When it comes to intricate molecular structures, researchers typically start by discovering nature’s handiwork, then build on it with their own creations. In a rare reversal of this order of events, however, investigators have only now identified naturally occurring examples of metal-organic frameworks (MOFs) that were first synthesized almost 20 years ago.

Since being developed in the late 1990s, the open, three-dimensional architecture of MOF crystals has attracted widespread interest for potential use as hydrogen or carbon dioxide storage media, powerful catalysts, or components of photovoltaic cells. Inorganic zeolite minerals demonstrate similar features but when chemists began employing organic constituents to create MOFs, the resulting guest inclusion complex was far larger, thereby offering a much broader range of potential applications.

As the development of MOFs in the laboratory continued, no one had ever come forward with a recovered organic mineral specimen demonstrating the same crystal arrangement. McGill University chemistry professor Tomislav Friscic was therefore struck when a Canadian mineralogical journal reported the details of two samples recovered from deep in a Siberian coal mine in 1942 that pointed toward just this kind of open architecture. Named stepanovite and zhemchuzhnikovite, the only account of their existence was found in the Russian research literature.

Curious, Friscic began to inquire about the two minerals and could find no one to help him. Finally, some four years after he had first read about them, a mineral vendor pointed him to a mining museum in Saint Petersburg, Russia, where staff members confirmed that the specimens were in fact stored there. Unfortunately, they could not be shipped out of the country for him to study.

In desperation, he asked his graduate student Igor Huskic to attempt the synthesis of artificial versions of the two minerals, based on the detailed description he had originally seen. The result indeed yielded a MOF, with all characteristics in agreement with those in the original mineral report. However, this work was not accepted for publication, as the only evidence for the existence of the minerals has been in an aging mineralogical report.

A breakthrough finally happened when Friscic managed to track professor Sergey Krivovichev of the Saint Petersburg State University and professor Igor Pekov of the Lomonosov Moscow State University, who were able not only to access the original mineral samples but also conduct a full single crystal X-ray diffraction experiment on them, which confirmed beyond doubt their exact structures.

Friscic’s six-year odyssey reached a decisive milestone at the beginning of August, when confirmation that stepanovite and zhemchuzhnikovite are MOFs was published in Science Advances. “What got me excited was not so much the structure of this mineral but that there were naturally occurring metal organic frameworks,” he says. “This is making us think that there are processes in nature — in the Earth itself — that lead to the formation of these metastable, open structures. That for me is a game-changer in how we look at MOFs.”

If MOFs are found in the earth’s crust, for example, then catalysis or gas absorption could be taking place there in a manner quite different than typically envisioned. That appears to have been the case in the coal mine where the samples were recovered from a drill core 230 metres beneath permafrost. “These are fairly abnormal conditions for a mineral to form,” Friscic says. Nevertheless, this example leads him to speculate that even biological molecules could be finding their way into these arrangements and producing some unusual chemistry.

For now, however, Friscic marvels at the fact that the inspiration for such speculation sat in storage for more than 70 years. “If a Russian team had been able to use technology in the 1940s that we use today, this whole idea of metal-organic frameworks could have been advanced by 30 or 40 years.”