NMR Crystallography: Evaluation of Hydrogen Positions in Hydromagnesite by ¹³C{¹H} REDOR Solid‐State NMR and Density Functional Theory Calculation of Chemical Shielding Tensors

Abstract

Solid‐state NMR measurements coupled with density functional theory (DFT) calculations demonstrate how hydrogen positions can be refined in a crystalline system. The precision afforded by rotational‐echo double‐resonance (REDOR) NMR to interrogate 13C–1H distances is exploited along with DFT determinations of the 13C tensor of carbonates (CO32−). Nearby 1H nuclei perturb the axial symmetry of the carbonate sites in the hydrated carbonate mineral, hydromagnesite [4 MgCO3⋅Mg(OH)2⋅4 H2O]. A match between the calculated structure and solid‐state NMR was found by testing multiple semi‐local and dispersion‐corrected DFT functionals and applying them to optimize atom positions, starting from X‐ray diffraction (XRD)‐determined atomic coordinates. This was validated by comparing calculated to experimental 13C{1H} REDOR and 13C chemical shift anisotropy (CSA) tensor values. The results show that the combination of solid‐state NMR, XRD, and DFT can improve structure refinement for hydrated materials.

Enhancing Structural Rigidity via a Strategy Involving Protons for Creating Water-Resistant Mn4+-Doped Fluoride Phosphors

“…Of these, 6.58 ppm corresponds to the O–H–O band of H 2 O in the air adsorbed, and 17.43 and −4.17 ppm represent the spinning side bands of H 2 O. However, the 1 H NMR spectrum of KHTFM also exhibits close signals at 1.82 and 4.97 ppm, which are consistent with the different F–H–F crystallographic sites in the KHF host, as previously reported, − respectively, indicating that the hydrogen bonds are incorporated into the rigid framework of the KHTFM phosphors, and the degree of ordering of the materials is mildly effected by co-doping of [HMnF 6 ] − complexes.…”

Characterization of Chemisorbed Species and Active Adsorption Sites in Mg–Al Mixed Metal Oxides for High-Temperature CO2 Capture

“…The direct 13 C NMR spectra of 13 CO 2 -dosed MMOs and MgO (Figure ) present two distinct regions of observed 13 C chemical shifts. The peak at 125.1 ppm is assigned to physisorbed CO 2 as it agrees well with previously reported chemical shifts of physisorbed CO 2 in similar LDH and crystalline MgO materials. , The peaks in the region 160–170 ppm are assigned to chemisorbed carbonate and bicarbonate species in comparison to the known shifts of such compounds. − …”

Multiresolution 3D-DenseNet for Chemical Shift Prediction in NMR Crystallography

“…In practice, NMR crystallography is a structural model building procedure that depends on a number of NMR data types, of which chemical shifts in particular play a prominent role. A strength of NMR chemical shift data is its excellent sensitivity to hydrogen, which, given the importance of hydrogen-bonding in most molecular systems, makes it very complementary to X-ray diffraction techniques.…”