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TU Dresden » Fakultät Mathematik und Naturwissenschaften » Fachrichtung Chemie und Lebensmittelchemie » Metal-Organic Frameworks
Overview of granted projects - Part II

Redox-Active Metal-Organic Frameworks: Novel Entatic State Catalysts?

 

        Consortium:

        Professor Dr. Karsten Reuter, Garching
        University of Technology München
        Institute of Catalysis Research
        Theoretical Chemistry

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

        Project:

        Redox-Active Metal-Organic Frameworks: Novel Entatic State Catalysts?

        Abstract:

        Porous, redox-active metal-organic frameworks (MOFs) shall be developed which are constructed from aromatic N-donor ligands (e.g. pyrazolate or triazolate moieties) and openshell 3d transition metal ions.
        Previous 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 special emphasis laid upon gas phase reactions. Quantum chemical 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) based on general gradient approximation (GGA) and hybrid functionals is applied to investigate ground and excited state properties of the MOFs. 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.


        Results:

        Figure 1. Synthesis of MFU-4l.






        Figure 2. Preparation of MFU-4l derivatives with active metal sites. (i) HCOOLi/MeOH, RT; (ii) 300 °C, 30 min, in vacuum; (iii) CuCl2, DMA, 60 °C; (iv) HCOOLi/MeOH, RT, (v) 180 °C, 1 h, in vacuum

        A novel highly porous member of isoreticular MFU-4-type frameworks, [Zn5Cl4(BTDD)3] (MFU-4l(arge)) {H2-BTDD = bis-(1H-1,2,3-triazolo-[4,5-b],[4’,5’-i])dibenzo-[1,4]-dioxin}, has been synthesized using ZnCl2 and H2-BTDD in N,N-dimethylformamide as a solvent. MFU-4l represents the first example of MFU-4-type frameworks featuring large pore apertures of 9.1 Å. TGA and variable temperature XRPD experiments carried out on MFU-4l indicate that it is stable up to 500°C (N2 atmosphere) and up to 350 °C in air. Heating up a MFU-4l suspension with MCl2 solutions in DMF or DMA leads to isostructural replacement of zinc by M(II) centres, where M = Mn, Fe, Co, Ni or Cu. The complete exchange of tetrahedrally coordinated zinc centers can only be achieved with CoCl2 and requires a huge excess of cobalt ions in the suspension (Co/Zn molar ratio > 5). The central octahedrally coordinated Zn center cannot be replaced at the given experimental conditions. Thus, the average chemical formula of obtained frameworks may be formulated as [Zno(MxtZn(4-x)tCl4(BTDD)3]. Postsynthetic metal-exchange in MFU-4l can be augmented by ligand exchange reactions (as exemplified for chloride/formate exchange in MFU-4l and Cu-MFU-4l) leading to a variety of frameworks with different redox active 3d transition metal ions. Upon thermal treatment of MFU-4l formates, coordinatively strongly unsaturated metal centers, such as Zn(II)-hydride or copper(I) species, are generated selectively. Cu(I)-MFU-4l, prepared in this way, is stable at ambient conditions and shows fully reversible chemisorption of small molecules such as O2, N2 and H2 with corresponding isosteric heats of adsorption of 53, 42 and 32 kJ mol-1, respectively, as determined by gas sorption measurements and confirmed by density-functional theory calculations (Table 1). Moreover, Cu(I)-MFU-4l forms stable complexes with C2H4 and CO, which have been characterized by FT-IR spectroscopy. The corresponding stretch modes of coordinatively bound CO and C2H4 molecules can be observed in the FT-IR spectra at 2081 cm-1 and 1541 cm-1, respectively and are shifted to lower wavenumbers, as compared to free gas molecules (2143 cm-1 for CO and 1623 cm-1 for C2H4). In all cases, a 1:1 stoichiometry of CuI-O2 (N2, H2, C2H4 or CO) coordination units has been observed. The chemisorption of O2, N2, H2 and C2H4 is fully reversible at ambient conditions, whereas CO can only be desorbed at 270 °C. MFU-4l hydride derivative 2 reacts with benzoyl chloride in benzene solution at RT, yielding benzaldehyde as the main product.


          Table 1. Experimental and DFT-calculated isosteric heats of adsorption in kJ mol-1 in Cu(I)-MFU-4l
            H2 N2 O2 C2H4
          Experiment 32.3±0.4 41.6±0.6 52.6±0.6 88±4
          DFT-B3LYP 25 44 46 84





         

        Figure 3. Binding geometries for H2 (a), N2 (b), O2 (c) and C2H4 (d) at the Cu(I) sites within the Kuratowski unit of MFU-4l as obtained from DFT calculations (atomic distances in Å).



        The demonstrated hydride transfer on electrophiles and strong binding of small gas molecules suggests these novel – yet robust – metal-organic frameworks with open metal sites as promising catalytic materials comprising earth-abundant metal elements. A density-functional theory (DFT) based screening of MFU-4l frameworks with different metal centers and side ligands, suitable for O2 activation, has been performed in order to support the synthesis endeavours (FHI - aims code: PBE vs. PBE0 functional (with vdW corrections)). As a model system, instead of full periodic MFU-4l, Kuratowski and Scorpionate complexes have been used. PBE systematically gives larger binding energies if compared to PBE0. Detailed analyses of Co-complex show that the major error here is not in the O2/complex interaction but rather in the re-hybridization of cobalt orbitals in the ligand field (largely independent of the specific ligand). A larger crystal field splitting in PBE0 creates a larger “cost” for rehybridization to octahedral configuration, which in turn implies the much smaller binding energy.


          Co-Kuratowski komplex
          Eb(O2)(eV) Cl-1 F-1 H-1 CN-1 OH-1 NH2-1 NO2-1
          PBE -0.58 -0.84 -1.99 -1.08 -1.02 -1.29 -1.01
          PBE0 0.9 0.57 -0.44 0.38 0.43 0.13 0.54


        Publications:

        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. 2011, 17, 1837–1848.
         

         

        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 Entactic States for Biomimetic Oxidation Processes"
        Chem. Eur. J. 2011, 17, 8671-8695.
         

         

        D. Denysenko, T. Werner, M. Grzywa, A. Puls, V. Hagen, G. Eickerling, J. Jelic, K. Reuter, D. Volkmer
        "Reversible gas-phase redox processes catalyzed by Co-exchanged MFU-4l(arge)"
        Chem. Commun. 2012, 48, 1236-1238.
         

         

        Y.-Y. Liu, K. Leus, M. Grzywa, D. Weinberger, K. Strubbe, H. Vrielinck, R. Van Deun, D. Volkmer, V. Van Speybroeck, P. Van Der Voort
        "Synthesis, Structural Characterization and Catalytic Performance of a Vanadium-Based Metal-Organic Framework (COMOC-3)"
        Eur. J. Inorg. Chem. 2012, 2819-2827.
         

         

        S. Biswas, S. Couck, M. Grzywa, J. F. M. Denayer, D. Volkmer, P. Van Der Voort
        "Vanadium Analogues of Nonfunctionalized and Amino-Functionalized MOFs with MIL-101 Topology - Synthesis, Characterization and Gas Sorption Properties"
        Eur. J. Inorg. Chem. 2012, 2481-2486.
         

         

        M. Grzywa, D. Denysenko, J. Hanss, E.-W. Scheidt, W. Scherer, M. Weil, D. Volkmer
        "CuN6Jahn-Teller centers in coordination frameworks comprising fully condensed Kuratowski-type secondary building units: phase transitions and magneto-structural correlations"
        Dalton Trans. 2012, 41, 4239-4248.
         

         

        A. S. Dorcheh, D. Denysenko, D. Volkmer, W. Donner, M. Hirscher
        "Nobel gases and microporous frameworks; from intercation to application"
        Micropor. Mesopor. Mat. 2012, 162, 64-68.
         

         

        A. Soleimani-Dorcheh, R. E. Dinnebier, A. Kuc, O. Magdysyuk, F. Adams, D. Denysenko, T. Heine, D. Volkmer, W. Donner, M. Hirscher
        "Novel characterization of the adsorption sites in large pore metal-organic frameworks: combination of X-ray powder diffraction and thermal desorption spectroscopy"
        Phys. Chem. Chem. Phys. 2012, 14, 12892-12897.
         

         

        J. Teufel, H. Oh, M. Hirscher, M. Wahiduzzaman, L. Zhechkov, A. Kuc, T. Heine, D. Denysenko, D. Volkmer
        "MFU-4 - A Metal-Organic Framework for Highly Effective H2/D2 Separation"
        Adv. Mater. 2013, 4, 635-639.
         

         

        M. Grzywa, C. Gessner, D. Denysenko, B. Bredenkötter, F. Gschwind, K. Fromm, W. Nitek, E. Klemm, D. Volkmer
        "CFA-2 and CFA-3 (Coordination Framework Augsburg University-2 and -3); Novel MOFs Assembled from Trinuclear Cu(I)/Ag(I) Secondary Building Units and 3,3',5,5'-Tetraphenyl-bipyrazolate Ligands"
        Dalton Trans. 2013, 42, 6909-6921
         

         

        P. Schmieder, D. Denysenko, M. Grzywa, B. Baumgärtner, I. Senkovska, S. Kaskel, G. Sastre, L. van Wüllen, D. Volkmer
        "CFA-1: the first chiral metal-organic framework containing Kuratowski-type secondary building units"
        Dalton Trans. 2013, 42, 10786-10797.
         

         

        M. Grzywa, B. Bredenkötter, D. Denysenko, S. Spirkl, N. Wojciech, D. Volkmer
        "A Metallosupramolecular Octahedron Assembled from Twelve Cu(I) Metal Ions and Six 4,4'-(1,2-Phenylene)bis(3,5-dimethylpyrazol-1-ide) Ligands"
        Z. Anorg. Allg. Chem. 2013, 639, 1461-1471.
         

         

        J. Jelic, D. Denysenko, D. Volkmer, K. Reuter
        "Computational screening study towards redox-active metal-organic frameworks"
        New. J. Phys. 2013, 15, 115004.
         

         

        P. Sippel, D. Denysenko, A. Loidl, P. Lunkenheimer, G. Sastre, D. Volkmer
        "Dielectric Relaxation Processes, Electronic Structure, and Band Gap Engineering of MFU-4-type Metal-Organic Frameworks: Towards a Rational Design of Semiconducting Microporous Materials"
        Adv. Funct. Mater. 2014, DOI: 10.1002/adfm.201400083.
         

         

        D. Denysenko, M. Grzywa, J. Jelic, K. Reuter, D. Volkmer
        "Scorpionate-Type Coordination in MFU-4l Metal–Organic Frameworks: Small-Molecule Binding and Activation upon the Thermally Activated Formation of Open Metal Sites"
        Angew. Chem. 2014, 126, 5942-5946; Angew. Chem. Int. Ed. 2014, 53, 5832-5836.
         

         

        G. Sastre, J. van den Bergh, F. Kapteijn, D. Denysenko, D. Volkmer
        "Unveiling the mechanism of selective gate-driven diffusion of CO2 over N2 in MFU-4 metal-organic framework"
        Dalton Trans. 2014, 43, 9612-9619.
         
 
 

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