Quantitative Analysis of Linker Composition and Spatial Arrangement of Multivariate Metal–Organic Framework UiO-66 through ¹H Fast MAS NMR

Abstract

Fast 1H magic-angle spinning (MAS) solid-state NMR spectroscopy was utilized for quantitative analysis of the linker composition and spatial arrangement of functional groups of MTV-UiO-66–(BDC–CH3) x –(BDC–OH) y –(BDC–NH2)1–x−y . 2D 1H–1H DQ–SQ MAS NMR experiments facilitate the 1H NMR chemical shift assignments. It was demonstrated that the fast 1H MAS technique could improve the resolution of 1H NMR spectra and allow the quantitative determination of the relative content of functional linkers without acid-digested treatment of MTV-UiO-66. The spatial proximities of various components including BDC–CH3 and BDC–OH were verified from the 2D 1H–1H spin diffusion homonuclear correlation experiments. The relative intensities of the 1H–1H spin-diffusion buildup curves via OH → CH3 and CH3 → OH pathways were closely related to the linker composition of MTV-UiO-66. Additionally, the extracted slices along with the CH3 site and OH site from the 2D 1H–1H spin diffusion NMR spectra are nearly the same as the corresponding 1D 1H MAS NMR spectra, indicating that the three functional linkers are in approximately random distribution in MTV-UiO-66-A and MTV-UiO-66-B. This work provides an efficient approach to examine the spatial arrangement of MTV-MOFs containing three distinct linkers.

Quantifiable Surface Methoxy Groups on Zr(OH) Groups of UiO-66 Metal–Organic Framework: Generation from Methanol-13C and Reactivity

“…In the next step, the UiO-66 material was investigated directly by means of MAS NMR spectroscopy. 1 H MAS NMR spectra in Figure show activated UiO-66 and the same material after adsorption of methanol- 13 C at 298 K. The 1 H peaks on activated UiO-66 were assigned based on literature. ,, According to these previous investigations, the aromatic C–H protons are found in a chemical shift ranging from δ 1H = 8 to 7 ppm, while distinct types of Zr­(OH) groups at δ 1H = 2.6 to 2.0 and at δ 1H = 1.5 to ∼1.1 ppm can be distinguished. It should be noted that, sometimes, only one of these groups is visible in 1 H MAS NMR spectra.…”

Unraveling the Surface Hydroxyl Network on In2O3 Nanoparticles with High-Field Ultrafast Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy

“…2D 1 H- 1 H DQ-SQ MAS NMR experiments were performed to further explore the hydroxyl pairs on a smaller scale (more restricted distances). The buildup trend of the DQ coherence signal is strongly dependent on the internuclear distances, , and this process is subjected to the dipolar truncation effect, which often prohibits the observation of long-range proximity between protons. , In addition, DQ coherence allows for the characterization of proximities between the same kind of hydroxyls, i.e., via autocorrelation peaks, which cannot be obtained from the SQ-SQ experiment . As depicted in Figure b, autocorrelation peaks along the diagonal line were observed for μ 1 -OH (H A and H B ) and μ 2 -OH (H C -H F ), indicating the correlation of these chemically identical hydroxyl groups.…”

Advances in the characterization of inorganic solids using NMR correlation experiments

“…Correlation NMR experiments are essential techniques to probe the structure of MOFs, and notably the location of defects, as well as the host-guest interactions in these materials. For instance, 2D 1 H 2Q-1Q homonuclear correlation at high MAS frequency has been used to assign the 1 H signals of MOFs (see Figure 6) and probe the interactions of caffeine with UiO-66(Zr) MOFs 111,340,341 , whereas 2D 1 H spin diffusion measurements have been employed to probe the spatial arrangement of linkers in MOFs made of different linkers 342,343 as well as the host-guest interactions and ethane/ethylene separation mechanism on zeolitic imidazolate frameworks 344,345 .…”