Research Highlights

1.  Non-Crystalline Metal-organic frameworks and coordination polymers

Metal–organic frameworks are a novel family of chemically diverse materials, with applications in a wide field covering engineering, physics, chemistry, biology and medicine. Research so far has focused almost entirely on crystalline structures, yet a clear trend has emerged shifting the emphasis onto disordered states of MOFs, including “defective by design” crystals, as well as amorphous phases such as glasses and gels. The group has pioneered the synthesis, characterization and potential applications of non-crystalline MOFs. These include liquids, glasses and, to some extent, gels.

Liquid, glass and amorphous solid states of coordination polymers and metal–organic frameworks

T. D Bennett* and S. Horike*, Nat. Rev. Mater.2018, DOI: 10.1038/s41578-018-0054-3

 2.  Metal-Organic Framework Liquids

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twitterHere we introduce a MOF liquid, a strongly associated liquid obtained by melting a zeolitic imidazolate framework (ZIF), with retention of chemical configuration, coordinative bonding modes, and porosity of the parent crystalline framework. We combine in-situ variable temperature X-ray, ex-situ neutron pair distribution function experiments, and first principles molecular dynamics simulations to study the melting phenomenon and the nature of the liquid obtained, focusing on structural characterization at the molecular scale, dynamics of the species, and thermodynamics of the solid–liquid transition.

Liquid Metal-Organic Frameworks

R. Gaillac, P. Pullumbi, K. A. Beyer, K. W. Chapman, D. A. Keen, T. D. Bennett and F. X. Coudert, Nat. Mater.2017, 16, 1149-1145

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3. Metal-Organic Framework Glasses

The glasses formed by quenching MOF liquids contain both inorganic, and organic components. They are thus the first new category of glass (outside of traditional inorganic, organic and metallic categories) to be discovered since the latter in the 1970s. After our initial discovery, we have worked to look at (i) the expansion of the glass forming MOF family, and (ii) the optical, porous and mechanical properties of the resultant glasses.

  1. Metal-organic framework glasses with permanent accessible porosity

C. Zhou, L. Longley, A. Krajnc, G. J. Smales, A. Qiao, I. Erucar, C. M. Doherty, A. W. Thornton, A. J. Hill, C. W. Ashling, O. T. Qazvini, S. J. Lee, P. A. Chater, N. J. Terrill, A. J. Smith, Y. Yue, G. Mali, D. A. Keen, S. G. Telfer and T. D. Bennett, Nat. Commum., 2018, 9, 5042.

2. Melt-Quenched Glasses of Metal-Organic Frameworks

T. D. Bennett*, Y. Yue, P. Lim A. Qiao, H. Tao, G. N. Greaves, T. Richards, G. I. Lampronti, Simon. A. T. Redfern, F. Blanc, O. K. Farha, J. T. Hupp, A. K. Cheetham and D. A. Keen, J. Am. Chem. Soc., 2016138, 3484-3492.

3. Halogenated metal-organic framework glasses and liquids

J. Hou, M. L. R. Gómez, A. Krajnc, A. McCaul, S. Li, A. M. Bumstead, A. F. Sapnik, Z. Deng, R. Lin, P. A. Chater, D. S. Keeble, D. A. Keen, D. Appadoo, B. Chan, V. Chen, G. Mali, T. D. Bennett,* J. Am. Chem. Soc., 2020, DOI: 10.1021/jacs.9b11639.

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4. metal-organic framework crystal-glass composites

The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. Recent research has revealed solid-liquid transitions within the family, which we use here to create a class of functional, stable and porous composite materials by embedding crystalline MOFs into a MOF-glass. In our work to date we have shown that these metal-organic framework crystal glass composites (MOF-CGCs) enable highly porous, unstable crystalline MOFs to exist at room temperature (Publication 1). For example, the coordinative bonding and chemical structure of a MIL-53 crystalline phase are preserved within the ZIF-62 glass matrix. Whilst separated phases, the interfacial interactions between the closely contacted microdomains improve the mechanical properties of the composite glass. More significantly, the high temperature open pore phase of MIL-53, which spontaneously transforms to a narrow pore upon cooling in the presence of water, is stabilised at room temperature in the crystal-glass composite. This leads to a significant improvement of CO2 adsorption capacity.

In a second publication, we explore in depth the room-temperature stabilization of the open-pore form of MIL-53(Al), and identify an upper limit of MIL-53(Al) that can be stabilized in the composite was determined for the first time. The nanostructure of the composites was probed using pair distribution function analysis and scanning transmission electron microscopy. Notably, the distribution and integrity of the crystalline component in a sample series were determined, and these findings were related to the MOF-CGC gas adsorption capacity in order to identify the optimal loading necessary for maximum CO2 sorption capacity.
  1. Metal-organic framework crystal-glass composites

J. Hou, C. W. Ashling, S. M. Collins, A. Krajnc, C. Zhou, L. Longley, D. N. Johnstone, P. Chater, S. Li, M. V. Coulet, P. L. Llewellyn, F. X. Coudert, D. A. Keen, P. A. Midgley, G. Mali, V. Chen, T. D. Bennett,* Nat. Commun., 2019, 10, 2580.

2. Synthesis and Properties of a Compositional Series of MIL-51(Al) Metal-Organic Framework Crystal-Glass Composites

C. W. Ashling, D. N. Johnstone, R. N. Widmer, J. Hou, S. M. Collins, A. F. Sapnik, A. Bumstead, P. A. Chater, D. A. Keen and Thomas. D. Bennett*, J. Am. Chem. Soc., 2019, 141, 15641-15648.

 

5. High Pressure – High Temperature Phase Diagrams of MOFs

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Metal–organic frameworks (MOFs) are microporous materials with huge potential for chemical processes. Structural collapse at high pressure, and transitions to liquid states at high temperature, have recently been observed in the zeolitic imidazolate framework (ZIF) family of MOFs. Here, we show that simultaneous high-pressure and high temperature conditions result in complex behaviour in ZIF-62 and ZIF-4, with distinct high- and low-density amorphous phases occurring over different regions  of the pressure–temperature phase diagram. In situ powder X-ray diffraction, Raman spectroscopy and optical microscopy  reveal that the stability of the liquid MOF state expands substantially towards lower temperatures at intermediate, industrially  achievable pressures and first-principles molecular dynamics show that softening of the framework coordination with pressure  makes melting thermodynamically easier. Furthermore, the MOF glass formed by melt quenching the high-temperature liquid  possesses permanent, accessible porosity. Our results thus imply a route to the synthesis of functional MOF glasses at low  temperatures, avoiding decomposition on heating at ambient pressure.
  1. Pressure promoted low-temperature melting of metal-organic frameworks

R. N. Widmer, G. I. Lampronti, S. Anzellini, R. Gaillac, S. Farsang, C. Zhou, A. M. Belenguer, H. Palmer, A. K. Kleppe, M. T. Wharmby,  S. A. T. Redfern, F. X. Coudert, S. G. Macleod, T. D. Bennett,* Nat. Mater., 2019, DOI: 10.1038/s41563-019-0317-4.

2. Rich polymorphism of a metal-organic framework in oressure-temperature space

R. N. Widmer, G. I. Lampronti, S. Chibani, C. W. Wilson, S. Anzellini, S. Farsang, A. K. Kleppe, N. P. M. Casati, S. G. MacLeod, S. A. T. Redfern, F. X. Coudert and T. D. Bennett*,   J. Am. Chem. Soc., 2019141, 9330-9337.

6. Metal-Organic Frameworks Gels and Monoliths

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The ability of metal-organic frameworks (MOFs) to gelate under specific synthetic conditions opens up new opportunities in the preparation and shaping of hierarchically porous MOF monoliths, which could be directly implemented for catalytic and adsorptive applications. In this work, we present the first examples of xero- or aerogel monoliths consisting solely of nanoparticles of several prototypical Zr4+ -based MOFs: UiO-66-X (X = H, NH2, NO2, (OH)2), UiO-67, MOF-801, MOF-808 and NU-1000. High reactant and water concentrations during synthesis were observed to induce the formation of gels, which were converted to monolithic materials by drying in air or supercritical CO2. Electron microscopy, combined with N2 physisorption experiments, was used to show that an irregular nanoparticle packing leads to pure MOF monoliths with hierarchical pore systems, featuring both intraparticle micropores and interparticle mesopores. Finally, UiO-66 gels were shaped into monolithic spheres of 600 m diameter using an oil-drop method, creating promising candidates for packedbed catalytic or adsorptive applications, where hierarchical pore systems can greatly mitigate mass transfer limitations.

  1. Gel-based Morphological Design of Metal-Organic Frameworks

B. Bueken, N. Van Velthoven, T. Willhammar, T. Stassin, I. Stassen, D. A. Keen, G. V. Baron, J. F. M. Denayer, R. Ameloot, S. Bals, D. De Vos* and T. D. Bennett* Chem. Sci., 2017, 8, 3939-3948.

2. Metal-Organic Framework Gels and Monoliths

J. Hou, A. F. Sapnik and T. D. Bennett*, Chem. Sci., 2020, 11, 310-323.

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