Jun.-Prof. Dr. Sebastian Henke
TU Dortmund University
- Defect Creation in Surface-Mounted Metal-Organic Framework Thin Films
Wang, Z. and Henke, S. and Paulus, M. and Welle, A. and Fan, Z. and Rodewald, K. and Rieger, B. and Fischer, R.A.
ACS Applied Materials and Interfaces 12 (2020)Defect engineering is a strategy for tailoring the properties of metal-organic frameworks (MOFs). Plenty of efforts have been devoted to study the defect chemistry and structures of bulk MOFs; however, the reported example of a defect-engineered surface-mounted MOF (SURMOF) thin film is rare. In this work, defects were incorporated in SURMOF thin films by using defect-generating linkers and taking advantage of the liquid-phase stepwise epitaxial layer-by-layer growth (LBL). Two methods based on the LBL, named mixing method and alternating method, are proposed for incorporating defects in the prototypical SURMOF HKUST-1 by partially substituting the parent H3btc (benzene-1,3,5-tricarboxylic acid) linker with a set of defect-generating linkers H2ip (isophthalic acid), H2OH-ip (5-hydroxyisophthalic acid), and H2pydc (3,5-pyridinedicarboxylic acid). The crystallinity and phase purity of the obtained "defected" SURMOFs were confirmed by X-ray diffraction, infrared reflection absorption spectroscopy, and Raman spectroscopy. The incorporation of the defect-generating linkers and the types of induced defects were characterized by ultraviolet-visible spectroscopy, time-of-flight secondary ion mass spectrometry, methanol adsorption, scanning electron microscopy, and 1H nuclear magnetic resonance spectroscopy (after digestion of the samples). These two methods provide avenues for controlling the defect formation in MOF thin films. © 2019 American Chemical Society.
view abstract 10.1021/acsami.9b18672
- Photochemical Approach to the Cyclohepta[b]indole Scaffold by Annulative Two-Carbon Ring-Expansion
Tymann, D.C. and Benedix, L. and Iovkova, L. and Pallach, R. and Henke, S. and Tymann, D. and Hiersemann, M.
Chemistry - A European Journal 26 (2020)We report on the implementation of the concept of a photochemically elicited two-carbon homologation of a π-donor–π-acceptor substituted chromophore by triple-bond insertion. Implementing a phenyl connector between the slide-in module and the chromophore enabled the synthesis of cylohepta[b]indole-type building blocks by a metal-free annulative one-pot two-carbon ring expansion of the five-membered chromophore. Post-irradiative structural elaboration provided founding members of the indolo[2,3-d]tropone family of compounds. Control experiments in combination with computational chemistry on this multibond reorganization process founded the basis for a mechanistic hypothesis. © 2020 The Authors. Published by Wiley-VCH GmbH
view abstract 10.1002/chem.202002581
- The synergistic effect of heterostructured dissimilar metal-organic framework thin films on adsorption properties
Wang, Z. and Wannapaiboon, S. and Henke, S. and Paulus, M. and Rodewald, K. and Rieger, B. and Fischer, R.A.
Journal of Materials Chemistry A 8 (2020)A metal-organic framework (MOF) heterostructured thin film of 3D Cu3btc2 on 2D SURMOF-2 was developed for VOC adsorption. This heterostructured thin film shows higher VOC storage capacity than the two components and a counter-intuitive uptrend of adsorption ability (dimensionless normalized storage capacity) with increasing the size of VOCs. This journal is © The Royal Society of Chemistry.
view abstract 10.1039/c9ta10264g
- Control of Metal–Organic Framework Crystallization by Metastable Intermediate Pre-equilibrium Species
Yeung, H.H.M. and Sapnik, A.F. and Massingberd-Mundy, F. and Gaultois, M.W. and Wu, Y. and Fraser, D.A.X. and Henke, S. and Pallach, R. and Heidenreich, N. and Magdysyuk, O.V. and Vo, N.T. and Goodwin, A.L.
Angewandte Chemie - International Edition 58 (2019)There is an increasing amount of interest in metal–organic frameworks (MOFs) for a variety of applications, from gas sensing and separations to electronics and catalysis. However, the mechanisms by which they crystallize remain poorly understood. Herein, an important new insight into MOF formation is reported. It is shown that, prior to network assembly, crystallization intermediates in the canonical ZIF-8 system exist in a dynamic pre-equilibrium, which depends on the reactant concentrations and the progress of reaction. Concentration can, therefore, be used as a synthetic handle to directly control particle size, with potential implications for industrial scale-up and gas sorption applications. These findings enable the rationalization of apparent contradictions between previous studies of ZIF-8 and opens up new opportunities for the control of crystallization in network solids more generally. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/anie.201810039
- Flexibility control in alkyl ether-functionalized pillared-layered MOFs by a Cu/Zn mixed metal approach
Schneemann, A. and Rudolf, R. and Baxter, S.J. and Vervoorts, P. and Hante, I. and Khaletskaya, K. and Henke, S. and Kieslich, G. and Fischer, R.A.
Dalton Transactions 48 (2019)Flexible metal-organic frameworks (MOFs) exhibit large potential as next-generation materials in areas such as gas sensing, gas separation and mechanical damping. By using a mixed metal approach, we report how the stimuli reponsive phase transition of flexible pillared-layered MOFs can be tuned over a wide range. Different Cu 2+ to Zn 2+ metal ratios are incorporated into the materials by using a simple solvothermal approach. The properties of the obtained materials are probed by differential scanning calorimetry and CO 2 sorption measurements, revealing stimuli responsive behaviour as a function of metal ratio. Pair distribution functions derived from X-ray total scattering experiments suggest a distortion of the M 2 paddlewheel as a function of the Cu content. We rationalize these phenomena by the different distortion energies of Cu 2+ and Zn 2+ ions to deviate from the square pyramidal structure of the relaxed paddlewheel node. Our work follows on from the large interest in tuning and understanding the materials properties of flexible MOFs, highlighting the large number of parameters that can be used for the targeted manipulation and design of properties of these fascinating materials. © 2019 The Royal Society of Chemistry.
view abstract 10.1039/c9dt01105f
- Meltable Mixed-Linker Zeolitic Imidazolate Frameworks and Their Microporous Glasses: From Melting Point Engineering to Selective Hydrocarbon Sorption
Frentzel-Beyme, L. and Kloß, M. and Kolodzeiski, P. and Pallach, R. and Henke, S.
Journal of the American Chemical Society 141 (2019)Porous glasses from metal-organic frameworks (MOFs) represent a new class of functional inorganic-organic materials, which have been proposed for applications ranging from solid electrolytes to radioactive waste storage. So far, just a few zeolitic imidazolate frameworks (ZIFs), a subset of MOFs, have been reported to melt and the structural and compositional requirements for MOF melting and glass formation are poorly understood. Here, we show how the melting point of the prototypical ZIF-4/ZIF-62(M) frameworks (composition M(im)2-x(bim)x; M2+ = Co2+, Zn2+ im- = imidazolate; bim- = benzimidazolate) can be controlled systematically by adjusting the molar ratio of the two imidazolate-type linkers im- and bim-. By covering the entire range from x = 0 to 0.35, we unveil a delicate transition from ZIF materials showing sequential amorphization/recrystallization to derivatives exhibiting coherent melting and a liquid phase that is stable over a large temperature window. The melting point of this ZIF system is a direct function of x and can be lowered from ca. 430 °C to only 370 °C, by far the lowest melting point reported for a three-dimensional porous MOF. On the basis of our results, we postulate compositional requirements for ZIF melting and glass formation, which may guide the search for other meltable ZIFs. Moreover, gas physisorption experiments establish that the ZIF glasses adsorb technologically relevant C3 and C4 hydrocarbons. Importantly, the adsorption kinetics are much faster for propylene compared to propane and are also dependent on the im-:bim- ratio, thus demonstrating the potential of these ZIF glasses for applications in gas separation. © 2019 American Chemical Society.
view abstract 10.1021/jacs.9b05558
- Porous purple glass-a cobalt imidazolate glass with accessible porosity from a meltable cobalt imidazolate framework
Frentzel-Beyme, L. and Kloß, M. and Pallach, R. and Salamon, S. and Moldenhauer, H. and Landers, J. and Wende, H. and Debus, J. and Henke, S.
Journal of Materials Chemistry A 7 (2019)We report the first microporous cobalt imidazolate glass obtained from a meltable cobalt-based zeolitic imidazolate framework, ZIF-62(Co). Crystalline ZIF-62(Co) is constructed from Co2+ cations and two different imidazolate-type linkers, namely conventional imidazolate and benzimidazolate. The microporous framework melts at ∼430 °C and converts into a glass upon cooling to room temperature. X-Ray total scattering and Raman spectroscopy reveal that the local structure of the glass and the crystalline parent material are very similar. Magnetic measurements and X-ray diffraction uncover that ZIF-62(Co) partially decomposes upon melting and glass formation resulting in the reduction of ∼3% of the Co2+ ions to metallic cobalt. Most importantly, the ZIF glass retains almost 50% of the porosity of crystalline ZIF-62(Co). Our results pave the way for the realisation of metal-organic framework glasses containing open shell metal ions, as well as the application of these porous glasses in gas separation, energy storage and catalysis. © 2019 The Royal Society of Chemistry.
view abstract 10.1039/c8ta08016j
- Redetermination of the crystal structure of tetrammineplatinum(II) dichloride – A microporous hydrogen-bonded 3D network exhibiting a temperature-dependent order-disorder phase transition
Brieger, L. and Henke, S. and Said Mohamed, A. and Jourdain, I. and Knorr, M. and Strohmann, C.
Inorganica Chimica Acta 495 (2019)The title compound [Pt(NH3)4]Cl2 (1), prepared by reaction of (NH4)2[PtCl4] with an excess of NH3 in aqueous solution, was crystallized from water and its structure redetermined by single-crystal X-ray diffraction at four different temperatures in the range from 273 K down to 100 K. 1 is composed of square-planar [Pt(NH3)4]2+ complex cations and Cl− anions and crystallizes in the tetragonal crystal system. Remarkably, the solid state structure is porous (approx. 20% of the crystal volume is void space) and features one-dimensional open channels of a diameter of ∼3–4 Å. Unexpectedly, these channels are free of solvent molecules, although the crystals were obtained from aqueous solutions. N[sbnd]H⋯Cl hydrogen bonding interactions between the square-planar [Pt(NH3)4]2+ dications and the Cl− counter ions result in a three-dimensional hydrogen bonding network that stabilizes the porous solid state structure. The hydrogen atoms of the ammonia ligands and their corresponding N[sbnd]H⋯Cl hydrogen bonds are localized at low temperature (space group I4/mmm) but disorder dynamically above 173 K (space group P4/mmm). The order-disorder transition is accompanied by significant changes in the Pt–Pt stacking distances and a fourfold reduction of the unit cell volume. © 2019 Elsevier B.V.
view abstract 10.1016/j.ica.2019.119002
- Different Breathing Mechanisms in Flexible Pillared-Layered Metal-Organic Frameworks: Impact of the Metal Center
Schneemann, A. and Vervoorts, P. and Hante, I. and Tu, M. and Wannapaiboon, S. and Sternemann, C. and Paulus, M. and Wieland, D.C.F. and Henke, S. and Fischer, R.A.
Chemistry of Materials 30 (2018)The pillared-layered metal-organic framework compounds M2(BME-bdc)2(dabco) (M2+ = Zn2+, Co2+, Ni2+, Cu2+; BME-bdc2- = 2,5-bis(2-methoxyethoxy)-1,4-benzenedicarboxylate; dabco = diazabicyclo[2.2.2]octane) exhibit structural flexibility and undergo guest and temperature-induced reversible phase transitions between a narrow pore (np) and a large pore (lp) form. These transitions were analyzed in detail by powder X-ray diffraction ex and in situ, isothermal gas adsorption measurements and differential scanning calorimetry. The threshold parameters (gas pressure or temperature), the magnitude of the phase transitions (volume change) as well as their transition enthalpies are strikingly dependent on the chosen metal cation M2+. This observation is assigned to the different electronic structures and ligand field effects on the coordination bonds. Accordingly, in situ powder X-ray diffraction measurements as a function of CO2 pressure reveal different mechanisms for the np to lp phase transition during CO2 adsorption. © 2018 American Chemical Society.
view abstract 10.1021/acs.chemmater.7b05052
- Fabrication of zinc-dicarboxylate- and zinc-pyrazolate-carboxylate-framework thin films through vapour-solid deposition
Medishetty, R. and Zhang, Z. and Sadlo, A. and Cwik, S. and Peeters, D. and Henke, S. and Mangayarkarasi, N. and Devi, A.
Dalton Transactions 47 (2018)Fabrication of three-dimensional metal-organic framework (MOF) thin films has been investigated for the first time through the conversion of a ZnO layer via a pure vapour-solid deposition reaction at ambient pressure. The fabrication of MOF thin films with a dicarboxylate linker, (DMA)2[Zn3(bdc)4] (1) (bdc = 1,4-benzenedicarboxylate), and a carboxy-pyrazolate linker, [Zn4O(dmcapz)6] (2) (dmcapz = 3,5-dimethyl-4-carboxypyrazole), involves the deposition of the linker and/or the preparation of a composite film preliminarily and its subsequent conversion into a MOF film using closed cell thermal treatment. Furthermore, it was possible to isolate thin films with a MOF-5 isotype structure grown along the  direction, using a carboxy-pyrazolate linker. This was achieved just by the direct reaction of the ZnO film and the organic linker vapors, employing a simple route that demonstrates the feasibility of MOF thin film fabrication using inexpensive routes at ambient pressure. © 2018 The Royal Society of Chemistry.
view abstract 10.1039/c8dt00352a
- Pore closure in zeolitic imidazolate frameworks under mechanical pressure
Henke, S. and Wharmby, M.T. and Kieslich, G. and Hante, I. and Schneemann, A. and Wu, Y. and Daisenberger, D. and Cheetham, A.K.
Chemical Science 9 (2018)We investigate the pressure-dependent mechanical behaviour of the zeolitic imidazolate framework ZIF-4 (M(im)2; M2+ = Co2+ or Zn2+, im- = imidazolate) with high pressure, synchrotron powder X-ray diffraction and mercury intrusion measurements. A displacive phase transition from a highly compressible open pore (op) phase with continuous porosity (space group Pbca, bulk modulus ∼1.4 GPa) to a closed pore (cp) phase with inaccessible porosity (space group P21/c, bulk modulus ∼3.3-4.9 GPa) is triggered by the application of mechanical pressure. Over the course of the transitions, both ZIF-4 materials contract by about 20% in volume. However, the threshold pressure, the reversibility and the immediate repeatability of the phase transition depend on the metal cation. ZIF-4(Zn) undergoes the op-cp phase transition at a hydrostatic mechanical pressure of only 28 MPa, while ZIF-4(Co) requires about 50 MPa to initiate the transition. Interestingly, ZIF-4(Co) fully returns to the op phase after decompression, whereas ZIF-4(Zn) remains in the cp phase after pressure release and requires subsequent heating to switch back to the op phase. These variations in high pressure behaviour can be rationalised on the basis of the different electron configurations of the respective M2+ ions (3d10 for Zn2+ and 3d7 for Co2+). Our results present the first examples of op-cp phase transitions (i.e. breathing transitions) of ZIFs driven by mechanical pressure and suggest potential applications of these functional materials as shock absorbers, nanodampers, or in mechanocalorics. © The Royal Society of Chemistry 2018.
view abstract 10.1039/c7sc04952h
- A New Class of Lasing Materials: Intrinsic Stimulated Emission from Nonlinear Optically Active Metal-Organic Frameworks
Medishetty, R. and Nalla, V. and Nemec, L. and Henke, S. and Mayer, D. and Sun, H. and Reuter, K. and Fischer, R.A.
Advanced Materials (2017)
view abstract 10.1002/adma.201605637
- Functional conductive nanomaterials: Via polymerisation in nano-channels: PEDOT in a MOF
Wang, T. and Farajollahi, M. and Henke, S. and Zhu, T. and Bajpe, S.R. and Sun, S. and Barnard, J.S. and Lee, J.S. and Madden, J.D.W. and Cheetham, A.K. and Smoukov, S.K.
Materials Horizons 4 (2017)Reactions inside the pores of metal-organic frameworks (MOFs) offer potential for controlling polymer structures with regularity to sub-nanometre scales. We report a wet-chemistry route to poly-3,4-ethylenedioxythiophene (PEDOT)-MOF composites. After a two-step removal of the MOF template we obtain unique and stable macroscale structures of this conductive polymer with some nanoscale regularity. © 2017 The Royal Society of Chemistry.
view abstract 10.1039/c6mh00230g
- Linker functionalisation triggers an alternative 3D-topology for Zn-isophthalate-4,4′-bipyridine frameworks
Schneemann, A. and Rudolf, R. and Henke, S. and Takahashi, Y. and Banh, H. and Hante, I. and Schneider, C. and Noro, S.-I. and Fischer, R.A.
Dalton Transactions 46 (2017)A series of four Zn2+ metal-organic frameworks containing functionalised isophthalate linkers and 4,4′-bipyridine pillars have been prepared and characterised. Isophthalates which contain -OC3H2n+1 alkoxy side chains (with n = 1, 2 or 3) form frameworks with a 3D pillared-layer topology instead of the typical 2D layer topology of the renowned coordination polymers with an interdigitated structure (CIDs), which is found for shorter -OC2H5 side chains. The gas adsorption properties of the materials were analysed using N2, CO2 and O2 adsorption measurements at low temperatures. © 2017 The Royal Society of Chemistry.
view abstract 10.1039/c7dt01195d
- Multi-Photon Absorption in Metal–Organic Frameworks
Medishetty, R. and Nemec, L. and Nalla, V. and Henke, S. and Samoć, M. and Reuter, K. and Fischer, R.A.
Angewandte Chemie - International Edition 56 (2017)Multi-photon absorption (MPA) is among the most prominent nonlinear optical (NLO) effects and has applications, for example in telecommunications, defense, photonics, and bio-medicines. Established MPA materials include dyes, quantum dots, organometallics and conjugated polymers, most often dispersed in solution. We demonstrate how metal–organic frameworks (MOFs), a novel NLO solid-state materials class, can be designed for exceptionally strong MPA behavior. MOFs consisting of zirconium- and hafnium-oxo-clusters and featuring a chromophore linker based on the tetraphenylethene (TPE) molecule exhibit record high two-photon absorption (2PA) cross-section values, up to 3600 GM. The unique modular building-block principle of MOFs allows enhancing and optimizing their MPA properties in a theory-guided approach by combining tailored charge polarization, conformational strain, three-dimensional arrangement, and alignment of the chromophore linkers in the crystal. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201706492
- Coordination environments and π-conjugation in dense lithium coordination polymers
Tominaka, S. and Yeung, H.H.-M. and Henke, S. and Cheetham, A.K.
CrystEngComm 18 (2016)The understanding of lithium-oxygen coordination systems is important for making better lithium conductors as well as active materials for lithium ion batteries. Here, we report a systematic investigation on coordination environments in lithium coordination polymers (LCPs) through the syntheses and analyses of six new crystals composed of lithium ions and anthraquinone (aq) derivative anions, where the negative charges are distributed in π-conjugation systems. Their structures were determined by single-crystal X-ray diffraction to be (1) [Li2(23dcaq)(H2O)] in space group P21/c, (2) [Li(23dcaqH)] in P21/c, (3) [Li2(15dhaq)(H2O)2] in P21/c, (4) [Li2(14dhaq)(H2O)2] in Pnma, (5) [Li(14dhaqH)(H2O)] in P212121 and (6) [Li(14hnaq)(H2O)] in P212121 (23dcaq2- = 2,3-dicarboxy-aq, 14dhaq2- = 1,4-dihydroxy-aq, 15dhaq2- = 1,5-dihydroxy-aq and 14hnaq- = 1-hydroxy-4-nitro-aq). Through the comprehensive structure analysis of these materials as well as other LCPs, we found that when considering the longest C-O bond in the π-conjugation system of an anionic organic molecule and its coordination to a Li ion, there is a weak inverse relationship between the C-O and Li-O bond lengths. In addition, despite exhibiting optical band edges below 2 eV and 1D π-stacking connectivity, conductivity measurements on single crystals of 1-6 confirmed that they are all electronic insulators. We rationalize this finding on the basis of π-orbital delocalization, which is more restricted in the aq-based LCPs compared to known semiconducting hybrid materials. © 2016 The Royal Society of Chemistry.
view abstract 10.1039/c5ce01658d
- Disorder and polymorphism in Cu(II)-polyoxometalate complexes: [Cu1.5(H2O)7.5PW12O40]·4.75H2O,: cis - & trans -[Cu2(H2O)10SiW12O40]·6H2O
Bajpe, S.R. and Henke, S. and Lee, J.-H. and Bristowe, P.D. and Cheetham, A.K.
CrystEngComm 18 (2016)Three highly crystalline Cu(ii)-polyoxometalate (POM) complexes, [Cu1.5(H2O)7.5PW12O40]·4.75H2O and cis- and trans-[Cu2(H2O)10SiW12O40]·6H2O, were successfully synthesized and characterized by single crystal and powder X-ray diffraction as well as thermogravimetric analysis. All complexes feature octahedrally coordinated, Jahn-Teller-distorted CuII centres, which are coordinated by one terminal oxygen atom of the POM anion and five water molecules. The crystal structure of [Cu1.5(H2O)7.5PW12O40]·4.75H2O, reveals four-fold disorder at one of the two Cu-sites, whereas [Cu2(H2O)10SiW12O40]·6H2O crystallizes in two fully-ordered polymorphic forms: a monoclinic structure containing an angled cis configuration of the Cu-POM-Cu molecule and a triclinic structure containing a linear trans configuration. Density functional theory (DFT) calculations show that the cis polymorph of [Cu2(H2O)10SiW12O40]·6H2O is more stable than the trans form by about 30 kJ mol-1. © The Royal Society of Chemistry 2016.
view abstract 10.1039/c5ce02088c
- In-situ observation of successive crystallizations and metastable intermediates in the formation of metal-organic frameworks
Yeung, H.H.-M. and Wu, Y. and Henke, S. and Cheetham, A.K. and O'Hare, D. and Walton, R.I.
Angewandte Chemie - International Edition 55 (2016)Understanding the driving forces controlling crystallization is essential for the efficient synthesis and design of new materials, particularly metal-organic frameworks (MOFs), where mild solvothermal synthesis often allows access to various phases from the same reagents. Using high-energy in situ synchrotron X-ray powder diffraction, we monitor the crystallization of lithium tartrate MOFs, observing the successive crystallization and dissolution of three competing phases in one reaction. By determining rate constants and activation energies, we fully quantify the reaction energy landscape, gaining important predictive power for the choice of reaction conditions. Different reaction rates are explained by the structural relationships between the products and the reactants; larger changes in conformation result in higher activation energies. The methods we demonstrate can easily be applied to other materials, opening the door to a greater understanding of crystallization in general. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201508763
- Liquid exfoliation of alkyl-ether functionalised layered metal-organic frameworks to nanosheets
Foster, J.A. and Henke, S. and Schneemann, A. and Fischer, R.A. and Cheetham, A.K.
Chemical Communications 52 (2016)We report the synthesis of a 2D-layered metal-organic framework incorporating weakly interacting chains designed to aid exfoliation of the layers into nanosheets. Dispersion of the nanosheets exposes labile metal-sites which are shown to exchange solvent molecules allowing the nanosheets to act as sensors in suspension. © 2016 The Royal Society of Chemistry.
view abstract 10.1039/c6cc05154e
- Mixed-linker solid solutions of functionalized pillared-layer MOFs - Adjusting structural flexibility, gas sorption, and thermal responsiveness
Schwedler, I. and Henke, S. and Wharmby, M.T. and Bajpe, S.R. and Cheetham, A.K. and Fischer, R.A.
Dalton Transactions 45 (2016)Flexible metal-organic frameworks (MOFs) can undergo fascinating structural transitions triggered by external stimuli, such as adsorption/desorption of specific guest molecules or temperature changes. In this detailed study we investigate the potentials and limitations of tuning framework flexibility systematically by exploiting the powerful concept of mixed-linker solid solutions. We chose the prototypical family of functionalized pillared-layer MOFs of the general type Zn2(fu1-bdc)2x(fu2-bdc)2-2xdabco (with x = 1.00, 0.75, 0.50, 0.25 and 0.00; fu-bdc = 2,5-dialkoxy-1,4-benzenedicarboxylate with varying alkoxy chain length, dabco = 1,4-diazabicyclo[2.2.2]octane) and examined their guest responsive, as well as intrinsic temperature dependent structural flexibility by X-ray diffraction, gas physisorption and calorimetric measurements. The ratio of the different fu-bdc linkers can be adjusted freely, offering opportunity for a targeted design of these functional materials by modulating their key features, such as magnitude of framework contraction upon guest removal, breathing behaviour upon CO2 adsorption/desorption, thermoresponsive phase behaviour, and their general thermal expansivity, by the careful choice of fu-bdc linkers and their combination. © The Royal Society of Chemistry 2016.
view abstract 10.1039/c5dt03825a
- Systematic molecular engineering of Zn-ketoiminates for application as precursors in atomic layer depositions of zinc oxide
O'Donoghue, R. and Peeters, D. and Rogalla, D. and Becker, H.-W. and Rechmann, J. and Henke, S. and Winter, M. and Devi, A.
Dalton Transactions 45 (2016)Molecular engineering of seven closely related zinc ketoiminates, namely, [Zn(dapki)2], [Zn(daeki)2], [Zn(epki)2], [Zn(eeki)2], [Zn(mpki)2], [Zn(meki)2], and [Zn(npki)2], leads to the optimisation of precursor thermal properties in terms of volatilisation rate, onset of volatilisation, reactivity and thermal stability. The influence of functional groups at the imine side chain of the ligands on the precursor properties is studied with regard to their viability as precursors for atomic layer deposition (ALD) of ZnO. The synthesis of [Zn(eeki)2], [Zn(epki)2] and [Zn(dapki)2] and the crystal structures of [Zn(mpki)2], [Zn(eeki)2], [Zn(dapki)2] and [Zn(npki)2] are presented. From the investigation of the physico-chemical characteristics, it was inferred that all compounds are monomeric, volatile and exhibit high thermal stability, all of which make them promising ALD precursors. Compound [Zn(eeki)2] is in terms of thermal properties the most promising Zn-ketoiminate. It is reactive towards water, possesses a melting point of 39 °C, is stable up to 24 days at 220 °C and has an extended volatilisation rate compared to the literature known Zn-ketoiminates. It demonstrated self-saturated, water assisted growth of zinc oxide (ZnO) with growth rates in the order of 1.3 Å per cycle. Moreover, it displayed a broad temperature window from TDep = 175-300 °C and is the first report of a stable high temperature (>200 °C) ALD process for ZnO returning highly promising growth rates. © 2016 The Royal Society of Chemistry.
view abstract 10.1039/c6dt03571j
- Time-Resolved InSitu X-ray Diffraction Reveals Metal-Dependent Metal-Organic Framework Formation
Wu, Y. and Henke, S. and Kieslich, G. and Schwedler, I. and Yang, M. S. and Fraser, D. A. X. and O'Hare, D.
Angewandte Chemie-international Edition 55 (2016)Versatility in metal substitution is one of the key aspects of metal-organic framework (MOF) chemistry, allowing properties to be tuned in a rational way. As a result, it important to understand why MOF syntheses involving different metals arrive at or fail to produce the same topological outcome. Frequently, conditions are tuned by trial-and-error to make MOFs with different metal species. We ask: is it possible to adjust synthetic conditions in a systematic way in order to design routes to desired phases? We have used insitu X-ray powder diffraction to study the solvothermal formation of isostructural M-2(bdc)(2)dabco (M=Zn, Co, Ni) pillared-paddlewheel MOFs in real time. The metal ion strongly influences both kinetics and intermediates observed, leading in some cases to multiphase reaction profiles of unprecedented complexity. The standard models used for MOF crystallization break down in these cases; we show that a simple kinetic model describes the data and provides important chemical insights on phase selection.
view abstract 10.1002/anie.201608463
- Transition metal coordination complexes of chrysazin
Beldon, P.J. and Henke, S. and Monserrat, B. and Tominaka, S. and Stock, N. and Cheetham, A.K.
CrystEngComm 18 (2016)Eleven novel coordination compounds, composed of chrysazin (1,8-dihydroxyanthraquinone) and different first-row transition metals (Fe, Co, Ni, Cu), were synthesised and the structures determined by single-crystal X-ray diffraction. The synthetic trends were investigated using high-throughput synthesis under systematic variation of concentration and reagent stoichiometry: for complexes containing Co, Ni or Cu crystallisation was improved by low ligand:metal ratios, while the effect of concentration depended on the metal used. The compounds crystallise as discrete clusters, apart from two, which contain long Cu-O bonds which may allow the two compounds to be considered one-dimensional coordination polymers. One of these compounds shows a distance between aryl rings of less than 3.26 Å, which is shorter than that in graphite, suggesting applications as an organic-inorganic semiconductor. The compound was found to be insulating by single-crystal and powder AC-impedance measurements, and this result is discussed with reference to the electronic structure calculated using density-functional theory. © The Royal Society of Chemistry 2016.
view abstract 10.1039/c5ce00792e
- Tuneable mechanical and dynamical properties in the ferroelectric perovskite solid solution [NH3NH2]1-x[NH3OH]xZn(HCOO)3
Kieslich, G. and Kumagai, S. and Forse, A.C. and Sun, S. and Henke, S. and Yamashita, M. and Grey, C.P. and Cheetham, A.K.
Chemical Science 7 (2016)We report how mechanical and dynamical properties in formate-based perovskites can be manipulated by the preparation of an A-site solid-solution. In the series [NH3NH2]1-x[NH3OH]xZn(HCOO)3 with xmax = 0.48, the substitution of [NH3NH2]+ by [NH3OH]+ is accompanied by a series of complex changes in crystal chemistry which are analysed using PXRD, SCXRD, 1H solid state NMR, DSC and nanoindentation. NMR shows increased motion of [NH3NH2]+ in [NH3NH2]0.52[NH3OH]0.48Zn(HCOO)3, which results in a shift of the ferroelectric-to-paraelectric phase transition temperature from Tc = 352 K (x = 0) to Tc = 324 K (x = 0.48). Additionally, the loss of hydrogen bonds directly influences the mechanical response of the framework; the elastic moduli and hardnesses decrease by around 25% from E110 = 24.6 GPa and H110 = 1.25 GPa for x = 0, to E110 = 19.0 GPa and H110 = 0.97 GPa for x = 0.48. Our results give an in-depth insight into the crystal chemistry of ABX3 formate perovskites and highlight the important role of hydrogen bonding and dynamics. © 2016 The Royal Society of Chemistry.
view abstract 10.1039/c6sc01247g
- Characteristics of flexibility in metal-organic framework solid solutions of composition [Zn2(BME-bdc)x(DB-bdc)2-xdabco]n: In situ powder X-ray diffraction, in situ NMR spectroscopy, and molecular dynamics simulations
Bon, V. and Pallmann, J. and Eisbein, E. and Hoffmann, H.C. and Senkovska, I. and Schwedler, I. and Schneemann, A. and Henke, S. and Wallacher, D. and Fischer, R.A. and Seifert, G. and Brunner, E. and Kaskel, S.
Microporous and Mesoporous Materials 216 (2015)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. © 2015 Elsevier Inc.
view abstract 10.1016/j.micromeso.2015.02.042
- Extreme flexibility in a zeolitic imidazolate framework: Porous to dense phase transition in desolvated ZIF-4
Wharmby, M.T. and Henke, S. and Bennett, T.D. and Bajpe, S.R. and Schwedler, I. and Thompson, S.P. and Gozzo, F. and Simoncic, P. and Mellot-Draznieks, C. and Tao, H. and Yue, Y. and Cheetham, A.K.
Angewandte Chemie - International Edition 54 (2015)Abstract Desolvated zeolitic imidazolate framework ZIF-4(Zn) undergoes a discontinuous porous to dense phase transition on cooling through 140 K, with a 23% contraction in unit cell volume. The structure of the non-porous, low temperature phase was determined from synchrotron X-ray powder diffraction data and its density was found to be slightly less than that of the densest ZIF phase, ZIF-zni. The mechanism of the phase transition involves a cooperative rotation of imidazolate linkers resulting in isotropic framework contraction and pore space minimization. DFT calculations established the energy of the new structure relative to those of the room temperature phase and ZIF-zni, while DSC measurements indicate the entropic stabilization of the porous room temperature phase at temperatures above 140 K. ZIF-4(Zn) undergoes a porous to non-porous transition on cooling from the high-temperature (HT) to low-temperature (LT) phase. The nature of this transition is elucidated by a combined approach of structure solution from powder diffraction, DSC measurement, and DFT calculations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201410167
- Hybrid glasses from strong and fragile metal-organic framework liquids
Bennett, T.D. and Tan, J.-C. and Yue, Y. and Baxter, E. and Ducati, C. and Terrill, N.J. and Yeung, H.H.-M. and Zhou, Z. and Chen, W. and Henke, S. and Cheetham, A.K. and Greaves, G.N.
Nature Communications 6 (2015)Hybrid glasses connect the emerging field of metal-organic frameworks (MOFs) with the glass formation, amorphization and melting processes of these chemically versatile systems. Though inorganic zeolites collapse around the glass transition and melt at higher temperatures, the relationship between amorphization and melting has so far not been investigated. Here we show how heating MOFs of zeolitic topology first results in a low density 'perfect' glass, similar to those formed in ice, silicon and disaccharides. This order-order transition leads to a super-strong liquid of low fragility that dynamically controls collapse, before a subsequent order-disorder transition, which creates a more fragile high-density liquid. After crystallization to a dense phase, which can be remelted, subsequent quenching results in a bulk glass, virtually identical to the high-density phase. We provide evidence that the wide-ranging melting temperatures of zeolitic MOFs are related to their network topologies and opens up the possibility of 'melt-casting' MOF glasses. © 2015 Macmillan Publishers Limited. All rights reserved.
view abstract 10.1038/ncomms9079
- Influence of Solvent-Like Sidechains on the Adsorption of Light Hydrocarbons in Metal-Organic Frameworks
Schneemann, A. and Bloch, E.D. and Henke, S. and Llewellyn, P.L. and Long, J.R. and Fischer, R.A.
Chemistry - A European Journal 21 (2015)A variety of strategies have been developed to adsorb and separate light hydrocarbons in metal-organic frameworks. Here, we present a new approach in which the pores of a framework are lined with four different C3 sidechains that feature various degrees of branching and saturation. These pendant groups, which essentially mimic a low-density solvent with restricted degrees of freedom, offer tunable control of dispersive host-guest interactions. The performance of a series of frameworks of the type Zn2(fu-bdc)2(dabco) (fu-bdc2-=functionalized 1,4-benzenedicarboxylate; dabco=1,4-diazabicyclo[2.2.2]octane), which feature a pillared layer structure, were investigated for the adsorption and separation of methane, ethane, ethylene, and acetylene. The four frameworks exhibit low methane uptake, whereas C2 hydrocarbon uptake is substantially higher as a result of the enhanced interaction of these molecules with the ligand sidechains. Most significantly, the adsorption quantities and selectivity were found to depend strongly upon the type of sidechains attached to the framework scaffold. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/chem.201503685
- Manganese tetraboride, MnB
4: High-temperature crystal structure, p-n transition, 55Mn NMR spectroscopy, solid solutions, and mechanical properties
Knappschneider, A. and Litterscheid, C. and Brgoch, J. and George, N.C. and Henke, S.c and Cheetham, A.K. and Hu, J.G. and Seshadri, R. and Albert, B.
Chemistry - A European Journal 21 (2015)The structural and electronic properties of MnB<inf>4</inf> were studied by high-temperature powder X-ray diffraction and measurements of the conductivity and Seebeck coefficient on spark-plasma-sintered samples. A transition from the room-temperature monoclinic structure (space group P2<inf>1</inf>/c) to a high-temperature orthorhombic structure (space group Pnnm) was observed at about 650K. The material remained semiconducting after the transition, but its behavior changed from p-type to n-type. 55Mn NMR measurements revealed an isotropic chemical shift of -1315ppm, confirming an oxidation state of Mn close to I. Solid solutions of Cr<inf>1-x</inf>Mn<inf>x</inf>B<inf>4</inf> (two phases in space groups Pnnm and P2<inf>1</inf>/c) were synthesized for the first time. In addition, nanoindentation studies yielded values of (496±26) and (25.3±1.7)GPa for the Young's modulus and hardness, respectively, compared to values of 530 and 37GPa obtained by DFT calculations. Phase transition: Monoclinic manganese tetraboride can be transformed into an orthorhombic phase thermally or by forming solid solutions with chromium tetraboride. The structural phase transition of semiconducting MnB<inf>4</inf> is accompanied by a p-n transition. 55Mn NMR spectroscopy confirmed the oxidation state I of the metal atom, and nanoindentation experiments resulted in hardness values that are in accordance with DFT calculations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/chem.201406631
- Mechanical Properties of a Calcium Dietary Supplement, Calcium Fumarate Trihydrate
Sun, S. and Henke, S. and Wharmby, M.T. and Yeung, H.H.-M. and Li, W. and Cheetham, A.K.
Inorganic Chemistry 54 (2015)The mechanical properties of calcium fumarate trihydrate, a 1D coordination polymer considered for use as a calcium source for food and beverage enrichment, have been determined via nanoindentation and high-pressure X-ray diffraction with single crystals. The nanoindentation studies reveal that the elastic modulus (16.7-33.4 GPa, depending on crystallographic orientation), hardness (1.05-1.36 GPa), yield stress (0.70-0.90 GPa), and creep behavior (0.8-5.8 nm/s) can be rationalized in view of the anisotropic crystal structure; factors include the directionality of the inorganic Ca-O-Ca chain and hydrogen bonding, as well as the orientation of the fumarate ligands. High-pressure single-crystal X-ray diffraction studies show a bulk modulus of ∼20 GPa, which is indicative of elastic recovery intermediate between small molecule drug crystals and inorganic pharmaceutical ingredients. The combined use of nanoindentation and high-pressure X-ray diffraction techniques provides a complementary experimental approach for probing the critical mechanical properties related to tableting of these dietary supplements. © 2015 American Chemical Society.
view abstract 10.1021/acs.inorgchem.5b01466
- Guest-dependent mechanical anisotropy in pillared-layered soft porous crystals - a nanoindentation study
Henke, S. and Li, W. and Cheetham, A. K.
Chemical Science 5 (2014)Soft porous crystals (SPCs) of the type [Zn-2(L)(2)(dabco)](n) (L _ linear dicarboxylate linker, dabco _ 1,4-diazabicyclo[2.2.2]octane) show exceptional mechanical anisotropy. Single-crystal nanoindentation experiments reveal very large changes of the elastic modulus and hardness triggered by exchange of the guests adsorbed in the porous metal-organic framework. The substantial variations of the mechanical properties as a function of the guest molecules can be explained by the responsive nature of these SPCs. Based on non-specific guest-framework interactions, crucial changes of the network geometry induce a complex and dynamical mechanical behaviour.
view abstract 10.1039/c4sc00497c
- Identifying the role of terahertz vibrations in metal-organic frameworks: From gate-opening phenomenon to shear-driven structural destabilization
Ryder, M.R. and Civalleri, B. and Bennett, T. and Henke, S. and Rudić, S. and Cinque, G. and Fernandez-Alonso, F. and Tan, J.-C.
Physical Review Letters 113 (2014)We present an unambiguous identification of low-frequency terahertz vibrations in the archetypal imidazole-based metal-organic framework (MOF) materials: ZIF-4, ZIF-7, and ZIF-8, all of which adopt a zeolite-like nanoporous structure. Using inelastic neutron scattering and synchrotron radiation far-infrared absorption spectroscopy, in conjunction with density functional theory (DFT), we have pinpointed all major sources of vibrational modes. Ab initio DFT calculations revealed the complex nature of the collective THz modes, which enable us to establish detailed correlations with experiments. We discover that low-energy conformational dynamics offers multiple pathways to elucidate novel physical phenomena observed in MOFs. New evidence demonstrates that THz modes are intrinsically linked, not only to anomalous elasticity underpinning gate-opening and pore-breathing mechanisms, but also to shear-induced phase transitions and the onset of structural instability. © 2014 American Physical Society.
view abstract 10.1103/PhysRevLett.113.215502
- Mechanical tunability via hydrogen bonding in metal-organic frameworks with the perovskite architecture
Li, W. and Thirumurugan, A. and Barton, P.T. and Lin, Z. and Henke, S. and Yeung, H.H.-M. and Wharmby, M.T. and Bithell, E.G. and Howard, C.J. and Cheetham, A.K.
Journal of the American Chemical Society 136 (2014)Two analogous metal-organic frameworks (MOFs) with the perovskite architecture, [C(NH2)3][Mn(HCOO)3] (1) and [(CH2)3NH2][Mn(HCOO)3] (2), exhibit significantly different mechanical properties. The marked difference is attributed to their distinct modes of hydrogen bonding between the A-site amine cation and the anionic framework. The stronger cross-linking hydrogen bonding in 1 gives rise to Young's moduli and hardnesses that are up to twice those in 2, while the thermal expansion is substantially smaller. This study presents clear evidence that the mechanical properties of MOF materials can be substantially tuned via hydrogen-bonding interactions. © 2014 American Chemical Society.
view abstract 10.1021/ja500618z
- Research Update: Mechanical properties of metal-organic frameworks - Influence of structure and chemical bonding
Li, W. and Henke, S. and Cheetham, A.K.
APL Materials 2 (2014)Metal-organic frameworks (MOFs), a young family of functional materials, have been attracting considerable attention from the chemistry, materials science, and physics communities. In the light of their potential applications in industry and technology, the fundamental mechanical properties of MOFs, which are of critical importance for manufacturing, processing, and performance, need to be addressed and understood. It has been widely accepted that the framework topology, which describes the overall connectivity pattern of the MOF building units, is of vital importance for the mechanical properties. However, recent advances in the area of MOF mechanics reveal that chemistry plays a major role as well. From the viewpoint of materials science, a deep understanding of the influence of chemical effects on MOF mechanics is not only highly desirable for the development of novel functional materials with targeted mechanical response, but also for a better understanding of important properties such as structural flexibility and framework breathing. The present work discusses the intrinsic connection between chemical effects and the mechanical behavior of MOFs through a number of prototypical examples. © 2014 Author(s).
view abstract 10.1063/1.4904966
- Targeted manipulation of metal-organic frameworks to direct sorption properties
Schneemann, A. and Henke, S. and Schwedler, I. and Fischer, R.A.
ChemPhysChem 15 (2014)Metal-organic frameworks are promising materials for manifold applications. This Minireview highlights approaches for the fine-tuning of specific sorption properties (e.g. capacity, selectivity, and breathing behavior) of this interesting class of materials. Central aspects covered are the control over the crystal morphology, the targeted tuning of sorption properties by judicious choice of metal centers and linkers, and the preparation of host-guest systems. We want to introduce the reader to these topics on the basis of the manipulation of a handful of outstanding prototypical metal-organic frameworks. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/cphc.201300976
- Coordination polymers of alkali metal trithiocyanurates: Structure determinations and ionic conductivity measurements using single crystals
Tominaka, S. and Henke, S. and Cheetham, A.K.
CrystEngComm 15 (2013)Six novel crystalline coordination polymers composed of alkali metal ions and trithiocyanurate anions (C3N3S3H 2 - = ttcH2 -) were synthesized. Single crystals were used both for structure determinations by X-ray diffraction and ionic conductivity measurements by AC impedance methods. The structures are: (i) sodium trithiocyanurate trihydrate, Na(ttcH2)(H 2O)3 in space group P21; (ii) potassium trithiocyanurate hydrate, K(ttcH2)(H2O) in P1; (iii) rubidium trithiocyanurate hydrate, Rb(ttcH2)(H2O) in P1; (iv) rubidium trithiocyanurate hydrate, Rb3(ttcH2) 2(ttcH3)2(H2O)5(OH) in P1; and (v, vi) two anhydrous polymorphs of caesium trithiocyanurates, Cs(ttcH2) in P1 and Cc. With the exception of the sodium phase, which is layered, all of these compounds consist of three dimensional coordination networks. In all systems, the inorganic regions are interleaved by arrays of ttcH2 - anions. The most interesting feature of this system is the thiol-rich environment formed between the trithiocyanurate layers, where alkali metal ions are located. Water molecules, where present, are always coordinated to a cation. Among these crystals, K(ttcH2)(H 2O) exhibited proton conductivity under atmospheric conditions (25 ± 0.2 °C): 1.1 × 10-5 S cm-1 in the direction perpendicular to the bc plane and 3.1 × 10-6 S cm-1 along the c axis. © 2013 The Royal Society of Chemistry.
view abstract 10.1039/c3ce41150h
- Massive anisotropic thermal expansion and thermo-responsive breathing in metal-organic frameworks modulated by linker functionalization
Henke, S. and Schneemann, A. and Fischer, R.A.
Advanced Functional Materials 23 (2013)Functionalized metal-organic frameworks (fu-MOFs) of general formula [Zn2(fu-L)2dabco]n show unprecedentedly large uniaxial positive and negative thermal expansion (fu-L = alkoxy functionalized 1,4-benzenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane). The magnitude of the volumetric thermal expansion is more comparable to property of liquid water rather than any crystalline solid-state material. The alkoxy side chains of fu-L are connected to the framework skeleton but nevertheless exhibit large conformational flexibility. Thermally induced motion of these side chains induces extremely large anisotropic framework expansion and eventually triggers reversible solid state phase transitions to drastically expanded structures. The thermo-responsive properties of these hybrid solid-liquid materials are precisely controlled by the choice and combination of fu-Ls and depend on functional moieties and chain lengths. In principle, this combinatorial approach allows for a targeted design of extreme thermo-mechanical properties of MOFs addressing the regime between crystalline solid matter and the liquid state. Extremely large thermal expansion is shown by pillared-layered metal-organic frameworks (MOFs) exhibiting alkoxy-functionalized 1,4-benzenedicarboxylate linkers. At a certain threshold temperature the materials reversibly switch from a narrow pore to large pore form. This unprecedented thermo-mechanical behavior is an intrinsic property of the materials and can be modulated substantially by mixing differently functionalized linkers to obtain mixed linker MOF solid solutions. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/adfm.201301256
- Directing the breathing behavior of pillared-layered metal-organic frameworks via a systematic library of functionalized linkers bearing flexible substituents
Henke, S. and Schneemann, A. and Wütscher, A. and Fischer, R.A.
Journal of the American Chemical Society 134 (2012)Flexible metal-organic frameworks (MOFs), also referred to as soft porous crystals (SPCs), show reversible structural transitions dependent on the nature and quantity of adsorbed guest molecules. In recent studies it has been reported that covalent functionalization of the organic linker can influence or even integrate framework flexibility ("breathing") in MOFs. However, rational fine-tuning of such responsive properties is very desirable but challenging as well. Here we present a powerful approach for the targeted manipulation of responsiveness and framework flexibility of an important family of pillared-layered MOFs based on the parent structure [Zn 2(bdc) 2(dabco)] n (bdc = 1,4-benzenedicarboxylate; dabco = 1,4-diazabicyclo[2.2.2]octane). A library of functionalized bdc-type linkers (fu-bdc), which bear additional dangling side groups at different positions of the benzene core (alkoxy groups of varying chain length with diverse functionalities and polarity), was generated. Synthesis of the materials [Zn 2(fu-bdc) 2(dabco)] n yields the respective collection of highly responsive MOFs. The parent MOF is only weakly flexible; however, the substituted frameworks of [Zn 2(fu-bdc) 2(dabco)] n contract drastically upon guest removal and expand again upon adsorption of DMF (N,N-dimethylformamide), EtOH, or CO 2, etc., while N 2 is hardly adsorbed and does not open the narrow-pored form. These "breathing" dynamics are attributed to the dangling side chains that act as immobilized "guests", which interact with mobile guest molecules as well as with themselves and with the framework backbone. The structural details of the guest-free, contracted form and the gas sorption behavior (phase transition pressure, hysteresis loop) are highly dependent on the nature of the substituent at the linker and can therefore be adjusted using our approach. Combining our library of functionalized linkers with the concept of mixed-component MOFs (solid solutions) offers very rich additional dimensions of tailoring the structural dynamics and responsiveness. Implementation of two differently functionalized linkers in varying ratios yields multicomponent single-phased [Zn 2(fu-bdc ) 2x(fu- bdc″) 2-2x(dabco)] n MOFs (0 < x < 1) of increased inherent complexity, which feature a non-linear dependence of their gas sorption properties on the applied ratio of components. Hence, the responsive behavior of such pillared-layered MOFs can be extensively tuned via an intelligent combination of functionalized linkers. © 2012 American Chemical Society.
view abstract 10.1021/ja302991b
- Fabrication of a CO2-selective membrane by stepwise liquid-phase deposition of an alkylether functionalized pillared-layered metal-organic framework [Cu2L2P]n on a macroporous support
Bétard, A. and Bux, H. and Henke, S. and Zacher, D. and Caro, J. and Fischer, R.A.
Microporous and Mesoporous Materials 150 (2012)Metal-organic framework (MOF) membranes were prepared by stepwise deposition of reactants. Two pillared layered MOFs with the general formula [Cu2L2P]n (L = dicarboxylate linker, P = pillaring ligand) were selected. Within this family, fine tuning of adsorption affinity and pore size is possible by variation or functionalization of the L and P linkers. Compound 1 was chosen to be non-polar (L = 1,4- naphtalenedicarboxylate = ndc, P = 1,4-diazabicyclo(2.2.2)octane = dabco); in contrast, compound 2 included a polar linker L with two conformationally flexible ether side chains (L = 2,5-bis(2-methoxyethoxy)-1,4-benzene- dicarboxylate = BME-bdc, P = dabco). The polar functionalization is expected to increase the framework affinity for CO2 compared to CH4. The step-by-step, liquid phase deposition of 1 and 2 resulted in pore-plugging of macroporous ceramic supports. The performances of the two MOF membranes were evaluated in gas separation experiments of equimolar CO2/CH 4 mixtures using a modified Wicke-Kallenbach technique. Anti-Knudsen CO2/CH4 separation factors in the range of ∼4-4.5 were obtained for the membrane consisting of the polar 2, whereas the separation of the membrane formed from the non-polar 1 was found to be Knudsen-like. © 2011 Elsevier Inc. All rights reserved.
view abstract 10.1016/j.micromeso.2011.09.006
- Zinc-1,4-benzenedicarboxylate-bipyridine frameworks - Linker functionalization impacts network topology during solvothermal synthesis
Henke, S. and Schneemann, A. and Kapoor, S. and Winter, R. and Fischer, R.A.
Journal of Materials Chemistry 22 (2012)Substitution of 1,4-benzenedicarboxylate (bdc) with additional alkoxy chains is the key to construct a family of metal-organic frameworks (MOFs) of the type [Zn 2(fu-bdc) 2(bipy)] n (fu-bdc = functionalized bdc; bipy = 4,4′-bipyridine) exhibiting a honeycomb-like topology instead of the default pillared square-grid topology. Both the substitution pattern of the phenyl ring of the fu-bdc linker and the chain length of the alkoxy substituents have a major impact on the structure of the derived frameworks. Substitution at positions 2 and 3 leads to the trivial pillared square-grid framework, and substitution at positions 2 and 5 or 2 and 6 yields MOFs with the honeycomb-like topology. Also, simple methoxy substituents lead to the construction of a pillared square-grid topology, whereas longer substituents like ethoxy, n-propoxy, and n-butoxy generate honeycomb-like framework structures. These honeycomb MOFs feature one-dimensional channels, which are tuneable in diameter and functionality by the choice of substituent attached to the bdc-type linker. Pure component sorption isotherms indicate that the honeycomb-like frameworks selectively adsorb CO 2 over N 2 and CH 4. © The Royal Society of Chemistry 2011.
view abstract 10.1039/c1jm14791a
- Flexibility and sorption selectivity in rigid metal-organic frameworks: The impact of ether-functionalised linkers (Chemistry - A European Journal (2010) (16))
Henke, S. and Schmid, R. and Grunwaldt, J.-D. and Fischer, R.A.
Chemistry - A European Journal 17 (2011)
view abstract 10.1002/chem.201190003
- Gated channels in a honeycomb-like zinc-dicarboxylate-bipyridine framework with flexible alkyl ether side chains
Henke, S. and Fischer, R.A.
Journal of the American Chemical Society 133 (2011)Covalent functionalization of 1,4-benzenedicarboxylate (bdc) with methoxyethoxy groups induces conformational freedom in this molecule. Applying these 2,5-disubstituted bdc derivatives in metal-organic framework synthesis together with 4,4′-bipyridine as coligand yields novel honeycomb-like structures. The cylindrical channels of these materials are populated with flexible groups, which act as molecular gates for guest molecules. This allows highly selective sorption of CO2 over N2 and CH 4. © 2011 American Chemical Society.
view abstract 10.1021/ja109317e
- Liquid-phase epitaxy of multicomponent layer-based porous coordination polymer thin films of [M(L)(P)0.5] type: Importance of deposition sequence on the oriented growth
Zacher, D. and Yusenko, K. and Bétard, A. and Henke, S. and Molon, M. and Ladnorg, T. and Shekhah, O. and Schüpbach, B. and Dea Losa Arcos, T. and Krasnopolski, M. and Meilikhov, M. and Winter, J. and Terfort, A. and Wöll, C. and Fischer, R.A.
Chemistry - A European Journal 17 (2011)The progressive liquid-phase layer-by-layer (LbL) growth of anisotropic multicomponent layer-based porous coordination polymers (PCPs) of the general formula [M(L)(P)0.5] (M: Cu2+, Zn2+; L: dicarboxylate linker; P: dinitrogen pillar ligand) was investigated by using either pyridyl- or carboxyl-terminated self-assembled monolayers (SAMs) on gold substrates as templates. It was found that the deposition of smooth, highly crystalline, and oriented multilayer films of these PCPs depends on the conditions at the early growth cycles. In the case of a two-step process with an equimolar mixture of L and P, growth along the  direction is strongly preferred. However, employing a three-step scheme with full separation of all components allows deposition along the  direction on carboxyl-terminated SAMs. Interestingly, the growth of additional layers on top of previously grown oriented seeding layers proved to be insensitive to the particular growth scheme and full retention of the initial orientation, either along the  or  direction, was observed. This homo- and heteroepitaxial LbL growth allows full control over the orientation and the layer sequence, including introduction of functionalized linkers and pillars. One layer at a time: The stepwise liquid-phase layer-by-layer growth of anisotropic, multicomponent layer-based porous coordination polymers (PCPs) of the general formula [M(L)(P) 0.5] (M: Cu2+, Zn2+; L: dicarboxylate linker, P: dinitrogen pillar ligand) was investigated by using either pyridyl- or carboxyl-terminated self-assembled monolayers as templates. Highly oriented PCP multilayers were selectively grown along the  and  directions (see figure). © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/chem.201002381
- Multiple phase-transitions upon selective CO 2 adsorption in an alkyl ether functionalized metal-organic framework - An in situ X-ray diffraction study
Henke, S. and Florian Wieland, D.C. and Meilikhov, M. and Paulus, M. and Sternemann, C. and Yusenko, K. and Fischer, R.A.
CrystEngComm 13 (2011)The flexible alkyl ether functionalized metal-organic framework [Zn 2(BME-bdc) 2(dabco)] n (BME-bdc = 2,5-bis(2-methoxyethoxy)-1,4-benzenedicarboxylate, dabco = 1,4-diazabicyclo[2.2. 2]octane) shows remarkable structural changes upon selective adsorption of CO 2 as determined by in situ X-ray diffraction at 195 K. Upon accommodation of carbon dioxide [Zn 2(BME-bdc) 2(dabco)] n transfers from a narrow pore form to an open pore form, which exhibits a much higher unit cell volume. Due to the slow adsorption kinetics an unexpected metastable intermediate form could be identified. © 2011 The Royal Society of Chemistry.
view abstract 10.1039/c1ce05446e
- Breathing and multivariant
Henke, S. and Fischer, R.A.
Nachrichten aus der Chemie 58 (2010)
view abstract 10.1002/nadc.201069160
- Flexibility and Sorption Selectivity in Rigid Metal-Organic Frameworks: The Impact of Ether-Functionalised Linkers
Henke, S. and Schmid, R. and Grunwaldt, J. D. and Fischer, R. A.
Chemistry-a European Journal 16 (2010)The functionalisation of well-known rigid metal organic frameworks (namely, [Zn4O(bdc)(3)](n), MOF-5, IRMOF-1 and [Zn-2(bdc)(2)(dabco)](n); bdc = 1,4-benzene dicarboxylate, dabco=diazabicyclo[2.2.2]octane) with additional alkyl ether groups of the type -O-(CH2)(n)-O-CH3 (n = 2-4) initiates unexpected structural flexibility, as well as high sorption selectivity towards CO2 over N-2 and CH, in the porous materials. These novel materials respond to the presence/absence of guest molecules with structural transformations. We found that the chain length of the alkyl ether groups and the substitution pattern of the bdc-type linker have a major impact on structural flexibility and sorption selectivity. Remarkably, our results show that a high crystalline order of the activated material is not a prerequisite to achieve significant porosity and high sorption selectivity.
view abstract 10.1002/chem.201002341