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Don't call them stiff: Metal organic frameworks show unexpected flexibility

Date:
July 29, 2015
Source:
American Chemical Society
Summary:
Metal organic frameworks (MOFs) are proving to be incredibly flexible with a myriad of potential applications including as antimicrobial agents, hydrogen-storage materials and solar-cell components. And despite their rigid-sounding name, researchers are reporting that MOF structures are also dynamic -- much more so than previously thought. This discovery could lead to the synthesis of brand-new types of materials.
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Over time, the zinc ions in MOF-5 (pink solutions) get replaced with cobalt ions, (blue solutions) demonstrating the dynamics of metal organic frameworks.
Credit: American Chemical Society

Metal organic frameworks (MOFs) are proving to be incredibly flexible with a myriad of potential applications including as antimicrobial agents, hydrogen-storage materials and solar-cell components. And despite their rigid-sounding name, researchers are reporting that MOF structures are also dynamic -- much more so than previously thought. They report this discovery, which could lead to the synthesis of brand-new types of materials, in ACS Central Science.

As the name implies, MOFs are composed of networks of organic (carbon-based) compounds interspersed with metal ions. Many different combinations of metals and organic components exist, but much of what we know about these systems comes from a zinc and benzene di-acid framework called MOF-5. For over 15 years, the prevailing view of MOF-5, and all MOFs, has been that they are static. But thanks to a serendipitous finding, Mircea Dinca and colleagues suspected that wasn't true.

During a routine characterization, the researchers found that some solvent molecules stuck to MOF-5 when they used a method that should have gotten rid of it all. That observation suggested there might be different species within the material than previously believed. So, the team investigated further and demonstrated that the zinc inside MOF-5 can adopt several different arrangements with both the organic components and the solvent. Over time, it can shift between these geometries. The change is gradual, with one atom changing at a time. Taking advantage of the slow exchange, the authors could dope in cobalt ions to form a MOF that would otherwise have been predicted to not be accessible. Dinca says that their finding could shed new light on how guest molecules, like gases, bind MOFs. Such an understanding could lead to even more flexibility in the applications of MOFs in the future.


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Journal Reference:

  1. Carl K. Brozek, Vladimir K. Michaelis, Ta-Chung Ong, Luca Bellarosa, Núria López, Robert G. Griffin, Mircea Dincă. Dynamic DMF Binding in MOF-5 Enables the Formation of Metastable Cobalt-Substituted MOF-5 Analogues. ACS Central Science, 2015; 150729073042006 DOI: 10.1021/acscentsci.5b00247

Cite This Page:

American Chemical Society. "Don't call them stiff: Metal organic frameworks show unexpected flexibility." ScienceDaily. ScienceDaily, 29 July 2015. <www.sciencedaily.com/releases/2015/07/150729085918.htm>.
American Chemical Society. (2015, July 29). Don't call them stiff: Metal organic frameworks show unexpected flexibility. ScienceDaily. Retrieved May 24, 2017 from www.sciencedaily.com/releases/2015/07/150729085918.htm
American Chemical Society. "Don't call them stiff: Metal organic frameworks show unexpected flexibility." ScienceDaily. www.sciencedaily.com/releases/2015/07/150729085918.htm (accessed May 24, 2017).

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