Reticular synthesis and the design of new materials

The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62718/1/nature01650.pd

Framework Mobility in the Metal−Organic Framework Crystal IRMOF-3: Evidence for Aromatic Ring and Amine

a b s t r a c t The framework motions in IRMOF-3 (Zn 4 O(BDC-NH 2 ) 3 ), where BDC-NH 2 represents 2-amino-1,4-ben zenedicarboxylate, have been investigated with 1 H NMR relaxation measurements. Isotopic enrichment of the 2-amino group with 15 N was critical in elucidating the lattice dynamics and enhancing spectral resolution. These results indicate a low energy process associated with rotation of the amino group, with an activation energy of 1.8 ± 0.6 kcal/mol, and full 180°rotation of the phenylene group in the BDC-NH 2 moiety with an activation energy of 5.0 ± 0.2 kcal/mol. A relatively low pre-exponential factor for amine rotation (1.3 Â 10 7 s À1 ) is tentatively associated with the need to break a hydrogen bond as the rate-limiting step. Both amine rotation and the aromatic ring flip occur at frequencies that provide an effective relaxation mechanism for the 99.6% natural abundance quadrupola

Luminescence tuning of MOFs via ligand to metal and metal to metal energy transfer by co-doping of 2∞[Gd2Cl6(bipy)3]*2bipy with europium and terbium

The series of anhydrous lanthanide chlorides LnCl3, Ln=Pr–Tb, and 4,4'-bipyridine (bipy) constitute isotypic MOFs of the formula 2∞[Ln2Cl6(bipy)3]*2bipy. The europium and terbium containing compounds both exhibit luminescence of the referring trivalent lanthanide ions, giving a red luminescence for Eu3+ and a green luminescence for Tb3+ triggered by an efficient antenna effect of the 4,4'-bipyridine linkers. Mixing of different lanthanides in one MOF structure was undertaken to investigate the potential of this MOF system for colour tuning of the luminescence. Based on the gadolinium containing compound, co-doping with different amounts of europium and terbium proves successful and yields solid solutions of the formula 2∞[Gd2-x-yEuxTbyCl6(bipy)3]*2bipy (1–8), 0≤x, y≤0.5. The series of MOFs exhibits the opportunity of tuning the emission colour in-between green and red. Depending on the atomic ratio Gd:Eu:Tb, the yellow region was covered for the first time for an oxygen/carboxylate-free MOF system. In addition to a ligand to metal energy transfer (LMET) from the lowest ligand-centered triplet state of 4,4'-bipyridine, a metal to metal energy transfer (MMET) between 4f-levels from Tb3+ to Eu3+ is as well vital for the emission colour. However, no involvement of Gd3+ in energy transfers is observed rendering it a suitable host lattice ion and connectivity centre for diluting the other two rare earth ions in the solid state. The materials retain their luminescence during activation of the MOFs for microporosity

Zeolite-like liquid crystals

Zeolites represent inorganic solid-state materials with porous structures of fascinating complexity. Recently, significant progress was made by reticular synthesis of related organic solid-state materials, such as metal-organic or covalent organic frameworks. Herein we go a step further and report the first example of a fluid honeycomb mimicking a zeolitic framework. In this unique self-assembled liquid crystalline structure, transverse-lying π-conjugated rod-like molecules form pentagonal channels, encircling larger octagonal channels, a structural motif also found in some zeolites. Additional bundles of coaxial molecules penetrate the centres of the larger channels, unreachable by chains attached to the honeycomb framework. This creates a unique fluid hybrid structure combining positive and negative anisotropies, providing the potential for tuning the directionality of anisotropic optical, electrical and magnetic properties. This work also demonstrates a new approach to complex soft-matter self-assembly, by using frustration between space filling and the entropic penalty of chain extension

Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding

Within the broad class of multiferroics (compounds showing a coexistence of magnetism and ferroelectricity), we focus on the subclass of "improper electronic ferroelectrics", i.e. correlated materials where electronic degrees of freedom (such as spin, charge or orbital) drive ferroelectricity. In particular, in spin-induced ferroelectrics, there is not only a {\em coexistence} of the two intriguing magnetic and dipolar orders; rather, there is such an intimate link that one drives the other, suggesting a giant magnetoelectric coupling. Via first-principles approaches based on density functional theory, we review the microscopic mechanisms at the basis of multiferroicity in several compounds, ranging from transition metal oxides to organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic frameworks, MOFs)Comment: 22 pages, 9 figure

A new method to position and functionalize metal-organic framework crystals

With controlled nanometre-sized pores and surface areas of thousands of square metres per gram, metal-organic frameworks (MOFs) may have an integral role in future catalysis, filtration and sensing applications. In general, for MOF-based device fabrication, well-organized or patterned MOF growth is required, and thus conventional synthetic routes are not suitable. Moreover, to expand their applicability, the introduction of additional functionality into MOFs is desirable. Here, we explore the use of nanostructured poly-hydrate zinc phosphate (α-hopeite) microparticles as nucleation seeds for MOFs that simultaneously address all these issues. Affording spatial control of nucleation and significantly accelerating MOF growth, these α-hopeite microparticles are found to act as nucleation agents both in solution and on solid surfaces. In addition, the introduction of functional nanoparticles (metallic, semiconducting, polymeric) into these nucleating seeds translates directly to the fabrication of functional MOFs suitable for molecular size-selective applications

Photophysical pore control in an azobenzene- containing metal-organic framework †

The synthesis and structure of an azobenzene functionalized isoreticular metal-organic framework (azo-IRMOF-74-III) [Mg 2 (C 26 H 16 O 6 N 2 )] are described and the ability to controllably release a guest from its pores in response to an external stimulus has been demonstrated. Azo-IRMOF-74-III is an isoreticular expansion of MOF-74 with an etb topology and a 1-D hexagonal pore structure. The structure of azo-IRMOF-74-III is analogous to that of MOF-74, as demonstrated by powder X-ray diffraction, with a surface area of 2410 m 2 g À1 BET. Each organic unit within azo-IRMOF-74-III is decorated with a photoswitchable azobenzene unit, which can be toggled between its cis and trans conformation by excitation at 408 nm. When propidium iodide dye was loaded into the MOF, spectroscopic studies showed that no release of the luminescent dye was observed under ambient conditions. Upon irradiation of the MOF at 408 nm, however, the rapid wagging motion inherent to the repetitive isomerization of the azobenzene functionality triggered the release of the dye from the pores. This light-induced release of cargo can be modulated between an on and an off state by controlling the conformation of the azobenzene with the appropriate wavelength of light. This report highlights the ability to capture and release small molecules and demonstrates the utility of self-contained photoactive switches located inside highly porous MOFs

Ischemic Stroke despite Oral Anticoagulant Therapy in Patients with Atrial Fibrillation

OBJECTIVE It is not known whether patients with atrial fibrillation (AF) with ischemic stroke despite oral anticoagulant therapy are at increased risk for further recurrent strokes or how ongoing secondary prevention should be managed. METHODS We conducted an individual patient data pooled analysis of 7 prospective cohort studies that recruited patients with AF and recent cerebral ischemia. We compared patients taking oral anticoagulants (vitamin K antagonists [VKA] or direct oral anticoagulants [DOAC]) prior to index event (OACprior) with those without prior oral anticoagulation (OACnaive). We further compared those who changed the type (ie, from VKA or DOAC, vice versa, or DOAC to DOAC) of anticoagulation (OACchanged) with those who continued the same anticoagulation as secondary prevention (OACunchanged). Time to recurrent acute ischemic stroke (AIS) was analyzed using multivariate competing risk Fine–Gray models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS We included 5,413 patients (median age = 78 years [interquartile range (IQR) = 71–84 years]; 5,136 [96.7%] had ischemic stroke as the index event, median National Institutes of Health Stroke Scale on admission = 6 [IQR = 2–12]). The median CHA2DS2‐Vasc score (congestive heart failure, hypertension, age≥ 75 years, diabetes mellitus, stroke/transient ischemic attack, vascular disease, age 65–74 years, sex category) was 5 (IQR = 4–6) and was similar for OACprior (n = 1,195) and OACnaive (n = 4,119, p = 0.103). During 6,128 patient‐years of follow‐up, 289 patients had AIS (4.7% per year, 95% CI = 4.2–5.3%). OACprior was associated with an increased risk of AIS (HR = 1.6, 95% CI = 1.2–2.3, p = 0.005). OACchanged (n = 307) was not associated with decreased risk of AIS (HR = 1.2, 95% CI = 0.7–2.1, p = 0.415) compared with OACunchanged (n = 585). INTERPRETATION Patients with AF who have an ischemic stroke despite previous oral anticoagulation are at a higher risk for recurrent ischemic stroke despite a CHA2DS2‐Vasc score similar to those without prior oral anticoagulation. Better prevention strategies are needed for this high‐risk patient group. ANN NEUROL 202

Methane adsorption in metal-organic frameworks containing nanographene linkers: a computational study

Metal-organic framework (MOF) materials are known to be amenable to expansion through elongation of the parent organic linker. For a family of model (3,24)-connected MOFs with the rht topology, in which the central part of organic linker comprises a hexabenzocoronene unit, the effect of the linker type and length on their structural and gas adsorption properties is studied computationally. The obtained results compare favourably with known MOF materials of similar structure and topology. We find that the presence of a flat nanographene-like central core increases the geometric surface area of the frameworks, sustains additional benzene rings, promotes linker elongation and the efficient occupation of the void space by guest molecules. This provides a viable linker modification method with potential for enhancement of uptake for methane and other gas molecules

Metal organic framework nanosheets in polymer composite materials for gas separation

[EN] Composites incorporating two-dimensional nanostructures within polymeric matrices have potential as functional components for several technologies, including gas separation. Prospectively, employing metal-organic frameworks (MOFs) as versatile nanofillers would notably broaden the scope of functionalities. However, synthesizing MOFs in the form of freestanding nanosheets has proved challenging. We present a bottom-up synthesis strategy for dispersible copper 1,4-benzenedicarboxylate MOF lamellae of micrometre lateral dimensions and nanometre thickness. Incorporating MOF nanosheets into polymer matrices endows the resultant composites with outstanding CO2 separation performance from CO2/CH4 gas mixtures, together with an unusual and highly desired increase in the separation selectivity with pressure. As revealed by tomographic focused ion beam scanning electron microscopy, the unique separation behaviour stems from a superior occupation of the membrane cross-section by the MOF nanosheets as compared with isotropic crystals, which improves the efficiency of molecular discrimination and eliminates unselective permeation pathways. This approach opens the door to ultrathin MOF-polymer composites for various applications.The research leading to these results has received funding (J.G., B.S.) from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement no. 335746, CrystEng-MOF-MMM. T.R. is grateful to TUDelft for funding. G.P. acknowledges the A. von Humboldt Foundation for a research grant. A.C., I.L. and F.X.L.i.X. thank Consolider-Ingenio 2010 (project MULTICAT) and the ‘Severo Ochoa’ programme for support. I.L. also thanks CSIC for a JAE doctoral grant.Ródenas Torralba, T.; Luz Mínguez, I.; Prieto González, G.; Seoane, B.; Miro, H.; Corma Canós, A.; Kapteijn, F.... (2015). Metal organic framework nanosheets in polymer composite materials for gas separation. Nature Materials. 14(1):48-55. https://doi.org/10.1038/nmat4113S4855141Stankovich, S. et al. Graphene-based composite materials. Nature 442, 282–286 (2006).Wang, Q. H., Kalantar-Zadeh, K., Kis, A., Coleman, J. N. & Strano, M. S. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nature Nanotech. 7, 699–712 (2012).Choi, S. et al. Layered silicates by swelling of AMH-3 and nanocomposite membranes. Angew. Chem. Int. Ed. 47, 552–555 (2008).Varoon, K. et al. Dispersible exfoliated zeolite nanosheets and their application as a selective membrane. Science 334, 72–75 (2011).Corma, A., Fornes, V., Pergher, S. B., Maesen, Th. L. M. & Buglass, J. G. Delaminated zeolite precursors as selective acidic catalysts. Nature 396, 353–356 (1998).Hernandez, Y. et al. High-yield production of graphene by liquid-phase exfoliation of graphite. Nature Nanotech. 3, 563–568 (2008).Li, P-Z., Maeda, Y. & Xu, Q. Top-down fabrication of crystalline metal-organic framework nanosheets. Chem. Commun. 47, 8436–8438 (2011).Choi, M. et al. Stable single-unit-cell nanosheets of zeolite MFI as active and long-lived catalysts. Nature 461, 246–249 (2009).Hu, G., Wang, N., O’Hare, D. & Davis, J. One-step synthesis and AFM imaging of hydrophobic LDH monolayers. Chem. Commun. 287–289 (2006).Yamamoto, K., Sakata, Y., Nohara, Y., Takahashi, Y. & Tatsumi, T. Organic-inorganic hybrid zeolites containing organic frameworks. Science 300, 470–472 (2003).Yaghi, O. M. et al. Reticular synthesis and the design of new materials. Nature 423, 705–714 (2003).Férey, G. Hybrid porous solids: Past, present, future. Chem. Soc. Rev. 37, 191–214 (2008).Gücüyener, C., Bergh, J., Gascon, J. & Kapteijn, F. Ethane/ethene separation turned on its head: Selective ethane adsorption on the metal-organic framework ZIF-7 through a gate-opening mechanism. J. Am. Chem. Soc. 132, 17704–17706 (2010).Deng, H. et al. Multiple functional groups of varying ratios in metal-organic frameworks. Science 12, 846–850 (2010).Khaletskaya, K. et al. Integration of porous coordination polymers and gold nanorods into core-shell mesoscopic composites toward light-induced molecular release. J. Am. Chem. Soc. 135, 10998–11005 (2013).Corma, A., Garcia, H. & Llabrés i Xamena, F. X. Engineering metal organic frameworks for heterogeneous catalysis. Chem. Rev. 110, 4606–4655 (2010).Mueller, U. et al. Metal-organic frameworks-prospective industrial applications. J. Mater. Chem. 16, 626–636 (2006).Gascon, J. & Kapteijn, F. Metal-organic framework membranes-high potential, bright future? Angew. Chem. Int. Ed. 49, 1530–1532 (2010).Li, Y. S. et al. Controllable synthesis of metal-organic frameworks: From MOF nanorods to oriented MOF membranes. Adv. Mater. 22, 3322–3326 (2010).Gascon, J. et al. Practical approach to zeolitic membranes and coatings: State of the art, opportunities, barriers, and future perspectives. Chem. Mater. 24, 2829–2844 (2012).Bae, T-H. et al. A high-performance gas-separation membrane containing submicrometer-sized metal-organic framework crystals. Angew. Chem. Int. Ed. 49, 9863–9866 (2010).Zornoza, B. et al. Functionalized flexible MOFs as fillers in mixed matrix membranes for highly selective separation of CO2 from CH4 at elevated pressures. Chem. Commun. 47, 9522–9524 (2011).Zornoza, B., Tellez, C., Coronas, J., Gascon, J. & Kapteijn, F. Metal organic frameworks based mixed matrix membranes: An increasingly important field of research with a large application potential. Microp. Mesop. Mater. 166, 67–78 (2013).Zhang, C., Dai, Y., Johnson, J. R., Karvan, O. & Koros, W. High performance ZIF-8/6FDA-DAM mixed matrix membrane for propylene/propane separations. J. Mem. Sci. 389, 34–42 (2012).Li, T., Pan, Y., Peinemann, K-V. & Lai, Z. Carbon dioxide selective mixed matrix composite membrane containing ZIF-7 nano-fillers. J. Mem. Sci. 425–426, 235–242 (2013).Makiura, R. et al. Surface nano-architecture of a metal-organic framework. Nature Mater. 9, 565–571 (2010).Mori, W. et al. Synthesis of new adsorbent copper(II) terephthalate. Chem. Lett. 26, 1219–1220 (1997).Xin, Z., Bai, J., Shen, Y. & Pan, Y. Hierarchically micro- and mesoporous coordination polymer nanostructures with high adsorption performance. Cryst. Growth Des. 10, 2451–2454 (2010).Adams, R., Carson, C., Ward, J., Tannenbaum, R. & Koros, W. Metal organic framework mixed matrix membranes for gas separations. Micropor. Mesopor. Mater. 131, 13–20 (2010).Carson, C. G. et al. Synthesis and structure characterization of copper terephthalate metal-organic framework. Eur. J. Inorg. Chem. 2009, 2338–2343 (2009).Ameloot, R. et al. Interfacial synthesis of hollow metal-organic framework capsules demonstrating selective permeability. Nature Chem. 3, 382–387 (2011).Chen, Z. et al. Microporous metal-organic framework with immobilized -OH functional groups within the pore surfaces for selective gas sorption. Eur. J. Inorg. Chem. 2010, 3745–3749 (2010).Karra, J. R. & Walton, K. S. Molecular simulations and experimental studies of CO2, CO, and N2 adsorption in metal-organic frameworks. J. Phys. Chem. C 114, 15735–15740 (2010).Liu, J., Thallapally, P. K., McGrail, B. P., Brown, D. R. & Liu, J. Progress in adsorption-based CO2 capture by metal-organic frameworks. Chem. Soc. Rev. 41, 2308–2322 (2012).Seki, K., Takamizawa, S. & Mori, W. Characterization of microporous copper(II) dicarboxylates (fumarate, terephthalate, and trans-1,4-cyclohexanedicarboxylate) by gas adsorption. Chem. Lett. 30, 122–123 (2001).Carson, C. G. et al. Structure solution from powder diffraction of copper 1,4-benzenedicarboxylate. Eur. J. Inorg. Chem. 2014, 2140–2145 (2014).Corma, A., Diaz, U., Domine, M. E. & Fornes, V. AlITQ-6 and TiITQ-6: Synthesis, characterization, and catalytic activity. Angew. Chem. Int. Ed. 39, 1499–1501 (2000).Corma, A., Fornes, V. & Diaz, U. ITQ-18 a new delaminated stable zeolite. Chem. Commun. 2642–2643 (2001).Rouquerol, F., Rouquerol, J. & Sing, K. Adsorption by Powders and Porous Solids (Academic, 1999).Dubinin, M. M. The potential theory of adsorption of gases and vapors for adsorbents with energetically nonuniform surfaces. Chem. Rev. 60, 235–241 (1960).Uchic, M. D., Holzer, L., Inkson, B. J., Principe, E. L. & Munroe, P. Three-dimensional microstructural characterization using focused ion beam tomography. Mater. Res. Soc. Bull. 32, 408–416 (2007).Rodenas, T. et al. Visualizing MOF mixed matrix membranes at the nanoscale: Towards structure-performance relationships in CO2/CH4 separation over NH2-MIL-53(Al)@PI. Adv. Funct. Mater. 24, 249–256 (2013).Wang, X. et al. Unusual rheological behaviour of liquid polybutadiene rubber/clay nanocomposite gels: The role of polymer-clay interaction, clay exfoliation, and clay orientation and disorientation. Macromology 39, 6653–6660 (2006).Yang, Y. et al. Progress in carbon dioxide separation and capture: A review. J. Environ. Sci. 20, 14–27 (2008).Yeo, Z. Y., Chew, T. L., Zhu, P. W., Mohamed, A. R. & Chai, S-P. Conventional processes and membrane technology for carbon dioxide removal from natural gas: A review. J. Nature Gas Chem. 21, 282–298 (2012).McKeown, N. B. & Budd, P. M. Polymers of intrinsic microporosity (PIMs): Organic materials for membrane separations, heterogeneous catalysis and hydrogen storage. Chem. Soc. Rev. 35, 675–683 (2006).Vinh-Thang, H. & Kaliaguine, S. Predictive models for mixed-matrix membrane performance: A review. Chem. Rev. 113, 4980–5028 (2013)