Investigating adsorption of organic compounds in metal-organic framework MIL-53

Abstract

Metal-organic frameworks (MOFs) are versatile materials that incorporate metal centers along with organic linkers in highly ordered, intricate structures. MIL-53 is a MOF that exhibits a "breathing effect," where the pore size and MOF topology are profoundly influenced by the identity and binding mechanism of guest molecules. This phenomenon renders MIL-53 a promising candidate for sensing applications. In this report, the adsorption of various organic compounds within MIL-53 is investigated using a combination of complementary techniques. Thermal gravimetric analysis experiments confirm loading of the guest molecules and yield insight into adsorption interactions and strengths. Significant guest-induced changes in the crystal structure of MIL-53 are revealed by powder X-ray diffraction experiments; specific unique phases of MIL-53 are related to the identity of the guest molecule and its binding mechanism to the framework. 27 Al and 13 C solid-state NMR experiments probe the interaction between guest molecules and MIL-53. The relationship between the nature of the guest, the structure of MIL-53, and 27 Al NMR parameters is explored. 27 Al NMR parameters are sensitive to the host-guest binding mechanism (i.e., hydrogenbonding or -stacking interactions) and yield valuable information regarding the influence of the adsorbates on the local aluminum environment. This combination of physical characterization techniques is a useful probe of guest adsorption and the breathing effect within MIL-53 and should prove useful for investigation of related MOFs. Résumé: Les réseaux métallo-organiques (MOF, acronyme anglais pour Metal-Organic Frameworks) sont des matériaux polyvalents où des centres métalliques sont incorporés dans un réseau organique formant des structures complexes et hautement ordonnées. Le MIL-53 est un réseau métallo-organique présentant un « effet de respiration », dont la taille des pores et la topologie du réseau métallo-organique dépendent fortement de l'identité et du mécanisme de liaison des molécules invitées. Ce phénomène fait du MIL-53 un candidat prometteur pour des applications dans le domaine des capteurs. Dans les présents travaux, nous avons étudié l'adsorption de divers composés organiques au MIL-53 à l'aide d'un ensemble de techniques complémentaires. Des analyses thermogravimétriques confirment la charge de molécules invitées et fournissent un aperçu des interactions et des forces d'adsorption. Des expériences de diffraction des rayons X sur poudre ont permis de révéler des modifications importantes de la structure cristalline du MIL-53 induites par l'invité; des phases uniques propres au MIL-53 sont liées à l'identité de l'invité et à son mécanisme de liaison au réseau. Des expériences de RMN 27 Al et 13 C à l'état solide ont permis d'explorer les interactions entre les molécules invitées et le MIL-53. Nous avons étudié la relation entre la nature de l'invité, la structure du MIL-53 et les paramètres RMN 27 Al. Ces derniers sont sensibles au mécanisme de liaison hôte-invité (c.-à -d. les l...

NMR crystallography to probe the breathing effect of the MIL-53(Al) metal–organic framework using solid-state NMR measurements of 13C–27Al distances

“…The experimental 13 C isotropic chemical shifts of the resonances are given in Table 1. These spectra are in full agreement with previous studies (Loiseau et al, 2004;Ibrahim et al, 2015;Jiang et al, 2010). The three resonances are non-ambiguously assigned to the three C-atom sites for both forms.…”

“…Isotropic chemical shifts iso ( 13 C) of the carbon sites and iso ( 27 Al fits of these spectra yield the NMR parameters given in Table 1, which agree well with the previously reported values (Loiseau et al, 2004;Lieder et al, 2010a;Ibrahim et al, 2015;Liu et al, 2013). 4.1.3.…”

“…Solid-state NMR spectroscopy (SS-NMR) complements PXRD since it allows a study of the location of extra-framework entities and atomic-level dynamics (Sutrisno & Huang, 2013;Martineau et al, 2014;Haouas et al, 2011Haouas et al, , 2012Bonhomme et al, 2014). Nevertheless, for MIL-53(Al), SS-NMR studies have been limited so far to one-dimensional (1D) 1 H, 27 Al or 13 C experiments (Loiseau et al, 2004;Horcajada et al, 2008;Springuel-Huet et al, 2010;Ibrahim et al, 2015;Liu et al, 2013;Jiang et al, 2010;Lieder et al, 2010b) or 1 H! 13 C HETCOR experiments (Goesten et al, 2011).…”

Complete multinuclear solid‐state NMR of metal‐organic frameworks: The case of α‐Mg‐formate

“…There have been many recent reports that include the use of metal SSNMR to characterize MOFs . Although metal centers are ubiquitous within MOFs and should serve as a convenient spectroscopic handle for SSNMR characterization, many MOFs feature multiple non‐equivalent metal sites that reside in similar chemical environments, which give rise to overlapping signals and pose a severe obstacle to metal SSNMR characterization.…”

“…Research in our group has been focused on MOF characterization by multinuclear NMR in several areas: interrogating the metal centres, probing linker atoms, monitoring the behavior of guest molecules in the MOFs, and understanding interactions between guest species and the framework . In this article, we aim to use the α‐Mg‐formate (Mg 3 (HCOO) 6 MOF as an example to illustrate the power of SSNMR for MOF characterization, as it features metal ( 25 Mg), linker ( 1 H, 13 C, 17 O), and guest ( 13 C, 2 H) isotopes that are all NMR‐active.…”