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.
MOF’s have many potential apps: antimicrobial agents, H-storage materials and solar-cell components.
Despite their rigid-sounding name, MOF structures are also dynamic – much more so than previously thought. This discovery could lead to the synthesis of brand-new types of materials. 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 MOF5. For over 15 yrs, 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, they 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. 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, thus they could dope in cobalt ions to form a MOF that would otherwise have been predicted to not be accessible. The 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. http://www.eurekalert.org/pub_releases/2015-07/acs-dct072415.php
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