Physical Chemistry of Ionic Liquids, Inorganic and Organic, Protic and Aprotic

Angell, C. Austen; Xu, Wu; Yoshizawa, Masahiro; Hayashi, Akitoshi; Bélières, Jean-Philippe; Lucas, Pierre; Videa, Marcelo

doi:10.1002/0471762512.ch2

Cited by 46 publications

(73 citation statements)

References 22 publications

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“…However there is very little written about what exactly is involved in achieving high ionicity. 13 If the ions created in forming the ionic liquid were to remain locked together in pairs, the liquids would not be found to be of very low vapor pressure, and their conductivities would also be poor. They would just represent an unusual group of polar liquids.…”

Section: Ionicity Of Ionic Liquids: Relation To Vapor Pressure and Comentioning

confidence: 99%

Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications

2007

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This Account covers research dating from the early 1960s in the field of low-melting molten salts and hydrates,which has recently become popular under the rubric of "ionic liquids". It covers understanding gained in the principal author's laboratories (initially in Australia, but mostly in the U.S.A.) from spectroscopic, dynamic, and thermodynamic studies and includes recent applications of this understanding in the fields of energy conversion and biopreservation. Both protic and aprotic varieties of ionic liquids are included, but recent studies have focused on the protic class because of the special applications made possible by the highly variable proton activities available in these liquids.In this Account, we take a broad view of ionic liquids (using the term in its current sense of liquids comprised of ions and melting below 100°C). We include, along with the general cases of organic cation systems, liquids in which common inorganic cations (like Mg 2+ and Ca 2+ ) strongly bind a hydration or solvation shell and then behave like large cation systems and melt below 100°C.We will try to organize a wide variety of measurements on low-melting ionic liquid systems into a coherent body of knowledge that is relevant to the ionic liquid field as it is currently developing.Under the expanded concept of the field, ionic liquid studies commenced in the Angell laboratory in 1962 with a study of the transport properties of the hydrates of Mg(NO 3 ) 2 and Ca(NO 3 ) 2 . These were described as melts of "large weak-field cations" 1 and their properties correlated with those of normal anhydrous molten salts via their effective cation radii, the sum of the normal radius plus one water molecule diameter. This notion was followed in 1966 with a full study under the title "A new class of molten salt mixtures" in which the hydrated cations were treated as independent cation species. The large cations mixed ideally with ordinary inorganic cations such as Na + and K + , to give solutions in which such cohesion indicators as the glass transition temperature, T g , changed linearly with composition. The concept proved quite fruitful, and a field ("hydrate melts" or "solvate melts") developed in its wake in which asymmetric anions like SCN -and NO 2 -were used with solvated cations to create a very wide range of systems that were liquid at room temperature, while remaining ionic in their general properties.The validity of the molten salt analogy was given additional conviction by the observation that transition metal ions such as Ni(II) and Co(II) could be found in the complex anion states NiCl 4 2-and CoCl 4 2-when added to the "hydrate melt" chlorides. 2 Of special interest here was the observation 3 of extreme downfield NMR proton chemical shifts of hydrate protons when the hydrated cation was Al 3+ . These lay much further downfield than did the protons in strong mineral acids at the same concentration, leading to the design of solutions of highly acidic character from salts that would usually be considered neutral. Inde...

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Section: Ionicity Of Ionic Liquids: Relation To Vapor Pressure and Comentioning

confidence: 99%

Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications

2007

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“…This process is reversible if the energy that is required for the proton jump is small; in this case, the formed liquid has low conductivity and high vapor pressure. Good properties of an IL are achieved when the proton largely remains on the cation due to the wide energy gap associated to the recovery of the pristine acid and base [25]. The strong long-range Coulomb interaction between the sostabilized cation and anion lowers the vapor pressure over the liquid.…”

Section: Protic Ilsmentioning

confidence: 99%

Potentialities of ionic liquids as new electrolyte media in advanced electrochemical devices

Fernicola

Scrosati

Ohno

2006

Ionics

240

156

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This paper reviews the various classes of ionic liquids (ILs) in view of their established and expected applications in advanced electrochemical devices, such as lithium batteries, fuel cells, and supercapacitors. In this respect, particular attention is devoted to aprotic and protic ILs, with a related discussion in terms of their thermal and transport properties. In addition, the role in the electrochemical technology of a new class of ILs having cation and anion tethered in an intramolecular form is stressed. Due to their emerging importance, IL-based polymers are finally reported and discussed. A conclusion, where the expected evolution of the ILs research and development is evaluated, is also included.

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“…1 The difference is only that, by use of large compound cations to reduce the coulomb attractions to anions and complicated shapes to confuse the ion packing problem, the crystalline state of the system is sufficiently destabilized for melting to occur near to or below ambient. 2 Because of the differences in properties between the average IL and the average high-temperature molten salt (e.g., 2 orders of magnitude in conductivity and fluidity, non-Arrhenius vs Arrhenius temperature dependences of these properties, etc. ), and because of the differences in their applications in industrial chemistry (e.g., winning of aluminum vs solvent function for synthetic inorganic chemistry) there has developed some sort of schism between the different branches of the IL field.…”

Section: Introductionmentioning

confidence: 99%

“…T g serves as a cohesive energy parameter, 2 and Figure 1b shows that when scaled for cohesive energy it is no longer possible to tell the difference between the salts with inorganic cations and those with molecular (organic) cations. The same type of scaling (using ideal glass temperatures) was used long ago to relate molten salt hydrates to anhydrous molten salts.…”

Section: Introductionmentioning

confidence: 99%

Protic Ionic Liquids: Preparation, Characterization, and Proton Free Energy Level Representation

2007

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We give a perspective on the relations between inorganic and organic cation ionic liquids (ILs), including members with melting points that overlap around the borderline 100°C. We then present data on the synthesis and properties (melting, boiling, glass temperatures, etc.) of a large number of an intermediate group of liquids that cover the ground between equimolar molecular mixtures and ILs, depending on the energetics of transfer of a proton from one member of the pair to the other. These proton-transfer ILs have interesting properties, including the ability to serve as electrolytes in solvent-free fuel cell systems. We provide a basis for assessing their relation to aprotic ILs by means of a Gurney-type proton-transfer free energy level diagram, with approximate values of the energy levels based on free energy of formation and pK a data. The energy level scheme allows us to verify the relation between solvent-free acidic and basic electrolytes, and the familiar aqueous variety, and to identify neutral protic electrolytes that are unavailable in the case of aqueous systems.

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Physical Chemistry of Ionic Liquids, Inorganic and Organic, Protic and Aprotic

Cited by 46 publications

References 22 publications

Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications

Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications

Potentialities of ionic liquids as new electrolyte media in advanced electrochemical devices

Protic Ionic Liquids: Preparation, Characterization, and Proton Free Energy Level Representation

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