Low Temperature Calorimetry Coupled with Molecular Simulations for an In-Depth Characterization of the Guest-Dependent Compliant Behavior of MOFs

In this study adsorption
microcalorimetry is employed to monitor
the adsorption of four probes (argon, oxygen, nitrogen, and carbon
monoxide) on a highly flexible mesoporous metal–organic framework
(DUT-49, DUT = Dresden University of Technology), precisely measuring
the differential enthalpy of adsorption alongside high-resolution
isotherms. This experimental approach combined with force field Monte
Carlo simulations reveals distinct pore filling adsorption behaviors
for the selected probes, with argon and oxygen showing abrupt adsorption
in the open pore form of DUT-49, in contrast with the gradual filling
for nitrogen and carbon monoxide. A complex structural transition
behavior of DUT-49 observed upon nitrogen adsorption is elucidated
through an isotherm deconvolution in order to quantify the fractions
of the open pore, contracted pore, and intermediate pore forms that
coexist at a given gas pressure. Finally, the heat flow measured during
the guest-induced structural contraction of DUT-49 allowed an exploration
of complex open-contracted pore transition energetics, leading to
a first assessment of the energy required to induce this spectacular
structural change.