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Room temperature ionic liquids of cyclic sulfonimide anions ncPFSI (ring size: n = 4-6) with the cations [EMIm]+ (1-ethyl-3-methylimidazolium), [BMIm]+ (1-butyl-3-methylimidazolium) and [BMPL]+ (BMPL = 1-butyl-1-methylpyrrolidinium) have been synthesized. Their solid-state structures have been elucidated by single-crystal X-ray diffraction and their physicochemical properties (thermal behaviour and stability, dynamic viscosity and specific conductivity) have been assessed. In addition, the ion diffusion was studied by pulsed field gradient stimulated echo (PFGSTE) NMR spectroscopy. The decisive influence of the ring size of the cyclic sulfonimide anions on the physicochemical properties of the ILs has been revealed. All ILs show different properties compared to those of the non-cyclic TFSI anion. While these differences are especially distinct for ILs with the very rigid 6cPFSI anion, the 5-membered ring anion 5cPFSI was found to result in ILs with relatively similar properties. The difference between the properties of the TFSI anion and the cyclic sulfonimide anions has been rationalized by the rigidity (conformational lock) of the cyclic sulfonimide anions. The comparison of selected IL properties was augmented by MD simulations. These highlight the importance of pi+-pi+ interactions between pairs of [EMIm]+ cations in the liquid phase. The pi+-pi+ interactions are evident for the solid state from the molecular structures of the [EMIm]+-ILs with the three cyclic imide anions determined by single-crystal X-ray diffraction. This journal is © The Royal Society of Chemistry.

Electrolytes that transport only Li ions play a crucial role in improving rapid charge and discharge properties in Li secondary batteries. Single Li-ion conduction can be achieved via liquid materials such as Li ionic liquids containing Li+ as the only cations because solvent-free fused Li salts do not polarise in electrochemical cells, owing to the absence of neutral solvents that allow polarisation in the salt concentration and the inevitably homogeneous density in the cells under anion-blocking conditions. However, we found that borate-based Li ionic liquids induce concentration polarisation in a Li/Li symmetric cell, which results in their transference (transport) numbers under anion-blocking conditions (tabcLi) being well below unity. The electrochemical polarisation of the borate-based Li ionic liquids was attributed to an equilibrium shift caused by exchangeable B–O coordination bonds in the anions to generate Li salts and borate-ester solvents at the electrode/electrolyte interface. By comparing borate-based Li ionic liquids containing different ligands, the B–O bond strength and extent of ligand exchange were found to be directly linked to the tabcLi values. This study confirms that the presence of dynamic exchangeable bonds causes electrochemical polarisation and provides a reference for the rational molecular design of Li ionic liquids aimed at achieving single-ion conducting liquid electrolytes.

Phosphorus-containing catalyst supports synthesized by coating and pyrolysis of phosphonium ionic liquids lead to improved fuel cell properties.

The present work investigates how mechanical properties and ion dynamics in ionic liquids (ILs) can be affected by ILs’ design while considering possible relationships between different mechanical and transport properties. Specifically, we study mechanical properties of quaternary ionic liquids with rigid anions by means of Dynamical Mechanical Analysis (DMA). We are able to relate the DMA results to the rheological and transport properties provided by viscosity, conductivity, and diffusion coefficient measurements. A good agreement is found in the temperature dependence of different variables described by the Vogel−Fulcher−Tammann model. In particular, the mechanical spectra of all the measured liquids showed the occurrence of a relaxation, for which the analysis suggested its attribution to a diffusive process, which becomes evident when the ion dynamics are not affected by the fast structural reorganization of flexible anions on a local level.

Ionic liquids (ILs) are promising electrolytes and many efforts have been made in basic scientific research as well as in applied research. In this contribution, we synthesised a variety of partly novel phosphonium ILs with different anions as well as with different compositions and lengths of the side chains of the cations. We measured a variety of their important transport properties such as viscosity, conductivity and diffusivity by means of stress-controlled rheology, impedance spectroscopy and PFGSTE NMR diffusometry. The results are analysed with respect to different models for derivation from ideal behaviours such as the ionicity and the (fractional) Walden rule depending on their molecular structure. These models are well established in the literature and are herein applied to rarely investigated but promising phosphonium ILs, with a particular emphasis placed on the effect of ether side chains. In comparison, the models show a qualitative correlation but distinct deviation in the quantification especially in the temperature dependent values and with other IL systems. These results aim to facilitate a better understanding of the IL properties depending on the molecular composition and by this way help to choose the ILs with optimal properties for practical applications.

Dynamics and structures of protic ionic liquids from the superbase guanidinium are analyzed in detail. The H-bond strength correlates with the proton affinity of the constituting acid and can be monitored by the 1H or 15N chemical shifts.

Understanding the connection between the molecular structure of ionic liquids and their properties is of paramount importance for practical applications. However, this connection can only be established if a broad range of physicochemical properties on different length and time scales is already available. Even then, the interpretation of the results often remains ambiguous due to the natural limits of experimental approaches. Here we use fast-field cycling (FFC) to access both translational and rotational dynamics of ionic liquids. These combined with a comprehensive physicochemical characterization and MD simulations provide a toolkit to give insight into the mechanisms of molecular mechanics. The FFC results are consistent with the computer simulation and conventional physicochemical approaches. We show that curling of the side chains around the positively charged cationic core is essential for the properties of ether-functionalized ionic liquids, and we demonstrate that neither geometry nor polarity alone are sufficient to explain the macroscopic properties.

Ionic liquids are becoming increasingly popular for practical applications such as biomass processing and lithium-ion batteries. However, identifying ionic liquids with optimal properties for specific applications by trial and error is extremely inefficient since there are a vast number of potential candidate ions. Here we combine experimental and computational techniques to determine how the interplay of fluorination, flexibility and mass affects the transport properties of ionic liquids with the popular imide anion. We observe that fluorination and flexibility have a large impact on properties such as viscosity, whereas the influence of mass is negligible. Using targeted modifications, we show that conformational flexibility provides a significant contribution to the success of fluorination as a design element. Contrary to conventional wisdom, fluorination by itself is thus not a guarantor for beneficial properties such as low viscosity.

Ionic liquids are extremely versatile and continue to find new applications in academia as well as industry. This versatility is rooted in the manifold of possible ion types, ion combinations, and ion variations. However, to fully exploit this versatility, it is imperative to understand how the properties of ionic liquids arise from their constituents. In this work, we discuss targeted modifications as a powerful tool to provide understanding and to enable design. A 'targeted modification' is a deliberate change in the structure of an ionic liquid. This includes chemical changes in an experiment as well as changes to the parameterisation in a computer simulation. In any case, such a change must be purposeful to isolate what is of interest, studying, as far as is possible, only one concept at a time. The concepts can then be used as design elements. However, it is often found that several design elements interact with each other - sometimes synergistically, and other times antagonistically. Targeted modifications are a systematic way of navigating these overlaps. We hope this paper shows that understanding ionic liquids requires experimentalists and theoreticians to join forces and provides a tool to tackle the difficult transition from understanding to design.

There are thousands of papers published every year investigating the properties and possible applications of ionic liquids. Industrial use of these exceptional fluids requires adequate understanding of their physical properties, in order to create the ionic liquid that will optimally suit the application. Computational property prediction arose from the urgent need to minimise the time and cost that would be required to experimentally test different combinations of ions. This review discusses the use of machine learning algorithms as property prediction tools for ionic liquids (either as standalone methods or in conjunction with molecular dynamics simulations), presents common problems of training datasets and proposes ways that could lead to more accurate and efficient models., In this review article, the authors discuss the use of machine learning algorithms as tools for the prediction of physical and chemical properties of ionic liquids.

In this work we investigate the structure–property relationships in a series of alkylimidazolium ionic liquids with almost identical molecular weight. Using a combination of theoretical calculations and experimental measurements, we have shown that re-arranging the alkyl side chain or adding functional groups results in quite distinct features in the resultant ILs. The synthesised ILs, although structurally very similar, cover a wide spectrum of properties ranging from highly fluid, glass forming liquids to high melting point crystalline salts. Theoretical ab initio calculations provide insight on minimum energy orientations for the cations, which then are compared to experimental X-ray crystallography measurements to extract information on hydrogen bonding and to verify our understanding of the studied structures. Molecular dynamics simulations of the simplest (core) ionic liquids are used in order to help us interpret our experimental results and understand better why methylation of C2 position of the imidazolium ring results in ILs with such different properties compared to their non-methylated analogues.

Room temperature ionic liquids are considered to have huge potential for practical applications such as batteries. However, their high viscosity presents a significant challenge to their use changing from niche to ubiquitous. The modelling and prediction of viscosity in ionic liquids is the subject of an ongoing debate involving two competing hypotheses: molecular and local mechanisms

The practical use of ionic liquids (ILs) is benefiting from a growing understanding of the underpinning structural and dynamic properties, facilitated through classical molecular dynamics (MD) simulations. The predictive and explanatory power of a classical MD simulation is inextricably linked to the underlying force field. A key aspect of the forcefield for ILs is the ability to recover charge based interactions. Our focus in this paper is on the description and recovery of charge transfer and polarisability effects, demonstrated through MD simulations of the widely used 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4C1im][NTf2] IL. We study the charge distributions generated by a range of ab initio methods, and present an interpolation method for determining atom-wise scaled partial charges. Two novel methods for determining the mean field (total) charge transfer from anion to cation are presented. The impact of using different charge models and different partial charge scaling (unscaled, uniformly scaled, atom-wise scaled) are compared to fully polarisable simulations. We study a range of Drude particle explicitly polarisable potentials and shed light on the performance of current approaches to counter known problems. It is demonstrated that small changes in the charge description and MD methodology can have a significant impact; biasing some properties, while leaving others unaffected within the structural and dynamic domains.

We report the complex phase behavior of the glass forming protic ionic liquid (PIL) d3-octylphosphonium bis(trifluoromethylsulfonyl)imide [C

Ionic liquids are modern liquid materials with potential and actual implementation in many advanced technologies. They combine many favourable and modifiable properties but have a major inherent drawback compared to molecular liquids – slower dynamics. In previous studies we found that the dynamics of ionic liquids are significantly accelerated by the introduction of multiple ether side chains into the cations. However, the origin of the improved transport properties, whether as a result of the altered cation conformation or due to the absence of nanostructuring within the liquid as a result of the higher polarity of the ether chains, remained to be clarified. Therefore, we prepared two novel sets of methylammonium based ionic liquids; one set with three ether substituents and another set with three butyl side chains, in order to compare their dynamic properties and liquid structures. Using a range of anions, we show that the dynamics of the ether-substituted cations are systematically and distinctly accelerated. Liquefaction temperatures are lowered and fragilities increased, while at the same time cation–anion distances are slightly larger for the alkylated samples. Furthermore, pronounced liquid nanostructures were not observed. Molecular dynamics simulations demonstrate that the origin of the altered properties of the ether substituted ionic liquids is primarily due to a curled ether chain conformation, in contrast to the alkylated cations where the alkyl chains retain a linear conformation. Thus, the observed structure–property relations can be explained by changes in the geometric shape of the cations, rather than by the absence of a liquid nanostructure. Application of quantum chemical calculations to a simplified model system revealed that intramolecular hydrogen-bonding is responsible for approximately half of the stabilisation of the curled ether-cations, whereas the other half stems from non-specific long-range interactions. These findings give more detailed insights into the structure–property relations of ionic liquids and will guide the development of ionic liquids that do not suffer from slow dynamics.

As a result of continuing ionic liquid research, it becomes clearer that charge transfer in ionic liquids has a physical reality. In a recent publication, we demonstrated the utility of simple density functional theory descriptors to estimate charge transfer for a large number of ion combinations, which is possible because the ions are treated separately. A major disadvantage found was that the charge transfer was systematically overestimated. In this work, we introduce a correction to account for the losses in Coulomb attraction when charge is transferred from the anion to the cation. We find that accounting for these losses is important to describe charge transfer in ionic liquids appropriately. The advantage that the calculations can be performed separately on the individual, isolated ions is maintained. The corrected as well as the uncorrected charge transfer have been calculated for over 4000 cation-anion combinations at the R(O)B3LYP/6-311+G(2d,p)//RB3LYP/6-31+G(d,p) level of theory. With the correction, the absolute values for the charge transfer are no longer unrealistically high and agree well with other charge transfer estimates from the literature. In general, the cumulative nature of the Haven ratio is now correctly mirrored in the relationship between the corrected theoretical charge transfer and the experimental estimate from the Nernst-Einstein relation. Earlier findings on the similarities between ether-functionalized and nonfunctionalized ionic liquids are confirmed. However, we also observe inconsistencies when using the experimental charge transfer estimates together with the ionicity interpretation of the Haven ratio. These can be interpreted as a hint toward the latter premise being wrong.

Ionic liquids (ILs) are a widely investigated topic in various technical disciplines at the present time. A main focus of the research on ILs lies on applications in the field of a more sustainable, ‘greener’ chemistry that benefits from their unique property combination. This allows for the improvement of existing technologies and the use in novel, innovative processes. Especially the synergistic combination with other concepts of green chemistry is expected to lead to promising application of ILs. Regardless of their presence in current scientific research, they are covered rarely in the didactics of chemistry, although they represent an ideal subject to incorporate fundamental relationships or chemical concepts into teaching. They can also be included in various demonstration or hands-on experiments. Therefore, the topic of ILs is very promising for the transfer of knowledge from chemical research and industry into didactical experiments especially in the greater context of green chemistry. In this contribution, we present some simple experiments that utilize a multifunctional IL as recyclable catalyst in a biphasic homogenous catalysis. The experiments demonstrate the ecological and economic benefits offered by ILs in an intelligent process design compared to the conventional protocols for esterification. It is shown that exploiting the potential offered by the tunability of functional ILs as high-performance chemicals rather than ‘simple solvents’ offers many possibilities for a more sustainable chemical production., World Journal of Chemical Education, vol. 7, no. 2, p. 153

Ionic liquids have been of great interest throughout this century and continue to find new applications in both academia and industry. This is largely due to their great versatility, with millions of potential combinations of cations and anions, which has led to them being described as 'designer solvents'. However, this leads to its own problems when it comes to choosing the optimum ionic liquid for any given application. To fully exploit this versatility, it is imperative to understand how the properties of ionic liquids arise from their constituent ions. To derive meaningful structure-property relationships for ionic liquids is a complex task. It can be particularly difficult to isolate the cause of any property change arising from even simple modifications of ions. For example, changing the length of the alkyl chain of a cation in an ionic liquid also changes the volume and mass of the ion, all of which can affect a property such as ion mobility and consequent properties such as the viscosity and conductivity of the ionic liquid. A ‘targeted modification’ is a deliberate change in the structure of an ionic liquid ion that is designed to minimise the introduction of such confounding factors. The change must isolate what is of interest, so that we can study only one concept at a time. Once these structure-property relationships have been clearly defined, it will be possible to use these as design elements for new ionic liquids. As well as experimental observations, it is possible to apply the targeted modification approach to a computer simulation. This provides both insight into experimental observations and predictions of potential targeted modifications before complex synthesis is attempted. Together, theory and experiment will enable the concept of ionic liquids as designer solvents to be realised. In this presentation we apply the targeted modifications approach to the transport properties of ionic liquids.

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.

Ionic liquids are an attractive material class due to their wide liquid range, intrinsic ionic conductivity, and high chemical as well as electrochemical stability. However, the widespread use of ionic liquids is hindered by significantly higher viscosities compared to conventional molecular solvents. In this work, we show how the transport properties of ionic liquids can be altered significantly, even for isostructural ions that have the same backbone. To this end, structure–property relationships have been determined for a set of 16 systematically varied representative ionic liquids. Variations in molecular structure include ammonium vs. phosphonium, ether vs. alkyl side chains, and rigid vs. flexible anions. Ab initio calculations are used to relate molecular structures to the thermal, structural and transport properties of the ionic liquids. We find that the differences in properties of ether and alkyl functionalised ionic liquids are primarily dependent on minimum energy geometries, with the conformational flexibility of ether side chains appearing to be of secondary importance. We also show unprecedented correlations between anion conformational flexibility and transport properties. Critically, increasing fluidity upon consecutive introduction of ether side chains and phosphonium centres into the cation is found to be dependent on whether the anion is flexible or rigid. We demonstrate that targeted design of functional groups based on structure–property relationships can yield ionic liquids of exceptionally high fluidity.

One of the few properties common to all ionic liquids is their inherent electrical conductivity, which makes them promising candidates for advanced electrochemical applications. A central finding in this respect is that the measured conductivity is almost always lower than the one obtained from the Nernst-Einstein relation. There has been much dispute about whether correlated motion, charge transfer, or some sort of aggregation is the reason for this difference. In this work, we apply density functional theory-based descriptors to estimate the charge transfer in ionic liquids, which allow predictions for a large number of systems with minimal effort. The theoretical charge transfer was obtained from vertical ionization potentials and electron affinities at the RB3LYP/6-311+G(2d,p)//RB3LYP/6-31+G(d,p) level of theory. To be able to compare and classify the values obtained with this approach, another measure for charge transfer, available directly from the Nernst-Einstein relation, is introduced. The two quantities show significant correlation for some subsets of ionic liquids for which a sufficient amount of information is available. Additionally, the purely theoretical charge-transfer values allow for identifying interesting systems that should be the subject of further investigation.

The identification of specific design concepts for the in silico design of ionic liquids (ILs) has been accomplished using theoretical methods. Molecular building blocks, such as interchangeable functional groups, are used to design a priori new ILs which have subsequently been experimentally investigated. The conformational design concepts are developed by separately and systematically changing the central (imide), bridging (sulfonyl) and end (trifluoromethyl) group of the bis(trifluoromethanesulfonyl)imide [N(Tf)2]− anion and examining the resultant potential energy surfaces. It is shown that these design concepts can be used to tune separately the minimum energy geometry, transition state barrier height and relative stability of different conformers. The insights obtained have been used to design two novel anions for ILs, trifluoroacetyl(methylsulfonyl)imide [N(Ms)(TFA)]− and acetyl(trifluoromethanesulfonyl)imide [N(Tf)(Ac)]−. The computationally predicted structures show excellent agreement with experimental structures obtained from X-ray crystallography. [C4C1im][N(Tf)(Ac)] and [C4C1im][N(Ms)(TFA)] ILs have been synthesised and ion diffusion coefficients examined using pulsed field gradient stimulated echo NMR spectroscopy. Significantly increased diffusion was observed for the more flexible [N(Tf)(Ac)]− compared with the more rigid [N(Ms)(TFA)]− analogue. Furthermore, a pronounced impact on the fluidity was observed. The viscosity of the IL with the rigid anion was found to be twice as high as the viscosity of the IL with the flexible anion. The design concepts presented in this work will enable researchers in academia and industry to tailor anions to provide ILs with specific desired properties.

Ionic liquids (ILs) are novel promising materials widely used in various fields. Their structures and properties can be tuned by means of external perturbations, thus further broadening their applications. Herein, forces proportional to atomic mass (mass-related field) and atomic charge (electric field) are applied in molecular dynamics simulations to the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to investigate the origin of the resulting changes in structures and dynamics. The results show that both electric and mass-related fields cause the ion cages to expand and deform, eventually leading to their breakdown to produce a transformation of ILs from the cage structure to a channel-like structure, which results in faster self-diffusion of ions in the directions of the applied force and to a lesser extent other directions. Further comparison of electric and mass-related fields demonstrates that only the electric fields reorientate cations to produce a hydrodynamically favored conformation in the force direction, which shows faster diffusion. The cis isomer of the anion is preferred in the presence of the electric fields, whereas applying the forces proportional to mass does not change the anion conformer equilibrium significantly. The results presented in this work aid in the understanding of how ions adjust their structures to adapt to external perturbations and facilitate the application of ILs as electrolytes.

Ionic liquids (ILs) are promising electrolytes, although their often high viscosity remains a serious drawback. The latter can be addressed by the introduction of multiple ether functionalization. Based on the highly atom efficient synthesis of tris(2-ethoxyethyl) phosphine, several new phosphonium ionic liquids were prepared, which allows studying the influence of the ether side chains. Their most important physicochemical properties have been determined and will be interpreted using established approaches like ionicity, hole theory, and the Walden plot. There is striking evidence that the properties of phosphonium ionic liquids with the methanesulfonate anion are dominated by aggregation, whereas the two triple ether functionalized ILs with the highest fluidity show almost ideal behavior with other factors being dominant. It is furthermore found that the deviation from ideality is not significantly changed upon introduction of the ether side chains, although a very beneficial impact on the fluidity of ILs is observed. Multiple ether functionalization therefore proves as a powerful tool to overcome the disadvantages of phosphonium ionic liquids with large cations.

A novel ionic liquid based on a highly fluorinated phosphonium cation was synthesized and its physicochemical properties were compared to its semi- and non-fluorinated analogue. The fluorinated ionic liquid was found to show a thermomorphic mixing behavior with organic solvents so that it could be applied as a substitute for volatile perfluorinated solvents in fluorous biphasic catalysis to achieve the recovery of perfluoro-tagged catalysts. Efficient immobilization of a perfluoro-tagged palladium catalyst in the fluorous ionic liquid phase was demonstrated for the Heck reaction as a model reaction of the widely applied Pd-catalysed C C coupling reactions. The reaction of iodobenzene and methyl acrylate resulted in 83% yield after 20 runs proofing the efficient immobilization in the fluorophilic ionic liquid.

Whether used as electrolytes or solvents for synthesis both the bulk viscosity and the microscopic dynamics of ions in ionic liquids often determine the applicability of these. Hence, it is important to understand the connection between the structures of ionic liquid ions and these key properties. Features that contribute to these behaviours include ion mass, size, interactions, and flexibility and the ability of the ions to give rise to nanoscale segregation of charged and nonpolar domains. In this work, we combine experimental and theoretical studies of a wide range of ionic liquids composed of structurally similar ions in an attempt to separate the relative contributions of these features to the transport properties of ionic liquids. We target a number of design parameters, such as the ions' central atoms (e.g., ammonium or phosphonium cations), ion substitution (e.g., alkyl chain length and degree of substitution of cations and fluorination of the anion). In addition to the direct effects of structural changes to an individual ion, we show that the significance of these changes is often moderated by the nature of the counter ion of the ionic liquid. We also demonstrate that targeted design of functional groups based on structure-property relations can yield ionic liquids of exceptionally high fluidity.

Ionic liquids (ILs) are a promising class of solvents, functional fluids and electrolytes that are of high interest for both basic as well as applied research. For further fundamental understanding of ILs and a successful implementation in technical processes, a deeper insight into transport properties and their interrelations is of particular importance. In this contribution we synthesised a series of mostly novel protic and aprotic ILs based on the tetramethylguanidinium (TMG) cation that is a derivative of the superbase guanidine. Different substitution patterns and anions from acids with broadly varied pKa values were investigated. We measured general properties, such as thermal transitions and densities of these ILs, as well as their transport quantities by means of rheology, impedance spectroscopy and NMR diffusometry. Different models for the correlation of the transport properties, namely the Nernst–Einstein, Walden and Stokes–Einstein–Sutherland relations were applied. The deviation from ideal behaviour of fully dissociated electrolytes, often termed as ionicity, was quantified by the reciprocal Haven ratio, fractional Walden rule and ionicity obtained from the Walden plot. Velocity cross-correlation coefficients were calculated to gain further insight into the correlation between ion movements. Both protic and aprotic TMG ILs show transport properties comparable to other ILs with similar molecular weight and high ionicity values especially in contrast to other protic ILs. Lowest ionicity values were found for the protic ILs with smallest ΔpKa values between constituting acid and base. This can either be explained by stronger hydrogen bonding between cation and anion or lower anti-correlations between the oppositely charged ions. These results aim to provide insight into the properties of this interesting cations class and a deeper understanding of the transport properties of ILs and their interrelations in general.