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Adsorption Contraction Mechanics: Understanding Breathing Energetics in Isoreticular Metal–Organic Frameworks

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journal contribution
posted on 25.07.2018, 00:00 by Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Ulrich Stoeck, Pascal G. Yot, Paul Iacomi, Philip Llewellyn, Guillaume Maurin, François-Xavier Coudert, Stefan Kaskel
A highly porous metal–organic framework DUT-48, isoreticular to DUT-49, is reported with a high surface area of 4560 m2·g–1 and methane storage capacity up to 0.27 g·g–1 (164 cm3·cm–3) at 6.5 MPa and 298 K. The flexibility of DUT-48 and DUT-49 under external and internal (adsorption-induced) pressure is analyzed and rationalized using a combination of advanced experimental and computational techniques. While both networks undergo a contraction by mechanical pressure, only DUT-49 shows adsorption-induced structural transitions and negative gas adsorption of n-butane and nitrogen. This adsorption behavior was analyzed by microcalorimetry measurements and molecular simulations to provide an explanation for the lack of adsorption-induced breathing in DUT-48. It was revealed that for DUT-48, a significantly lower adsorption enthalpy difference and a higher framework stiffness prevent adsorption-induced structural transitions and negative gas adsorption. The mechanical behavior of both DUT-48 and DUT-49 was further analyzed by mercury porosimetry experiments and molecular simulations. Both materials exhibit large volume changes under hydrostatic compression, demonstrating noteworthy potential as shock absorbers with unprecedented high work energies.