Ionic Liquids as Smart Hybrid Materials

Background and Motivation

Incorporating d– and f-element cations into ionic liquids can endow them with further assets that originate from the metal cations such as luminescent, magnetic and catalytic properties. By this addition it is possible to obtain hybrid materials that combine the fluidic properties of ionic liquids with functions that are typical of transition metal compounds.

Research Questions

Can ionic liquids be realized that show a strong response to magnetic fields? How will these magnetorheological fluids behave? Can magnetic exchange be observed in the liquid state? How can they mechanically be manipulated by magnetic fields? How will the internal order change upon application of an external magnetic field?

Is it possible to use these materials in applications such as magnetic cooling or tribotronics?

Is it possible to obtain highly luminescent ionic liquids, i.e., can ionic liquids with long lifetimes, hence, high quantum yield be obtained? Even in the liquid state and at elevated temperatures where typically radiationless decay is favoured? What kind of stimuli can be used to create light emission? VUV-, UV-, vis-light? Electric fields and currents?

Is it possible to use these materials in applications, such as in signage, signaling or energy efficient lighting?

Research at the Mudring laboratory

In the Mudring laboratory d– and f-element cation containing ionic liquids get synthesized and characterized with emphasis on their magnetic and optical properties.

1: Magnetic ionic liquids

Ionic liquids that can be manipulated by external magnetic field are obtained through the incorporation of transition-metal and lanthanide-metal cations with high single ion magnetic moments such as hs-Fe2+ or Gd3+, Tb3+, and Dy3+. Recently, we uncovered a family of bis(trifluoromethanesulfonyl)amide-based ionic liquids of the composition [RE5(C2H5-C3H3N2-CH2COO)16(H2O)8](Tf2N)15 (RE = Er, Ho, Tm; C3H3N2 ≡ imidazolium). It features the cationic, record quindecim {15+} charged pentanuclear lanthanide (RE)-containing cation [RE5(C2H5-C3H3N2-CH2COO)16(H2O)8]15+. In addition, due to the presence of rare-earth metal ions, these ionic liquids show a response to magnetic fields with the highest effective magnetic moment observed so far for an ionic liquid and are a rare example of ionic liquids showing luminescence in the near-infrared. These ionic liquids were also successfully employed in the three-component synthesis of 2-pyrrolo-3′-yloxindole with extremely low (<0.035 mol%) catalyst’s loading rates.

We also managed to show that anti-ferromagnetic coupling between transition metal ions in an ionic liquid can persist in the liquid state, even at elevated temperatures. (C2mim)2[Cl3FeOFeCl3] is an ionic liquid which exhibits a linear dependence of magnetic susceptibility on temperature over its extreme liquid range (-90° to 320 °C).

2: Luminescent ionic liquids

We managed to provide a comparatively rigid environment for emissive transition metal and lanthanide ions with ionic liquids, so that radiation-less decay through activation of intermolecular vibrations is less likely to occur than in traditional solvents. It was even possible to produce ionic liquids that exhibit luminescence in the near-infrared. There, the energy gap between the excited and ground state is very small and only a few O-H, N-H or C-H vibrations need to be activated for radiation-less decay. Emission of highest color purity could be achieved through the use of lanthanide ions. The problem of a low absorption coefficient for most lanthanide ions could be overcome by providing suitable ligands for the metal ion that allow for efficient sensitization, without compromising the liquid character of the salt.



” Smart Materials from Ionic Liquids for Energy Applications”, Kungl. Vetenskapsadademien, Göran Gustaffson Prize in Chemistry, PI, 2018-2020


“Ljusemitterande elektrokemiska celler som energieffektiva

ljuskällor”, Energimyndigheten (Sweden), 3346676-1,

PI, 2019-2021


”REFIT – Minskad friktion genom jonteknologi”,

Swedish Foundation for Strategic Research, SSF (Sweden)

EM16-0013, Co-PI, 2019-2023



”Reaktive Selten-Erd-Verbindungen in ionischen Flüssigkeiten,

Deutsche Forschungsgemeinschaft (Germany), # 5426104, PI, 2004-2010


”Magnetische und lumineszierende Ionische Flüssigkeiten auf Basis von Lanthanid-Elementen“, Deutsche Forschungsgemeinschaft (Germany), #69301940, PI, 2008-2011


”Lanthanide-based ionic liquids: Novel soft materials with luminescent and magnetic

properties”, National Science Foundation (USA), # 1465071, co-PI, 2015-2018


“Rare Earths in Ionic Liquids”, Critical Materials Institute #1.2.2,

U.S. Department of Energy, 2014-2017


“Energy Efficient Lighting”, Critical Materials Institute #2.2.6,

U.S. Department of Energy, 2015-2017



Reviews (R) and Book Chapters (B)

R7.  D. Prodius, A.-V. Mudring, Rare earth metal-containing ionic liquids, Coord. Chem. Rev. 2018, 363, 1-16.

R2. A.-V. Mudring, S.-F. Tang: Ionic Liquids for Lanthanide and Actinide Chemistry, Eur. J. Inorg. Chem., 2010, 2569-2581. DOI: 10.1002/ejic.201000297.

B11. D. Prodius, A.-V. Mudring, Coordination Chemistry in Rare Earth Containing Ionic Liquids, Handbook on the Physics and Chemistry of Rare Earths, 2016, 50, 395-420. DOI:

B7. A.-V. Mudring,  Complexation studies of f-elements in ionic liquids. Solvent Extraction: Fundamentals to Industrial Applications, Proceedings of ISEC 2008 International Solvent Extraction Conference, Tucson, AZ, United States, Sept. 15-19, 2008, 2008 (2) 1271.

B6. A.-V. Mudring: Ionic Liquids as Versatile Media in Lanthanide Chemistry, in: R. Rogers, K. Seddon (Eds.) ACS Symposium Series (2007).

Original, peer-reviewed research publications 

1: Magnetic ionic liquids

  1. D. Prodius, V. Smetana, S. Steinberg, M. Wilk-Kozubek, Y. Mudryk, V. K. Pecharsky, A.-V. Mudring, Breaking the paradigm: record quindecim charged magnetic ionic liquids, Materials Horizon 2017, 4, 217-222. DOI: 10.1039/C6MH00468G. Inside Front Cover.
  2. T. Bäcker, A.-V. Mudring: Betaine Chloride-Betaine Tetrachloridoferrate(III)—An Ionic Liquid Related Crystal Structure Governed by the Pearson Concept, Crystals, 2012, 2, 110-117. DOI: 10.3390/cryst2010110.
  3. T. Bäcker, O. Breunig, M. Valldor, K. Merz, V. Vasylyeva, A.-V. Mudring: In-situ crystal growth and properties of the magnetic ionic liquid [C2mim][FeCl4], Cryst. Growth Des., 2011, 11, 2564-2571. DOI: 10.1021/cg200326n.
  4. A. Getsis, B. Balke, C. Felser, A.-V. Mudring: Dysprosium-Based Ionic Liquid Crystals: Thermal, Structural, Photo- and Magnetophysical Properties, Cryst. Growth Des., 2009, 9, 4429-4437. DOI: 10.1021/cg900463b.
  5. B. Mallick, H. Kierspel, -V. Mudring: (CrCl3)3@2[C4mim][OMe]-Molecular Cluster-Type Chromium(III) Chloride Stabilized in a Salt Matrix, J. Am. Chem. Soc., 2008, 130, 10068-10069. DOI: 10.1021/ja803322k.
  6. B. Mallick, B. Balke, C. Felser, -V. Mudring: Dysprosium Room-Temperature Ionic Liquids with Strong Luminescence and Response to Magnetic Fields, Angew. Chem. Int. Ed., 2008, 47, 7635-7638. DOI: 10.1002/anie.200802390.


2: Luminescent ionic liquids

  1. S.F. Tang, C. Lorbeer, X. Wang, P. Ghosh, A.-V. Mudring, Highly luminescent molten salts containing well shielded lanthanide centered complex anions and bulky imidazolium countercations, Inorg. Chem. 2014, 53, 9027-99035. DOI:10.1021/ic500979p.
  2. P. Campbell, M. Yang, J. Cybinska, D. Pitz, A.-V. Mudring, Highly luminescent and colour-tuneable salicylate ionic liquids, Chem. Eur. J., 2014, 20, 4704-4712. DOI:10.1002/ chem.201301363.
  3. J. Bäcker, S. Mihm, B. Mallick, M. Yang, G. Meyer, A.-V. Mudring: Crystalline and Liquid Crystalline Organic-Inorganic Hybrid Salts with Cation-Sensitized Hexanuclear Molybdenum Cluster Complex Anion Luminescence: Eur. J. Inorg.Chem., 2011, 4089-4095. DOI: 10.1002/ ejic.201100365.
  4. A. Getsis, A.-V. Mudring: Switchable Green and White Luminescence in Terbium-based Ionic Liquid Crystals, Eur. J. Inorg. Chem., 2011, 3207–3213. DOI: 10.1002/ejic.201100168.
  5. A. Getsis, -V. Mudring: A Luminescent Ionic Liquid Crystal: [C12mim]4[EuBr6]Br, Eur. J. Inorg. Chem., 2010, 2172-2177. DOI: 10.1002/ejic.200901220.
  6. S. Pitula, -V. Mudring: Synthesis, Structure, and Physico-optical Properties of Manganate(II)-Based Ionic Liquids, Chemistry – Eur. J., 2010, 16, 3355-3365. DOI: 10.1002/ chem.200802660.
  7. A. Getsis, A.-V. Mudring: Lanthanide Containing Ionic Liquid Crystals: EuBr2, SmBr3, TbBr3 and DyBr3 in C12mimBr, Z. Allg. Anorg. Chem., 2010, 636, 1726-1734. DOI: 10.1002/ zaac.201000070.
  8. S-F. Tang, -V. Mudring: Terbium β-Diketonate Based Highly Luminescent Soft Materials, Eur. J. Inorg. Chem., 2009, 2769-2775. DOI: 10.1002/ejic.200900114.
  9. S.-F. Tang, J. Cybinska, -V. Mudring: Luminescent Soft Material: Two New Europium-Based Ionic Liquids, Helv. Chim. Acta, 2009, 92, 2375-2386.
  10. S.-F. Tang, A. Babai, -V. Mudring: Europium-Based Ionic Liquids as Luminescent Soft Materials, Angew. Chem. Int. Ed., 2008, 47, 7631-7634. DOI: 10.1002/anie.200801159.
  11. A.-V. Mudring, A. Babai, S. Arenz, R. Giernoth, K. Binnemans, K. Driesen, P. Nockemann: Strong luminescence of rare earth compounds in ionic liquids: Luminescent properties of lanthanide(III) iodides in the ionic liquid 1-dodecyl-3-methylimidazolium bis(trifluoro-methanesulfonyl)imide, J. Alloys and Comp., 2006, 418, 204-208.
  12. S. Arenz, A. Babai, K. Binnemans, K. Driesen, R. Giernoth, -V. Mudring, P. Nockemann: Intense near-infrared luminescence of anhydrous lanthanide(III) iodides in an imidazolium ionic liquid, Chem. Phys. Lett. 2005, 402, 75-79. DOI: 10.1016/j.cplett.2004.12.008.
  13. A. Babai, A.-V. Mudring: Anhydrous Praseodymium Salts in the Ionic Liquid
    [bmpyr][Tf2N]: Structural and Optical Properties of [bmpyr]4[PrI6][Tf2N] and [bmpyr]2[Pr(Tf2N)5], Chem. Mater., 2005, 17, 6230-6238.

3: Light emitting electrochemical cells

  1. J.E. Namanga, N. Gerlitzki, V. Smetana, A.-V. Mudring, Optimizing green light emitting electrochemical cells: Stability improvement without compromising the efficiency, ACS Appl. Mat. Interf. 2018, 10, 11026–11036. DOI: 10.1021/acsami.7b18159.
  2. M. Di Marcantonio, J. E. Namanga, N. Gerlitzki, F. Vollkommer, A.-V. Mudring, G. Bacher, E. Nannen, Bright and Stable Greenish Hybrid Light Emitting Electrochemical Cells, J. Mat. Chem. C, 2017, 5, 12062-12068. DOI: 10.1039/C7TC02976D.
  3. J.E. Namanga, N. Gerlitzki, B. Mallick, A.-V. Mudring, Long term stable deep red light-emitting electrochemical cell based on an emissive, rigid cationic Ir(III) complex, J. Mat. Chem. C 2017, 5, 3049-3055, DOI: 10.1039/C6TC04547B.
  4. J.E. Namanga, N. Gerlitzki, V. Smetana, A.-V. Mudring, Scrutinizing design principles towards efficient, long-term stable green light emitting light emitting electrochemical cells, Adv. Funct. Mat. 2017, 27, 1605588 (8 pages) DOI: 10.1002/adfm.201605588.

4: Transition metal-, lanthanide- and actinide-containing ionic liquids

  1. E.T. Spielberg, E. Edengeißer, B. Mallick, M. Havenith, A.-V. Mudring: (C1C4mpyr)[Cu(SCN)2]: Coordination Polymer and Ionic Liquid, Chem. Eur. J. , 2014, 20, 5338-5345. DOI:10.1002/chem.201302777.
  2. D. Yaprak, E.T. Spielberg, T. Bäcker, M. Richter, B. Mallick, A. Klein, A.-V. Mudring, A roadmap to uranium ionic liquids: anti-crystal engineering, Chem. Eur. J. 2014, 20, 6482-6493. DOI:10.1002/chem.201303333.
  3. A. Metlen, B. Mallick, R.W. Murphy, A.-V. Mudring, R.D. Rogers, Phosphonium Chloromercurate Room Temperature Ionic Liquids of Variable Composition, Inorg. Chem., 2013, 52, 13997-14009. DOI:10.1021/ic401676r.
  4. B. Mallick, A. Melten, M. Nieuwenhuyzen, R.-D. Rogers, A.-V. Mudring: Mercuric Ionic Liquids: [Cnmim][HgX3], where n = 3, 4 and X = Cl, Br, Inorg. Chem., 2012, 51, 193-200. DOI: 10.1021/ic201415d.
  5. A. Babai, S. Pitula, -V. Mudring: Structural and Electrochemical Properties of YbIII in Various Ionic Liquids, Eur. J. Inorg. Chem., 2010, 4933-4937. DOI: 10.1002/ejic.201000323.
  6. A. Babai, -V. Mudring: Crystal Engineering in Ionic Liquids. The Crystal Structures of [Mppyr]3[NdI6] and [Bmpyr]4[NdI6][Tf2N], Inorg. Chem., 2006, 45, 4874-4876.
  7. A. Babai, -V. Mudring: Homoleptic Alkaline Earth Metal Bis(trifluoromethanesulfonyl)-imide Complex Compounds Obtained from an Ionic Liquid, Inorg. Chem., 2006, 45, 3249-3255.
  8. A. Babai, A.-V. Mudring: The first homoleptic bis(trifluoromethanesulfonyl)amide complex compounds of trivalent f-elements, Dalton Trans., 2006, 1828-1830.
  9. A. Babai, A.-V. Mudring: Rare-earth iodides in ionic liquids: Crystal structures of [bmpyr]4[LnI6][Tf2N] (Ln = La, Er), J. Alloys and Comp., 2006, 418, 122-127.
  10. A. Babai, -V. Mudring: Rare-Earth Iodides in Ionic Liquids: The Crystal Structure of [SEt3]3[LnI6] (Ln = Nd, Sm), Inorg. Chem., 2005, 44, 8168-8169.
  11. A.-V. Mudring, A. Babai, S. Arenz, R. Giernoth: The “Noncoordinating” Anion Tf2N Coordinates to Yb2+: A Structurally Characterized Tf2N− Complex from the Ionic Liquid [mppyr][Tf2N], Angew. Chem. Int. Ed., 2005, 44, 5485-5488. DOI: 10.1002/anie.200501297.