This illustration shows how neon is captured within the pores of NiMOF-74 at 100K and 100 bar of neon gas pressure. Image: CCDC.
This illustration shows how neon is captured within the pores of NiMOF-74 at 100K and 100 bar of neon gas pressure. Image: CCDC.

In a new study, researchers from the Cambridge Crystallographic Data Centre (CCDC) in the UK and the US Department of Energy’s (DOE’s) Argonne National Laboratory have teamed up to capture neon within a porous crystalline framework.

Neon is the most unreactive element and is a key component in semiconductor manufacturing, but it has never been studied within an organic or metal-organic framework (MOF) until now. These new results, which include critical studies carried out at the Advanced Photon Source (APS), a DOE Office of Science user facility at Argonne, also point the way towards a more economical and greener industrial process for neon production.

Although best known for its iconic use in neon signs, industrial applications of neon have recently become dominated by its use in excimer lasers to produce semiconductors. Despite being the fifth most abundant element in the atmosphere, the cost of pure neon gas has risen significantly over the years, increasing the demand for better ways to separate and isolate the gas.

In 2015, CCDC scientists presented a talk at the annual American Crystallographic Association (ACA) meeting on the array of elements that have been studied within an organic or metal-organic environment. They challenged the crystallographic community to find the next and possibly last element to be added to the Cambridge Structural Database (CSD). A chance encounter at that meeting with Andrey Yakovenko, a beamline scientist at the APS, resulted in a collaborative project to capture neon – the 95th element to be observed in the CSD.

Neon’s low reactivity, along with the weak scattering of X-rays due to its relatively low number of electrons, means that conclusive experimental observation of neon captured within a crystalline framework is very challenging. By conducting in situ high pressure gas flow experiments at X-Ray Science Division beamline 17-BM at the APS using the X-ray powder diffraction technique at low temperatures, the researchers have now managed to elucidate the structure of two different metal-organic frameworks (MOFs) with neon gas captured inside them.

“This is a really exciting moment representing the latest new element to be added to the CSD and quite possibly the last given the experimental and safety challenges associated with the other elements yet to be studied” said Peter Wood, senior research scientist at the CCDC and lead author of a paper on this work in Chemical Communications. “More importantly, the structures reported here show the first observation of a genuine interaction between neon and a transition metal, suggesting the potential for future design of selective neon capture frameworks.”

The structure of neon captured within a MOF known as NiMOF-74, a porous framework built from nickel metal centers and organic linkers, shows clear nickel-to-neon interactions forming at low temperatures. These interactions are significantly shorter than would be expected from a typical weak contact.

“These fascinating results show the great capabilities of the scientific program at 17-BM and the Advanced Photon Source,” said Yakovenko. “Previously we have been doing experiments at our beamline using other much heavier, and therefore easily detectable, noble gases such as xenon and krypton. However, after meeting co-authors Pete, Colin, Amy and Suzanna at the ACA meeting, we decided to perform these much more complicated experiments using the very light and inert gas – neon. In fact, only by using a combination of in situ X-ray powder diffraction measurements, low temperature and high pressure have we been able to conclusively identify the neon atom positions beyond reasonable doubt”.

“This is a really elegant piece of in situ crystallography research and it is particularly pleasing to see the collaboration coming about through discussions at an annual ACA meeting,” said Chris Cahill, past president of the ACA and professor of chemistry at George Washington University.

This story is adapted from material from the Cambridge Crystallographic Data Centre, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.