Unraveling the Guest‐Induced Switchability in the Metal‐Organic Framework DUT‐13(Zn)

The switching mechanism of the flexible framework Zn4O(benztb)1.5 (benztb=N,N,N’,N’‐benzidine tetrabenzoate), also known as DUT‐13, was studied by advanced powder X‐ray diffraction (PXRD) and gas physisorption techniques. In situ synchrotron PXRD experiments upon physisorption of nitrogen (77 K) and n‐butane (273 K) shed light on the hitherto unnoticed guest‐induced breathing in the MOF. The mechanism of contraction is based on the conformationally labile benztb ligand and accompanied by a reduction in specific pore volume from 2.03 cm3 g−1 in the open‐pore phase to 0.91 cm3 g−1 in the contracted‐pore phase. The high temperature limit for adsorption‐induced contraction of 170 K, determined by systematic temperature variation of methane adsorption isotherms, indicates that the DUT‐13 framework is softer than other mesoporous MOFs like DUT‐49 and does not support the formation of overloaded metastable states required for negative gas‐adsorption transitions. Breathe! Combining synchrotron in situ PXRD with gas adsorption has shed light on the mechanism of guest‐induced breathing in dynamic DUT‐13 framework. In the contracted‐pore phase, the crystal has pores half the volume of those in the open‐pore phase; this is consistent with the adsorption isotherms. Methane physisorption isotherms at different temperatures indicate the softness of the framework.