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

In this article we report the synthesis and detailed analysis of the highly porous metal-organic framework DUT-48, isoreticular to DUT-49 a material which shows an adsorption-induced structural transition. DUT-48 has impressive porosity and methane storage capacity, however displays conventional adsorption behaviour. The contrasting flexibility of DUT-48 and DUT-49 were analysed and rationalised using a combination of novel experimental and computational techniques. Microcalorimetry measurements, in conjunction with molecular simulations, demonstrate that DUT-48 has a significantly lower adsorption enthalpy difference and a higher framework stiffness which leads to an absence of adsorption-induced transitions and negative gas adsorption (NGA). However, by analysing the mechanical behaviour of both DUT-48 and DUT-49, employing mercury porosimetry experiments, we discovered that both materials exhibit large volume changes under hydrostatic compression, demonstrating noteworthy potential as shock absorbers, and directly linking internal adsorption-induced contraction to external hydrostatic compression.