Dmytro Denysenko

MFU‐4 – A Metal‐Organic Framework for Highly Effective H2/D2 Separation

The metal-organic framework, MFU-4, possessing small cavities and apertures, is exploited for quantum sieving of hydrogen isotopes. Quantum mechanically, a molecule confined in a small cavity shows an increase in effective size depending on the particle mass, which leads to a faster deuterium adsorption from a H(2)/D(2) isotope mixture.

Scorpionate‐Type Coordination in MFU‐4l Metal–Organic Frameworks: Small‐Molecule Binding and Activation upon the Thermally Activated Formation of Open Metal Sites

Postsynthetic metal and ligand exchange is a versatile approach towards functionalized MFU-4l frameworks. Upon thermal treatment of MFU-4l formates, coordinatively strongly unsaturated metal centers, such as zinc(II) hydride or copper(I) species, are generated selectively. Cu(I)-MFU-4l prepared in this way was stable under ambient conditions and showed 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 DFT calculations. Moreover, Cu(I)-MFU-4l formed stable complexes with C2H4 and CO. These complexes were characterized by FTIR spectroscopy. The demonstrated hydride transfer to 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.

Capture of heavy hydrogen isotopes in a metal-organic framework with active Cu(I) sites

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.

Novel characterization of the adsorption sites in large pore metal-organic frameworks: combination of X-ray powder diffraction and thermal desorption spectroscopy.

The preferred adsorption sites of xenon in the recently synthesized metal-organic framework MFU-4l(arge) possessing a bimodal pore structure (with pore sizes of 12 Å and 18.6 Å) were studied via the combination of low temperature thermal desorption spectroscopy and in situ X-ray powder diffraction. The diffraction patterns were collected at 110 K and 150 K according to the temperature of the desorption maxima. The maximum entropy method was used to reconstruct the electron density distribution of the structure and to localize the adsorbed xenon using refined data of the Xe-filled and empty sample. First principles calculations revealed that Xe atoms exclusively occupy the Wyckoff 32f position at approximately 2/3 2/3 2/3 along the body diagonal of the cubic crystal structure. At 110 K, Xe atoms occupy all 32 f positions (8 atoms per pore) while at 150 K the occupancy descends to 25% (2 atoms per pore). No Xe occupation of the small pores is observed by neither experimental measurements nor theoretical studies.

CuN6 Jahn–Teller centers in coordination frameworks comprising fully condensed Kuratowski-type secondary building units: phase transitions and magneto-structural correlations

The metal-organic framework [Cu(ta)(2)] (Hta = 1H-1,2,3-triazole), containing Jahn-Teller active Cu(II) ions and 1,2,3-triazolate ligands, is prepared under solvothermal reaction conditions. The compound shows a reversible phase transition from the tetragonal crystal system (α-[Cu(ta)(2)]: space group I4(1)/amd (no. 141), a = 11.8447(7) Å, c = 18.9782(13) Å, V = 2662.6(3) Å(3)) to the cubic crystal system (β-[Cu(ta)(2)]: space group Fd3m (no. 227), a = 17.4416(15) Å, V = 5305.9(8) Å(3)) within the temperature range of 120-160 °C. Both [Cu(ta)(2)] polymorphs have identical bonding topologies that might be described as fully condensed Kuratowski-type pentanuclear secondary building units of local T(d) point group symmetry in which four Cu(II) ions occupy the vertices of an imaginary tetrahedron. α-[Cu(ta)(2)], as opposed to the high-temperature β-phase, shows a strong tetragonal Jahn-Teller distortion of CuN(6) coordination octahedra. The compounds are characterized by elemental and thermogravimetric analyses, single crystal and powder X-ray diffraction, FTIR-, UV-vis and fluorescence spectroscopy. Magnetic susceptibility investigations reveal two different Cu(II) sites at a ratio of 1 : 2, in agreement with the solid state structure of [Cu(ta)(2)]. At low temperatures the formation of antiferromagnetically coupled Cu(II) dimers is observed, leading to a spin frustration of roughly 1/3 of all magnetically active Cu(II) sites.

Computational screening study towards redox-active metal-organic frameworks

The metal-organic framework (MOF) MFU-4 l containing Co(II) centers and Cl− ligands has recently shown promising redox activity. Aiming for further improved MOF catalysts for oxidation processes employing molecular oxygen we present a density-functional theory (DFT) based computational screening approach to identify promising metal center and ligand combinations within the MFU-4 l structural family. Using the O2 binding energy as a descriptor for the redox property, we show that relative energetic trends in this descriptor can reliably be obtained at the hybrid functional DFT level and using small cluster (scorpionate-type complex) models. Within this efficient computational protocol we screen a range of metal center/ligand combinations and identify several candidate systems that offer more exothermic O2 binding than the original Co/Cl-based MFU-4 l framework.

Flexible chiral pyrazolate-based metal–organic framework containing saddle-type CuI4(pyrazolate)4 units

The syntheses and crystal structures of [CuI2(phbpz)]·MeOH (lp-CFA-9, lp = large-pore) and [CuI2(phbpz)] (np-CFA-9, np = narrow-pore; H2-phbpz = 3,3′,5,5′-tetraphenyl-1H,1′H-4,4′-bipyrazole) are described. The copper(I)-containing metal–organic framework (termed oordination ramework ugsburg University-9, lp-CFA-9) crystallizes in the trigonal crystal system, within the chiral space group P3221 (no. 154) and with the following unit cell parameters: a =18.2348(6), c = 16.3950(4) A, and V = 4721.1(2) A3. Lp-CFA-9 features a 3-D microporous framework structure of Cu4pz4 (pz = pyrazolate) SBUs with the D2d (= 2m) symmetry connected by single bonds creating one-dimensional channels expanding in the c-direction of the crystal lattice. The framework flexibility of CFA-9 has been demonstrated by single-crystal and powder X-ray analyses as well as by sorption measurements. CFA-9 exhibits weak binding of carbon monoxide on Cu(I) centers. The reactivity of CFA-9 towards oxidizing agents, such as H2O2, t-BuOOH and Br2 was also investigated. Additionally, CFA-9 shows luminescence upon exposure to UV radiation.

Magnetodielectric coupling in a non-perovskite metal–organic framework

Multiferroicity and magnetodielectric coupling in metal–organic frameworks (MOFs) are rare and so far restricted mainly to formate-based systems with a perovskite structure. In the course of this work we designed a tetragonal framework [Co(C16H15N5O2)], exhibiting spin-chains of Co2+ ions, which are bridged by an organic linker containing a dipolar nitrobenzene moiety. This compound shows relaxor-like ferroelectricity at 100 K, which is followed by the onset of complex magnetic order at 15 K, indicative of weak ferromagnetism. The clear anomaly of the dielectric constant at the magnetic ordering transition indicates magnetodielectric coupling, which is also confirmed by magnetic-field dependent dielectric measurements. Both weak ferromagnetism and magnetodielectric couplingprobably result from a significant Dzyaloshinskii–Moriya interaction, which cants the spin structure and locally breaks inversion symmetry. We document that the introduction of dipolar nitrobenzene as a building block into the crystal structure paves the way to designing new multiferroic and magnetodielectric MOFs.

Fast Surface Acoustic Wave-Based Sensors to Investigate the Kinetics of Gas Uptake in Ultra-Microporous Frameworks

Observation of the kinetics and measurement of the activation energies for gas diffusion in porous materials requires very fast and sensitive sensors. In this work, thin films of metal-organic frameworks (MOFs) with different pore sizes are grown on a surface acoustic wave (SAW) substrate, resulting in very sensitive and specific sensor systems for the detection of various gases at very short time scales. Using specially designed SAW delay lines for the detection, up to 200-nm-wide cubic MOF crystals were grown directly from a solution on the sensitive sensor chip area. One example, MFU-4, exhibits a smallest pore aperture of 2.5 Å and shows a highly sensitive and specific response to CO2, H2, He, NH3, and H2O. It is shown that such a MOF@SAW sensor responds within milliseconds to gas loading and its sensitivity reaches levels as low as 1 ppmv, currently only limited by the gas mixing system. This unique combination of sensitivity and fast response characteristics allows even for real-time investigations of the sorption kinetics during gas uptake and release. As is typical for SAW sensors, the production of the chips is very straightforward and inexpensive and-combined with the unique properties of the MOFs with their tunable pore sizes and adjustable internal surface properties-holds promise for different sensor applications.

New directions in gas sorption and separation with MOFs: general discussion

Matthew Addicoat, Thomas Bennett, Karena Chapman, Dmytro Denysenko, Mircea Dincă, Huan Doan, Timothy Easun, Mohamed Eddaoudi, Omar Farha, Laura Gagliardi, Frederik Haase, Amir Hajiahmadi Farmahini, Christopher Hendon, Miguel Jorge, Susumu Kitagawa, Carlo Lamberti, Jet-Sing M. Lee, Karen Leus, Jing Li, Wenbin Lin, Xiaowei Liu, Gareth Lloyd, Connie Lu, Shengqian Ma, Jeffrey Paulo H. Perez, Marco Ranocchiari, Nathaniel Rosi, Ivo Stassen, Valeska Ting, Monique van der Veen, Pascal Van Der Voort, Christophe M. L. Vande Velde, Dirk Volkmer, Simon Vornholt, Aron Walsh and Omar M. Yaghi