By Josh Perry, Editor
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Researchers at the Ghent University Center for Molecular Modeling in Belgium have discovered through computer simulations that the temperature at which metal-organic frameworks expand or shrink can be tuned, which makes it possible to use them in thermostats that work at the molecular level.

Researchers made a breakthrough that could lead to the development of molecular-level thermostats. (Ghent University)

“Metal-organic frameworks are riddled with minuscule pores, no more than a billionth of a meter in diameter,” an article from the university explained. “Despite this limited size, the pores offer opportunities for a wide array of cutting-edge applications. Metal-organic frameworks thus far attracted attention for the detection of chemical weapons, the transport of drugs in blood or the capture of greenhouse gases.”

The specific metal-organic frameworks that Ghent researchers studied have pores that open or close when heated or cooled. This causes a sudden increase or decrease in volume. Researchers determined that the temperature at which this occurs depends on the make-up of the framework.

“Their molecular building blocks can therefore be selected as a function of the temperature at which a reaction is required,” the article continued. “In particular, the switching temperature results from a subtle balance between the attraction between the pore walls and the mobility of the atoms.”

This study gives scientists new ideas for creating thermostats from a handful of molecules, which could be helpful as the miniaturization of electronics continues.

The research was recently published in Nature Communications. The abstract read:

“Temperature-responsive flexibility in metal-organic frameworks (MOFs) appeals to the imagination. The ability to transform upon thermal stimuli while retaining a given crystalline topology is desired for specialized sensors and actuators. However, rational design of such shape-memory nanopores is hampered by a lack of knowledge on the nanoscopic interactions governing the observed behavior.

“Using the prototypical MIL-53(Al) as a starting point, we show that the phase transformation between a narrow-pore and large-pore phase is determined by a delicate balance between dispersion stabilization at low temperatures and entropic effects at higher ones.

“We present an accurate theoretical framework that allows designing breathing thermo-responsive MOFs, based on many-electron data for the dispersion interactions and density-functional theory entropy contributions. Within an isoreticular series of materials, MIL-53(Al), MIL-53(Al)-FA, DUT-4, DUT-5 and MIL-53(Ga), only MIL-53(Al) and MIL-53(Ga) are proven to switch phases within a realistic temperature range.”