal stability is required or desired. Herein, we present a new class of thermally robust ionic liquids containing inexpensive benezenesulfonate anions with profound long-term, high-temperature aerobic stability - i.e., no mass loss in 96 hours at 300 °C in air. A coherent correlation between melting and glass transition temperatures and the location and type of the anions was observed. Our work indicates that these systems can be designed to form thermally stable, low-melting organic salts, providing valuable design insights for engineering of their structure-property-function relationships.

Anticancer Agents as Design Archetypes: Insights into the Structure-Property Relationships of Ionic Liquids with a Triarylmethyl Moiety.

A fundamental challenge underlying the design principles of ionic liquids (ILs) entails a lack of understanding into how tailored properties arise from the molecular framework of the constituent ions. Herein, we present detailed analyses of novel functional ILs containing a triarylmethyl (trityl) motif. Combining an empirically driven molecular design, thermophysical analysis, X-ray crystallography, and computational modeling, we achieved an in-depth understanding of structure-property relationships, establishing a coherent correlation with distinct trends between the thermophysical properties and functional diversity of the compound library. We observe a coherent relationship between melting (T m) and glass transition (T g) temperatures and the location and type of chemical modification of the cation. Furthermore, there is an inverse correlation between the simulated dipole moment and the T m/T g of the salts. Specifically, chlorination of the ILs both reduces and reorients the dipole moment, a key property controlling intermolecular interactions, thus allowing for control over T m/T g values. The observed trends are particularly apparent when comparing the phase transitions and dipole moments, allowing for the development of predictive models. Ultimately, trends in structural features and characterized properties align with established studies in physicochemical relationships for ILs, underpinning the formation and stability of these new lipophilic, low-melting salts.

Cyclopropane as an Unsaturation "Effect Isostere": Lowering the Melting Points in Lipid-like Ionic Liquids.

The replacement of unsaturation with a cyclopropane motif as a (bio)isostere is a widespread strategy in bacteria to tune the fluidity of lipid bilayers and protect membranes when exposed to adverse environmental conditions, e.g., high temperature, low pH, etc. Inspired by this phenomenon, we herein address the relative effect of the cyclopropanation, both cis and trans configurations, on melting points, packing efficiency, and order of a series of lipid-like ionic liquids via a combination of thermophysical analysis, X-ray crystallography, and computational modeling. The data indicate there is considerable structural latitude possible when designing highly lipophilic ionic liquids that exhibit low melting points. While cyclopropanation of the lipid-like ionic liquids provides more resistance to aerobic degradation than their olefin analogs, the impact on the melting point decrease is not as pronounced. Our results demonstrate that incorporating one or more cyclopropyl moieties in long aliphatic chains of imidazolium-based ionic liquids is highly effective in lowering the melting points of such materials relative to their counterparts bearing linear, saturated, or thioether side chains. It is shown that the cyclopropane moiety effectively disrupts packing, favoring formation of gauche conformer in the side chains, resulting in enhancement of fluidity. This was irrespective of the configuration of the methylene bridge, although marked differences in the effect of cis- and trans-monocyclopropanated ILs on the melting points were observed.

1-Methyl-5-nitro-imidazolium chloride.

The title salt, C4H6N3O2 +·Cl-, exhibits multiple hydrogen-bonding inter-actions involving the nitro-imidazolium cation and the chloride anion. Strong hydrogen bonds between the amine hydrogen atom and the chloride anion link the ionic moieties. Of note, with respect to H⋯Cl inter-actions, the central aromatic hydrogen atom displays a shorter inter-action than the other aromatic hydrogen atom. Finally, inter-actions are observed between the nitro moiety and methyl H atoms. While no π-π stacking is observed, anion-π inter-actions are present. The crystal was refined as a two-component twin.

Contrasting the Noncovalent Interactions of Aromatic Sulfonyl Fluoride and Sulfonyl Chloride Motifs via Crystallography and Hirshfeld Surfaces.

A heteroaryl sulfonyl(VI) fluoride, 4-chloro-7-fluorosulfonyl-2,1,3-benzoxadiazole, was synthesized from its chloride counterpart (4-chloro-7-chlorosulfonyl-2,1,3-benzoxadiazole) and the X-ray structure analysis of these compounds and the interactions in the solid-state were thoroughly examined. Hirshfeld surface analysis is used to provide a thorough and complete picture of the changes arising from the different halides in the functional groups. Surface analysis reveals that the fluoride does not participate in any hydrogen interactions as opposed to the chloride. However, the fluorine atom is observed to form close interactions with several π bonds. For both moieties, however, the sulfonyl oxygens show comparable interactions with respect to both magnitude and interatomic distances. The Hirshfeld surface analysis is coupled with computational studies to help elucidate the observed interactions that are found from the distinct nitrogen, chlorine, and oxygen atoms present in the molecules, providing new physical insights to the correlation between their structures and properties.

Quinine di-hydro-chloride hemihydrate.

Numerous non-covalent inter-actions link together discrete mol-ecules in the crystal structure of the title compound, 2C20H26N2O2 2+·4Cl-·H2O {systematic name: 4-[(5-ethenyl-1-azonia-bicyclo-[2.2.2]octan-2-yl)(hy-droxy)meth-yl]-6-meth-oxy-quinolin-1-ium dichloride hemihydrate}. A combination of hydrogen bonding between acidic H atoms and the anions in the asymmetric unit forms a portion of the observed hydrogen-bonded network. π-π inter-actions between the aromatic portions of the cation appear to play a role in the formation of the long-range ordering. One ethyl-ene double bond was found to be disordered. The disorder extends to the neighboring carbon and hydrogen atoms.

Developing Structural First Principles for Alkylated Triphenylphosphonium-Based Ionic Liquids.

While ionic liquids have proved to be versatile materials for a wide spectrum of applications, e.g., energy, materials, and medicine, several challenges remain concerning the rational design of novel materials. In light of this, a series of four triphenylphosphonium-based ionic liquids have been synthesized for the first time. These compounds exhibit high thermal stability with decomposition temperatures up to 450 °C. Their solid-state structures are characterized by single-crystal X-ray diffraction and the intermolecular interactions rigorously analyzed via Hirshfeld surface analysis. It was found that the unique geometries of the anions used in the study form distinct interactions with the cations. The interactions in the crystalline state are correlated with the thermal properties of the four ionic liquids to rationalize the melting points and phase transitions for each compound. The observed arrangements of the alkyl chains on the cations are investigated computationally to gain an understanding of how rotational freedom may impact the thermal properties of the compounds. By intention, each IL reported in this work offers a unique property profile and contributes to the ever-growing ionic liquid catalog.

Design Principles of Lipid-like Ionic Liquids for Gene Delivery.

We developed lipid-like ionic liquids, containing 2-mercaptoimidazolium and 2-mercaptothiazolinium headgroups tethered to two long saturated alkyl chains, as carriers for in vitro delivery of plasmid HEK DNA into 293T cells. We employed a combination of modular design, synthesis, X-ray analysis, and computational modeling to rationalize the self-assembly and desired physicochemical and biological properties. The results suggest that thioamide-derived ionic liquids may serve as a modular platform for lipid-mediated gene delivery. This work represents a step toward understanding the structure-function relationships of these amphiphiles with long-range ordering and offering insight into design principles for synthetic vectors based on self-assembly behavior.

Pt(II)-Decorated Covalent Organic Framework for Photocatalytic Difluoroalkylation and Oxidative Cyclization Reactions.

A new covalent organic framework (COF) based on imine bonds was assembled from 2-(4-formylphenyl)-5-formylpyridine and 1,3,6,8-tetrakis(4-aminophenyl)pyrene, which showed an interesting dual-pore structure with high crystallinity. Postmetallation of the COF with Pt occurred selectively at the N donor (imine and pyridyl) in the larger pores. The metallated COF served as an excellent recyclable heterogeneous photocatalyst for decarboxylative difluoroalkylation and oxidative cyclization reactions.

2,3-Dimethyl-1H-imidazol-3-ium benzene-sulfonate-1,2-dimethyl-1H-imidazole co-crystal.

In the title co-crystal, C5H9N2 +·C6H5O3S-·C5H8N2, the two 1,2-di-methyl-imidazole rings exist as partially protonated moieties in the asymmetric unit as a two-part disordered unit wherein the acidic hydrogen atom is bound to each ring. The two imidazolium cations share a strong hydrogen bond via the acidic hydrogen atom, which is disordered between two positions, being bonded to the first versus second imidazole ring in a 0.33 (2) to 0.67 (2) ratio. A benzene sulfonate anion is present for charge balance and inter-acts with the aromatic H atoms on both imidazole rings as well as with the methyl groups on the rings.