Roland A. Fischer

Nanjing University of Technology, Nan-ching, Jiangsu Sheng, China

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Publications (437)2319.06 Total impact

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    ABSTRACT: The bottom-up synthesis of organometallic zinc clusters is described. The cation {[Zn10 ](Cp*)6 Me}(+) (1) is obtained by reacting [Zn2 Cp*2 ] with [FeCp2 ][BAr4 (F) ] in the presence of ZnMe2 . In the presence of suitable ligands, the high reactivity of 1 enables the controlled abstraction of single Zn units, providing access to the lower-nuclearity clusters {[Zn9 ](Cp*)6 } (2) and {[Zn8 ](Cp*)5 ((t) BuNC)3 }(+) (3). According to DFT calculations, 1 and 2 can be described as closed-shell species that are electron-deficient in terms of the Wade-Mingos rules because the apical ZnCp* units that constitute the cluster cage do not have three, but only one, frontier orbitals available for cluster bonding. Zinc behaves flexibly in building the skeletal metal-metal bonds, sometimes providing one major frontier orbital (like Group 11 metals) and sometimes providing three frontier orbitals (like Group 13 elements).
    No preview · Article · Feb 2016 · Angewandte Chemie International Edition

  • No preview · Article · Feb 2016
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    ABSTRACT: Metal–organic frameworks (MOFs) feature a great possibility for a broad spectrum of applications. Hollow MOF structures with tunable porosity and multifunctionality at the nanoscale with beneficial properties are desired as hosts for catalytically active species. Herein, we demonstrate the formation of well-defined hollow Zn/Co-based zeolitic imidazolate frameworks (ZIFs) by use of epitaxial growth of Zn-MOF (ZIF-8) on preformed Co-MOF (ZIF-67) nanocrystals that involve in situ self-sacrifice/excavation of the Co-MOF. Moreover, any type of metal nanoparticles can be accommodated in Zn/Co-ZIF shells to generate yolk–shell metal@ZIF structures. Transmission electron microscopy and tomography studies revealed the inclusion of these nanoparticles within hollow Zn/Co-ZIF with dominance of the Zn-MOF as shell. Our findings lead to a generalization of such hollow systems that are working effectively to other types of ZIFs.
    Full-text · Article · Jan 2016 · Chemistry - A European Journal
  • Teng-Hao Chen · Andreas Schneemann · Roland A. Fischer · Seth M. Cohen
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    ABSTRACT: A series of unprecedented crown ether- and thiacrown ether-derivatized benzene dicarboxylic acid (H2bdc) ligands has been synthesized and incorporated into the prototypical isoreticular metal-organic framework (IRMOF) and UiO-66 materials. In the case of UiO-66, only MOFs comprised from a mixed-ligand composition, requiring both unsubstituted bdc and crown ether containing ligands, could be prepared. These are among the few ligand derivatives, and resulting MOFs, that incorporate a macrocyclic group directly on the bdc ligand, providing a new, modular platform for exploring new supramolecular and coordination chemistry within MOFs.
    No preview · Article · Jan 2016 · Dalton Transactions

  • No preview · Article · Jan 2016 · Advanced Functional Materials
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    ABSTRACT: Copper(II) oxide thin films were grown by atomic layer deposition (ALD) using bis-(dimethylamino-2-propoxide)copper [Cu(dmap)2] and ozone in a temperature window of 80–140 °C. A thorough characterization of the films was performed using x-ray diffraction, x-ray reflectivity, UV‐Vis spectrophotometry, atomic force microscopy, field emission scanning electron microscopy, x-ray photoelectron spectroscopy, and time-of-flight elastic recoil detection analysis techniques. The process was found to produce polycrystalline copper(II) oxide films with a growth rate of 0.2–0.3 Å per cycle. Impurity content in the films was relatively small for a low temperature ALD process.
    No preview · Article · Jan 2016 · Journal of Vacuum Science & Technology A Vacuum Surfaces and Films
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    ABSTRACT: Superhydrophobic/superoleophilic composites HFGO@ZIF-8 have been prepared from highly fluorinated graphene oxide (HFGO) and the nanocrystalline zeolite imidazole framework ZIF-8. The structure-directing and coordination-modulating properties of HFGO allow for the selective nucleation of ZIF-8 nanoparticles at the graphene surface oxygen functionalities. This results in localized nucleation and size-controlled ZIF-8 nanocrystals intercalated in between HFGO layers. The composite microstructure features fluoride groups bonded at the graphene. Self-assembly of a unique micro-mesoporous architecture is achieved, where the micropores originate from ZIF-8 nanocrystals, while the functionalized mesopores arise from randomly organized HFGO layers separated by ZIF-8 nanopillars. The hybrid material displays an exceptional high water contact angle of 162° and low oil contact angle of 0° and thus reveals very high sorption selectivity, fast kinetics, and good absorbencies for nonpolar/polar organic solvents and oils from water. Accordingly, Sponge@HFGO@ZIF-8 composites are successfully utilized for oil-water separation.
    No preview · Article · Dec 2015 · Angewandte Chemie International Edition

  • No preview · Article · Dec 2015
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    Full-text · Article · Dec 2015
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    ABSTRACT: Continuous stepwise liquid-phase epitaxial (LPE) growth is one of the most effective procedures for structuring metal-organic frameworks (MOFs) as two-dimensional superstructures, such as thin-films. Alternation of the building block precursors between the individual LPE growth cycles (i.e. from one linker to the other) allows heterostructured MOF films consisting of two different MOFs with different structural or chemical properties to be synthesized with a precise control of the growth sequence. Here, we employ the LPE growth strategy for the preparation of highly functional, hierarchically structured core-shell architectures consisting of [Zn4O(3,5-dialkylcarboxypyrazolate)3]n-based frameworks. Specifically, the small-pore [Zn4O(3-methyl-5-isopropyl-4-carboxypyrazolate)3]n (Zn-MI) and [Zn4O(3,5-diethyl-4-carboxypyrazolate)3]n (Zn-DE) frameworks are respectively deposited as a size selective layer upon larger-pore [Zn4O(3,5-dimethyl-4-carboxypyrazolate)3]n (Zn-DM) and [Zn4O(3-methyl-5-ethyl-4-carboxypyrazolate)3]n (Zn-ME) layers. Direct growth of the MOF layers on the Au surfaces of quartz crystal microbalance (QCM) sensors allowed the adsorption properties of the heterostructures to be probed in real-time. Multiple-component adsorption experiments in an environment-controlled QCM apparatus revealed size selectivity with respect to the adsorption of alcohols, as well as the molecular recognition of methanol over water. These properties stem from the positioning of the small-pore Zn-MI (or Zn-DE) layer on the larger-pore Zn-DM (or Zn-ME) layer, facilitating attractive synergistic properties for adsorptive selectivity and providing a possibility for further development in MOF-based sensing applications.
    Full-text · Article · Nov 2015 · Journal of Materials Chemistry A
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    ABSTRACT: A variety of strategies have been developed to adsorb and separate light hydrocarbons in metal-organic frameworks. Here, we present a new approach in which the pores of a framework are lined with four different C3 sidechains that feature various degrees of branching and saturation. These pendant groups, which essentially mimic a low-density solvent with restricted degrees of freedom, offer tunable control of dispersive host-guest interactions. The performance of a series of frameworks of the type Zn2 (fu-bdc)2 (dabco) (fu-bdc(2-) =functionalized 1,4-benzenedicarboxylate; dabco=1,4-diazabicyclo[2.2.2]octane), which feature a pillared layer structure, were investigated for the adsorption and separation of methane, ethane, ethylene, and acetylene. The four frameworks exhibit low methane uptake, whereas C2 hydrocarbon uptake is substantially higher as a result of the enhanced interaction of these molecules with the ligand sidechains. Most significantly, the adsorption quantities and selectivity were found to depend strongly upon the type of sidechains attached to the framework scaffold.
    No preview · Article · Nov 2015 · Chemistry - A European Journal
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    ABSTRACT: Flexible metal-organic frameworks (MOFs) can undergo fascinating structural transitions triggered by external stimuli, such as adsorption/desorption of specific guest molecules or temperature changes. In this detailed study we investigate the potentials and limitations of tuning framework flexibility systematically by exploiting the powerful concept of mixed-linker solid solutions. We chose the prototypical family of functionalized pillared-layer MOFs of the general type Zn2(fu(1)-bdc)2x(fu(2)-bdc)2-2xdabco (with x = 1.00, 0.75, 0.50, 0.25 and 0.00; fu-bdc = 2,5-dialkoxy-1,4-benzenedicarboxylate with varying alkoxy chain length, dabco = 1,4-diazabicyclo[2.2.2]octane) and examined their guest responsive, as well as intrinsic temperature dependent structural flexibility by X-ray diffraction, gas physisorption and calorimetric measurements. The ratio of the different fu-bdc linkers can be adjusted freely, offering opportunity for a targeted design of these functional materials by modulating their key features, such as magnitude of framework contraction upon guest removal, breathing behaviour upon CO2 adsorption/desorption, thermoresponsive phase behaviour, and their general thermal expansivity, by the careful choice of fu-bdc linkers and their combination.
    No preview · Article · Nov 2015 · Dalton Transactions
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    ABSTRACT: Titania exhibits unique photophysical and -chemical properties and can be used for potential applications in the field of photocatalysis. The control of TiO2 in terms of phase, shape, morphology, and especially nanoscale synthesis of TiO2 particles still remains a challenge. Ti-containing metal-organic frameworks (MOFs), such as MIL-125, can be used as sacrificial precursors to obtain TiO2 materials with diverse phase compositions, morphologies, sizes, and surface areas. MIL-125 is composed of Ti/O clusters as the secondary building units (SBUs) bridged by 1,4-benzenedicarboxylate (bdc). In this study, preformed and surfactant-stabilized gold nanoparticles (GNPs) were deposited onto the surface of amino functionalized NH2-MIL-125 during solvothermal synthesis. Targeted gold/titania nanocomposites, GNP/TiO2, were fabricated through the pyrolysis of GNP/NH2-MIL-125 nanocrystals. The modification of TiO2 with GNPs significantly increased the photocatalytic activity of the MOF derived TiO2 material for the reduction of CO2 to CH4 as compared to TiO2 reference samples such as P-25 and AUROlite (Au/TiO2). The new materials GNP/TiO2 and TiO2 derived by the MOF precursor route were thoroughly characterized by PXRD, FTIR and Raman, TEM, and N2 adsorption studies.
    No preview · Article · Oct 2015 · Chemistry of Materials
  • Jiyeon Kim · Markus Halbherr · Christian Gemel · Roland A Fischer
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    ABSTRACT: Uncommon Ni(I) cationic complexes were synthesized by treating [Ni(ECp*)2(PPh3)2] (E = Al, Ga; Cp* = pentamethylcyclopentadienyl) with 1 equiv of [FeCp2][BAr4(F)]. All compounds have been prepared readily in high yield. The paramagnetic compounds were characterized by single-crystal X-ray crystallography, mass spectrometry, elemental analysis, magnetic susceptibility, and electron paramagnetic resonance spectroscopy.
    No preview · Article · Oct 2015 · Inorganic Chemistry
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    ABSTRACT: Nanostructure engineering has been demonstrated to improve the electrochemical performance of iron oxide based electrodes in Li-ion batteries (LIBs). However, the synthesis of advanced functional materials often requires multiple steps. Herein, we present a facile one-pot synthesis of carbon-coated nanostructured iron oxide on few-layer graphene through high-pressure pyrolysis of ferrocene in the presence of pristine graphene. The ferrocene precursor supplies both iron and carbon to form the carbon-coated iron oxide, while the graphene acts as a high-surface-area anchor to achieve small metal oxide nanoparticles. When evaluated as a negative-electrode material for LIBs, our composite showed improved electrochemical performance compared to commercial iron oxide nanopowders, especially at fast charge/discharge rates.
    No preview · Article · Sep 2015 · Chemistry - A European Journal
  • Zhenlan Fang · Bart Bueken · Dirk E. De Vos · Roland A. Fischer
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    ABSTRACT: Review: overview of defects in coordination network compounds (CNCs) (including their classification and characterizations) and applications of defective CNCs/MOFs; 133 refs.
    No preview · Article · Aug 2015 · ChemInform
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    ABSTRACT: A controlled secondary building unit approach (CSA) was employed to obtain a series of ruthenium metal-organic frameworks (MOFs) of the general formula [Ru3(BTC)2Xx]·Gg (BTC = 1,3,5-benzenetricarboxylate; X = counter-anion, G = guest molecules) which are structural analogues of [M3(BTC)2] (M = Cu, Zn, Ni, Cr, Mo). The compounds [Ru2(OOCR)4X] and [Ru2(OOCCH3)4]Y were varied as Ru sources for CSA; namely strong coordinating X (Cl–) and weakly coordinating Y ([BF4]– or [BPh4]–) as well as the alkyl groups at the carboxylate ligand [R = CH3 or C(CH3)3] were utilized. Four phase-pure Ru-MOFs were obtained: [Ru3(BTC)2Cl0.5(OH)]·(AcOH)1.5 (1), [Ru3(BTC)2Cl1.2(OH)0.3]·(H3BTC)0.15(AcOH)2.4(PivOH)0.45 (2), [Ru3(BTC)2F0.5(OH)]·(AcOH)1.0 (3) and [Ru3(BTC)2(OH)1.5]·(H3BTC)0.5·(AcOH)1.4 (4) {AcOH = CH3COOH, PivOH = (CH3)3CCOOH}. The series of characterization data support the analytical composition and isostructural nature of 1–4, i.e. powder X-ray diffraction (PXRD), IR- and 1H-NMR spectroscopy, thermal gravimetric analysis (TGA) and N2 sorption were employed. The valence state of the Ru-sites were studied by X-ray absorption spectroscopy (XAS). The chosen precursors for CSA and optimized synthesis, work-up and activation protocols allowed improvement of the overall crystallinity, purity (i.e., residual solvent molecules) and surface area of the Ru-MOF materials.
    Full-text · Article · Jul 2015 · Berichte der deutschen chemischen Gesellschaft
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    ABSTRACT: Host-guest inclusion properties of UiO-66 and UiO-67 metal-organic frameworks have been studied using ferrocene (FeCp2) as probe molecule. According to variable-temperature solid-state 1H and 13C CP-MAS-NMR, two different environments exist for adsorbed FeCp2 inside UiO-66 and UiO-67, which have been assigned to octahedral and tetrahedral cavities. At room temperature, a rapid exchange between these two adsorption sites occurs in UiO-67, while at –80 °C the intracrystalline traffic of FeCp2 through the triangular windows is largely hindered. In UiO-66, FeCp2 diffusion is already impeded at room temperature, in agreement with the smaller pore windows. Palladium nanoparticles (Pd NPs) encapsulated inside UiO-66 and UiO-67 have been prepared by chemical vapor infiltration of (allyl)Pd(Cp) followed by UV light irradiation. Infiltration must be carried out at low temperature (–10 °C) to avoid uncontrolled decomposition of the organometallic precursor and formation of Pd NPs at the external surface of the MOF. The resulting Pd-MOFs are shape selective catalysts, as shown for the hydrogenation of carbonyl compounds with different steric hindrance.
    No preview · Article · Jul 2015 · Berichte der deutschen chemischen Gesellschaft
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    ABSTRACT: Copper sulfide nanocrystals (Cu2-xS NCs) consisting of earth-abundant and nontoxic elements have attracted attention for optoelectronic and plasmonic applications due to their tunable light absorption and emission properties. In this work, we present a study of the electronic changes induced in organic-capped Cu2-xS NCs by surface modification treatments using charge transport and optical spectroscopy measurements. We have investigated surface treatments yielding ligand exchange and also ligand removal as well as changes in electronic defect density. The structural and morphological changes induced by the treatments were monitored by infrared spectroscopy, electron microscopy, and electron paramagnetic resonance. Untreated Cu2-xS NCs exhibit a strong absorption band arising from a localized surface plasmon resonance (LSPR). We found that using a ligand exchange procedure (ethanedithiol treatment), the electrical conductivity in films of Cu2-xS NCs can be enhanced by 5 orders of magnitude, while maintaining other electronic properties of the individual NCs like optical absorption and LSPR. The improvements in the electrical conductivity were attributed to the reduction of the inter-NC separation in the films, as revealed by the structural and morphological studies. We also have observed that ligand removal treatments such as thermal annealing and hydrazine treatment yield a LSPR red-shift, while the electrical conductivity increases by up to 5 and 7 orders of magnitude, respectively. We proposed a model for the surface reactions taking place during these treatments. Our work highlights the potential of simple chemical or thermal treatments in tailoring the electronic properties of Cu2-xS NCs, making thermally treated Cu2-xS NCs interesting for tunable plasmonic and optoelectronic applications.
    Full-text · Article · Jul 2015 · The Journal of Physical Chemistry C
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    Zhenlan Fang · Bart Bueken · Dirk E. De Vos · Roland A. Fischer
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    ABSTRACT: Defect engineering in metal-organic frameworks (MOFs) is an exciting concept for tailoring material properties, which opens up novel opportunities not only in sorption and catalysis, but also in controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties. It is challenging to structurally characterize the inherent or intentionally created defects of various types, and there have so far been few efforts to comprehensively discuss these issues. Based on selected reports spanning the last decades, this Review closes that gap by providing both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs. Moreover, we will highlight important aspects of "defect-engineering" concepts applied for CNCs, also in comparison with relevant solid materials such as zeolites or COFs. Finally, we discuss the future potential of defect-engineered CNCs. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution Non-Commercial NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
    Preview · Article · Jun 2015 · Angewandte Chemie International Edition

Publication Stats

11k Citations
2,319.06 Total Impact Points

Institutions

  • 2015
    • Nanjing University of Technology
      Nan-ching, Jiangsu Sheng, China
  • 1998-2015
    • Ruhr-Universität Bochum
      • • Inorganic Chemistry
      • • Faculty of Chemistry and Biochemistry
      Bochum, North Rhine-Westphalia, Germany
  • 1998-2014
    • Philipps University of Marburg
      • Faculty of Chemistry
      Marburg, Hesse, Germany
  • 1999
    • Hochschule Bochum
      Bochum, North Rhine-Westphalia, Germany
  • 1996-1997
    • Universität Heidelberg
      • Institute of Inorganic Chemistry
      Heidelburg, Baden-Württemberg, Germany
  • 1995-1996
    • Technische Universität München
      • Walter Schottky Institut (WSI)
      München, Bavaria, Germany
  • 1980-1996
    • Deutsches Herzzentrum München
      München, Bavaria, Germany
  • 1988
    • Hochschuelerschaft an der Technischen Universitaet Graz
      FRG, New York, United States