Prediction of the Conditions for Breathing of Metal Organic Framework Materials Using a Combination of X-ray Powder Diffraction, Microcalorimetry, and Molecular Simulation

Abstract

The adsorption of C1 to C4 linear hydrocarbons in the flexible metal organic framework MIL-53(Cr) has been followed by adsorption manometry coupled with microcalorimetry and Synchrotron X-ray powder diffraction. This experimental investigation was completed by molecular modeling. In the case of methane, the solid remains rigid whatever the adsorbate amount. However for the C2-C4 series, an increasing flexibility of the structure is observed, which is ascribed first to a breathing of the material from a large pore to a narrow pore form followed by a further expansion at high pressure. The collected thermodynamic and structural information suggests that a minimum adsorption enthalpy of ca. 20 kJ mol (-1) in the initial large pore structure of MIL-53(Cr) is required to induce the structural transition "large to narrow pore". Further, the enthalpy of adsorption can be used to predict the pressure at which the structure reopens. Finally, the magnitude of the breathing can be related to the size of the probe molecule via the van der Waals volume. The above trends have been successfully verified in the case of water and carbon dioxide. This combined experimental and theoretical approach gives the first elements for the prediction of whether or not the MIL53 and similar flexible structures will respond to gas loading and what would be the pressure required and further the amplitude of the induced breathing.

Double Structural Transition in Hybrid Material MIL-53 upon Hydrocarbon Adsorption: The Thermodynamics Behind the Scenes

“…1 The MIL-53 materials family, 2 a particularly eye-catching case of the last category, has attracted a lot of attention due to its large flexibility and the occurrence of a double structural transition upon adsorption of some gases (CO 2 , H 2 O, C 2 H 6 ,...) but not others (H 2 , CH 4 ). 3 It was also reported very recently 4 that liquid phase adsorption of para-xylene does induce a structural transition, while ortho-and meta-xylene do not. The studies performed so far, both experimentally and by molecular simulation, mainly focused on structural characterization and energetics (by calorimetry, forcefield-based calculations and DFT).…”

“…8 We now turn to the issue of how the presence or absence of guest-induced structural transitions can be related to the properties of the guest molecule. New experimental data on the adsorption of various species in the pores of MIL-53 have been published very recently, in both gas phase (for C n H 2n+2 , n e 4) 3 and liquid phase (for o-, m-, and p-xylene). 4 In the case of materials such as MIL-53, where the large-pore (lp) form is intrinsically more stable than the narrow-pore (np) form at room temperature, our taxonomy predicts either the occurrence of two structural transitions upon gas adsorption or the absence of any transition.…”

Crystallography of Representative MOFs Based on Pillared Cyanonickelate (PICNIC) Architecture

“…Many PICNICs exhibit hysteretic adsorption-desorption behavior which is often associated with the 'gate-opening' effect ( Figure 4). They also show dynamic host-guest behavior due to structural transitions which occur between the guest-free and guest-loaded states [78][79][80][81][82].…”

Bio-Inspired Metal-Organic Frameworks in the Pharmaceutical World: A Brief Review

“…Some MOFs can present structural flexibility or "breathing effects," which allows them to modulate their pore size upon adsorption of organic molecules into the pores, while their crystallinity is maintained [22,50,54,59]. One example of BioMOFs presenting a "breathing effect" is MIL-53 [22,54,100].…”

“…Less toxic systems, using iron and more flexible MILs, are under study [25], and the first biodegradable therapeutic MOF, BioMIL-1, was reported by Miller et al in 2010 [27]. The large breathing effect that MOFs can attain is another particularly interesting feature for potential applications in drug delivery [54,59,52].…”