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Our Research Activities

The Feldmann group is interested in novel synthesis strategies, novel compounds, and high-quality nanomaterials. For the as-prepared compounds and nanomaterials, we address a wide range of material properties, functions and applications including structure, morphology, shape, luminescence, imaging, drug delivery, catalysis, photocatalysis, conductivity, magnetism, sorption.

 

Some of our major achievements are:

  • 2003: Polyol synthesis as suitable access to crystalline oxide nanoparticles
    C. Feldmann, H. O. Jungk, Angew. Chem. 2001, 113, 372-374; Angew. qChem. Int. Ed. 2001, 40, 359–362
  • 2006: IL-made fluorescent nanoparticles with excellent quantum yield
    G. Bühler, C. Feldmann*, Angew. Chem. 2006, 118, 4982–4986; Angew. Chem. Int. Ed. 2006, 45, 4864–4867
  • 2007: Hollow nanospheres made via microemulsions for the first time
    C. Zimmermann, C. Feldmann*, M. Wanner, D. Gerthsen, Small 2007, 3, 1347–1349
  • 2009: Microemulsion synthesis as general approach to hollow nanospheres
    H. Gröger, F. Gyger, P. Leidinger, C. Zurmühl, C. Feldmann*, Adv. Mater. 2009, 21, 1586–1590
  • 2010: First inorganic-organic hybrid nanoparticles (IOH-NPs) for multimodal imaging and drug delivery
    M. Roming, H. Lünsdorf, K. E. J. Dittmar, C. Feldmann*, Angew. Chem. 2010, 122, 642–647; Angew. Chem. Int. Ed. 2010, 49, 632−637
  • 2011: First 3D polybromide realized with [C4MPyr]2Br2×9Br2
    M. Wolff, J. Meyer, C. Feldmann*, Angew. Chem. 2011, 123, 5073–5077; Angew. Chem. Int. Ed. 2011, 50, 4970–4973
  • 2012: β-SnWO4 photocatalyst with shape and morphology control
    J. Ungelenk, C. Feldmann*, Chem. Commun. 2012, 48, 7838–7840
  • 2012: First full-metal adamantine-like cluster with [{Fe(CO)3}4{SnI}6I4]2-
    S. Wolf, F. Winter, R. Pöttgen, N. Middendorf, W. Klopper, C. Feldmann*, Chem. Europ. J. 2012, 18, 13600–13604
  • 2013: First microemulsion with liquid ammonia as polar phase
    F. Gyger, P. Bockstaller, D. Gerthsen, C. Feldmann*, Angew. Chem. 2013, 125, 12671–12675;          Angew. Chem. Int. Ed. 2013, 52, 12443–12447
  • 2014: Polyol-made C-dots with Eu3+-based red emission
    H. Dong, A. Kuzmanoski, D. M. Gößl, R. Popescu, D. Gerthsen, C. Feldmann*, Chem. Commun. 2014, 50, 7503–7506
  • 2015: Inorganic-organic hybrid nanoparticles (IOH-NPs) established as general platform concept for multimodal imaging and drug delivery
    J. G. Heck, J. Napp, S. Simonato, J. Möllmer, M. Lange, H. R. Reichardt, R. Staudt, F. Alves,* C. Feldmann*, J. Am. Chem. Soc. 2015, 137, 7329−7336
  • 2015: Reliable access to reactive base metal nanoparticles
    C. Schöttle, P. Bockstaller, R. Popescu, D. Gerthsen, C. Feldmann*, Angew. Chem. 2015, 127, 10004–10008; Angew. Chem. Int. Ed. 2015, 54, 9866–9870
  • 2015: Fe2O3 hollow nanospheres for tuberculosis treatment
    P. Leidinger, J. Treptow, K. Hagens, J. Eich, N. Zehethofer, D. Schwudke, W. Öhlmann, H. Lünsdorf, O. Goldmann, U. E. Schaible*, K. E. J. Dittmar,* C. Feldmann*, Angew. Chem. 2015, 127, 12786–12791; Angew. Chem. Int. Ed. 2015, 54, 12597–12601
  • 2017: Liquids phase synthesis of reactive Gd0 and U0 nanoparticles
    C. Schöttle, S. Rudel, R. Popescu, D. Gerthsen, F. Kraus,* C. Feldmann*, ACS Omega 2017, 2, 9144−9149
  • 2018: Au@Nb@HxK1-xNbO3 Nanopeapods for NIR-activated photocatalysis and water splitting
    Y.-C. Chen, Y.-K. Hsu, R. Popescu, D. Gerthsen, Y.-G. Lin, C. Feldmann*, Nature Commun. 2018, 9, 232:1–11
  • 2018: IOH-NPs for red-light driven 1O2 production and phototherapy
    M. Poß, E. Zittel, C. Seidl, A. Meschkov, L. Muñoz, U. Schepers,* C. Feldmann*, Adv. Funct. Mater. 2018, in press
     
    For the synthesis of novel compounds and high-quality nanomaterials, we have different liquid-phase methods available to address specific conditions and requirements:
  • Polyol synthesis (synthesis in high-boiling alcohols)
  • Ionic-liquid-based synthesis
  • Liquid-ammonia-based synthesis
  • Microemulsion techniques
  • Solvothermal hydrothermal methods
  • Aqueous synthesis
     
    In terms of material characterization, material properties and potential application, we address the following:
  • Chemical composition
    (metals, oxides, halogen-rich compounds and polyhalides, inorganic-organic hybrids, metal clusters)
  • Shape and morphology
    (nanoparticles, hollow nanospheres, nanorods, nanotubes, single crystals)
  • Catalysis and photocatalysis
  • Luminescence
  • Semiconductors
  • Gas sorption and gas separation
  • Multimodal imaging
  • Drug delivery and drug release
     

     

Figure 1: Overview of our research activities.
 
 
For more information see our reviews:
C. Feldmann*, Polyol-mediated Synthesis of Nanoscale Functional Materials, Adv. Funct. Mater. 2003, 13, 101–107.
H. Goesmann, C. Feldmann*, Nanopartikuläre Funktionsmaterialien (Review). Angew. Chem. 2010, 122, 1402–1437; Nanoparticulate Functional Materials (Review). Angew. Chem. Int. Ed. 2010, 49, 1362–1395.
D. Freudenmann, S. Wolf, M. Wolff, C. Feldmann*, Ionische Flüssigkeiten - Neue Perspektiven für die anorganische Synthesechemie? (Review). Angew. Chem. 2011, 123, 11244–11255. Ionic Liquids – New Perspectives for Inorganic Synthesis Chemistry? (Review). Angew. Chem. Int. Ed. 2011, 50, 11050–11060.
H. Dong, Y.-C. Chen, C. Feldmann*, Polyol Synthesis of Nanoparticles: Status and Options regarding Metals, Oxides, Chalcogenides, and Non-Metal Elements (Review). Green Chem. 2015, 17, 4107–4132.
S. Wolf, C. Feldmann*, Mikroemulsionen: neue Möglichkeiten zur Erweiterung der Synthese anorganischer Nanopartikel (Review). Angew. Chem. 2016, 128, 15958–15984; Microemulsions: Options to Expand the Synthesis of Inorganic Nanoparticles (Review). Angew. Chem. Int. Ed. 2016, 55, 15728–15752.

 

 

 

 

 

 

The synthesis of metal nanoparticles is the more challenging the lower the electrochemical potential of the respective metal. Thus, base metals are highly reactive; they are instantaneously reoxidized by oxygen or water. Due to the great surface area, nanoscale base metals, furthermore, are much more reactive than the respective bulk metals. Thus, specific strategies of synthesis are necessary for preparation. Moreover, the complete analytical characterization, including sample transfer from synthesis to analytical equipment (e.g. electron microscopy) essentially needs strict inert conditions. To obtain reactive base metal nanoparticles, we have established three different synthesis strategies:

  • Liquid-ammonia-in-oil microemulsions (a/o-microemulsions) using liquid ammonia as the polar micelle phase
  • The sodium-driven reduction in liquid ammonia (lq-NH3)
  • The sodium-naphthalenide-driven ([NaNaph]) reduction in ethers

 

As a result we can prepare reactive base metals such as Bi0, Re0, Mo0, W0, Fe0, Zn0, U0 and Gd0 as nanoparticles with mean diameters of 1-8 nm (Figures 2-4).

Based on the above synthesis strategies, we are interested in:

  • Synthesis / characterization of reactive base metals
    (the more reactive the more interesting)
  • Properties of base metals (reactivity, catalysis, structure)
  • Synthesis of intermetallics and bimetallics (core-shell, Janus-like)
  • Follow-up reactions
  • Synthesis of metal nitrides

 

 

Figure 2. Base metal nanoparticles made via liquid-ammonia-in-oil microemulsions (a/o-microemulsions) (Angew. Chem. Int. Ed. 2013, 52, 12443–12447).

 

 

Figure 3. Base metal nanoparticles made via sodium-driven reduction in liquid ammonia (lq-NH3) (Chem. Commun. 2014, 50, 4547–4550).

 

 

Figure 4. Base metal nanoparticles made via sodium-naphthalenide-driven ([NaNaph]) reduction in ethers (Angew. Chem. Int. Ed. 2015, 54, 9866–9870).

 

In addition to the synthesis of reactive base metal nanoparticles, the above synthesis strategies are also suitable for obtaining metal nitride nanoparticles as well as high-porosity metal nitrides. In this regard, we could realize GaN, Si3N4, TiN, VN, CoN or Mg3N2 nanoparticles and nanostructures (Figure 5).

 

 

Figure 5. Si3N4 nanoparticles made via liquid-phase methods and H2 sorption (Chem. Mater. 2016, 28, 7816–7824).

 

 

For more information see:

F. Gyger, P. Bockstaller, D. Gerthsen, C. Feldmann*, Ammonia-in-Oil-Microemulsions and Their Application. Angew. Chem. Int. Ed. 2013, 52, 12443–12447.

C. Schöttle, P. Bockstaller, D. Gerthsen, C. Feldmann*, Tungsten Nanoparticles from Liquid-Ammonia-based Synthesis. Chem. Commun. 2014, 50, 4547–4550.

C. Schöttle, P. Bockstaller, R. Popescu, D. Gerthsen, C. Feldmann*, Sodium-Naphthalenide-driven Synthesis of Base Metal Nanoparticles and Specific Follow-up Reactions. Angew. Chem. Int. Ed. 2015, 54, 9866–9870.

F. Gyger, P. Bockstaller, D. Gerthsen, C. Feldmann*, Liquid-Crystalline Phases with Liquid Ammonia: Synthesis of Porous Si3N4, TiN, VN and H2-Sorption of Si3N4 and Pd@Si3N4. Chem. Mater. 2016, 28, 7816–7824.

C. Schöttle, S. Rudel, R. Popescu, D. Gerthsen, F. Kraus,* C. Feldmann*, Nanosized Gadolinium and Uranium – Two Representatives of High-Reactivity Lanthanide and Actinide Metal Nanoparticles. ACS Omega 2017, 2, 9144−9149.

 

 

 

 

 

 

 

 

 

 

 

Hollow nanospheres are intensely discussed regarding their properties (e.g., large specific surface, low specific weight, container-type morphology) and their functions (e.g., catalysis, gas storage, low-weight building materials, drug delivery). Starting in 2004, our research group has established a novel microemulsion-based strategy to obtain hollow nanospheres. In contrast to standard microemulsion techniques, the reaction was not performed inside a micelle, but at its phase boundary (Figure 6). Thus, one reactant is added to the polar phase; the second reactant is added to the non-polar phase. By this measure the reaction is restricted to the phase boundary resulting in various types of hollow spheres (Figure 7). Typically, the as-prepared hollow nanospheres exhibit outer diameters of 20 to 50 nm, a wall thickness of 3 to 20 nm and an inner diameter of 10 to 30 nm. Our activities, especially, focus on the following aspects:

  • Synthesis / characterization of hollow nanospheres
  • Variation of size, surface area, porosity
  • Properties of hollow nanospheres
  • Catalysis and sensing
  • Drug delivery and drug release
  • Gas sorption and gas separation
     


Figure 6. Synthesis of hollow nanospheres via microemulsion techniques (Angew. Chem. Int. Ed. 2016, 55, 15728–15752).


 

 
Figure 7. Various hollow nanospheres made via microemulsion synthesis.
 
The microemulsion strategy also allows an independent modification of the inner and outer surface of the hollow nanospheres, which is highly interesting for catalysis and sensing. This is illustrated with Pd0 encapsulated by SnO2 shells (Pd@SnO2) and SnO2 shells covered with Pd0 (SnO2@Pd) and the application for sensing of CO (Figure 8).


Figure 8. CO sensing with Pd@SnO2 and SnO2@Pd core@shell nanostructures (Part. Part. Syst. Charact. 2014, 31, 591–596).


 
Hollow nanospheres are also highly promising nanocontainers for drug delivery and drug release. As an example, INH@Fe2O3 hollow nanospheres (INH: isoniacide) serve as effective drug-delivery system for antibiotic tuberculosis therapy. INH@Fe2O3 hollow nanospheres are highly promising, on the one hand, due to the high antibiotics load (48 wt% INH), and on the other hand, due to active iron acquisition by infected macrophages as well as by the mycobacteria themselves (Figure 9).
 


Figure 9. INH@Fe2O3 hollow nanospheres containing antibiotic isoniacide (INH) for tuberculosis therapy (Angew. Chem. Int. Ed. 2015, 54, 12597–12601).
 
Doxorubicin (DOX) filled nanocontainers (DOX@Gd2(CO3)3) were evaluated in view of potential theranostic application (Figure 10). They can become very interesting as theranostic nanoagents including synergistic physical (magnetothermal effect) and cytostatic (DOX release) tumor treatment as well as multimodal imaging (emission of DOX, magnetism of Gd3+).
 


Figure 10. Doxorubicin-filled AlO(OH) nanocontainers and their use for synergistic physical (magnetothermal effect) and cytostatic (DOX release) tumor treatment (Nanoscale 2017, 9, 8362–8372).
 
 
For more information see:
D. H. M. Buchold, C. Feldmann*, Nanoscale g-AlO(OH) Hollow Spheres: Synthesis and Container-Type Functionality. Nano Lett. 2007, 7, 3489–3492.
H. Gröger, F. Gyger, P. Leidinger, C. Zurmühl, C. Feldmann*, Microemulsion Approach to Nanocontainers and its Variability in Composition and Load. Adv. Mater. 2009, 21, 1586–1590.
F. Gyger, A. Sackmann, M. Hübner, P. Bockstaller, D. Gerthsen, H. Lichtenberg, J.-D. Grunwaldt, N. Barsan*, U. Weimar*, C. Feldmann*, Pd@SnO2 and SnO2@Pd Core@Shell Nanocomposite Sensors. Part. Part. Syst. Charact. 2014, 31, 591–596.
F. Gyger, P. Bockstaller, D. Gerthsen, C. Feldmann*, Ammonia-in-Oil-Microemulsions and Their Application. Angew. Chem. Int. Ed. 2013, 52, 12443–12447.
P. Leidinger, J. Treptow, K. Hagens, J. Eich, N. Zehethofer, D. Schwudke, W. Öhlmann, H. Lünsdorf, O. Goldmann, U. E. Schaible*, K. E. J. Dittmar,* C. Feldmann*, Isoniazid@Fe2O3 Nanocontainers and Their Antibacterial Effect on Tuberculosis Mycobacteria. Angew. Chem. Int. Ed. 2015, 54, 12597–12601.
S. Wolf, C. Feldmann*, Mikroemulsionen: neue Möglichkeiten zur Erweiterung der Synthese anorganischer Nanopartikel (Review). Angew. Chem. 2016, 128, 15958–15984; Microemulsions: Options to Expand the Synthesis of Inorganic Nanoparticles (Review). Angew. Chem. Int. Ed. 2016, 55, 15728–15752.

 

 

 

Inorganic-organic hybrid nanoparticles (IOH-NPs) represent a novel concept and a new class of materials for biomedical application including multimodal imaging and drug release. The material concepts serves as a wide platform of compounds so that we can realize about >50 different IOH-NPs by now. The concept was originally developed by our research group and filed in international patents.

The saline IOH-NPs with a general composition [ZrO]2+[RfunctionOPO3]2- or [GdO]+[RfunctionSO3]- consist of equimolar amounts of an inorganic cation (i.e., [ZrO]2+, [GdO]+) and a functional organic anion [RFunctionOPO3]2- or [RFunctionSO3]- (RFunction: functional organic group). Herein, the functional organic anion entails specific functions such as fluorescence (i.e., [RDyeOPO3]2-, [RDyeSO3]-) or pharmaceutical activity (i.e., [RDrugOPO3]2-, [RDrugSO3]-). The essential role of the inorganic cation is to guarantee the insolubility of the IOH-NP in water. IOH-NP exhibit an unprecedented high dye and/or drug load (i.e. 70-85 wt-% of total IOH-NP weight). Specific examples of IOH-NPs are, for instance, [ZrO]2+[PUP]2-, [ZrO]2+[MFP]2-, [ZrO]2+[RRP]2-, [ZrO]2+[DUT]2-, [GdO]+[AMA], or [GdO]+[ICG] that show blue, green, red and infrared fluorescence (PUP: phenylumbelliferon phosphate; MFP: methylfluorescein phosphate; RRP: resorufin phosphate; DUT: Dyomics-647 uridine triphosphate; AMA: amaranth red; ICG: indocyanine green) (Figure 11). [GdO]+[ICG] turned out as a novel, multi-modality contrast agent for optical (OI), photoacoustic (PAI) and magnetic resonance imaging (MRI) (Figure 12).

The material concept of the IOH-NP can be further expanded to drug delivery and drug release including [ZrO]2+[BMP]2-, [ZrO]2+[FdUMP]2-, and [ZrO]2+[CLP]2- with the anti-inflammatory agent betamethason phosphate (BMP), the cytostatic agent 5’-fluoro-2’-deoxyuridine 5’-monophosphate (FdUMP) or the antibiotic clindamycinephosphate (CLP). In vitro and in vivo studies confirm excellent activity and high biocompatibility. [ZrO]2+[BMP]2- shows an effective inflammatory response in vitro and in vivo. [ZrO]2+[FdUMP]2- IOH-NPs, moreover, shows strong anti-proliferative activity, which was even prominently higher than the effect of clinically applied 5-fluorouracil. [ZrO]2+[CLP]2- shows high uptake and results in extremely high antibiotic internalization, especially, in comparison to free clindamycinphosphate in solution (Figure 13).

Our activities related to IOH-NPs address the following aspects:

  • Aqueous synthesis / characterization of IOH-NPs
  • Establish IOH-NPs as new material concept and platform
  • Multimodal imaging
  • Drug delivery and drug release based on extremely high drug load (70-85 wt-%)
  • Application in medicine to treat cancer, inflammation, infection
     
     


Figure 11: Fluorescence of different IOH-NPs (ChemNanoMat 2018, submitted).
 


Figure 12: Multimodal imaging (OI, PAI, MRI) with IOH-NPs (ChemNanoMat 2018, submitted).
 

 

Figure 13: Drug delivery with IOH-NPs (ACS Omega 2018, submitted).
 
 
For more information see:

J. G. Heck, J. Napp, S. Simonato, J. Möllmer, M. Lange, H. R. Reichardt, R. Staudt, F. Alves,* C. Feldmann*, Multifunctional Phosphate-based Inorganic-Organic Hybrid Nanoparticles. J. Am. Chem. Soc. 2015, 137, 7329−7336.
M. Poß, R. J. Tower, J. Napp, L. C. Appold, T. Lammers, F. Alves, C.-C. Glüer, S. Boretius, C. Feldmann*, Multimodal [GdO]+[ICG] Nanoparticles for Optical, Photoacoustic and Magnetic Resonance Imaging. Chem. Mater. 2017, 29, 3547–3554 J.
G. Heck, K. Rox, H. Lünsdorf, T. Lückerath, N. Klaassen, E. Medina, O. Goldmann*, C. Feldmann*, Zirconyl Clindamycin Phosphate Antibiotic Nanocarriers for Targeting Intracellular Persisting Staphylococcus aureus. ACS Omega 2018, in press.
M. Poß, E. Zittel, C. Seidl, A. Meschkov, L. Muñoz, U. Schepers,* C. Feldmann*, Gd43+[AlPCS4]34–: Multi-functional Nanoagent Generating 1O2 for Photodynamic Therapy. Adv. Funct. Mater. 2018, in press. B. L. Neumeier, M. Khorenko, C. Feldmann*, Fluorescent Inorganic-Organic Hybrid Nanoparticles (Review), ChemNanoMat 2018, submitted.

 

 

 

The exploration of efficient daylight-activated photocatalysts remains a most essential challenge. Here, anatas-TiO2 is most widely applied but due to it wide band gap (2.8 eV) only active under UV-light excitation. Yet known daylight-activated photocatalysts often contain toxic and/or expensive constituents (e.g., CdS, BiVO4).

Our activities related to catalysis and photocatalysis address metal tungstates, metal molybdates, metal vanadates, metal niobates and metal tantalates in regard of the following aspects:

  • Realization of crystalline nanostructures via liquid-phase synthesis
  • Morphology control
  • Evaluation of properties including color, catalysis, photocatalysis, conductivity
  • Daylight-activated catalysis

 

For the first time, we could present β-SnWO4 as a new photocatalyst. This compound is as elusive as promising. Thermodynamically favored above 670 °C, but metastable at room temperature, the synthesis of crystalline and nanoscaled β-SnWO4 at room temperature is a challenge. Via precise control of the experimental conditions, we could prepare high-quality nanoparticles as well as facetted microcrystals of β-SnWO4 including dodecahedra, cubes, and hierarchically multiarmed architectures entitled as spikecubes (Figure 14). β-SnWO4 nanoparticles turned out as highly promising for photodynamic therapy (PDT). Thus, reiterated 5-minutes illumination with a blue-light LED is sufficient to induce high cytotoxicity (Figure 15).

 

 

 

Figure 14. β-SnWO4 photocatalyst with specific morphology: dodecahedra, cubes, spikecubes (ACS Catal. 2016, 6, 2357–2367).

 

 

 

Figure 15. β-SnWO4 photocatalyst showing high phototoxicity in vitro and in vivo (ACS Nano 2016, 10, 3149–3157).

 

As a highly promisiong photocatalyst with peculiar composition and structure we could recently prepare Au@Nb@HxK1-xNbO3 nanopeapods (Figure 16). This structure emulates the growth pattern of natural plant: peapods. Thus, core-shell Au@Nb nanoparticles (the nanopeas) are seeding in the cavity of semiconducting HxK1-xNbO3 nanoscrolls (the nanopods). This unique structure promotes near-field plasmon-plasmon coupling between bimetallic Au@Nb nanoantennas, endowing the UV-active HxK1-xNbO3 semiconductor with strong VIS and NIR light harvesting abilities to trigger dye photodegradation and water photoelectrolysis.

 

 

 

Figure 16. Au@Nb@HxK1-xNbO3 nanopeapods with core-shell Au@Nb nanoparticles as nanopeas located in HxK1-xNbO3 nanoscrolls as nanopods (Nature Commun. 2018, 9, 232:1–11).

 

 

For more information see:

J. Ungelenk, C. Feldmann*, Synthesis of Faceted β-SnWO4 Microcrystals and Enhanced Visible-light Photocatalytic Properties, Chem. Commun. 2012, 48, 7838–7840.

J. Ungelenk, C. Seidl, E. Zittel, S. Roming, U. Schepers*, C. Feldmann*, In-vitro Fluorescence and Phototoxicity of ß-SnWO4 Nanoparticles. Chem. Commun. 2014, 50, 6600–6603.

C. Seidl, J. Ungelenk, E. Zittel, T. Bergfeldt, J. P. Sleeman, U. Schepers*, C. Feldmann*, Tin Tungstate Nanoparticles: A Photosensitizer for Photodynamic Tumor Therapy. ACS Nano 2016, 10, 3149–3157.

Y.-C. Chen, Y.-G. Lin,* L.-C. Hsu, A. Tarasov, P.-T. Chen, M. Hayashi, J. Ungelenk, Y.-K. Hsu,* C. Feldmann*, Tungstate Nanoparticles: A Photosensitizer for Photodynamic Tumor Therapy. β-SnWO4 Photocatalyst with Controlled Morphological Transition of Cubes to Spikecubes. ACS Catal. 2016, 6, 2357–2367.

Y.-C. Chen, Y.-K. Hsu, R. Popescu, D. Gerthsen, Y.-G. Lin, C. Feldmann*, Au@Nb@HxK1-xNbO3 Nanopeapods with Near-infrared Active Plasmonic Hot-Electron Injection for Water Splitting. Nature Commun. 2018, 9, 232:1–11.

 

 

 

Our activities related to ionic liquids address the question: What is special about ionic liquids in inorganic synthesis? As there are various syntheses strategies available in inorganic chemistry, the question regarding the specific advantage of ionic liquids is even more interesting. Generally, ionic liquids (ILs) are known for their unusual properties (e.g., wide liquid range, excellent thermal stability, wide electrochemical window, weakly coordinating constituents). For our studies, two aspects are most interesting: the weakly coordinating properties and the wide electrochemical window of ionic liquids. In principle, selected ionic liquids can make it possible to work with elemental fluorine (E0 = +3.1 V) and with elemental caesium (E0 = -2.9 V), without the solvent decomposing! Based on these conditions, we address reactions with highly oxidizing starting materials (i.e. halogens) as well as with highly reducing starting materials (i.e. carbonyl metals) in ionic liquids.

 

This is illustrated in the following with two examples: (a) The polybromide [C4MPyr+]2[(Br)2×9(Br2)] representing the first three-dimensional polybromide network (Figure 16), and (b) the carbonyl cluster [BMIm]2[{Fe(CO)3}4Sn6I10] containing the first adamantane-like (metal) Fe4Sn6 cluster (Figure 17).

 

 

 

Figure 17: [C4MPyr]2[Br20] with [(Br)2(Br2)9] network composed of central bromide anions (light red) that are interlinked via molecular bromine (dark red) (Angew. Chem. Int. Ed. 2011, 50, 4970–4973).

 

 

Figure 18: [BMIm]2[{Fe(CO)3}4Sn6I10] containing an adamantane-type Fe4Sn6 cluster (Chem. Europ. J. 2012, 18, 13600–13604).

 

 

For more information see:

D. Freudenmann, S. Wolf, M. Wolff, C. Feldmann*, Ionische Flüssigkeiten - Neue Perspektiven für die anorganische Synthesechemie? (Review). Angew. Chem. 2011, 123, 11244–11255. Ionic Liquids – New Perspectives for Inorganic Synthesis Chemistry? (Review). Angew. Chem. Int. Ed. 2011, 50, 11050–11060.
M. Wolff, J. Meyer, C. Feldmann*, [C4MPyr]2[Br20] − Ionic Liquid based Synthesis of the first three-dimensional Polybromide Network. Angew. Chem. Int. Ed. 2011, 50, 4970–4973.

S. Wolf, F. Winter, R. Pöttgen, N. Middendorf, W. Klopper, C. Feldmann*, [{Fe(CO)3}4{SnI}6I4]2- – The First Bimetallic Adamantane-like Cluster. Chem. Europ. J. 2012, 18, 13600–13604.

S. Wolf, K. Reiter, F. Weigend, W. Klopper, C. Feldmann*, [(Pb6I8){Mn(CO)5}6]2– – an Octahedral (M6Xn)-like Cluster with Unprecedented Inverted Bonding. Inorg. Chem. 2015, 54, 3989–3994.

D. Hausmann, C, Feldmann*, The Bromine-rich Zinc Bromides Zn6Br12(18-crown-6)2(Br2)5, Zn4Br8(18-crown-6)2(Br2)3 and Zn6Br12(18-crown-6)2(Br2)2. Inorg. Chem. 2016, 55, 6141–6147.

S. Wolf, W. Klopper, C. Feldmann*, Ge12(μ-I)4{Fe(CO)3}8: A Germanium-Iron Cluster with Ge4, Ge2 and Ge Units. Chem. Commun. 2018, 54, 1217–1220.