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Overview of granted projects - Part I

Redox-Active MOF-5 Isotypes: Novel Entatic State Catalysts?

 

        Consortium:

        Professor Dr. Joachim Sauer, Berlin
        Humboldt University Berlin
        Department of Mathematics and Natural Sciences
        Institute of Chemistry

        Professor Dr. Dirk Volkmer, Augsburg
        University of Augsburg
        Institute of Physics
        Chair of Solid State Chemistry

        Project:

        Redox-Active MOF-5 Isotypes: Novel Entatic State Catalysts?

        Abstract:

        Porous, redox-active metal-organic frameworks (MOFs) shall be developed which are structurally isotypic with MOF-5 ([Zn4O(BDC)3], BDC =1,4-benzenedicarboxylate). These compounds, in contrast to MOF-5, are constructed from aromatic N-donor ligands (e.g. pyrazolate moieties) and open-shell 3d transition metal ions.
        Preliminary investigations have demonstrated that the use of heterocyclic aromatic N-donors leads to greatly enhanced hydrolytic stability of the MOF compounds, which is a necessary condition for catalytic oxidation processes. Particular attention will be addressed to the specific advantages of embedding a multinuclear transition metal cluster into a rigid 3D coordination framework (“entatic state catalyst”). Thus, the spectroscopic and catalytic properties of solid MOF catalysts shall be compared with isostructural model compounds in solution. Quantum mechanical investigations will address different oxidation states of the electronically coupled metal sites in multinuclear clusters, and their role in catalytic oxidation or oxygenation cycles. Density functional theory (DFT) with general gradient approximation (GGA) and with hybrid functionals is applied to investigate ground and excited state properties of both synthesized MOFs and molecular models. Special attention will be paid to important properties like vibrational and UV/VIS spectroscopy as well as to the redox behaviour of the envisaged compounds. At a later project stage reaction intermediates shall be characterized computationally to interpret experimental findings.

        Results:

         

        Structurally related to MOF-5, the cobalt(II)-containing metal-organic framework MFU-1 is stable to hydrolysis. Catalytic turnover is achieved in oxidation reactions with redox-active MFU-1, and the solid catalyst is easily recovered from the reaction mixture. Catalytic transformations have been shown to occur inside the pores of the microporous solid.

         

        Two novel metal coordination polymers, [Zn5Cl4(BBTA)3]•3 DMF ( 1), and [ZnCl(BBTA)0.5(DMA)] ( 2) {H2-BBTA = 1H,5H-benzo(1,2-d:4,5-d )bistriazole}, have been synthesized under solvothermal conditions using ZnCl2 and H2-BBTA in DMF (DMF = N,N -dimethylformamide) or DMA (DMA = N,N -dimethylacetamide). Moreover, a highly efficient microwave synthetic route has been developed for 1. The structures of both compounds have been determined by single crystal X-ray diffraction. Compound 1 represents the first example of a novel family of cubic microporous metal–organic frameworks (MFU-4; Metal-Organic Framework Ulm University-4), consisting of dianionic BBTA2– linkers and pentanuclear {Zn5Cl4}6+ secondary building units, whereas compound 2 forms a dense 2D layered framework. Phase purity of both compounds was confirmed by X-ray powder diffraction (XRPD), IR spectroscopy, and elemental analysis. TGA and variable temperature XRPD (VTXRPD) experiments carried out on 1 indicate that solvent molecules occluded in the large cavities of 1 can be removed at a temperature >250 °C in high vacuum without significant loss of crystallinity, giving rise to a metal–organic framework with void cavities. Due to the small diameter of the aperture joining the two types of cavities present in 1, the diffusion of guest molecules across the crystal lattice is largely restricted at ambient conditions. Compound 1 therefore exhibits a highly selective adsorption for hydrogen vs. nitrogen at -196 °C. The framework is stable against moisture and has a specific pore volume of 0.42 cm3 g-1 estimated from the water adsorption isotherm.

        Publications:

        Markus Tonigold, Ying Lu, Björn Bredenkötter, Bernhard Rieger, Stefan Bahnmüller, Julia Hitzbleck, Gerhard Langstein und Dirk Volkmer
        "Heterogene Oxidationskatalyse durch MFU-1, eine Cobalt(II)-haltige Metall-organische Gerüststruktur"
        Angew. Chem. 2009, 121, 7682 –7687
         

         

        Markus Tonigold, Ying Lu, Björn Bredenkötter, Bernhard Rieger, Stefan Bahnmüller,Julia Hitzbleck, Gerhard Langstein, and Dirk Volkmer
        "Heterogeneous Catalytic Oxidation by MFU-1: A Cobalt(II)-Containing Metal–Organic Framework"
        Angew. Chem. Int. Ed. 2009, 48, 7546 –7550
         

         

        Shyam Biswas, Maciej Grzywa, Hari Pada Nayek, Stefanie Dehnen, Irena Senkovska, Stefan Kaskel and Dirk Volkmer
        "A cubic coordination framework constructed from benzobistriazolate ligands and zinc ions having selective gas sorption properties"
        Dalton Trans., 2009, 6487–6495
         

         

        Ying Lu, Markus Tonigold, Björn Bredenkötter, Dirk Volkmer, Julia Hitzbleck, and Gerhard Langstein
        "A Cobalt(II)-containing Metal-Organic Framework Showing Catalytic Activity in Oxidation Reactions"
        Z. Anorg. Allg. Chem. 2008, 634, 2411-2417
         

         

        Kaido Sillar, Alexander Hofmann, and Joachim Sauer
        "Ab Initio Study of Hydrogen Adsorption in MOF-5"
        J. Am. Chem. Soc., 2009, 131 (11), 4143-4150
         

         

        Y.-Y. Liu, M. Grzywa, M. Weil, D. Volkmer
        "[Cu4OCI6(DABCO)2] •0.5DABCO • 4CH3OH (‘‘MFU-5’’): Modular synthesis of a zeolite-like metal-organic framework constructed from tetrahedral {Cu4OCI6} secondary building units and linear organic linkers"
        J. Solid State Chem. 2010, 183, 208–217
         

         

        S. Biswas, M. Tonigold, M. Speldrich, P. Kögerler, D. Volkmer
        "Nonanuclear Coordination Compounds Featuring {M9L12}6+ Cores (M = NiII, CoII , or ZnII; L = 1,2,3-Benzotriazolate). "
        Eur. J. Inorg. Chem. 2009, 3094–3101.
         

         

        S. Biswas, M. Tonigold, M. Speldrich, P. Kögerler, M. Weil, D. Volkmer
        "Syntheses and Magnetostructural Investigations on Kuratowski-Type Homo- and Heteropentanuclear Coordination Compounds [MZn4CI4(L)6] (MII = Zn, Fe, Co, Ni, or Cu; L = 5,6-Dimethyl-1,2,3-benzotriazolate) Represented by the Nonplanar K3,3 Graph. "
        Inorg. Chem. 2010, 49, 7424–7434
         

         

        S. Biswas, M. Tonigold, H. Kelm, Hans-Jörg Krüger, D. Volkmer
        "Thermal spin-crossover in the [M3Zn6CI6L12] (M= Zn, FeII; L = 5,6-dimethoxy-1,2,3-benzo-triazolate) system: structural, electrochemical, Mössbauer, and UV-Vis spectroscopic studies"
        Dalton Trans. 2010, 39, 9851–9859.
         

         

        D. Denysenko, M. Grzywa, M. Tonigold, B. Streppel, I. Krkljus, M. Hirscher, E. Mugnaioli, U. Kolb, J. Hanss, D. Volkmer
        "Elucidating Gating Effects for Hydrogen Sorption in MFU-4-Type Triazolate-Based Metal–Organic Frameworks Featuring Different Pore Sizes"
        Chem. Eur. J. 2010, DOI: 10.1002/chem.201001872
         

         

        M. Tonigold, Y. Lu, A. Mavrandonakis, A. Puls, R. Staudt, J. Möllmer, J. Sauer, D. Volkmer
        "Pyrazolate-Based Cobalt(II)-Containing Metal-Organic Frameworks in Heterogeneous Catalytic Oxidation Reactions: Elucidating the Role of Entatic States for Biomimetic Oxidation Processes"
        Chem. Eur. J. 2011, chem.201003173, accepted
         
 
 

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