Unlike traditional polymers, this structure allows MOFs to have well-defined, open interior spaces that can allow certain molecules to pass through and filter out others. In addition, the presence of metals provides an interesting chemical composition. Metals can serve as catalysts or preferentially bind to one molecule in a mixture.
Knowing what we know now, it seems obvious that this will work. But when Robeson began his work at the University of Melbourne, the few people who thought about the problem at all expected that the molecules he created would be unstable and would break down.
The first MOF built by Robson used copper as the base metal. It was bound to an organic molecule that retained its rigid structure due to the presence of a benzene ring that did not bend. Both the organic molecule and the copper can form four different bonds, allowing the structure to grow, performing the rough equivalent of stacking triangular pyramids—a conscious choice by Robson.
However, the internal cavities remained filled with the solvent in which the MOF was formed. But the solvent could move freely through the material. However, based on this example, Robson predicted many properties that have since been incorporated into various MOFs: the ability to retain their structure even after solvents are removed, the presence of catalytic sites, and the ability of MOFs to act as filters.
Expansion of the concept
This may all seem very optimistic for someone's first attempt. But the measure of Robeson's success is that he convinced other chemists of its potential. One of them was Susumu Kitagawa from Kyoto University. Kitagawa and his colleagues built MOFs with large internal channels extending along the entire length of the material. Made in an aqueous solution, MOF can be dried and a gas stream passed through it, and the structure will retain molecules such as oxygen, nitrogen and methane.
