Guest-Induced Switchable Breathing Behavior in a Flexible Metal–Organic Framework with Pronounced Negative Gas Pressure

Abstract

Flexible metal-organic frameworks (MOFs) have attracted great interest for their dynamically structural transformability in response to external stimuli. Herein, we report a switchable "breathing" or "gate-opening" behavior associated with the phase transformation between a narrow pore (np) and a large pore (lp) in a flexible pillared-layered MOF, denoted as MOF-1 as, which is also confirmed by SCXRD and PXRD. The desolvated phase (MOF-1 des) features a unique stepwise adsorption isotherm for N coupled with a pronounced negative gas adsorption pressure. For comparison, however, no appreciable CO adsorption and gate-opening phenomenon with stepwise sorption can be observed. Furthermore, the polar micropore walls decorated with thiophene groups in MOF-1 des reveals the selective sorption of toluene over benzene and p-xylene associated with self-structural adjustment in spite of the markedly similar physicochemical properties of these vapor molecules.

The impact of crystal size and temperature on the adsorption-induced flexibility of the Zr-based metal–organic framework DUT-98

“…Only few reports on the cycling behavior of flexible MOFs can be found in the literature. Shi et al reported on a shift of the gate pressure towards higher pressures upon cycling of the nitrogen adsorption/desorption at 77 K in Zn 2 (tdc) 2 (pvq) (H 2 tdc = 2,5-thiophenedicarboxylic acid, pvq = 5-(2-(pyridin-4-yl)vinyl)quinoline) [24]. Similar results are reported by Su et al on a redox-active flexible MOF [25].…”

Collective Breathing in an Eightfold Interpenetrated Metal–Organic Framework: From Mechanistic Understanding towards Threshold Sensing Architectures

“…The quest for switchable MOFs is driven to a large extent by a range of promising applications exemplified in reports on methane storage, molecular sensing, gas separation, proton conduction, and in reviews on drug delivery . Additionally, the studies of flexible MOFs are motivated by recently revealed novel counterintuitive phenomena such as negative gas adsorption or pronounced negative gas pressure . Their functional exploitation, however, remains challenging owing to the lack of design criteria for switchable MOFs .…”

Meta-MOFs: Framework Materials with Anomalous Behavior

“…The initial report from Tanaka et al suggests similar kinetically delayed gateopening processes should be observed for other gate-opening materials, when gases lacking strong intermolecular forces are used. In fact three doubly interpenetrated MOFs with wine-rack-like topology have been reported to show a similar kinetic gate-opening process with N 2 adsorption [99,100,101]. We note that careful analysis of adsorption kinetics is required to ensure the pressure step is due a long-lived metastable state and not caused by inadequate equilibration.…”