Ionicity of Ionic Liquids

The reorientational dynamics of charge-neutral ion couples [C4mim]⋯[PF6], [C4mim]+ and surprisingly, also [PF6]− ions, are in the nanosecond (ns) time regime. The NMRD profile analysis reveals detailed information about ionicity and free anion fraction, f, based on transient correlated/non-correlated ion dynamics.

The reorientational dynamics of charge-neutral ion couples [C4mim]⋯[PF6], [C4mim]+ and surprisingly, also [PF6]− ions, are in the nanosecond (ns) time regime. The NMRD profile analysis reveals detailed information about ionicity and free anion fraction, f, based on transient correlated/non-correlated ion dynamics.

"The interest in ionic liquids (ILs) as replacements for more hazardous solvents has been growing over the last years, especially in industrial synthesis and liquid-liquid separations. Consequently, it is important to study their degree of dissociation (α), which quantifies the ratio of IL molecules dissociated into their ions and significantly influences viscosity, density, and surface tension. In this work, the dissociation degree of ILs in binary mixtures was predicted based on liquid-liquid equilibria (LLE) data. To do so, the UNIversal QUAsi-Chemical (UNIQUAC) model, which describes short-range interactions, was combined with the Pitzer-Debye-Hückel (PDH) equation, which accounts for long-range interactions. In total, 31 systems comprising 15 different ionic liquids and 4 solvents (water, ethanol, 1-propanol and 1-butanol) were studied. The degree of dissociation as function of the systems' composition was determined by thermodynamic modelling and the results presented a low deviation from the experimental data available in literature, validating this novel approach."

"Ionic liquids (ILs) have been deeply investigated as possible substitutes for hazardous organic solvents, but their recently acknowledged ionicity, together with their generally high viscosity, has been hampering their further application. The ionicity (or degree of dissociation) of electrolytes affects properties such as viscosity, solubility and density, so it is of the utmost importance for the proper thermodynamic description of systems containing electrolytes. However, the experimental quantifications of this property are difficult to perform, which creates the need for more predictive approaches. In this work, the ionicity of 12 ionic liquids in binary mixtures composed of water, ethanol, 1-propanol or 1-butanol was predicted based on solubility data available in literature by the Pitzer-Debye-Hückel (PDH) equation combined with the UNIversal QUAsi-Chemical (UNIQUAC) model, which is often referred as PDH+UNIQUAC. The ionicity of the ionic liquids was modelled as function of mole composition for a total of 17 binary systems, comprising ILs of three chemical families: hexafluorophosphates, tetrafluoroborates, and bis(trifluoromethylsulfonyl)imides, continuing a previous work. This novel methodology provided a useful tool to estimate the ionicity of ionic liquids containing imidazolium cations without undergoing long experimental determinations, which could be applied in the design of separation processes."

"Ionic liquids (ILs) are ionic compounds which are liquid at room temperature and pressure, and can be applied in many fields, such as industrial synthesis, catalysis, electrochemistry, and liquid-liquid separations. To enhance the description of mixtures containing ILs and, consequently, to allow a more rigorous evaluation of the feasibility of chemical processes, it is important to study properties such as the ionicity (α) of ionic liquids, i.e., the fraction of dissociated molecules. However, experimental determinations of ionicity (also known as dissociation degree or dissociation extent) are time-consuming and require the handling of expensive equipment, so the prediction of this property as a function of the system's composition using thermodynamic modelling is of great relevance. For that purpose, the UNIversal QUAsi-Chemical (UNIQUAC) model was combined with the Pitzer-Debye-Hückel (PDH) equation, which is often referred as PDH+UNIQUAC, and it was used to predict the ionicity of ILs in binary mixtures based on liquid-liquid equilibria (LLE) data. The results were compared with the available experimental data from literature and low deviations were observed, validating thereafter the developed approach. In total, the IL ionicity was predicted, as function of composition, for fourteen ionic liquid / solvent (water or 1-butanol) binary systems. Further, a sensitivity analysis was performed to evaluate the influence of the LLE uncertainties on ionicity (α), and it was concluded that α was not significantly affected by small deviations, for which the methodology proposed in this work was considered robust. The prediction of IL ionicity with composition using PDH+UNIQUAC thermodynamic modelling was considered a breakthrough, since very accurate results were achieved without the need of undergoing complex experiments."

The reorientational dynamics of charge-neutral ion couples [C4mim]⋯[PF6], [C4mim]+ and surprisingly, also [PF6]− ions, are in the nanosecond (ns) time regime. The NMRD profile analysis reveals detailed information about ionicity and free anion fraction, f, based on transient correlated/non-correlated ion dynamics.

The reorientational dynamics of charge-neutral ion couples [C4mim]⋯[PF6], [C4mim]+ and surprisingly, also [PF6]− ions, are in the nanosecond (ns) time regime. The NMRD profile analysis reveals detailed information about ionicity and free anion fraction, f, based on transient correlated/non-correlated ion dynamics.

In this paper, we have investigated the electronic properties of rare earth mono-pnictides in rock-salt structured using the plasma oscillations theory of solids. We have presented the expressions relating the homopolar gap (Eh), ionic gap (Ec), average energy gap (Eg), crystal ionicity (fi) and electronic polarizability (αe) for rare earth monopnictides with the plasmon energy (ћωp). The electronic properties such as homopolar gap, ionic gap, average energy gap, crystal ionicity and electronic polarizability of these compounds exhibit a linear relationship when plotted on a loglog scale against the plasmon energy (ћωp). A fairly good agreement has been found between observed and calculated values of Eh, Ec, Eg, fi, and αe for rare earth monopnictides.

We report temperature dependent 1 H NMR relaxation measurements of the powder thiourea-hexachloroethane inclusion compound, [2.95(NH 2) 2 CS]´C 2 Cl 6 , at different resonance frequencies, from 23 to 55.5 MHz. Signi®cant reduction of spin± lattice relaxation time at 38±47 MHz is caused by the cross-relaxation of protons via the quadrupole chlorine nuclei. We conclude that the effective 1 H± 35 Cl cross-relaxation observed in powder sample is due to a slow mode process, when the molecules of the domain wall exhibit a correlated translational and rotational motion over the channel. Such a propagation of the domain wall was predicted by atom-atomic potential calculation. We show that the NMR cross-relaxation effect is an effective tool in studying ultraslow motions, in particular in incommensurate structures.

The out-of-plane motion of the pyridinium cation in the bis-thiourea pyridinium chloride inclusion compound has been studied in a wide temperature range using 1 H NMR, dielectric spectroscopy and quasielastic neutron scattering. The geometry of this motion is obtained from the Q-dependence of the elastic incoherent structure factor determined from the quasielastic neutron scattering measurements. We find that the pyridinium cation performs out-of-plane reorientations around the axis passing through two opposite atoms of the ring. The correlation times as a function of temperature were measured in the three known crystallographic phases, finding a good agreement between the three techniques employed. The activation energy for this motion changes from 5 AE 1 kJ mol À1 in the low-temperature phase to 1.2 AE 0.2 kJ mol À1 in the intermediate and high-temperature phases.

The reorientational dynamics of charge-neutral ion couples [C4mim]⋯[PF6], [C4mim]+ and surprisingly, also [PF6]− ions, are in the nanosecond (ns) time regime. The NMRD profile analysis reveals detailed information about ionicity and free anion fraction, f, based on transient correlated/non-correlated ion dynamics.

The reorientational dynamics of charge-neutral ion couples [C4mim]⋯[PF6], [C4mim]+ and surprisingly, also [PF6]− ions, are in the nanosecond (ns) time regime. The NMRD profile analysis reveals detailed information about ionicity and free anion fraction, f, based on transient correlated/non-correlated ion dynamics.

The ionic nature of a functionalized protic ionic liquid cannot be rationalized simply through the differences in aqueous proton dissociation constants between the acid precursor and the conjugate acid of the base precursor. The extent of proton transfer, i.e. the equilibrium ionicity, of a tertiary ammonium acetate protic ionic liquid can be significantly increased by introducing an hydroxyl functional group on the cation, compared to the alkyl or amino-functionalized analogues. This increase in apparent ionic nature correlates well with variations in solvent-solute and solvent-solvent interaction parameters, as well as with physicochemical properties such as viscosity.

Structural properties, electronic band structure, real and imaginary parts of complex dielectric function of alkali chloride XCl (K, Rb and Li) compounds were investigated under various pressures using first principles calculations. Moreover, Gibbs free energies were also calculated at those pressures. Calculated results of the Gibbs free energy show that LiCl does not show any structural phase transition. However, structural phase transitions of KCl and RbCl occur from NaCl (B1) to CsCl (B2) at 4.5 and 1.7 GPa pressures, respectively. The electronic band gaps under pressure were also calculated. The calculated physical properties of these compounds are compared with the previous theoretical and experimental results and a good agreement was observed.

We have conducted 75 As and 69 Ga Nuclear Magnetic Resonance (NMR) experiments to investigate order/disorder in Al x Ga 1Àx As lift-off films with x B 0.297 and 0.489. We were able to identify all possible As(Al n Ga 4Àn ) sites with n = 0-4 coordinations in 75 As NMR spectra using spin-echo experiments at 18.8 Tesla. This was achieved by employing high rf field strengths using a small solenoid coil and an NMR probe specifically designed for this purpose. Spectral deconvolution, using an evolutionary algorithm, complies with the absence of long-range order if a CuAu based order parameter is imposed. An unconstrained fit shows a deviation of the statistics imposed by this type of ordering. The occupational disorder in the Ga and Al positions is reflected in a distribution of the Electric Field Gradients (EFGs) experienced at the different arsenic sites. We established that this can be modelled by summing the effects of the first coordination sphere and a Czjzek type distribution resulting from the compositional variation in the Al/Ga sub-lattice in the higher coordination spheres. 69 Ga 3QMAS and nutation data exclude the presence of highly symmetric sites and also show a distribution in EFG. The experimentally obtained quadrupolar interactions are in good agreement with calculations based on Density Functional Theory (DFT). Using additivity of EFG tensors arising from distant charge perturbations, we could use DFT to model the EFG distributions of the n = 0-4 sites, reproducing the Czjzek and extended Czjzek distributions that were found experimentally. On the basis of these calculations we conclude that the 75 As quadrupolar interaction is sensitive to compositional modulations up to the 7th coordination shell in these systems.

Newly synthesised halogen-free boron based ionic liquids (hf-BILs) composed of chelated orthoborate anions and phosphonium cations have hydrolytic stability, low melting point and outstanding wear and friction reducing properties. We report here the peculiarities of self-diffusion in one representative from this class, trihexyltetradecylphosphonium bis(mandelato)borate, [P 6,6,6,14 ][BMB], in the temperature range of its practical interest, 20-100 1C. NMR techniques demonstrated complicated diffusional behaviour -the ionic liquid can exist in one or two liquid ''phases''. In the low-temperature range (20-50 1C), two phases coexist where the cations, [P 6,6,6,14 ], are contained mainly in the phase with slower diffusion coefficients while the anions, [BMB], are in the phase with faster diffusion coefficients. Cations have lower diffusion coefficients with a factor of 20 as compared with the anions, an effect which is caused by aggregation of cations into domains due to so-called ''hydrophobic interaction'' of their hydrocarbon chains. As the temperature rises above 60 1C, the two phases merge into one where both ions have equal diffusion coefficients. This is caused by thermal motion making the cation domains smaller in size and more easily interacting with anions. As a result, anions and cations diffuse in this high-temperature range as a pair.

We have conducted 75 As and 69 Ga Nuclear Magnetic Resonance (NMR) experiments to investigate order/disorder in Al x Ga 1Àx As lift-off films with x B 0.297 and 0.489. We were able to identify all possible As(Al n Ga 4Àn ) sites with n = 0-4 coordinations in 75 As NMR spectra using spin-echo experiments at 18.8 Tesla. This was achieved by employing high rf field strengths using a small solenoid coil and an NMR probe specifically designed for this purpose. Spectral deconvolution, using an evolutionary algorithm, complies with the absence of long-range order if a CuAu based order parameter is imposed. An unconstrained fit shows a deviation of the statistics imposed by this type of ordering. The occupational disorder in the Ga and Al positions is reflected in a distribution of the Electric Field Gradients (EFGs) experienced at the different arsenic sites. We established that this can be modelled by summing the effects of the first coordination sphere and a Czjzek type distribution resulting from the compositional variation in the Al/Ga sub-lattice in the higher coordination spheres. 69 Ga 3QMAS and nutation data exclude the presence of highly symmetric sites and also show a distribution in EFG. The experimentally obtained quadrupolar interactions are in good agreement with calculations based on Density Functional Theory (DFT). Using additivity of EFG tensors arising from distant charge perturbations, we could use DFT to model the EFG distributions of the n = 0-4 sites, reproducing the Czjzek and extended Czjzek distributions that were found experimentally. On the basis of these calculations we conclude that the 75 As quadrupolar interaction is sensitive to compositional modulations up to the 7th coordination shell in these systems.

An interaction potential including chloride anion polarization effects, constructed from first-principles calculations, is used to examine the structure and transport properties of a series of chloroaluminate melts. A particular emphasis was given to the study of the equimolar mixture of aluminium chloride with 1-ethyl-3-methylimidazolium chloride, which forms a room temperature ionic liquid EMI + -AlCl À 4 . The structure yielded by the classical simulations performed within the framework of the polarizable ion model is compared to the results obtained from entirely electronic structure-based simulations: An excellent agreement between the two flavors of molecular dynamics is observed. When changing the organic cation EMI + by an inorganic cation with a smaller ionic radius (Li + , Na + , K + ), the chloroaluminate speciation becomes more complex, with the formation of Al 2 Cl À 7 in small amounts. The calculated transport properties (diffusion coefficients, electrical conductivity and viscosity) of EMI + -AlCl À 4 are in good agreement with experimental data.

A~~ analysis 6f the phot~I~tic effect in ionic crystafs has been presented withm the framework of Ciau~u~Mo~ot~ theory of the dieMric constant. The values of the strain derivative of the eIectronic dielectric constant have been calculated in alkali halides and h&O crystals by taking into account the variation of electronic polarizabilities with compressive stress. The results obtained are found closer to the experimental values. The photoelastic behaviour of MgO crystal is predicted to be of opposite nature to that of alkali halides, in conformity with the experimental observations.

Based on the well-known Phillips —Van Vechten and Penn-type models, we present here an analysis of the effective charges and ionicity in alkali halides. This analysis is made in the light of the recently reported experimental results of  Lowndes and Martin. It is essentially
seen that Zeff = 8 gives results which are in good accord with those of Van Vechten and Lawaetz. The power law governing the variation of the homopolar gap with the nearest-neighbor distance, which has earlier been proposed for elemental semiconductors, is also shown to hold for the alkali halides. We then extrapolate this result to obtain an
estimate of the hitherto-unknown homopolar gap of cesium fluoride. Other related properties of CsF are then derived.

Knowledge of ionicity is requisite for successful identification of those salt qualities required to design and couple the most appropriate fluid for performance of an intended chemical function. We report on utilisation of 35 Cl À quadrupolar coupling constants (C Q ) to quantitatively assess the ionicities of given chloride salts, by exploiting the electronic response of the quadrupolar chlorine atom as a function of its immediate chemical environment. We find that protic salts in particular, like their aprotic analogues, are highly ionised, while at the same time being highly associated, in stark contrast to literature reports claiming in general that they are of sub-ionic origin.

While liquid electrolyte salts, comprised predominantly of ions and ion pairs, were studied already in the early half of the 1800s (see for example papers by Faraday [1] or Hittorf ), modern advancements of ionic materials have given rise to various combinations resulting in liquid phases at convenient temperatures. For this reason, a "renewed" interest in ionic liquids (ILs) has exploded worldwide, with hopes to solve problems of interest to the industrial chemistry community. Furthermore, it emerges that their unique physical properties lead to challenging solvation characteristics, [3] ultimately the result of complex reorientational ion dynamics. Of fundamental importance to understanding the solvation properties of liquids, aside from enlightening dielectric relaxation studies, are nuclear spin dynamics, obtained using experimental NMR relaxation techniques. In this context, the nuclear spin is allowed to return to its equilibrium magnetisation (i.e. relaxation occurs) after being disturbed by an externally applied radiofrequency (rf) magnetic field. Experiments yield selective information regarding the rotational dynamics of the assembly containing the nuclei of interest because the return to equilibrium is governed by the assembly's reorientational motion. For a 13 C nucleus in a planar asymmetric skeleton, such as ring carbons comprising any imidazolium based IL, two sources of relaxation must be considered: that due to dipole-dipole (DD) interactions and that due to the chemical shift anisotropy (CSA).

Crystalline solids, co-existing in equilibrium with the 3methyl-1H-imidazolium bromohydrogenates(I) ionic liquid, have been characterised by X-ray diffraction analysis. The Brønsted acidic, homo-conjugate [H 2 Br 3 ]anions presented are discussed in terms of their structure and reactivity, in efforts to advance the understanding of Brønsted acidity in ionic liquid media.