Imaging defects and their evolution in a metal–organic framework at sub-unit-cell resolution

Defect engineering of metal–organic frameworks (MOFs) offers promising opportunities for tailoring their properties to specific functions and applications. However, determining the structures of defects in MOFs—either point defects or extended ones—has proved challenging owing to the difficulty of directly probing local structures in these typically fragile crystals. Here we report the real-space observation, with sub-unit-cell resolution, of structural defects in the catalytic MOF UiO-66 using a combination of low-dose transmission electron microscopy and electron crystallography. Ordered ‘missing linker’ and ‘missing cluster’ defects were found to coexist. The missing-linker defects, reconstructed three-dimensionally with high precision, were attributed to terminating formate groups. The crystallization of the MOF was found to undergo an Ostwald ripening process, during which the defects also evolve: on prolonged crystallization, only the missing-linker defects remained. These observations were rationalized through density functional theory calculations. Finally, the missing-cluster defects were shown to be more catalytically active than their missing-linker counterparts for the isomerization of glucose to fructose.Structural defects are known to exist in metal–organic frameworks (MOFs), and to affect the materials’ properties, but their exact structures have remained difficult to determine. Now, missing-linker and missing-cluster defects have been observed in a MOF using low-dose transmission electron microscopy, enabling their distributions, evolutions during crystallization and effects on the material’s catalytic activity to be explored.

[1]  M. Vandichel,et al.  Active site engineering in UiO-66 type metal-organic frameworks by intentional creation of defects: a theoretical rationalization , 2015 .

[2]  N. D. Browning,et al.  Low-Dose and In-Painting Methods for (Near) Atomic Resolution STEM Imaging of Metal Organic Frameworks (MOFs) , 2017, Microscopy and Microanalysis.

[3]  Dorina F. Sava,et al.  Zeolite-like metal-organic frameworks (ZMOFs): design, synthesis, and properties. , 2015, Chemical Society reviews.

[4]  Carlo Lamberti,et al.  A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability. , 2008, Journal of the American Chemical Society.

[5]  A. Cooper,et al.  Modular and predictable assembly of porous organic molecular crystals , 2011, Nature.

[6]  J. Hupp,et al.  Probing the correlations between the defects in metal-organic frameworks and their catalytic activity by an epoxide ring-opening reaction. , 2016, Chemical communications.

[7]  Yuriy Román‐Leshkov,et al.  Activation of Methyltrioxorhenium for Olefin Metathesis in a Zirconium-Based Metal-Organic Framework. , 2018, Journal of the American Chemical Society.

[8]  R. Fischer,et al.  Defect-Engineered Metal–Organic Frameworks , 2015, Angewandte Chemie.

[9]  Michael O'Keeffe,et al.  Reticular synthesis and the design of new materials , 2003, Nature.

[10]  C. Serre,et al.  A Chromium Terephthalate-Based Solid with Unusually Large Pore Volumes and Surface Area , 2005, Science.

[11]  B. L. Mehdi,et al.  Bridging Zirconia Nodes within a Metal-Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires. , 2017, Journal of the American Chemical Society.

[12]  François-Xavier Coudert,et al.  Correlated Defect Nano-Regions in a Metal–Organic Framework , 2014, Nature Communications.

[13]  Michael W. Anderson,et al.  Crystal form, defects and growth of the metal organic framework HKUST-1 revealed by atomic force microscopy , 2008 .

[14]  J. Ying,et al.  A tri-continuous mesoporous material with a silica pore wall following a hexagonal minimal surface. , 2009, Nature chemistry.

[15]  Bartolomeo Civalleri,et al.  Disclosing the Complex Structure of UiO-66 Metal Organic Framework: A Synergic Combination of Experiment and Theory , 2011 .

[16]  Michael O'Keeffe,et al.  Systematic Design of Pore Size and Functionality in Isoreticular MOFs and Their Application in Methane Storage , 2002, Science.

[17]  Yasuhiro Sakamoto,et al.  Direct imaging of the pores and cages of three-dimensional mesoporous materials , 2000, Nature.

[18]  Sanliang Ling,et al.  Dynamic acidity in defective UiO-66 , 2015, Chemical science.

[19]  Michel Waroquier,et al.  Synthesis modulation as a tool to increase the catalytic activity of metal-organic frameworks: the unique case of UiO-66(Zr). , 2013, Journal of the American Chemical Society.

[20]  Carlo Lamberti,et al.  Detailed Structure Analysis of Atomic Positions and Defects in Zirconium Metal‒Organic Frameworks , 2014 .

[21]  David S. Sholl,et al.  How Reproducible Are Isotherm Measurements in Metal–Organic Frameworks? , 2017 .

[22]  Hans-Beat Bürgi,et al.  Definitive molecular level characterization of defects in UiO-66 crystals. , 2015, Angewandte Chemie.

[23]  T. Loiseau,et al.  Three-dimensional MOF-type architectures with tetravalent uranium hexanuclear motifs (U6O8). , 2013, Chemistry.

[24]  M. Tsapatsis,et al.  Selective Glucose‐to‐Fructose Isomerization over Modified Zirconium UiO‐66 in Alcohol Media , 2018 .

[25]  S. Iijima,et al.  Direct evidence for atomic defects in graphene layers , 2004, Nature.

[26]  R. Fischer,et al.  Defective Metal‐Organic Frameworks , 2018, Advanced materials.

[27]  Ian D. Williams,et al.  A chemically functionalizable nanoporous material (Cu3(TMA)2(H2O)3)n , 1999 .

[28]  M. O'keeffe,et al.  Design and synthesis of an exceptionally stable and highly porous metal-organic framework , 1999, Nature.

[29]  Kenji Sumida,et al.  Carbon dioxide capture in metal-organic frameworks. , 2012, Chemical reviews.

[30]  S. Kitagawa,et al.  Soft porous crystals. , 2009, Nature chemistry.

[31]  C. Detavernier,et al.  Atomic Layer Deposition of Pt Nanoparticles within the Cages of MIL-101: A Mild and Recyclable Hydrogenation Catalyst , 2016, Nanomaterials.

[32]  D. Lamb,et al.  Chemical diversity in a metal–organic framework revealed by fluorescence lifetime imaging , 2018, Nature Communications.

[33]  Ryan P. Lively,et al.  Defects in Metal-Organic Frameworks: Challenge or Opportunity? , 2015, The journal of physical chemistry letters.

[34]  K. Lillerud,et al.  Structural determination of a highly stable metal-organic framework with possible application to interim radioactive waste scavenging: Hf-UiO-66 , 2012 .

[35]  E. Andreoli,et al.  Post-Synthetic Ligand Exchange in Zirconium-Based Metal-Organic Frameworks: Beware of The Defects! , 2018, Angewandte Chemie.

[36]  I. Díaz,et al.  Atomic Observations of Microporous Materials Highly Unstable under the Electron Beam: The Cases of Ti‐Doped AlPO4‐5 and Zn–MOF‐74 , 2015 .

[37]  Omar K Farha,et al.  Metal-organic framework materials as catalysts. , 2009, Chemical Society reviews.

[38]  Bin Zheng,et al.  Unravelling surface and interfacial structures of a metal-organic framework by transmission electron microscopy. , 2017, Nature materials.

[39]  Sachin Chavan,et al.  Defect Engineering: Tuning the Porosity and Composition of the Metal–Organic Framework UiO-66 via Modulated Synthesis , 2016 .

[40]  François-Xavier Coudert,et al.  Interplay between defects, disorder and flexibility in metal-organic frameworks. , 2019, Nature chemistry.

[41]  Hong-Cai Zhou,et al.  Selective gas adsorption and separation in metal-organic frameworks. , 2009, Chemical Society reviews.

[42]  Ping Chen,et al.  Unusual and highly tunable missing-linker defects in zirconium metal-organic framework UiO-66 and their important effects on gas adsorption. , 2013, Journal of the American Chemical Society.

[43]  Sachin Chavan,et al.  Tuned to Perfection: Ironing Out the Defects in Metal–Organic Framework UiO-66 , 2014 .

[44]  R. Sougrat,et al.  Atomic-resolution transmission electron microscopy of electron beam–sensitive crystalline materials , 2018, Science.