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Ion Pairing in Ionic Liquids

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Encyclopedia of Ionic Liquids

What Is Ion Pairing?

The nature and degree of ion pairing in ionic liquids (ILs) led to controversial debate in literature [1,2,3]. Simply put, several factions of contrasting views – on one end describing ILs as systems of mostly free, dissociated ions and on the other end holding the view that ILs are mainly composed of associated, neutral ion pairs – seek to find a solution for what seems to be contradictory evidence. No definitive answer could be reached to this day, with new evidence still emerging on both sides. Despite the fact that this debate has been going on for over a decade, a clear and generally accepted definition of what constitutes an ion pair in a system that is composed solely of ionic particles is still missing. Usually a helpful definition includes the distinction between penetrated or contact ion pairs (two associated ions penetrating each other or in direct contact), solvent-shared ion pairs (the ions are associated but separated by solvent molecules), and...

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References

  1. Kirchner B, Malberg F, Firaha DS, Hollóczki O (2015) Ion pairing in ionic liquids. J Phys Condens Matter 27(46):463002

    Google Scholar 

  2. Hollóczki O, Malberg F, Welton T, Kirchner B (2014) On the origin of ionicity in ionic liquids. Ion pairing versus charge transfer. Phys Chem Chem Phys 16(32):16880–16890

    Google Scholar 

  3. Zhao W, Leroy F, Heggen B, Zahn S, Kirchner B, Balasubramanian S, Müller-Plathe F (2009) Are There Stable Ion-Pairs in Room-Temperature Ionic Liquids? Molecular Dynamics Simulations of 1-n-Butyl-3-methylimidazolium Hexafluorophosphate. J Am Chem Soc 131(43):15825–15833

    Google Scholar 

  4. Rogers RD, Seddon KR (2003) Ionic liquids--solvents of the future? Science 302(5646):792–793

    Google Scholar 

  5. Seddon KR (2003) A taste of the future. Nat Mater 2(6):363–365

    Google Scholar 

  6. Chaumont A, Wipff G (2009) Polyoxometalate Keggin anions at aqueous interfaces with organic solvents, ionic liquids, and graphite: a molecular dynamics study. J Phys Chem C 113(42):18233–18243

    Google Scholar 

  7. Chaumont A, Wipff G (2008) Chloride complexation by uranyl in a room temperature ionic liquid. A computational study. J Phys Chem B 112(38):12014–12023

    Google Scholar 

  8. Lui MY, Crowhurst L, Hallett JP, Hunt PA, Niedermeyer H, Welton T (2011) Salts dissolved in salts: ionic liquid mixtures. Chem Sci 2(8):1491–1496

    Google Scholar 

  9. Hallett JP, Liotta CL, Ranieri G, Welton T (2009) Charge screening in the SN2 reaction of charged electrophiles and charged nucleophiles: an ionic liquid effect. J Org Chem 74(5):1864–1868

    Google Scholar 

  10. Kuzmina O, Bordes E, Schmauck J, Hunt PA, Hallett JP, Welton T (2016) Solubility of alkali metal halides in the ionic liquid [C4C1im][OTf]. Phys Chem Chem Phys 18(24):16161–16168

    Google Scholar 

  11. Ma C, Laaksonen A, Liu C, Lu X, Ji X (2018) The peculiar effect of water on ionic liquids and deep eutectic solvents. Chem Soc Rev 47:8685–8720

    Google Scholar 

  12. Smith EL, Abbott AP, Ryder KS (2014) Deep eutectic solvents (DESs) and their applications. Chem Rev 114(21):11060–11082

    Google Scholar 

  13. Korotkevich A, Firaha DS, Padua AAH, Kirchner B (2017) Ab initio molecular dynamics simulations of SO2 solvation in choline chloride/glycerol deep eutectic solvent. Fluid Phase Equilib 448:59–68

    Google Scholar 

  14. Robinson RA, Stokes RH (2002) Electrolyte Solutions. 2nd ed. Dover, Mineola

    Google Scholar 

  15. Clare B, Sirwardana A, MacFarlane DR (2009) Synthesis, purification and characterization of ionic liquids. In: Kirchner B (ed) Ionic Liquids, Springer, Berlin, Heidelberg, pp 1–40

    Google Scholar 

  16. MacFarlane DR, Forsyth M, Izgorodina EI, Abbott AP, Annat G, Fraser K (2009) On the concept of ionicity in ionic liquids. Phys Chem Chem Phys 11(25):4962–4967

    Google Scholar 

  17. Johnson KE (2007) What's an ionic liquid? Interface 16(1):38–41

    Google Scholar 

  18. Xu W, Cooper EI, Angell CA (2003) Ionic liquids: ion mobilities, glass temperatures, and fragilities. J Phys Chem B 107(25):6170–6178

    Google Scholar 

  19. Yoshizawa M, Xu W, Angell CA (2003) Ionic liquids by proton transfer: vapor pressure, conductivity, and the relevance of ΔpKa from aqueous solutions. J Am Chem Soc 125(50):15411–15419

    Google Scholar 

  20. Zhao C, Burrell G, Torriero AAJ, Separovic F, Dunlop NF, MacFarlane DR, Bond AM (2008) Electrochemistry of room temperature protic ionic liquids. J Phys Chem B 112(23):6923–6936

    Google Scholar 

  21. Walden P (1906) Organic solvents and ionization media. III. Interior friction and its relation to conductivity. Phys Z Chem 55:207–249

    Google Scholar 

  22. Tokuda H, Tsuzuki S, Susan MABH, Hayamizu K, Watanabe M (2006) How ionic are room-temperature ionic liquids? An indicator of the physicochemical properties. J Phys Chem B 110(39):19593–19600

    Google Scholar 

  23. Belieres JP, Angell CA (2007) Protic ionic liquids: preparation, characterization, and proton free energy level representation. J Phys Chem B 111(18):4926–4937

    Google Scholar 

  24. Schreiner C, Zugmann S, Hartl R, Gores HJ (2009) Fractional Walden rule for ionic liquids: examples from recent measurements and a critique of the so-called ideal KCl line for the Walden plot. J Chem Eng Data 55(5):1784–1788

    Google Scholar 

  25. Abbott AP, Ryder K, Licence P, Taylor AW (2015) What is an ionic liquid? In: Plechkova NV, Seddon KR (eds) Ionic Liquids Completely UnCOILed: Critical Expert Overviews, John Wiley & Sons, Hoboken, New Jersey, pp 1–12

    Google Scholar 

  26. Gebbie MA, Valtiner M, Banquy X, Fox ET, Henderson WA, Israelachvili JN (2013) Ionic liquids behave as dilute electrolyte solutions. Proc Natl Acad Sci 110(24):9674–9679

    Google Scholar 

  27. Rupp A, Roznyatovskaya N, Scherer H, Beichel W, Klose P, Sturm C, Hoffmann A, Tübke J, Koslowski T, Krossing I (2014) Size matters! On the way to ionic liquid systems without ion pairing. Chem Eur J 20(31):9794–9804

    Google Scholar 

  28. Lee AA, Vella D, Perkin S, Goriely A (2014) Are room-temperature ionic liquids dilute electrolytes? J Phys Chem Lett 6(1):159–163

    Google Scholar 

  29. Perkin S, Salanne M, Madden P, Lynden-Bell R (2013) Is a Stern and diffuse layer model appropriate to ionic liquids at surfaces? Proc Natl Acad Sci 110(44):E4121

    Google Scholar 

  30. Perkin S, Salanne M (2014) Interfaces of ionic liquids. Preface. J Phys Condens Matter 26(28):280301

    Google Scholar 

  31. Gebbie MA, Valtiner M, Banquy X, Henderson WA, Israelachvili JN (2013) Reply to Perkin et al.: Experimental observations demonstrate that ionic liquids form both bound (Stern) and diffuse electric double layers. Proc Natl Acad Sci 110(44):E4122

    Google Scholar 

  32. Malberg F, Hollóczki O, Thomas M, Kirchner B (2015) En route formation of ion pairs at the ionic liquid–vacuum interface. Struct Chem 26(5–6):1343–1349

    Google Scholar 

  33. Gehrke S, Reckien W, Palazzo I, Welton T, Hollóczki O (2019) On the carbene-like reactions of imidazolium acetate ionic liquids: can theory and experiments agree? Eur J Org Chem 2019(2–3):504–511

    Google Scholar 

  34. Neto BAD, Meurer EC, Galaverna R, Bythell BJ, Dupont J, Cooks RG, Eberlin MN (2012) Vapors from ionic liquids: reconciling simulations with mass spectrometric data. J Phys Chem Lett 3(23):3435–3441

    Google Scholar 

  35. Ma Y, Gao W, Yu H, Li M (2014) Rapid method for determination of homologue imidazolium ionic liquid cations by ion-pair chromatography using a monolithic column. J Liq Chromatogr Relat Technol 37(1):73–87

    Google Scholar 

  36. Ingenmey J, von Domaros M, Perlt E, Verevkin SP, Kirchner B (2018) Thermodynamics and proton activities of protic ionic liquids with quantum cluster equilibrium theory. J Chem Phys 148(19):193822

    Google Scholar 

  37. Köddermann T, Wertz C, Heintz A, Ludwig R (2006) Ion-pair formation in the ionic liquid 1-ethyl-3-methylimidazolium bis(triflyl)imide as a function of temperature and concentration. Chem Phys Chem 7(9):1944–1949

    Google Scholar 

  38. Weingärtner H (2008) Understanding ionic liquids at the molecular level: facts, problems, and controversies. Angew Chem Int Ed 47(4):654–670

    Google Scholar 

  39. Daguenet C, Dyson PJ, Krossing I, Oleinikova A, Slattery J, Wakai C, Weingärtner H (2006) Dielectric response of imidazolium-based room-temperature ionic liquids. J Phys Chem B 110(25):12682–12688

    Google Scholar 

  40. Tokuda H, Hayamizu K, Ishii K, Susan MABH, Watanabe M (2004) Physicochemical properties and structures of room temperature ionic liquids. 1. Variation of anionic species. J Phys Chem B 108(42):16593–16600

    Google Scholar 

  41. Tokuda H, Hayamizu K, Ishii K, Susan MABH, Watanabe M (2005) Physicochemical properties and structures of room temperature ionic liquids. 2. Variation of alkyl chain length in imidazolium cation. J Phys Chem B 109(13):6103–6110

    Google Scholar 

  42. Turton DA, Sonnleitner T, Ortner A, Walther M, Hefter G, Seddon KR, Stana S, Plechkova NV, Buchner R, Wynne K (2012) Structure and dynamics in protic ionic liquids: a combined optical Kerr-effect and dielectric relaxation spectroscopy study. Faraday Discuss 154:145–153

    Google Scholar 

  43. Weingärtner H, Sasisanker P, Daguenet C, Dyson PJ, Krossing I, Slattery JM, Schubert T (2007) The dielectric response of room-temperature ionic liquids: effect of cation variation. J Phys Chem B 111(18):4775–4780

    Google Scholar 

  44. Chen H, Chen X, Deng J, Zheng J (2018) Isotropic ordering of ions in ionic liquids on the sub-nanometer scale. Chem Sci 9(6):1464–1472

    Google Scholar 

  45. Zhang Y, Maginn EJ (2015) Direct correlation between ionic liquid transport properties and ion pair lifetimes: a molecular dynamics study. J Phys Chem Lett 6(4):700–705

    Google Scholar 

  46. Kohagen M, Brehm M, Thar J, Zhao W, Müller-Plathe F, Kirchner B (2010) Performance of quantum chemically derived charges and persistence of ion cages in ionic liquids. A molecular dynamics simulations study of 1-n-butyl-3-methylimidazolium bromide. J Phys Chem B 115(4):693–702

    Google Scholar 

  47. Thar J, Brehm M, Seitsonen AP, Kirchner B (2009) Unexpected hydrogen bond dynamics in imidazolium-based ionic liquids. J Phys Chem B 113(46):15129–15132

    Google Scholar 

  48. Kirchner B, Hollóczki O, Canongia Lopes JN, Pádua AAH (2015) Multiresolution calculation of ionic liquids. WIREs Comp Mol Sci 5(2):202–214

    Google Scholar 

  49. Hardacre C, Holbrey JD, Mullan CL, Youngs TGA, Bowron DT (2010) Small angle neutron scattering from 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids ([Cnmim][PF6], n=4, 6, and 8). J Chem Phys 133(7):074510

    Google Scholar 

  50. Xu W, Angell CA (2003) Solvent-free electrolytes with aqueous solution-like conductivities. Science 302(5644):422–245

    Google Scholar 

  51. Hayes R, Imberti S, Warr GG, Atkin R (2013) The nature of hydrogen bonding in protic ionic liquids. Angew Chem Int Ed 52(17):4623–4627

    Google Scholar 

  52. Fumino K, Wulf A, Ludwig R (2009) Hydrogen bonding in protic ionic liquids: reminiscent of water. Angew Chem Int Ed 48(17):3184–3186

    Google Scholar 

  53. Alder BJ, Wainwright TE (1970) Decay of the velocity autocorrelation function. Phys Rev A 1(1):18

    Google Scholar 

  54. Hansen JP, McDonald IR (2013) Theory of simple liquids. 4th ed. Academic Press, Amsterdam

    Google Scholar 

  55. Del Pópolo MG, Voth GA (2004) On the structure and dynamics of ionic liquids. J Phys Chem B 108(5):1744–1752

    Google Scholar 

  56. Cremer T, Kolbeck C, Lovelock KRJ, Paape N, Wölfel R, Schulz PS, Wasserscheid P, Weber H, Thar J, Kirchner B, Maier F, Steinbrück HP (2010) Towards a molecular understanding of cation–anion interactions—probing the electronic structure of imidazolium ionic liquids by NMR spectroscopy, X-ray photoelectron spectroscopy and theoretical calculations. Chem Eur J 16(30):9018–9033

    Google Scholar 

  57. Morrow TI, Maginn EJ (2002) Molecular dynamics study of the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate. J Phys Chem B 106(49):12807–12813

    Google Scholar 

  58. Kortüm G (1966) Lehrbuch der Elektrochemie. 4th ed. Verlag Chemie, Weinheim

    Google Scholar 

  59. Breneman CM, Wiberg KB (1990) Determining atom-centered monopoles from molecular electrostatic potentials. The need for high sampling density in formamide conformational analysis. J Comput Chem 11(3):361–373

    Google Scholar 

  60. Philippi F, Rauber D, Springborg M, Hempelmann R (2019) Density functional theory descriptors for ionic liquids and the charge-transfer interpretation of the Haven ratio. J Phys Chem A 123(4):851–861

    Google Scholar 

  61. Greaves TL, Drummond CJ (2015) Protic ionic liquids: evolving structure–property relationships and expanding applications. Chem Rev 115(20):11379–11448

    Google Scholar 

  62. Rana UA, Forsyth M, MacFarlane DR, Pringle JM (2012) Toward protic ionic liquid and organic ionic plastic crystal electrolytes for fuel cells. Electrochim Acta 84:213–222

    Google Scholar 

  63. Zahn S, Bruns G, Thar J, Kirchner B (2008) What keeps ionic liquids in flow? Phys Chem Chem Phys 10(46):6921–6924

    Google Scholar 

  64. Hunt PA (2007) Why does a reduction in hydrogen bonding lead to an increase in viscosity for the 1-butyl-2,3-dimethyl-imidazolium-based ionic liquids? J Phys Chem B 111(18):4844–4853

    Google Scholar 

  65. Ingenmey J, Gehrke S, Kirchner B (2018) How to harvest Grotthuss diffusion in protic ionic liquid electrolyte systems. ChemSusChem 11(12):1900–1910

    Google Scholar 

  66. Byrne N, Angell CA (2008) Protein unfolding, and the “tuning in” of reversible intermediate states, in protic ionic liquid media. J Mol Biol 378(3):707–714

    Google Scholar 

  67. Kanzaki R, Uchida K, Xuedan S, Umebayashi Y, Ishiguro SI (2008) Acidity and basicity of aqueous mixtures of a protic ionic liquid, ethylammonium nitrate. Anal Sci 24(10):1347–1349

    Google Scholar 

  68. Kanzaki R, Doi H, Song X, Hara S, Ishiguro SI, Umebayashi Y (2012) Acid–base property of N-methylimidazolium-based protic ionic liquids depending on anion. J Phys Chem B 116(48):14146–14152

    Google Scholar 

  69. Brüssel M, Perlt E, Lehmann SBC, von Domaros M, Kirchner B (2011) Binary systems from quantum cluster equilibrium theory. J Chem Phys 135(19):194113

    Google Scholar 

  70. Blasius J, Ingenmey J, Perlt E, von Domaros M, Holloczki O, Kirchner B (2019) Predicting mole-fraction-dependent dissociation for weak acids. Angew Chem Int Ed 58(10):3212–3216

    Google Scholar 

  71. Kirchner B (2005) Cooperative versus dispersion effects: What is more important in an associated liquid such as water? J Chem Phys 123(20):204116

    Google Scholar 

  72. Kirchner B (2007) Theory of complicated liquids: Investigation of liquids, solvents and solvent effects with modern theoretical methods. Phys Rep 440(1–3):1–111

    Google Scholar 

  73. Hollóczki O, Gerhard D, Massone K, Szarvas L, Németh B, Veszprémi T, Nyulászi L (2010) Carbenes in ionic liquids. New J Chem 34(12):3004–3009

    Google Scholar 

  74. Doi H, Song X, Minofar B, Kanzaki R, Takamuku T, Umebayashi Y (2013) A new proton conductive liquid with no ions: pseudo-protic ionic liquids. Chem Eur J 19(35):11522–11526

    Google Scholar 

  75. Hollóczki O (2018) Toward anionic structural diffusion and highly conducting ionic liquid electrolytes. ACS Sustain Chem Eng 7(2):2626–2633

    Google Scholar 

  76. Hollóczki O, Wolff A, Pallmann J, Whiteside RE, Hartley J, Grasser MA, Nockemann P, Brunner E, Doert T, Ruck M (2018) Spontaneous substitutions at phosphorus trihalides in imidazolium halide ionic liquids: grotthuss diffusion of anions? Chem Eur J 24(61):16323–16331

    Google Scholar 

  77. McDaniel JG, Yethiraj A (2017) Grotthuss transport of iodide in EMIM/I3 ionic crystal. J Phys Chem B 122(1):250–257

    Google Scholar 

  78. Elfgen R, Hollóczki O, Ray P, Groh MF, Ruck M, Kirchner B (2017) Theoretical investigation of the Te4Br2 molecule in ionic liquids. Z Anorg Allg Chem 643(1):41–52

    Google Scholar 

  79. Fumino K, Fossog V, Stange P, Wittler K, Polet W, Hempelmann R, Ludwig R (2014) Ion pairing in protic ionic liquids probed by far-infrared spectroscopy: effects of solvent polarity and temperature. Chem Phys Chem 15(12):2604–2609.

    Google Scholar 

  80. Huang J, Fu A, Li H, Li H, Chu T, Wang Z (2017) A computational study of ion speciation in mixtures of protic ionic liquids with various molecular solvents: insight into the solvent polarity and anion basicity. Int J Quantum Chem 117(3):170–179

    Google Scholar 

  81. Welton T (2018) Ionic liquids: a brief history. Biophys Rev 10:691–706

    Google Scholar 

  82. Martins MAR, Pinho SP, Coutinho JAP (2019) Insights into the nature of eutectic and deep eutectic mixtures. J Solut Chem 48(7):962–982

    Google Scholar 

  83. Marcus Y (2019) Deep eutectic solvents. 1st ed. Springer, Cham

    Google Scholar 

  84. Abbott AP, Boothby D, Capper G, Davies DL, Rasheed RK (2004) Deep eutectic solvents formed between choline chloride and carboxylic acids: versatile alternatives to ionic liquids. J Am Chem Soc 126(29):9142–9147

    Google Scholar 

  85. Troter DZ, Todorović ZB, Đokić-Stojanović DR, Đorđević BS, Todorović V, Konstantinović SS, Veljković VB (2017) The physicochemical and thermodynamic properties of the choline chloride-based deep eutectic solvents. J Serb Chem Soc 82(9):1039–1052

    Google Scholar 

  86. Bahadori L, Chakrabarti MH, Mjalli FS, AlNashef IM, Manan NSA, Hashim MA (2013) Physicochemical properties of ammonium-based deep eutectic solvents and their electrochemical evaluation using organometallic reference redox systemsPhysicochemical properties of ammonium-based deep eutectic solvents and their electrochemical evaluation using organometallic reference redox systems. Electrochim Acta 113:205–211

    Google Scholar 

  87. Cardellini F, Tiecco M, Germani R, Cardinali G, Corte L, Roscini L, Spreti N (2014) Novel zwitterionic deep eutectic solvents from trimethylglycine and carboxylic acids: characterization of their properties and their toxicity. RSC Adv 4(99):55990–56002

    Google Scholar 

  88. Cardellini F, Germani R, Cardinali G, Corte L, Roscini L, Spreti N, Tiecco M (2015) Room temperature deep eutectic solvents of (1S)-(+)-10-camphorsulfonic acid and sulfobetaines: hydrogen bond-based mixtures with low ionicity and structure-dependent toxicity. RSC Adv 5(40):31772–31786

    Google Scholar 

  89. Abbott AP, D’Agostino C, Davis SJ, Gladden LF, Mantle MD (2016) Do group 1 metal salts form deep eutectic solvents? Phys Chem Chem Phys 18(36):25528–25537

    Google Scholar 

  90. Kaur S, Gupta A, Kashyap HK (2016) Nanoscale spatial heterogeneity in deep eutectic solvents. J Phys Chem B 120(27):6712–6720

    Google Scholar 

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Acknowledgments

The authors would like to thank the DFG (SPP 1708 KI 768/15-1 and KI 768/19-1) under the projects and the BMBF under the LuCaMag project 03EK3051A.

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  1. Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Universität Bonn, Bonn, Germany

    Johannes Ingenmey, Oldamur Hollóczki & Barbara Kirchner

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  1. Johannes Ingenmey
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  1. Institute of Process Engineering, Chinese Academy of Science, Institute of Process Engineering, Beijing, China

    Suojiang Zhang

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  1. Huazhong University of Science and Technology (HUST), Wuhan, China

    Guang Feng

  2. Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, USA

    Peter T. Cummings

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Ingenmey, J., Hollóczki, O., Kirchner, B. (2021). Ion Pairing in Ionic Liquids. In: Zhang, S. (eds) Encyclopedia of Ionic Liquids. Springer, Singapore. https://doi.org/10.1007/978-981-10-6739-6_63-1

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