The Ideal Ionic Liquid Salt Bridge for Direct Determination of Gibbs Energies of Transfer of Single Ions,Part II: Evaluation of the Role of Ion Solvation and Ion Mobilities

An important intermediate goal to evaluate our concept for the assumption‐free determination of single‐ion Gibbs transfer energies Δ_trG°(i, S₁→S₂) is presented. We executed the crucial steps a) and b) of the methodology, described in Part I of this treatise, exemplarily for Ag⁺ and Cl^‐ with S₁ being water and S₂ being acetonitrile. The experiments showed that virtually all parts of the liquid junction potentials (LJPs) at both ends of a salt bridge cancel, if the bridge electrolyte is an “ideal” ionic liquid, that is, one with nearly identical diffusion of anion and cation. This ideality holds for [N₂₂₂₅]⁺[NTf₂]^‐ in the pure IL, but also in water and acetonitrile solution. Electromotive force measurements of solvation cells between S₁ and S₂ demonstrated Nernstian behavior for Ag⁺ concentration cells and constant like cell potentials for solutions with five tested Ag⁺ counterions.     

Superionic Conduction over a Wide Temperature Range in a Metal–Organic Framework Impregnated with Ionic Liquids

Most molecules in confined spaces show markedly different behaviors from those in the bulk. Large pores are composed of two regions: an interface region in which liquids interact with the pore surface, and a core region in which liquids behave as bulk. The realization of a highly mobile ionic liquid (IL) in a mesoporous metal–organic framework (MOF) is now reported. The hybrid shows a high room‐temperature conductivity (4.4×10^?3 S cm^?1) and low activation energy (0.20 eV); both not only are among the best values reported for IL‐incorporated MOFs but also are classified as a superionic conductor. The conductivity reaches over 10^?2 S cm^?1 above 343 K and follows the Vogel–Fulcher–Tammann equation up to ca. 400 K. In particular, the hybrid is advantageous at low temperatures (<263 K), where the ionic conduction is superior to that of bulk IL, making it useful as solid‐state electrolytes for electrochemical devices operating over a wide temperature range.     

Preorganization and Cooperation for Highly Efficient and Reversible Capture of Low‐Concentration CO2 by Ionic Liquids

A novel strategy based on the concept of preorganization and cooperation has been designed for a superior capacity to capture low‐concentration CO₂ by imide‐based ionic liquids. By using this strategy, for the first time, an extremely high gravimetric CO₂ capacity of up to 22 wt % (1.65 mol mol⁻¹) and excellent reversibility (16 cycles) have been achieved from 10 vol. % of CO₂ in N₂ when using an ionic liquid having a preorganized anion. Through a combination of quantum‐chemical calculations and spectroscopic investigations, it is suggested that cooperative interactions between CO₂ and multiple active sites in the preorganized anion are the driving force for the superior CO₂ capacity and excellent reversibility.     

Delineating the Mechanism of Ionic Liquids in the Synthesis of Quinazoline‐2,4(1H,3H)‐dione from 2‐Aminobenzonitrile and CO2

Ionic liquids (ILs) are versatile solvents and catalysts for the synthesis of quinazoline‐2,4‐dione from 2‐aminobenzonitrile and CO₂. However, the role of the IL in this reaction is poorly understood. Consequently, we investigated this reaction and showed that the IL cation does not play a significant role in the activation of the substrates, and instead plays a secondary role in controlling the physical properties of the IL. A linear relationship between the pK _a of the IL anion (conjugate acid) and the reaction rate was identified with maximum catalyst efficiency observed at a pK _a of >14.7 in DMSO. The base‐catalyzed reaction is limited by the acidity of the quinazoline‐2,4‐dione product, which is deprotonated by more basic catalysts, leading to the formation of the quinazolide anion (conjugate acid pK _a 14.7). Neutralization of the original catalyst and formation of the quinazolide anion catalyst leads to the observed reaction limit.     

Self‐Assembled Gels Formed in Deep Eutectic Solvents: Supramolecular Eutectogels with High Ionic Conductivity

1,3:2,4‐Dibenzylidene‐d ‐sorbitol (DBS), a simple, commercially relevant compound, was found to self‐assemble as a result of intermolecular noncovalent interactions into supramolecular gels in deep eutectic solvents (DESs) based on choline chloride combined with alcohols/ureas. DBS formed gels at a loading of 5 % w/v. Rheology confirmed the gel‐like nature of the materials, electron microscopy and X‐ray diffraction indicated underpinning nanofibrillar DBS networks, and differential scanning calorimetry showed the DES nature of the liquid‐like phase was retained. The ionic conductivities of the gels were similar to those of the unmodified DESs, thus proving the deep eutectic nature of the ionic liquid‐like phase. Gelation was tolerant of ionic additives Li⁺, Mg²⁺, and Ca²⁺; the resulting gels had similar conductivities to electrolyte dissolved in the native DES. The low‐molecular‐weight gelator DBS is thus a low‐cost additive that forms gels in DESs from readily available constituents, with conductivity levels suitable for practical applications.     

Characterization of Doubly Ionic Hydrogen Bonds in Protic Ionic Liquids by NMR Deuteron Quadrupole Coupling Constants: Differences to H‐bonds in Amides,Peptides, and Proteins

We present the first deuteron quadrupole coupling constants (DQCCs) for selected protic ionic liquids (PILs) measured by solid‐state NMR spectroscopy. The experimental data are supported by dispersion‐corrected density functional theory (DFT‐D3) calculations and molecular dynamics (MD) simulations. The DQCCs of the N−D bond in the triethylammonium cations are the lowest reported for deuterons in PILs, indicating strong hydrogen bonds between ions. The NMR coupling parameters are compared to those in amides, peptides, and proteins. The DQCCs show characteristic behavior with increasing interaction strength of the counterion and variation of the H‐bond motifs. We report the similar presence of the quadrupolar splitting pattern and the narrow liquid line in the NMR spectra over large temperature ranges, indicating the heterogeneous nature of PILs.