¹²⁹Xe NMR Study of the Framework Flexibility of the Porous Hybrid MIL-53(Al)

Abstract

The metal-organic framework MIL-53 exhibits a structural transition between two possible porous structures, so-called large-pore (lp) and narrow-pore (np) forms, depending on the temperature or when guest molecules are adsorbed. (129)Xe NMR has been used to study the lp --> np transition induced by the adsorption of xenon as revealed by the adsorption isotherms. The NMR spectra show that the two structures, characterized by two distinct lines, coexist for xenon pressures above 5 x 10(4) Pa at room temperature, but a complete transformation is achieved when the temperature is decreased. An original interpretation of the NMR results allowed us to quantify the rate of the structural transformation. In particular, at room temperature, we have shown that 28% of the channels remain open. Two possible interpretations of the hysteresis observed in the chemical shift variation versus xenon pressure are proposed.

Solid-State NMR Spectroscopy of Metal–Organic Framework Compounds (MOFs)

“…This phenomenon is in general observed for xenon in anisotropic local environments and was first described by Springuel-Huet and Fraissard [188]. Much more pronounced anisotropies could be observed previously for the metal–organic framework MIL-53(Al) [182] and other materials with narrow-pore channels (see, e.g., [172,174]). Moreover, the exchange of xenon between the adsorbed state inside the UMCM-1 pore system and the gas phase surrounding the crystallites can be visualized by 2D exchange spectroscopy (EXSY, see Figure 12).…”

“…A first application of 129 Xe NMR spectroscopy to MOFs has been reported in 2006 [179]. Subsequently, other authors made use of the favorable properties of 129 Xe NMR in order to study MOFs [23,180,181,182,183]. …”

129Xenon NMR: Review of recent insights into porous materials

“…The two conformations are easily distinguished by 129 Xe NMR and the transition between the two stable states has been thoroughly studied by Springuel-Huet et al [206]. At room temperature, the dehydrated solid adopts the lp form.…”

129Xe NMR chemical shift in Xe@C60 calculated at experimental conditions: Essential role of the relativity, dynamics, and explicit solvent

“…This includes studies of ordering and dynamics in liquid crystals, [3,4] solvent dynamics in liquids, [5,6] structure of porous solids, [7,8] polymers, [9,10] and clathrates. [11,12] Glasses, [13] metallo-organic frameworks, [14,15] and crystals [16] have been also studied by means of 129 Xe NMR.…”