Solid‐State NMR Spectroscopy: A Powerful Technique to Directly Study Small Gas Molecules Adsorbed in Metal–Organic Frameworks

Abstract

Metal-organic frameworks (MOFs) have shown great potential in gas separation and storage, and the design of MOFs for these purposes is an on-going field of research. Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a valuable technique for characterizing these functional materials. It can provide a wide range of structural and motional insights that are complementary to and/or difficult to access with alternative methods. In this Concept article, the recent advances made in SSNMR investigations of small gas molecules (i.e., carbon dioxide, carbon monoxide, hydrogen gas and light hydrocarbons) adsorbed in MOFs are discussed. These studies demonstrate the breadth of information that can be obtained by SSNMR spectroscopy, such as the number and location of guest adsorption sites, host-guest binding strengths and guest mobility. The knowledge acquired from these experiments yields a powerful tool for progress in MOF development.

Solid‐state NMR studies of the acidity of functionalized metal–organic framework UiO‐66 materials

“…[35] Solid-state NMR spectroscopy was frequently utilized for the exploration of the chemical structures, dynamic behavior, and host-guest interaction of MOFs. [36][37][38][39][40][41][42][43][44] To investigate the chemical composition of these activated UiO-66-X (X = -H, -2COOH, -SO 3 H) and multivariate functionalized UiO-66-X samples, 1 H and 13 C MAS NMR experiments were conducted. Figure 2 shows the 1 H MAS and 13 C CP/MAS NMR spectra of dehydrated UiO-66, UiO-66-SO 3 H, UiO-66-2COOH and multivariate functionalized UiO-66-X samples.…”

“…Solid‐state NMR spectroscopy was frequently utilized for the exploration of the chemical structures, dynamic behavior, and host–guest interaction of MOFs . To investigate the chemical composition of these activated UiO‐66‐X (X = ‐H, ‐2COOH, ‐SO 3 H) and multivariate functionalized UiO‐66‐X samples, 1 H and 13 C MAS NMR experiments were conducted.…”

Flexible Quasi‐Solid‐State Composite Electrolyte Membrane Derived from a Metal‐Organic Framework for Lithium‐Metal Batteries

“…In initial Uio‐67, Zr 4+ is connected to four ester groups, every ester group are in the same chemical environment, only one peak appears in 13 C NMR. After Li−IL is absorbed into the nanopore of MOF, some −COO groups disconnect with Zr 4+ , instead, they interact with [EMIM] + , at the same time, Zr 4+ interacts with [TFSI] − , therefore, chemical environment of some −COO changes, and new peak appears in NMR spectrum . Additionally, according to the N 2 adsorption‐ desorption isothermal curve tested at 77 K shown in Figure d, the BET surface area of the pristine Uio‐67 MOF host is 2253 m 2 g −1 , demonstrating its high porosity, while it drops to 13 m 2 g −1 for the Li−IL@Uio, suggesting a high occupation ratio of Li−IL guest in the pores of MOF host.…”

“…After LiÀ IL is absorbed into the nanopore of MOF, some À COO groups disconnect with Zr 4 + , instead, they interact with [EMIM] + , at the same time, Zr 4 + interacts with [TFSI] À , therefore, chemical environment of some À COO changes, and new peak appears in NMR spectrum. [30] Additionally, according to the N 2 adsorption-desorption isothermal curve tested at 77 K shown in Figure 1d, the BET surface area of the pristine Uio-67 MOF host is 2253 m 2 g À 1 , demonstrating its high porosity, while it drops to 13 m 2 g À 1 for the LiÀ IL@Uio, suggesting a high occupation ratio of LiÀ IL guest in the pores of MOF host. Moreover, the absorption-desorption curve shows a typical Type I isotherms, [34] suggesting the microporous adsorption characteristic of Uio-67.…”

New insights into solvent-induced structural changes of 13C labelled metal–organic frameworks by solid state NMR

“…NMR is widely used to study MOFs and their host-guest interactions with adsorbed species by probing either the host or the guest molecules. [18][19][20][21][22][23][24][25][26][27][28][29][30][31] Sensitivity is often a major limitation of NMR spectroscopy, especially for nuclei with low natural abundance like 13 C. Isotope enrichment is then highly desirable. In the present contribution, we describe the application of solid-state NMR to study the interaction of various organic solvent molecules with the flexible MOF DUT-8(Ni) 32 (Ni 2 (2,6ndc) 2 (dabco) (2,6ndc = 2,6-naphthalene-dicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane)) to analyse structural changes and underlying, potentially selective host-guest interactions.…”