Roland A. Fischer

Ruhr-Universität Bochum, Bochum, North Rhine-Westphalia, Germany

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Publications (395)1983.88 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A new titanium precursor, [Ti(OPri)2(deacam)2] (deacam = N,N-diethylacetoacetamide), was developed by the reaction of the parent Ti alkoxide with the β-ketoamide. The compound, obtained as a monomeric six-coordinated complex, was used in metal organic chemical vapor deposition (MOCVD) of TiO2 both as a single source precursor (SSP) and in the presence of oxygen. The high thermal stability of [Ti(OPri)2(deacam)2] enabled the fabrication of TiO2 films over a wide temperature range, with steady growth rates between 500 and 800 °C. The microstructure of the obtained systems was analyzed by X-ray diffraction (XRD) and Raman spectroscopy, whereas atomic force microscopy (AFM) and field emission-scanning electron microscopy (FE-SEM) measurements were performed to investigate the surface morphology and nanoorganization. Film composition was investigated by complementary techniques like Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). The electrical properties of the layers were investigated by performing capacitance voltage (C–V) and leakage current measurements.
    Physica Status Solidi (A) Applications and Materials 05/2015; DOI:10.1002/pssa.201532271 · 1.53 Impact Factor
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    ABSTRACT: Porosity switching in the crystalline solid state is a unique phenomenon observed only in a limited number of materials. The switching behavior of two metal-organic frameworks as well as their respective solid solutions of composition [Zn2(BME-bdc)x(DB-bdc)2-xdabco]n (x = 2; 1.5; 1.0; 0.5; 0) is studied in situ during the adsorption of CO2 and Xe using X-ray diffraction and NMR techniques. The diffraction data, measured during the adsorption suggest a direct one-step phase transition (switching) from the narrow pore phase to the large pore phase beyond the transition pressure. An intermediate phase was found only in one compound within a narrow pressure range around the phase transition pressure region. In situ high-pressure 13C NMR spectroscopy of adsorbed CO2 also allowed following the gating behavior of the studied materials by monitoring the signal of adsorbed CO2. The 13C NMR spectra exhibit a pronounced broadening indicating a certain degree of order for the adsorbed molecules inside the pores. This ordering effect and the resulting line broadening depend on the linker functionalization as could be confirmed by corresponding molecular dynamics (MD) simulations.
    Microporous and Mesoporous Materials 03/2015; DOI:10.1016/j.micromeso.2015.02.042 · 3.21 Impact Factor
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    Lars Heinke, Min Tu, Suttipong Wannapaiboon, Roland A. Fischer, Christof Wöll
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    ABSTRACT: Thin films of metal-organic frameworks (MOFs) enable various applications ranging from membrane separations over sensor techniques to potential (micro-) electronic uses. Recent progresses of thin and homogenous surface-mounted MOF (SURMOF) films, which are prepared in a well-defined layer-by-layer fashion on a solid substrate surface, are highlighted in this review. Various substrate surfaces, ranging from plain metal, metal-oxide and polymer surfaces over metal-oxide membranes to magnetic nanoparticles, can be coated with SURMOFs. Multilayered SURMOF films with either identical or different MOF lattice constants or even different MOF structures were prepared, enabling the preparation of functional surface coatings. This allows, by incorporating photoswitchable azobenzene in the MOF structure, the preparation of multilayered, nanoporous films with remote-controllable properties. By means of crosslinking the SURMOF structure employing post-synthetic modifications, water stable thin films, SURGELs, can be prepared. Their thin and homogenous morphology also makes SURMOFs perfectly suited as coatings for electrochemical and electronic applications, where the small dielectric constant k as well as the option to tune the conductivity by loading the pores are very promising features of these porous solids. Furthermore, SURMOFs are very well suited for investigations of MOF-specific properties, since e.g. photoelectron spectroscopies can be applied to these thin films in a straightforward fashion. In additions, mass transfer and diffusion properties in MOFs can be studied for such thin films with high precision using a quartz-crystal microbalance (QCM).
    Microporous and Mesoporous Materials 03/2015; DOI:10.1016/j.micromeso.2015.03.018 · 3.21 Impact Factor
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    ABSTRACT: Die dreieckigen Cluster [Zn3Cp*3]+ und [Zn2CuCp*3] wurden durch Addition der in situ generierten, elektrophilen und isolobalen Spezies [ZnCp*]+ und [CuCp*] an das Carmona-Reagens [Cp*ZnZnCp*] synthetisiert, wobei die Zn-Zn-Bindung des Letzteren erhalten blieb. Die Verwendung von nichtkoordinierenden fluorierten aromatischen Lösungsmitteln ist dabei essenziell. Die Bindungssituation der ligandenstabilisierten Cluster wurde mit quantenchemischen Methoden untersucht, wobei sich ein hohes Maß an σ-Aromatizität zeigte, ähnlich der Bindungssituation im Triwasserstoffkation [H3]+. Die neuen Spezies dienen als molekulare Bausteine für CunZnm-Cluster (Nanomessing), die auch im LIFDI-Massenspektrum der neuen Verbindungen detektiert werden können.
    Angewandte Chemie 02/2015; 127(14). DOI:10.1002/ange.201410737
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    ABSTRACT: The triangular clusters [Zn3 Cp*3 ](+) and [Zn2 CuCp*3 ] were obtained by addition of the in situ generated, electrophilic, and isolobal species [ZnCp*](+) and [CuCp*] to Carmona's compound, [Cp*ZnZnCp*], without splitting the ZnZn bond. The choice of non-coordinating fluoroaromatic solvents was crucial. The bonding situations of the all-hydrocarbon-ligand-protected clusters were investigated by quantum chemical calculations revealing a high degree of σ-aromaticity similar to the triatomic hydrogen ion [H3 ](+) . The new species serve as molecular building units of Cun Znm nanobrass clusters as indicated by LIFDI mass spectrometry. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Angewandte Chemie International Edition in English 02/2015; 54(14). DOI:10.1002/anie.201410737 · 13.45 Impact Factor
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    ABSTRACT: The synthesis and characterisation of the solvent-stabilized salt [Zn2(THF)6]2+[BAr4F]2− (1) is presented, which features the dizinc dication [Zn2]2+ as an analogue of the calomel dication [Hg2]2+. The labile tetrahydrofuran (THF) solvate molecules of 1 can be readily substituted by other ligands. Reaction with the strong donor ligand PMe3 (Me = CH3) leads to the Zn(II) complex [Zn(PMe3)4]2+[BAr4F]2− by disproportionation, while the π-acceptor-ligand phenylisocyanide (PhNC) gives the substitution product [Zn2(PhNC)6]2+[BAr4F]2− (2) with an intact Zn–Zn bond.
    Chemical Communications 01/2015; 51(11). DOI:10.1039/C4CC08850F · 6.72 Impact Factor
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    ABSTRACT: The synthesis and characterization of the cationic mixed metal Ga/Zn cluster [Zn2(GaCp*)6](2+) (1) is presented. The reaction of [Zn2Cp*2] with [Ga2Cp*][BAr4(F)] leads to the formation of the novel complex being the first example of a [Zn2](2+) core exclusively ligated by metalloid group-13 organyl-ligands. Compound 1 exhibits two different coordination modes: In the solid state, two of the six GaCp* ligands occupy bridging positions, whereas VT (1)H NMR indicates the coexistence of a second isomer in solution featuring six terminal GaCp* ligands. Quantum chemical calculations have been carried out to assign the gallium and zinc positions; the bonding situation in 1 is characterized and the importance of dispersion forces is discussed.
    Inorganic Chemistry 12/2014; 54(1). DOI:10.1021/ic502532g · 4.79 Impact Factor
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    ABSTRACT: The zinc-imidazolate-based framework ZIF-8 was loaded with preformed surfactant-stabilized bimetallic Pd/Au nanoparticles and its corresponding monometallic counterparts Au and Pd by a controlled encapsulation process during the ZIF-8 crystal growth. The nanoparticle-loaded materials were characterized by powder X-ray diffraction (PXRD), FTIR spectroscopy, N2-sorption measurements, as well as by transmission electron microscopy (TEM). The ZIF-8 matrix material remained intact and the NP@ZIF-8 materials revealed the permanent porosity of Brunauer–Emmett–Teller (BET) surface areas above 1100 m2 g–1. The nanoparticles are exclusively found inside the volume of the nanocrystals and exhibit unchanged composition and size distribution as revealed by TEM investigations. Additionally, scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX) confirmed the solid solution-type alloying of Pd and Au in the embedded Pd/Au nanoparticles. The materials were briefly evaluated in aqueous-phase aerobic alcohol oxidation to investigate the synergetic effects of alloyed Pd/Au nanoparticles and the microporous, hydrophobic matrix ZIF-8.
    Berichte der deutschen chemischen Gesellschaft 11/2014; 2014(32). DOI:10.1002/ejic.201402409
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    ABSTRACT: The novel all-hydrocarbon ligand-stabilized binuclear clusters of metal-core composition Ni2Zn7E, [(η(5)-Cp*)Ni2(ZnMe)6(ZnCp*)(ECp*)] (1-Zn, E = Zn; 1-Ga, E = Ga) and [(η(6)-toluene)Ni2(ZnCp*)2(ZnMe)6] (2; Cp* = pentamethylcyclopentadienyl), were obtained via Ga/Zn and Al/Zn exchange reactions using the starting compounds [Ni2(ECp*)3(η(2)-C2H4)2] (E = Al/Ga) and an excess of ZnMe2 (Me = CH3). Compounds 1-Zn and 1-Ga are very closely related and differ only by one Zn or Ga atom in the group 12/13 metal shell (Zn/Ga) around the two Ni centers. Accordingly, 1-Zn is EPR-active and 1-Ga is EPR-silent. The compounds were derived as a crystalline product mixture. All new compounds were characterized by (1)H and (13)C NMR and electron paramagnetic resonance (EPR) spectroscopy, mass spectrometric analysis using liquid-injection field desorption ionization, and elemental analysis, and their molecular structures were determined by single-crystal X-ray diffraction studies. In addition, the electronic structure has been investigated by DFT and QTAIM calculations, which suggest that there is a Ni1-Ni2 binding interaction. Similar to Zn-rich intermetallic phases of the Hume-Rothery type, the transition metals (here Ni) are distributed in a matrix of Zn atoms to yield highly Zn-coordinated environments. The organic residues, ancillary ligands (Me, Cp*, and toluene), can be viewed as the "protecting" shell of the 10-metal-atom core structures. The soft and flexible binding properties of Cp* and transferability of Me substituents between groups 12 and 13 are essential for the success of this precedence-less type of cluster formation reaction.
    Inorganic Chemistry 09/2014; 53(19). DOI:10.1021/ic5014335 · 4.79 Impact Factor
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    Min Tu, Roland A. Fischer
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    ABSTRACT: Solvent mixture controlled rapid room temperature syntheses for facile access to uniform zeolitic-imidazolate framework nanocrystals (ZIF-7, ZIF-65-Zn and ZIF-71) are reported. ZIF thin film devices for sensing volatile organic chemicals were fabricated by dip-coating nano-ZIF (80-130 nm) suspensions.
    Chemical Communications 09/2014; 50(87). DOI:10.1039/C4CC06491G · 6.72 Impact Factor
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    ABSTRACT: A small angle neutron scattering (SANS) study is presented, which investigates the impact of a modulator on nucleation and growth of MOF-5 nanopartides. Two DMF solutions, one with the secondary building unit Zn4O(C6H5COO)(6) (SBU) and one with terephthalic acid (BDC) as a linker, were mixed, and 5 min after generation of the mixture, monodentate 4-n-decylbenzoic acid was added as a modulator agent. Time-resolved SANS during the initial stages of the particle formation process offered insight into morphological transformations during the first hours. Subsequently, it could be demonstrated that a shell is formed by the modulator wrapping around the growing MOF-5 particles while directing the formation of MOP-5 nanopartides. This has been made possible by an identification of a mixture of deuterated and hydrogenated solvent (DMF), which matches the scattering contrast of MOF-5, thus giving access to the scattering signal of the modulator.
    Crystal Growth & Design 09/2014; 14(9):4859-4863. DOI:10.1021/cg501025g · 4.56 Impact Factor
  • Christoph Rösler, Roland A. Fischer
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    ABSTRACT: The fabrication of metal nanoparticles (NP) in porous host matrices, especially metal-organic frameworks (MOFs) has become of great interest in recent years, due to the broad field of applications. In this article we summarize the progress in the field of NP@MOF materials and illustrate the different preparation methods as well as suitable characterisation techniques. Furthermore, practical applications in the fields of hydrogen storage and heterogeneous catalysis are briefly discussed.
    CrystEngComm 08/2014; 17(2). DOI:10.1039/C4CE01251H · 3.86 Impact Factor
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    ABSTRACT: Control of localized metal–organic framework (MOF) thin film formation is a challenge. Zeolitic imidazolate frameworks (ZIFs) are an important sub-class of MOFs based on transition metals and imidazolate linkers. Continuous coatings of intergrown ZIF crystals require high rates of heterogeneous nucleation. In this work, substrates coated with zinc oxide layers are used, obtained by atomic layer deposition (ALD) or by magnetron sputtering, to provide the Zn2+ ions required for nucleation and localized growth of ZIF-8 films ([Zn(mim)2]; Hmim = 2-methylimidazolate). The obtained ZIF-8 films reveal the expected microporosity, as deduced from methanol adsorption studies using an environmentally controlled quartz crystal microbalance (QCM) and comparison with bulk ZIF-8 reference data. The concept is transferable to other MOFs, and is applied to the formation of [Al(OH)(1,4-ndc)]n (ndc = naphtalenedicarboxylate) thin films derived from Al2O3 nanolayers.
    Advanced Functional Materials 08/2014; 24(30). DOI:10.1002/adfm.201400559 · 10.44 Impact Factor
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    ABSTRACT: Definierte molekulare Modelle für katalyserelevante Oberflächenreaktionen an Hume-Rothery-Nanophasen sind sehr selten. Der intermetalloide Al-Cu-Cluster [(Cp*AlCu)6H4] wird selektiv bei der Reaktion von [(Cp*Al)4] und [(PPh3CuH)6] gebildet. Die höhere Affinität von Cp*Al zu Kupfer ermöglicht die Substitution der Phosphinliganden der Kupferhydridvorstufe und die Stabilisierung des Cu6-Kerns durch dessen Einbettung in einen Al6-Käfig. Der erhaltene Hydridocluster M12H4 reagiert mit Benzonitril in einer stöchiometrischen Hydrometallierung zu [(Cp*AlCu)6H3(NCHPh)].
    Angewandte Chemie 07/2014; 126(30). DOI:10.1002/ange.201402149
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    ABSTRACT: Defined molecular models for the surface chemistry of Hume-Rothery nanophases related to catalysis are very rare. The Al-Cu intermetalloid cluster [(Cp*AlCu)6 H4 ] was selectively obtained from the clean reaction of [(Cp*Al)4 ] and [(Ph3 PCuH)6 ]. The stronger affinity of Cp*Al towards Cu sweeps the phosphine ligands from the copper hydride precursor and furnishes an octahedral Al6 cage to encapsulate the Cu6 core. The resulting hydrido cluster M12 H4 reacts with benzonitrile to give the stoichiometric hydrometalation product [(Cp*AlCu)6 H3 (N=CHPh)].
    Angewandte Chemie International Edition in English 07/2014; 53(30). DOI:10.1002/anie.201402149 · 13.45 Impact Factor
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    ABSTRACT: Four organic amine-based solvents were discovered which enable direct exfoliation of graphite to produce high-quality and oxygen-free graphene nanosheets. These solvents outperform previously used solvents and additives such as N-methyl-pyrrolidone and surfactants in terms of their dispersing capacity. The resulting dispersions allow the facile fabrication of zeolitic imidazolate framework (ZIF)-graphene nanocomposites with remarkable CO2 storage capability.
    Chemical Communications 07/2014; 50(72). DOI:10.1039/c4cc03923h · 6.72 Impact Factor
  • Roland A. Fischer, Inke Schwedler
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    ABSTRACT: Im Folgenden werden Begriffe, Definitionen und Empfehlungen für die Klassifizierung von Koordinationspolymeren, Netzwerken und Metall-organischen Gerüstverbindungen (MOFs) erläutert. Es wird eine hierarchische Terminologie empfohlen, die vom Koordinationspolymer als Oberbegriff ausgeht. Koordinationsnetzwerke sind dann eine Untergruppe der Koordinationspolymere und MOFs wiederum eine Untergruppe der Koordinationsnetzwerke. Eines der Kriterien für MOFs sind potenzielle Hohlräume, ohne dass physikalische Messungen der Porosität oder anderer Eigenschaften per se erforderlich sind. Die Verwendung von Topologien und Topologiedeskriptoren wird zur Verbesserung der Kristallstrukturbeschreibung von MOFs und 3D-Koordinationspolymeren dringend empfohlen.
    Angewandte Chemie 07/2014; 126(27). DOI:10.1002/ange.201400619
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    ABSTRACT: Das Konzept der “festen Lösungen mit gemischten Linkern” (mixed-linker solid solution concept) ist angewendet worden, um die Metallzentren des gemischtvalenten RuII/III-Analogons der bekannten Familie der [M3II,II(btc)2]-MOFs (M=Cu, Mo, Cr, Ni oder Zn; btc=Benzol-1,3,5-tricarboxylat) zu modellieren und strukturelle Defekte in das Gerüst mit teilweise fehlenden Carboxylatliganden an den Ru2-“Schaufelradeinheiten” einzubringen. Pyridin-3,5-dicarboxylat (pydc) als zweiter, Defekt-bildender Linker von ähnlicher Größe wie btc, aber geringerer Ladung führt zu einem porösen Derivat von Ru-MOF mit Eigenschaften, die sich von denen des Defekt-freien MOF unterscheiden. So bewirkt das Einbringen von pydc außer der Bildung von zusätzlichen koordinativ ungesättigten Metallzentren auch eine partielle Reduktion des Rutheniums. Die modifizierten Ru-Zentren sind für die Aktivität der “defekten” Varianten hinsichtlich dissoziativer Chemisorption von CO2, erhöhter CO-Sorption, Bildung von Ru-H-Spezies und katalytischer Hydrierung von Olefinen verantwortlich.
    Angewandte Chemie 07/2014; 126(27). DOI:10.1002/ange.201311128
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    ABSTRACT: The first example of ligand protected Cu-Zn clusters is described. Reaction of [CpCu(CN(t)Bu)] with [Zn2Cp*2] yields [(CuCN(t)Bu)4(ZnCp*)4] () and [(CuCN(t)Bu)4(ZnCp*)3(ZnCp)] (). According to DFT calculations, the [Cu4Zn4] unit fulfils the unified superatom model for cluster valence shell closing.
    Chemical Communications 06/2014; 50(63). DOI:10.1039/c4cc03401e · 6.72 Impact Factor

Publication Stats

6k Citations
1,983.88 Total Impact Points

Institutions

  • 1998–2015
    • Ruhr-Universität Bochum
      • • Inorganic Chemistry
      • • Fakultät für Chemie und Biochemie
      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
    • Technische Universität München
      München, Bavaria, Germany
  • 1980–1996
    • Deutsches Herzzentrum München
      München, Bavaria, Germany
  • 1988
    • Hochschuelerschaft an der Technischen Universitaet Graz
      FRG, New York, United States