Duet of Acetate and Water at the Defects of Metal–Organic Frameworks

Abstract

Metal−organic frameworks (MOFs) are porous crystalline materials with promising applications in molecular adsorption, separation, and catalysis. It has been discovered recently that structural defects introduced unintentionally or by design could have a significant impact on their properties. However, the exact chemical composition and structural evolution under different conditions at the defects are still under debate. In this study, we performed multidimensional solid-state nuclear magnetic resonance (SSNMR) coupled with computer simulations to elucidate an important scenario of MOF defects, uncovering the dynamic interplay between residual acetate and water. Acetate, as a defect modulator, and water, as a byproduct, are prevalent defect-associated species, which are among the key factors determining the reactivity and stability of defects. We discovered that acetate molecules coordinate to a single metal site monodentately and pair with water at the neighboring position. The acetates are highly flexible, which undergo fast libration as well as a slow kinetic exchange with water through dynamic hydrogen bonds. The dynamic processes under variable temperatures and different hydration levels have been quantitatively analyzed across a broad time scale from microseconds to seconds. The integration of SSNMR and computer simulations allows a precision probe into defective MOF structures with intrinsic dynamics and disorder.

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.…”

Centerband‐Only Detection of Exchange NMR with Natural‐Abundance Correction Reveals an Expanded Unit Cell in Phenylalanine Crystals

“…[21] In the same year, Kong and Wang applied 13 C CODEX to measure the distribution of acetate on metal organic framework (MOF) surfaces and describe the potential defects caused by acetate in the MOF structure. [22] However, previous reports of 13 C CODEX data considered only spin diffusion taking place between singly labelled carbon sites without consideration of the magnetization exchange to the 13 C from unlabeled sites, which occurs with a natural abundance of 1 %. Consideration of spins at 1 % abundance is not needed for small molecular size, such that the previous studies are clearly valid.…”

Defect‐Assisted Loading and Docking Conformations of Pharmaceuticals in Metal–Organic Frameworks

“…UiO-66). [36][37][38][39] Without the need of complex chemical modifications,the defects alter local chemical environment as well as the pore size and connectivity.F or many adsorbed pharmaceutical compounds,the defects in MOFs could be the real contributor behind the scenes.F or instance,s urface defects can greatly enhance the loading of DNAm olecules onto UiO-66 nanoparticles taking advantage of the zirconium-phosphate coordination. [40,41] Defective UiO-66 also demonstrates excellent utility for the loadings of single or multivariate drug molecules.…”