ABSTRACT
The synthesis and crystal structure of the perfluorinated metal-organic framework (MOF) CFA-14 (Coordination Framework Augsburg University-14), CoII2(tfpb)(OH)2 (H2-tfpb = 1,4-bis(3,5-bis(trifluoromethyl)-1H-pyrazole-4-yl)benzene) are described. The cobalt-containing MOF crystallizes in the tetragonal crystal system within the space group I41/acd (no. 142) and the unit cell parameters are as follows: a = 20.3213(11) Å, c = 12.4045(8) Å, V = 5122.5(6) Å3. CFA-14 features a porous two-fold interpenetrated 3-D microporous structure constructed from 1-D chains of cobalt(ii) ions expanding in the c-direction, bridged by OH- groups and tfpb2- ligands. The structure exhibits quadratic channels running along the c-axis. CFA-14 is fully characterized by synchrotron single crystal X-ray diffraction, thermogravimetric analysis, variable temperature powder X-ray diffraction, IR- and UV-Vis spectroscopy, photoluminescence and gas sorption measurements. Moreover, the magnetic properties of CFA-14 are examined via SQUID measurements.
ABSTRACT
The synthesis and crystal structure of the mixed-valent perfluorinated metal-organic framework (Me2NH2)[CFA-13] (Coordination Framework Augsburg University-13), (Me2NH2)[CuCu(tfpc)4] (H2-tfpc = 3,5-bis(trifluoromethyl)-1H-pyrazole-4-carboxylic acid) is described. The copper-containing MOF crystallizes in the monoclinic crystal system within the space group P21/n (no. 14) and the unit cell parameters are as follows: a = 22.3887(19), b = 13.6888(8), c = 21.1804(13) Å, ß = 90.495(3)°, V = 6491.0(8) Å3. (Me2NH2)[CFA-13] features a porous 3-D structure constructed from two types of secondary building units (SBUs). Besides novel trinuclear [Cu(pz)4]- coordination units, the network also exhibits Cu(ii) paddle-wheel SBUs. (Me2NH2)[CFA-13] is fully characterized by single crystal X-ray diffraction, thermogravimetric analysis, variable temperature powder X-ray diffraction, IR spectroscopy, photoluminescence, gas sorption measurements and pulse chemisorption experiments. M[CFA-13] (M = K+, Cs+) frameworks were prepared by postsynthetic exchange of interchannel dimethylammonium cations. Moreover, it was shown that CO molecules can be selectively bound at Cu(i) sites of [Cu(pz)4]- units, whereas Cu(ii) paddle-wheel units bind selectively NH3 molecules.
ABSTRACT
The cubic metal-organic framework MFU-4l ([Zn5Cl4(BTDD)3], H2-BTDD = bis(1H-1,2,3-triazolo[4,5-b],[4',5'-i])dibenzo[1,4]dioxin) featuring large pore apertures can be modified post-synthetically via partial or complete substitution of peripheral metal sites and chloride side-ligands, thus opening a route towards a large variety of functionalized MOFs. In this way, Ni-MFU-4l-nitrite (or Ni-MFU-4l-NO2) with an analytically determined chemical composition [Zn2.6Ni2.4(NO2)2.9Cl1.1(BTDD)3], containing accessible Ni-NO2 units, was prepared. Ni-MFU-4l-NO2 undergoes selective heterogeneous gas-phase reduction by carbon monoxide at 350 °C, leading to formation of Ni-NO units at the peripheral sites of the MFU-4l framework (Ni-MFU-4l-NO). The crystallinity and porosity of the MFU-4l framework are completely retained upon this transformation. The so-formed nickel nitrosyl complex, showing high thermal stability, readily reacts with nitrogen monoxide at room temperature, producing Ni-NO2 units and dinitrogen monoxide (N2O). Hence, the reaction of Ni-MFU-4l-NO2 with CO followed by NO represents a cyclic process with an overall stoichiometry 2NO + CO â N2O + CO2, in which the Ni-MFU-4l framework serves as a catalyst. It can be considered as a model process for the removal of highly toxic NO and CO gases, which are converted to non-toxic CO2 and N2O. Diffuse reflectance infrared Fourier transform spectroscopic studies show that at least 10 cycles can be repeated. The framework's reactivity drops down by ca. 50% after 10 cycles, which is most likely due to the accumulation of highly reactive NO2 and N2O4 contaminants. Therefore, further investigations on characterizing reaction intermediates should be done in order to improve the catalyst's performance. Our results confirm the potential of MFU-4l frameworks as selective single-site catalysts for heterogeneous gas-phase transformations and provide a motivation for further studies.
ABSTRACT
The syntheses and crystal structures of the fluorinated linker 1,4-bis(3,5-bis(trifluoromethyl)-1H-pyrazole-4-yl)benzene (H2-tfpb; 1) and the novel metal-organic framework family M[CFA-4] (Coordination Framework Augsburg University-4), M[Cu5(tfpb)3] (M = Cu(i), K, Cs, Ca(0.5)), are described. The ligand 1 is fully characterized by single crystal X-ray diffraction, photoluminescence-, NMR-, IR spectroscopy, and mass spectrometry. The copper(i)-containing MOF crystallizes in the hexagonal crystal system within the chiral space group P6322 (no. 182) and the unit cell parameters are as follows: a = 23.630(5) Å, c = 41.390(5) Å, V = 20 015(6) Å3. M[CFA-4] features a porous 3-D structure constructed from pentanuclear copper(i) secondary building units {Cu(pz)6}- (pz = pyrazolate). Cu(I)[CFA-4] is fully characterized by synchrotron single crystal X-ray diffraction, thermogravimetric analysis, variable temperature powder X-ray diffraction, IR spectroscopy, photoluminescence and gas sorption measurements. Moreover, thermal stability and gas sorption properties of K[CFA-4] and Cu(I)[CFA-4] are compared.
ABSTRACT
The production of pure deuterium and the removal of tritium from nuclear waste are the key challenges in separation of light isotopes. Presently, the technological methods are extremely energy- and cost-intensive. Here we report the capture of heavy hydrogen isotopes from hydrogen gas by selective adsorption at Cu(I) sites in a metal-organic framework. At the strongly binding Cu(I) sites (32 kJ mol-1) nuclear quantum effects result in higher adsorption enthalpies of heavier isotopes. The capture mechanism takes place most efficiently at temperatures above 80 K, when an isotope exchange allows the preferential adsorption of heavy isotopologues from the gas phase. Large difference in adsorption enthalpy of 2.5 kJ mol-1 between D2 and H2 results in D2-over-H2 selectivity of 11 at 100 K, to the best of our knowledge the largest value known to date. Combination of thermal desorption spectroscopy, Raman measurements, inelastic neutron scattering and first principles calculations for H2/D2 mixtures allows the prediction of selectivities for tritium-containing isotopologues.
ABSTRACT
The novel metal-organic framework CFA-8 (Coordination Framework Augsburg University-8), [Cu2(tqpt)], containing the organic linker H2-tqpt {H2-tqpt = 6,6,14,14-tetramethyl-6,14-dihydroquinoxalino[2,3-b]phenazinebis-triazole}, has been synthesized. Reaction of H2-tqpt and anhydrous CuCl2 in N,N-dimethylacetamide (DMA) yields CFA-8 as orange crystals with lenticular shape. This framework shows a reversible breathing effect and is robust upon solvent removal. It has been characterized by single-crystal and powder X-ray diffraction, TGA, IR spectroscopy and gas sorption measurements. CO adsorption isotherms show that Cu(i) sites in this framework are able to bind carbon monoxide forming a weak complex which has been additionally characterized by IR spectroscopy and synchrotron powder X-ray diffraction measurements.
ABSTRACT
In this work, we examine the use of metal-organic framework (MOF) systems as host materials for the investigation of glassy dynamics in confined geometry. We investigate the confinement of the molecular glass former glycerol in three MFU-type MOFs with different pore sizes (MFU stands for "Metal-Organic Framework Ulm-University") and study the dynamics of the confined liquid via dielectric spectroscopy. In accord with previous reports on confined glass formers, we find different degrees of deviations from bulk behavior depending on pore size, demonstrating that MOFs are well-suited host systems for confinement investigations.
