Magic Angle Spinning NMR Spectra Research Articles

The germanides ScTGe2 (T = Fe, Co, Ru, Rh) – crystal chemistry, 45Sc solid-state NMR and 57Fe Mössbauer spectroscopy

Abstract The TiMnSi2-type (space group Pbam) germanides ScTGe2 (T = Fe, Co, Ru, Rh) were synthesized from the elements by arc-melting. Single crystals were grown by annealing sequences of the arc-melted buttons in an induction furnace. The structures of ScFeGe2, ScRuGe2 and ScRhGe2 were refined from single-crystal X-ray diffraction data. In ScRuGe2, the ruthenium atoms have distorted octahedral germanium coordination (242–268 pm Ru–Ge). Three trans-face-sharing octahedra form a sub-unit which is condensed via common edges in c direction and connected via common corners with four adjacent blocks, forming a three-dimensional [RuGe2 type] substructure. The two crystallographically independent scandium sites have coordination numbers 15 (Sc1@Ge8Ru4Sc3) and 17 (Sc2@Ge7Ru6Sc4). Electronic band structure calculations for ScCoGe2 and ScRuGe2 show a net charge transfer from the scandium to the transition metal and germanium atoms, leading to a description with polyanionic networks Sc δ+[TGe2]δ−. The two crystallographically independent Sc sites are easily distinguishable by 45Sc magic-angle spinning (MAS)-NMR spectroscopy. Isotropic chemical shift values and nuclear electric quadrupolar interaction parameters were deduced from an analysis of the triple-quantum (TQ)-MAS NMR spectra. The electric field gradient parameters deduced from these experiments are in good agreement with quantum-chemical calculations using the Wien2k code. Likewise, the two crystallographically independent iron sites in ScFeGe2 could be discriminated in the 57Fe Mößbauer spectra through their isomer shifts and quadrupole splitting parameters: δ = 0.369(1) mm s−1 and ∆E Q = 0.232(2) mm s−1 for Fe1 and δ = 0.375(2) mm s−1 and ∆E Q = 0.435(4) mm s−1 for Fe2 (data at T = 78 K).

Development of in situ high resolution NMR: Proof-of-principle for a new (spinning) cylindrical mini-pellet approach applied to a Lithium ion battery

Solid-state nuclear magnetic resonance (ssNMR) spectroscopy is a powerful technique for characterizing the local structure and dynamics of battery and other materials. It has been widely used to investigate bulk electrode compounds, electrolytes, and interfaces. Beside common ex situ investigations, in situ and operando techniques have gained considerable importance for understanding the reaction mechanisms and cell degradation of electrochemical cells.Herein, we present the recent development of in situ magic angle spinning (MAS) NMR methodologies to study batteries with high spectral resolution, setting into context possible advances on this topic. A mini cylindrical cell type insert for 4 mm MAS rotors is introduced here, being demonstrated on a Li/VO2F electrochemical system, allowing the acquisition of high-resolution 7Li MAS NMR spectra, spinning the electrochemical cell up to 15 kHz.

Identification of phosphorus sites in amorphous LiPON thin film by observing internuclear proximities

Amorphous lithium phosphorus oxynitrides (LiPON), prepared by reactive magnetron sputtering, have become the electrolytes of choice for all-solid-state thin film microbatteries since its discovery in early 1990s. Nevertheless, there is still a lack of understanding of their atomic-level structure and its influence on ionic conductivity. Solid-state NMR spectroscopy represents a promising technique to determine the atomic-level structure of LiPON glasses but is challenging owing to its low sensitivity in the case of thin film materials. Recently, 31P solid-state NMR spectra of LiPON thin films were acquired under magic-angle spinning (MAS) conditions and assigned with the help of density functional theory (DFT) calculations of NMR parameters. However, the identification of the different P local environments in these materials is still a challenge owing to their amorphous structure and the lack of resolution of the 31P MAS NMR spectra. We show herein how the NMR observation of internuclear proximities helps to establish the nature of P sites in LiPON thin films. The 31P-14N proximities are probed by a transfer of population in double resonance (TRAPDOR) experiment, whereas 31P-31P proximities are observed using one-dimensional (1D) 31P double-quantum (DQ)-filtered and two-dimensional (2D) 31P homonuclear correlation spectra as well as dipolar dephasing experiments using DQ-DRENAR (DQ-based dipolar-recoupling effects nuclear alignment reduction) technique. The obtained NMR data further support the recently proposed assignment of 31P NMR signals of LiPON thin films. With the help of this assignment, the simulation of the quantitative 1D 31P NMR spectrum indicates that PO43- orthophosphate anions prevail in LiPON thin films and N atoms are mainly incorporated in [O3PNPO3]5− dimeric anions. PO3N4− isolated tetrahedra and [O3POPO3]4− anions are also present but in smaller amounts.

Mapping Hydrogens in Hydrous Materials

Hydrous materials such as clays, cements, hydroxyapatite, and metal hydroxides have been known and extensively used since antiquity. However, experimental elucidation of hydrogen in hydrous materials remains challenging due to the intrinsic insensitivity, limited accessibility, sample damage, or poor spectral resolution of many characterization methods. 1H solid-state NMR spectroscopy has evolved into an ideal site-specific characterization tool of hydrogen-containing materials, but its current application in hydrous materials is hampered by the low resolution of 1H NMR spectra in the solid state due to the presence of intense dipolar coupling networks and a narrow 1H chemical shift range. Herein, a significant advance in the characterization of hydrogens in hydrous materials is reported. A combination of magic-angle spinning (MAS) NMR, moderate 2H substitution, and high magnetic fields has unlocked the capacity of identifying many chemically similar while crystallographically distinct hydrogen sites in a prototypical hydrous material Y4(OH)10Br2·3H2O (LYH-Br) by 1D 1H solid-state NMR experiments. 1H NMR peaks were first tentatively assigned in accordance with the density functional theory (DFT) calculation results, and the assignment was further refined by 2D 1H–89Y heteronuclear correlation (HETCOR) and 1H–1H double-quantum (DQ) MAS NMR data. The order of 1H chemical shift (δiso) values provides valuable information on the relative strength of hydrogen bond for ten hydroxide hydrogen sites. The power of very high spectral resolution is further described by observing all triple-quantum (TQ) coherences in the 2D 1H–1H TQ MAS NMR spectrum, in which all spatial proximities among three hydrogen sites are resolved. This demonstration of the very high spectral resolution obtained in 1D and 2D 1H solid-state NMR experiments illustrates how scientists in various communities can now study the multiple hydrous species of hydrous materials and obtain previously inaccessible fine structural information.

Discovering the Solid-State Secrets of Lorlatinib by NMR Crystallography: To Hydrogen Bond or not to Hydrogen Bond

Lorlatinib is an active pharmaceutical ingredient (API) used in the treatment of lung cancer. Here, an NMR crystallography analysis is presented whereby the single-crystal X-ray diffraction structure (CSD: 2205098) determination is complemented by multinuclear (1H, 13C, 14/15N, 19F) magic-angle spinning (MAS) solid-state NMR and gauge-including projector augmented wave (GIPAW) calculation of NMR chemical shifts. Lorlatinib crystallises in the P21 space group, with two distinct molecules in the asymmetric unit cell, Z′ = 2. Three of the four NH2 hydrogen atoms form intermolecular hydrogen bonds, N30-H…N15 between the two distinct molecules and N30-H…O2 between two equivalent molecules. This is reflected in one of the NH21H chemical shifts being significantly lower, 4.0 ppm compared to 7.0 ppm. Two-dimensional 1H–13C, 14N-1H and 1H (double-quantum, DQ)-1H (single-quantum, SQ) MAS NMR spectra are presented. The 1H resonances are assigned and specific HH proximities corresponding to the observed DQ peaks are identified. The resolution enhancement at a 1H Larmor frequency of 1 GHz as compared to 500 or 600 MHz is demonstrated.

The Chloronium Cation [(C2H3)2Cl+] and Unsaturated C4-Carbocations with C=C and C≡C Bonds in Their Solid Salts and in Solutions: An H1/C13 NMR and Infrared Spectroscopic Study.

Solid salts of the divinyl chloronium (C2H3)2Cl+ cation (I) and unsaturated C4H6Cl+ and C4H7+ carbocations with the highly stable CHB11Hal11− anion (Hal=F, Cl) were obtained for the first time. At 120 °C, the salt of the chloronium cation decomposes, yielding a salt of the C4H5+ cation. This thermally stable (up to 200 °C) carbocation is methyl propargyl, CH≡C-C+-H-CH3 (VI), which, according to quantum chemical calculations, should be energetically much less favorable than other isomers of the C4H7+ cations. Cation VI readily attaches HCl to the formal triple C≡C bond to form the CHCl=CH-C+H-CH3 cation (VII). In infrared spectra of cations I, VI, and VII, frequencies of C=C and C≡C stretches are significantly lower than those predicted by calculations (by 400–500 cm−1). Infrared and 1H/13C magic-angle spinning NMR spectra of solid salts of cations I and VI and high-resolution 1H/13C NMR spectra of VII in solution in SO2ClF were interpreted. On the basis of the spectroscopic data, the charge and electron density distribution in the cations are discussed.

Probing Acid Sites in MOR Zeolite Using Low-Temperature 13C Solid-State NMR Spectroscopy of Adsorbed Carbon Monoxide

Understanding the structure of Lewis and Brønsted acid sites in zeolites is a key step toward unraveling mechanisms of catalytic reactions, establishing molecular-level structure–activity relationships and thereby rational improvement of their performance. Acid sites are typically studied indirectly, using probe molecules, whose spectroscopic signatures are linked to the nature of specific sites. In this context, carbon monoxide and pyridine (Py) are the most frequently used probe molecules due to their sensitivity toward the nature and strength of surface acid sites. Although infrared and solid-state NMR spectroscopies of adsorbed Py are now widely used, the utilization of carbon monoxide to study surface sites has been mainly limited to infrared spectroscopy. Considering that NMR spectroscopy parameters, such as isotropic chemical shift (δiso) and chemical shift anisotropy (CSA), provide detailed structural information, we have explored the capabilities of low-temperature carbon-13 NMR spectroscopy of adsorbed 13CO on dehydrated mordenite. One-dimensional (1D) and two-dimensional (2D) 13C low-temperature magic-angle spinning NMR spectra show that carbon monoxide interacting with Lewis (LAS) and Brønsted (BAS) acid sites displays distinct 13C NMR signatures, in line with density functional theory (DFT) calculations. Furthermore, {1H}13C HETCOR NMR allows the observation of surface OH groups interacting with CO and points to the spatial proximity (within 1 nm) of BAS to both Si-OH and Al-OH groups, while LAS predominantly comprises the Al-OH group. These observations suggest the formation of defective aluminum sites with one and/or two OH groups bound to aluminum, upon calcination of a NH4-MOR with Si/Al = 6 at high temperature (580 °C). The NMR protocol discussed is perfectly suited to explore the surface sites of other solid materials.

Adsorption of HF on gibbsite calcined at various temperatures: A solid-state NMR study of low-level fluorinated systems

The fluorination mechanism of low-level fluorinated materials obtained by calcination of Bayer gibbsite at different temperatures was studied by 27Al and 19F solid-state NMR spectroscopy and X-ray diffraction. Gibbsite was calcined at 400, 600, 800, and 1000 °C followed by treatment with anhydrous HF/N2 gas at 100 °C. Three types of Al–F species on the surface of fluorinated gibbsite calcined at 400, 600, and 800 °C are proposed on the basis of the 19F magic angle spinning (MAS) NMR spectra, which show peaks at about −132, −137, and −163 ppm, while the spectrum of fluorinated gibbsite calcined at 1000 °C showed five additional peaks, at about −139, −164, −176, −183, and −191 ppm. The fluorination process in aluminas is based on elementary exchange reactions in which F− replaces surface –OH groups according to their basicity. The 27Al MAS NMR and 19F-27Al cross-polarization–MAS experiments confirmed the presence of octahedral Al species.

Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77Se and 113Cd Solid-State NMR Spectroscopy.

Dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) spectroscopy was used to obtain detailed surface structures of zinc blende CdSe nanocrystals (NCs) with plate or spheroidal morphologies which are capped by carboxylic acid ligands. 1D 113Cd and 77Se cross-polarization magic angle spinning (CPMAS) NMR spectra revealed distinct signals from Cd and Se atoms on the surface of the NCs, and those residing in bulk-like environments, below the surface. 113Cd cross-polarization magic-angle-turning (CP-MAT) experiments identified CdSe3O, CdSe2O2, and CdSeO3 Cd coordination environments on the surface of the NCs, where the oxygen atoms are presumably from coordinated carboxylate ligands. The sensitivity gain from DNP enabled natural isotopic abundance 2D homonuclear 113Cd-113Cd and 77Se-77Se and heteronuclear 113Cd-77Se scalar correlation solid-state NMR experiments which revealed the connectivity of the Cd and Se atoms. Importantly, 77Se{113Cd} scalar heteronuclear multiple quantum coherence (J-HMQC) experiments were used to selectively measure one-bond 77Se-113Cd scalar coupling constants (1J(77Se, 113Cd)). With knowledge of 1J(77Se, 113Cd), heteronuclear 77Se{113Cd} spin echo (J-resolved) NMR experiments were used to determine the number of Cd atoms bonded to Se atoms and vice versa. The J-resolved experiments directly confirmed that major Cd and Se surface species have CdSe2O2 and SeCd4 stoichiometries, respectively. Considering the crystal structure of zinc blende CdSe and the similarity of the solid-state NMR data for the platelets and spheroids, we conclude that the surface of the spheroidal CdSe NCs is primarily composed of {100} facets. The methods outlined here will generally be applicable to obtain detailed surface structures of various main group semiconductor nanoparticles.

Proton Detected Solid-State NMR of Membrane Proteins at 28 Tesla (1.2 GHz) and 100 kHz Magic-Angle Spinning.

The available magnetic field strength for high resolution NMR in persistent superconducting magnets has recently improved from 23.5 to 28 Tesla, increasing the proton resonance frequency from 1 to 1.2 GHz. For magic-angle spinning (MAS) NMR, this is expected to improve resolution, provided the sample preparation results in homogeneous broadening. We compare two-dimensional (2D) proton detected MAS NMR spectra of four membrane proteins at 950 and 1200 MHz. We find a consistent improvement in resolution that scales superlinearly with the increase in magnetic field for three of the four examples. In 3D and 4D spectra, which are now routinely acquired, this improvement indicates the ability to resolve at least 2 and 2.5 times as many signals, respectively.

Synergy of Solid-State NMR, Single-Crystal X-ray Diffraction, and Crystal Structure Prediction Methods: A Case Study of Teriflunomide (TFM).

In this work, for the first time, we present the X-ray diffraction crystal structure and spectral properties of a new, room-temperature polymorph of teriflunomide (TFM), CSD code 1969989. As revealed by DSC, the low-temperature TFM polymorph recently reported by Gunnam et al. undergoes a reversible thermal transition at −40 °C. This reversible process is related to a change in Z’ value, from 2 to 1, as observed by variable-temperature 1H–13C cross-polarization (CP) magic-angle spinning (MAS) solid-state NMR, while the crystallographic system is preserved (triclinic). Two-dimensional 13C–1H and 1H–1H double-quantum MAS NMR spectra are consistent with the new room-temperature structure, including comparison with GIPAW (gauge-including projector augmented waves) calculated NMR chemical shifts. A crystal structure prediction procedure found both experimental teriflunomide polymorphs in the energetic global minimum region. Differences between the polymorphs are seen for the torsional angle describing the orientation of the phenyl ring relative to the planarity of the TFM molecule. In the low-temperature structure, there are two torsion angles of 4.5 and 31.9° for the two Z’ = 2 molecules, while in the room-temperature structure, there is disorder that is modeled with ∼50% occupancy between torsion angles of −7.8 and 28.6°. These observations are consistent with a broad energy minimum as revealed by DFT calculations. PISEMA solid-state NMR experiments show a reduction in the C–H dipolar coupling in comparison to the static limit for the aromatic CH moieties of 75% and 51% at 20 and 40 °C, respectively, that is indicative of ring flips at the higher temperature. Our study shows the power of combining experiments, namely DSC, X-ray diffraction, and MAS NMR, with DFT calculations and CSP to probe and understand the solid-state landscape, and in particular the role of dynamics, for pharmaceutical molecules.

A new quaternary Li0.19Al2.72O3.64N0.36 transparent ceramic with high hardness

A new quaternary Li0.19Al2.72O3.64N0.36 transparent ceramic with the Vickers hardness of 17.91 ± 0.2 GPa at a load of 9.8 N and the in-line transmittance of 83.4% at 3.5 µm was prepared by hot isostatic press sintering (HIP) after pressureless sintering. The 7Li and 27Al magic-angle spinning (MAS) NMR spectra combined with the XRD Rietveld refinement was adopted to analyze the crystal structure. It is revealed that all the lithium ions are located in octahedra and the cation vacancies are mainly concentrated in tetrahedra. Based on the bond valance models, the complicated relationship among composition, crystal structure and intrinsic hardness of the spinel-type transparent ceramic were disclosed. Compared with the γ-AlON, the higher hardness of Li0.19Al2.72O3.64N0.36 transparent ceramic is attributed to the coupling effect of enhanced hardness of bonds in octahedra and the slightly weakened hardness of bonds in tetrahedra.

An indirect CO2 utilization for the crystallization control of CaCO3 using alkylcarbonate

Carbon mineralization into calcium carbonate (CaCO3) has been widely studied as a promising CO2 resource utilization pathway. In this work, CO2 was fixed to alkylcarbonate through phase change absorption in polyethylene glycol 200 (PEG) plus ethanediamine (EDA) system at ambient conditions. This alkylcarbonate was identified by FTIR and 13C cross-polarization magic-angle spinning (CP-MAS) NMR spectra. It was used as both CO32− source and crystal modifier to induce crystallization of CaCO3 particles. The CaCO3 microsphere with uniform morphology and vaterite crystal phase was acquired by adjusting quality of alkylcarbonate, concentration of Ca2+ concentration, and crystallization period without any additives. Furthermore, a plausible self-assembly formation mechanism toward inducing crystallization of vaterite CaCO3 microsphere also was proposed. This synthesis strategy is environmentally friendly and offers an alternative strategy for indirect utilization of CO2.

On the stability of Li intercalated fine-grained graphitic material

In order to study the performance, cycling stability and safety of electrochemical storage devices, various characterisation methods are applied. Magic angle spinning (MAS) NMR enables ex situ studies of electrochemical reactions with high resolution. In the present work, we follow the changes that occur in the MAS NMR spectra of lithiated graphitic materials after storage. The measuring time has been significantly shortened by using fine-grained graphitic material with 65% 13C-isotope enrichment. Our results show that for 13C graphitic electrode material with a low lithiation degree, visible changes in the 13C NMR spectra are observed already in few hours, whereas the samples with a higher lithiation degree demonstrated greater stability even after several days. We analyzed the deintercalation behavior in these materials using 7Li MAS NMR and oxidation processes using in situ X-ray photoelectron spectroscopy. During storage Li ions migrate to the other interlayers (redistribution), large pores and to the surface, where interaction with air takes place. Effects of charge transfer from Li to graphite across four graphitic layers guarantees that 13C NMR spectra are less affected by these effects. The key finding is that special care has to be paid to the ex situ characterisation of electrochemically prepared graphitized materials.

Local Structures of Two-Dimensional Zeolites-Mordenite and ZSM-5-Probed by Multinuclear NMR.

Mesostructured pillared zeolite materials in the form of lamellar phases with a crystal structure of mordenite (MOR) and ZSM-5 (MFI) were grown using CTAB as an agent that creates mesopores, in a one-pot synthesis; then into the CTAB layers separating the 2D zeolite plates were introduced by diffusion the TEOS molecules which were further hydrolyzed, and finally the material was annealed to remove the organic phase, leaving the 2D zeolite plates separated by pillars of silicon dioxide. To monitor the successive structural changes and the state of the atoms of the zeolite framework and organic compounds at all the steps of the synthesis of pillared MOR and MFI zeolites, the nuclear magnetic resonance method (NMR) with magic angle spinning (MAS) was applied. The 27Al and 29Si MAS NMR spectra confirm the regularity of the zeolite frameworks of the as synthetized materials. Analysis of the 1H and 13C MAS NMR spectra and an experiment with variable contact time evidence a strong interaction between the charged “heads” –[N(CH3)3]+ of CTAB and the zeolite framework at the place of [AlO4]− location. According to 27Al and 29Si MAS NMR the evacuation of organic cations leads to a partial but not critical collapse of the local zeolite structure.

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

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.

Detonation nanodiamonds fabricated from tetryl: Synthesis, NMR, EPR and XRD study

Fabrication of bulk quantities of detonation nanodiamonds from a new low-cost explosive, tetryl, necessitates the study of the properties and quality of new materials in comparison with those obtained from TNT-RDX mixtures. Here we report on preparation of detonation nanodiamonds from tetryl and their characterization by XRD, NMR and EPR techniques. XRD patterns, EPR spectra and 13C MAS NMR spectra and relaxation rates in tetryl-fabricated samples were measured and compared with those in “conventional” nanodiamonds prepared from the mixture of TNT and RDX explosives. Our data result in conclusion that the size and structure of new nanoparticles are similar to those obtained in the TNT-RDX fabricated nanodiamonds. Magic angle spinning (MAS) of the samples does not affect spin-lattice relaxation but results in the narrowing of the 13C spectrum and elongation of spin-spin relaxation time with increased MAS rate. These data also correlate with those of the “conventional” nanodiamonds. Our study shows that tetryl is a promising material for the nanodiamond production.

Lithium conduction and the role of alkaline earth cations in Li2S–P2S5–MS (M = Ca, Sr, Ba) glasses

There has been considerable interest in lithium-sulfide glasses with high lithium ion conductivities because of their potential applications in solid-state electrolytes. Here, new sulfide glasses containing alkaline earth cations, Li2S–P2S5–MS (M = Ca, Sr, Ba), were synthesized by melt quenching. Furthermore, the glass-forming regions in these glasses were identified.Three samples containing equimolar alkaline earth cations (60Li2S–30P2S5–10MS) were selected and their Li+ conductivities were measured. Lower Li+ conductivities were observed in 60Li2S–30P2S5–10MS than in Li2S–P2S5. The local structures of P and Li were characterized by 31P and 6Li solid-state magic angle spinning (MAS) NMR to determine the cause for the observed decrease in the Li+ conductivities and understand the role of alkaline earth cations in the Li2S–P2S5 glasses. A higher-field shift of the PS43− was observed in the 31P MAS NMR spectra of the glasses containing alkaline earth cations, which was attributed to the formation of bridging structures between PS43− units by alkaline earth cations. Moreover, more than half of the Li had low mobility, which is consistent with the conductivity. These results highlight the presence of an effective conduction path around the PS43− in contrast to P2S74− and P2S64−.

Hydrogen Impurities in ZnO: Shallow Donors in ZnO Semiconductors and Active Sites for Hydrogenation of Carbon Species.

ZnO, as a low-cost yet significant semiconductor, has been widely used in solar energy conversion and optoelectronic devices. In addition, Cu/ZnO-based catalysts can convert syngas (H2, CO, and CO2) into methanol. However, the main concern about the intrinsic connection between the physical and chemical properties and the structure of ZnO still remains. In this work, efforts are made to decipher the physical and chemical information encoded into the structure. Through using NMR-IR techniques, we, for the first time, report a new ZnO model with three H+ cations incorporated into one Zn vacancy. 1H magic-angle spinning NMR and IR spectra demonstrate that Ga3+ cations are introduced into the Zn vacancies of the ZnO lattice, which replace the H+ cation, and thus further confirm the feasibility of our proposed model. The exchange between the H+ cation in Zn vacancies and the D2 gas phase shows that ZnO can activate H2 because of the quantized three H+ cations in the defect site.

Direct and Indirect Dynamic Nuclear Polarization Transfer Observed in Mesoporous Materials Impregnated with Nonionic Surfactant Solutions of Polar Polarizing Agents

Mesoporous silica materials (SBA-15) with surfaces modified with aminopropyltriethoxysilane (APTES) of two different surface coverages were synthesized, and their structural pore characteristics were analyzed. These two mesoporous silica materials were impregnated with various solutions of radicals in a nonionic surfactant solvent. Differential scanning calorimetry (DSC) analysis of the impregnated mesoporous silica materials confirmed that the surfactant solutions were confined into the pores. Dynamic nuclear polarization (DNP)-enhanced solid-state 13C magic-angle spinning (MAS) NMR spectra recorded for these impregnated mesoporous silica materials showed the presence of superimposed spectra from direct and indirect channel polarization transfer processes not only for the confined surfactant solvent but also for the APTES surface modification. The observation of the indirect channel resonances implies that the surfactant solvents as well as the APTES exhibit molecular motions with correlation times on th...