Nuclear Magnetic Resonance Line Research Articles

Understanding Ion Dynamics in Closoborate-Type Lithium-Ion Conductors on Different Time-Scales.

The lithium-ion transport mechanism in 0.7Li(CB9H10)-0.3Li(CB11H12) complex hydride solid electrolyte was studied over a wide time-scale (ns-ms) by choosing appropriate techniques for assessing ionic motion on the desired time-scale using nuclear magnetic resonance (NMR) relaxation, AC impedance, and pulsed field gradient-NMR (PFG-NMR) measurements. The 7Li NMR line width decreased with increasing temperature, and the spin-lattice relaxation time T1 for the cation and anions showed a minimum near 303 K, indicating that the lithium ions and the anions were highly mobile. The activation energy estimated from the analysis of the NMR relaxation time matched well with the values estimated from the AC impedance and PFG-NMR. This confirms that the lithium-ion motion in 0.7Li(CB9H10)-0.3Li(CB11H12) is the same over a wide time-scale, suggesting steady Li-ion motion over a wide transport range. This understanding offers insights into strategies for designing complex hydride lithium superionic conductors.

Exploring Crystal-Phase Molecular Dynamics of the Low-Viscous Mesogen 6CHBT: A Combined FFC and High-Field NMR Relaxometry Investigation.

The molecular dynamics study of thermotropic mesogens exhibiting the crystal phases is valuable in unraveling the complex global (collective) and local (noncollective) motions executed by liquid crystal molecules, which would further advance the existing knowledge on orientationally disordered crystalline (ODIC) phases. Toward the fulfillment of such a task, a combined nuclear magnetic resonance (NMR) relaxometry approach employing the fast field cycling (FFC) NMR (10 kHz-30 MHz) and high-field pulsed NMR (400 MHz) techniques is utilized to sample the broad frequency range offered by molecular motions in the crystal phase of 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The validity of the observed relaxation data is tested and interpreted by the Bloembergen-Purcell-Pound (BPP) model involving the superposition of four mutually independent Lorentzian spectral densities, reflecting molecular dynamical processes on different time scales. The salient feature of the detailed analysis reveals that the lengthening of temporal dynamics in the crystal phase due to molecular rotations by jumps, which are of intermolecular origin, is evident and further supports the presence of collective-like local dynamics. The analysis does permit decoupling of the molecular reorientations about their short axes (∼100 ns) as well as long axes (∼50 ns) and methyl group rotations (∼0.5 ns) on distinct time scales. The activation energies for reorientations about the short axes and methyl group rotations are found to be 27.3 ± 2.7 and 15.8 ± 1.1 kJ/mol, respectively. The fast methyl rotations in the crystal phase of 6CHBT obtained from FFC NMR are further well complemented by high-field NMR, where 1H NMR line shapes are relatively narrow when compared to those of the nematic phase.

Nuclear induction line shape: Non-Markovian diffusion with boundaries.

The dynamics of viscoelastic fluids are governed by a memory function, essential yet challenging to compute, especially when diffusion faces boundary restrictions. We propose a computational method that captures memory effects by analyzing the time-correlation function of the pressure tensor, a viscosity indicator, through the Stokes-Einstein equation's analytic continuation into the Laplace domain. We integrate this equation with molecular dynamics simulations to derive necessary parameters. Our approach computes nuclear magnetic resonance (NMR) line shapes using a generalized diffusion coefficient, accounting for temperature and confinement geometry. This method directly links the memory function with thermal transport parameters, facilitating accurate NMR signal computation for non-Markovian fluids in confined geometries.

Li-Ion Dynamics in Li2S:LiI Composites – on the Effect of Solid-Solution Formation on Overall Li+ Transport

The enormous interest in developing powerful all-solid-state Li-ion batteries led to a boost in electrolyte research. Some Li-ion conductors have Ag-bearing analogs; the fast Ag+ ion conductor, Ag3SI, could be one of such materials. So far, no clear evidence is available that the Li-counterpart, Li3SI, does exist. Here, we treated an equimolar mixture of Li2S and LiI in high-energy ball mills and followed structural changes via X-ray diffraction (XRD) and magic-angle spinning (MAS) 6,7Li nuclear magnetic resonance (NMR) measurements. Differences in local structures as sensed by MAS NMR will be discussed for annealed and non-annealed samples, that is, powder samples directly obtained after finishing the ball-milling procedure. For nanocrystalline, non-annealed Li2S:LiI, the MAS NMR response is characterized by a broad distribution of NMR lines showing chemical shifts between that of pure Li2S and LiI, hence pointing to the formation of solid-solution like regions.Ion dynamics on different length scales was probed with variable-temperature, potentiostatic conductivity spectroscopy as well as solid-state NMR spin-lattice relaxation (SLR) measurements. Defect-rich nanocrystalline Li2S:LiI has to be characterized by an overall conductivity that is 2 orders of magnitude higher as compared to that of the microcrystalline, annealed reference sample. SLR NMR experiments supports this result and reveal lower activation energies for both the fast local hopping ion dynamics and long-range ion diffusivity in the sample directly obtained after ball milling. Finally, mixing-time dependent 6Li 2D exchange NMR spectroscopy reveals even (very) slow Li+ exchange between the Li2S-rich and LiI-rich regions in the nanocrystalline sample. Off-diagonal intensities are especially seen for mixing times longer than 80 ms.

Non-uniform orientation of H2 molecules in a magnetic field as a critical condition for the appearance of partially negative NMR lines of o-H2 in hyperpolarization experiments using p-H2.

In hyperpolarization experiments using parahydrogen, a partially negative line (PNL) of o-H2 is occasionally spotted in the nuclear magnetic resonance (NMR) spectra. This is a manifestation of the two-spin order (TSO) of the proton spins, appearing transiently in o-H2 molecules freshly derived from p-H2. For the TSO to be observable, the o-H2 NMR signal must be split into a doublet. In the literature, the splitting is believed to originate from a slow exchange of the dissolved dihydrogen with the dihydride moiety bound to a catalyst present in the reaction mixture. Because this hypothesis may be debatable, in this work a different splitting mechanism is proposed. It employs a residual dipolar coupling (RDC) between the hydrogen protons, originating from a partial orientation of the H2 molecules by the external magnetic field. The orientation effect is due to the anisotropic magnetic polarizability of H2. In a magnetic field of 11.74T at room temperature, the currently predicted value of the RDC is -0.0024Hz. Even such small RDC values are sufficient for the PNL effect to be clearly visible in NMR spectra for physically reasonable levels of the TSO in the o-H2 molecules. For RDC values much smaller than the natural linewidth of o-H2, the theoretical frequency distance between the minimum and maximum of PNL proves to be practically independent of the RDC and is of the order of the linewidth. The calculated amplitudes of the PNLs are proportional to the RDC values used in the calculations.

Anion and cation dynamics in a carbon-substituted cesium closo-hydroborate CsCB11H12: 1H and 133Cs NMR studies

Cesium monocarba-hydroborate CsCB11H12 belongs to the family of alkali-metal closo- hydroborate salts which are considered as promising solid electrolytes for battery applications. To study the dynamical properties of this compound at the microscopic level, we have measured the 1H and 133Cs nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates over the temperature range of 80–434 K. Our measurements have revealed a coexistence of two types of reorientational jump processes of the complex [CB11H12]− anions. For the faster of these processes characterized by the average activation energy of 310 meV, the anion reorientations are not “frozen” at the NMR frequency scale down to 120 K. The behavior of the 133Cs NMR line width in CsCB11H12 is consistent with the onset of long-range diffusive motion of Cs+ ions at the frequency scale of ∼104 s−1 above 340 K, and the distinct effects of the diffusive Cs+ jumps on both the 1H and 133Cs spin-lattice relaxation rates become observable above 380 K.

Effects of glycerol content on structure and molecular motion in thermoplastic starch-based nanocomposites during long storage

Thermoplastic starch-based nanocomposites with varying glycerol content and montmorillonite as a nanofiller were studied using dynamic-mechanical analysis (DMA), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) during one-year storage. DMA results showed that starch-rich and glycerol-rich domains were present in the samples and during storage for up to one year the content of the amorphous phase decreased and molecular mobility changed. 13C NMR and XRD measurements confirmed that ordered structures were formed during storage and its content was larger for samples with higher glycerol content and increased with the storage time. The data obtained from deconvolutions of 1H broad line NMR spectra indicate increased overall molecular mobility in the samples up to four months of storage, while after nine months the trends were opposite. Lower free water content compared to the total water content in the samples determined according to deconvoluted 1H MAS (magic-angle spinning) NMR spectra indicated that a part of water molecules was immobilized in the ordered structures.

Structure of amorphous materials in the NASICON system NaTi2Si x PO12

The structure of glasses in the sodium (Na) super-ionic conductor (NASICON) system NaTi2Si x PO12 with x = 0.8 and x = 1.0 was explored by combining neutron and high-energy x-ray diffraction with 29Si, 31P and 23Na solid-state nuclear magnetic resonance (NMR) spectroscopy. The 29Si magic angle spinning (MAS) NMR spectra reveal that the silica component remains fully polymerized in the form of Si4 units, i.e. the silicon atoms are bound to four bridging oxygen atoms. The 31P{23Na} rotational echo adiabatic passage double resonance (REAPDOR) NMR data suggest that the 31P MAS NMR line shape originates from four-coordinated P n units, where n = 1, 2 or 3 is the number of bridging oxygen atoms per phosphorus atom. These sites differ in their 31P-23Na dipolar coupling strengths. The results support an intermediate range order scenario of a phosphosilicate mixed network-former glass in which the phosphate groups selectively attract the Na+ modifier ions. Titanium takes a sub-octahedral coordination environment with a mean Ti–O coordination number of 5.17(4) for x = 0.8 and 4.86(4) for x = 1.0. A mismatch between the P–O and Si–O bond lengths of 8% is likely to inhibit the incorporation of silicon into the phosphorus sites of the NASICON crystal structure.

125Te NMR study of the bulk of topological insulators Bi2Te3 and Sb2Te3

AbstractThe narrow band gap semiconductors Bi2Te3 and Sb2Te3 are well known for their room temperature thermoelectric performance. Recently, they were shown to serve as model systems of three‐dimensional topological insulators with a bulk band gap and very robust, spin‐resolved surface states due to a special band inversion in their periodic bulk. Evidently, it is of interest to investigate the special surface states with a local probe like nuclear magnetic resonance (NMR). However, especially the bulk NMR of these materials shows peculiar and rather unexpected phenomena, e. g., a magnetic field induced deformation of the local charge symmetry and excessive line broadening due to a special internuclear coupling. Here we report a comprehensive account of the room temperature NMR properties of the spin‐1/2 nucleus 125Te of single crystalline Bi2Te3 and Sb2Te3. This includes a very unusual spin‐lattice relaxation that seems not to be reflected in the NMR shift, as well as an exchange enhanced NMR line broadening.

Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex.

Dynamic solution nuclear magnetic resonance (NMR) spectroscopy is the typical method of characterizing the dynamic rearrangements of atoms within the coordination sphere for transition metal polyhydride complexes. Line shape fitting of the dynamic NMR spectra can lead to estimates for the activation parameters of the dynamic rearrangement processes. A combination of dynamic 31P-{1H} NMR spectroscopy of metal-bound phosphorus atoms with dynamic 1H-{31P} NMR spectroscopy of hydride ligands may identify hydride ligand rearrangements that occur in conjunction with a phosphorus atom rearrangement. For molecules that exhibit such a coupled pair of rearrangements, dynamic NMR spectroscopy can be used to test theoretical models for the ligand rearrangements. Dynamic 1H-{31P} NMR spectroscopy and line shape fitting can also identify the presence of an exchange process that moves a specific hydride ligand beyond the metal's inner coordination sphere through a proton exchange with a solvent molecule such as adventitious water. The preparation of a new compound, ReH5(PPh3)2(sec-butyl amine), that exemplifies multiple dynamic rearrangement processes is presented along with line shape fitting of dynamic NMR spectra of the complex. Line shape fitting results can be analyzed by the Eyring equation to estimate the activation parameters for the identified dynamic processes.

Solid-State Characterization of Acetylpyridine Copper Complexes for the Activation of H2 O2 in Advanced Oxidation Processes.

This work describes the synthesis of 4-(4-AcPy) and 3-acetylpyridine (3-AcPy) copper soluble complexes for the activation of hydrogen peroxide and the concomitant generation of reactive oxygen species (ROS). Given the paramagnetic effects of copper ions in the Nuclear Magnetic Resonance (NMR) lines, we aimed at demonstrating that the combination of high-resolution 2D solid-state NMR experiments, Electron Paramagnetic Resonance (EPR), single-crystal X-ray crystallography and Density Functional Theory (DFT) calculations allows a detailed study of the chemical structure of the ligands and the surrounding metal ions. The copper complexes synthesized with CuCl2 were useful for the activation of H2 O2 during which the only ROS was the hydroxyl one, as demonstrated by EPR experiments. A removal of methyl orange (MO) azo-dye higher than 85 % was achieved in 200 minutes, combining 1.7 mM of copper complexes with 60 mM of H2 O2 and 40 μM of MO.

Slow spin dynamics in the hyperhoneycomb lattice [(C2H5)3NH]2Cu2(C2O4)3 revealed by H1 NMR studies

We report the results of magnetic susceptibility $\chi$ and $^1$H nuclear magnetic resonance (NMR) measurements on a three-dimensional hyper-honeycomb lattice compound [(C$_2$H$_5$)$_3$NH]$_2$Cu$_2$(C$_2$O$_4$)$_3$ (CCCO). The average value of the antiferromagnetic (AFM) exchange coupling between the Cu$^{2+}$ ($S$ = 1/2) spins was determined to be $J$~$\sim$~50 K from the $\chi$ measurements. No long-range magnetic ordering has been observed down to $T$ = 50 mK, although NMR lines become slightly broader at low temperatures below 1 K. The broadening of the NMR spectrum observed below 1 K reveals that the Cu spin moments remain at this temperature, suggesting a non-spin-singlet ground state. The temperature and magnetic field dependence of 1/$T_1$ at temperatures above 20 K is well explained by paramagnetic thermal spin fluctuations where the fluctuation frequency of Cu$^{2+}$ spins is higher than the NMR frequency of the order of MHz. However, a clear signature of the slowing down of the Cu$^{2+}$ spin fluctuations was observed at low temperatures where 1/$T_1$ shows a thermally-activated behavior. The magnetic field dependence of the magnitude of the spin excitation gap suggests that the magnetic behaviors of CCCO are characterized as an AFM chain at low temperatures.

Incommensurate and commensurate antiferromagnetic states in CaMn2As2 and SrMn2As2 revealed by As75 NMR

We carried out $^{75}\mathrm{As}$ nuclear magnetic resonance (NMR) measurements on the trigonal $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ and $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ insulators exhibiting antiferromagnetic (AFM) ordered states below N\'eel temperatures ${T}_{\mathrm{N}}=62$ and 120 K, respectively. In the paramagnetic state above ${T}_{\mathrm{N}}$, typical quadrupolar-split $^{75}\mathrm{As}$ NMR spectra were observed for both systems. The $^{75}\mathrm{As}$ quadrupolar frequency ${\ensuremath{\nu}}_{\mathrm{Q}}$ for $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ decreases with decreasing temperature, while ${\ensuremath{\nu}}_{\mathrm{Q}}$ for $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ increases, showing an opposite temperature dependence. In the AFM state, the relatively sharp and distinct $^{75}\mathrm{As}$ NMR lines were observed in $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ and the NMR spectra were shifted to lower fields for both magnetic fields $H\ensuremath{\parallel}c$ axis and $H\ensuremath{\parallel}ab$ plane, suggesting that the internal fields ${B}_{\mathrm{int}}$ at the As site produced by the Mn ordered moments are nearly perpendicular to the external magnetic field direction. No obvious distribution of ${B}_{\mathrm{int}}$ was observed in $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$, which clearly indicates a commensurate AFM state. In sharp contrast to $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$, broad and complex NMR spectra were observed in $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ in the AFM state, which clearly shows a distribution of ${B}_{\mathrm{int}}$ at the As site, indicating an incommensurate state. From the analysis of the characteristic shape of the observed spectra, the AFM state of $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ was determined to be a two-dimensional incommensurate state where Mn ordered moments are aligned in the $ab$ plane. A possible origin for the different AFM states in the systems was discussed. Both $\mathrm{Ca}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ and $\mathrm{Sr}{\mathrm{Mn}}_{2}{\mathrm{As}}_{2}$ show very large anisotropy in the nuclear spin-lattice relaxation rate $1/{T}_{1}$ in the paramagnetic state. $1/{T}_{1}$ for $H\ensuremath{\parallel}ab$ is much larger than that for $H\ensuremath{\parallel}c$, indicating strong anisotropic AFM spin fluctuations in both compounds.

Through-Space Scalar 19F-19F Couplings between Fluorinated Noncanonical Amino Acids for the Detection of Specific Contacts in Proteins.

Fluorine atoms are known to display scalar 19F-19F couplings in nuclear magnetic resonance (NMR) spectra when they are sufficiently close in space for nonbonding orbitals to overlap. We show that fluorinated noncanonical amino acids positioned in the hydrophobic core or on the surface of a protein can be linked by scalar through-space 19F-19F (TSJFF) couplings even if the 19F spins are in the time average separated by more than the van der Waals distance. Using two different aromatic amino acids featuring CF3 groups, O-trifluoromethyl-tyrosine and 4-trifluoromethyl-phenylalanine, we show that 19F-19F TOCSY experiments are sufficiently sensitive to detect TSJFF couplings between 2.5 and 5 Hz in the 19 kDa protein PpiB measured on a two-channel 400 MHz NMR spectrometer with a regular room temperature probe. A quantitative J evolution experiment enables the measurement of TSJFF coupling constants that are up to five times smaller than the 19F NMR line width. In addition, a new aminoacyl-tRNA synthetase was identified for genetic encoding of N6-(trifluoroacetyl)-l-lysine (TFA-Lys) and 19F-19F TOCSY peaks were observed between two TFA-Lys residues incorporated into the proteins AncCDT-1 and mRFP despite high solvent exposure and flexibility of the TFA-Lys side chains. With the ready availability of systems for site-specific incorporation of fluorinated amino acids into proteins by genetic encoding, 19F-19F interactions offer a straightforward way to probe the spatial proximity of selected sites without any assignments of 1H NMR resonances.

5f -electron magnetism in single crystal UN probed by N14 NMR

Spin susceptibility and low-frequency dynamics of uranium $5f$ electrons have been investigated by nuclear magnetic resonance (NMR) on the $^{14}\mathrm{N}$ nuclei in paramagnetic and magnetically ordered phases for single crystalline and polycrystalline samples of uranium mononitride (UN). NMR spectra, shifts of the $^{14}\mathrm{N}$ NMR lines, and the spin-lattice relaxation times ${T}_{1}$ have been obtained in the temperature range $T=10--760\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in magnetic field $B=92.8\phantom{\rule{0.16em}{0ex}}\mathrm{kOe}$. It is shown that in the UN paramagnetic phase, temperature dependence of the $^{14}\mathrm{N}$ NMR line shift is proportional to the spin susceptibility of the uranium $5f$ electrons. Joint analysis of NMR and magnetic susceptibility data allows us to determine temperature dependence of spin fluctuation energy ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{nmr}}(T)$ of the uranium $5f$ electrons and to demonstrate that its temperature variation is close to $\mathrm{\ensuremath{\Gamma}}(T)\ensuremath{\propto}{T}^{0.5}$ dependence which is characteristic of the concentrated Kondo systems above the coherent state formation temperature. In the magnetically ordered UN phase the $^{14}\mathrm{N}$ NMR spectra consist of several lines that can be explained in terms of the model of type $I$ antiferromagnetic order corresponding to $1k$ structure in the presence of magnetic domains.

1H NMR Study of the HCa2Nb3O10 Photocatalyst with Different Hydration Levels.

The photocatalytic activity of layered perovskite-like oxides in water splitting reaction is dependent on the hydration level and species located in the interlayer slab: simple or complex cations as well as hydrogen-bonded or non-hydrogen-bonded H2O. To study proton localization and dynamics in the HCa2Nb3O10·yH2O photocatalyst with different hydration levels (hydrated—α-form, dehydrated—γ-form, and intermediate—β-form), complementary Nuclear Magnetic Resonance (NMR) techniques were applied. 1H Magic Angle Spinning NMR evidences the presence of different proton containing species in the interlayer slab depending on the hydration level. For α-form, HCa2Nb3O10·1.6H2O, 1H MAS NMR spectra reveal H3O+. Its molecular motion parameters were determined from 1H spin-lattice relaxation time in the rotating frame (T1ρ) using the Kohlrausch-Williams-Watts (KWW) correlation function with stretching exponent β = 0.28: eV, s. For the β-form, HCa2Nb3O10·0.8H2O, the only 1H NMR line is the result of an exchange between lattice and non-hydrogen-bonded water protons. T1ρ(1/T) indicates the presence of two characteristic points (224 and 176 K), at which proton dynamics change. The γ-form, HCa2Nb3O10·0.1H2O, contains bulk water and interlayer H+ in regular sites. 1H NMR spectra suggest two inequivalent cation positions. The parameters of the proton motion, found within the KWW model, are as follows: eV, s.

Insulator:conductor interfacial regions — Li ion dynamics in the nanocrystalline dispersed ionic conductor LiF:TiO2

Lithium fluoride is known to be a very poor ionic conductor. Here, we used it as a model substance to investigate the influence of the insulator TiO2 on ion dynamics in nanocrystalline composites of LiF and TiO2. In such two-phase systems a percolation network of fast Li+ pathways at the conductor:insulator interfaces may lead to enhanced overall, through-going ionic (and electronic) transport. Indeed, we observed such an effect and characterized it by conductivity spectroscopy as well as by variable-temperature 7Li and 19F Nuclear Magnetic Resonance (NMR) line shape measurements and diffusion-induced NMR relaxometry. Compared to nanocrystalline LiF, a remarkable increase in total conductivity of almost four orders of magnitude, that is, from 6×10−11 S cm−1 up to 2×10−7 S cm−1 (100 °C) was observed for LiF:TiO2 containing 40 vol.-% of TiO2. Direct current polarization measurements revealed that principally ionic charge carriers are responsible for this enhancement. As both ions in LiF, Li+ and F−, might be mobile, NMR helped revealing that Li+ is the charge carrier being mainly responsible for the increase in ionic conductivity. Compared to SiO2 and Al2O3 [see, S. Breuer et al. J. Phys. Chem. C, 2019, 123, 5222], with TiO2 the largest increase in conductivity was achieved. Hence the introduction of heterogeneous conductor:insulator contacts turned out to be a highly suitable tool to effectively engineer the interfacial regions in such two-phase systems. In general, such a composite effect is important for ion transport in components for energy storage devices and in the solid electrolyte interphase region that generally passivates the anode material in lithium-ion batteries.

Solid-State Nuclear Magnetic Resonance Techniques for the Structural Characterization of Geminal Alane-Phosphane Frustrated Lewis Pairs and Secondary Adducts.

The first comprehensive solid‐state nuclear magnetic resonance (NMR) characterization of geminal alane‐phosphane frustrated Lewis pairs (Al/P FLPs) is reported. Their relevant NMR parameters (isotropic chemical shifts, direct and indirect 27Al‐31P spin‐spin coupling constants, and 27Al nuclear electric quadrupole coupling tensor components) have been determined by numerical analysis of the experimental NMR line shapes and compared with values computed from the known crystal structures by using density functional theory (DFT) methods. Our work demonstrates that the 31P NMR chemical shifts for the studied Al/P FLPs are very sensitive to slight structural inequivalences. The 27Al NMR central transition signals are spread out over a broad frequency range (>200 kHz), owing to the presence of strong nuclear electric quadrupolar interactions that can be well‐reproduced by the static 27Al wideband uniform rate smooth truncation (WURST) Carr‐Purcell‐Meiboom‐Gill (WCPMG) NMR experiment. 27Al chemical shifts and quadrupole tensor components offer a facile and clear distinction between three‐ and four‐coordinate aluminum environments. For measuring internuclear Al⋅⋅⋅P distances a new resonance‐echo saturation‐pulse double‐resonance (RESPDOR) experiment was developed by using efficient saturation via frequency‐swept WURST pulses. The successful implementation of this widely applicable technique indicates that internuclear Al⋅⋅⋅P distances in these compounds can be measured within a precision of ±0.1 Å.

NMR investigation on the honeycomb iridate Ag3LiIr2O6

We investigate the structural and magnetic properties of a Kitaev spin liquid candidate material Ag$_3$LiIr$_2$O$_6$ based on $^7$Li nuclear magnetic resonance line shape, Knight shift and spin-lattice relaxation rate $1/T_1$. The first sample A shows signatures of magnetically ordered spins, and exhibits one sharp $^7$Li peak with FWHM increasing significantly below 14~K. $1/T_1^{stretch}$ of this sample displays a broad local maximum at 40~K, followed by a very sharp peak at $T_N = 9\pm1$~K due to critical slowing down of Ir spin fluctuations, a typical signature of magnetic long range order. In order to shed light on the position-by-position variation of $1/T_1$ throughout the sample, we use Inverse Laplace Transform $T_1$ analysis based on Tikhonov regularization to deduce the density distribution function $P(1/T_1)$. We demonstrate that $\sim 60\%$ of Ir spins are statically ordered at the NMR measurement timescale but the rest of the sample volume remains paramagnetic even at 4.2~K, presumably because of structural disorder induced primarily by stacking faults. In order to further investigate the influence of structural disorder, we compare these NMR results with those of a second sample B, which has been shown by transmission electron microscope to have domains with unwanted Ag inclusion at Li and Ir sites within the Ir honeycomb planes. The sample B displays an additional NMR peak with relative intensity of $\sim 17\%$. The small Knight shift and $1/T_1$ of these defect-induced $^7$Li sites and the enhancement of bulk susceptibility at low temperatures suggest that these defects generate domains of only weakly magnetic Ir spins accompanied by free spins, leading to a lack of clear signatures of long-range order. The apparent lack of long-range order could be easily misinterpreted as evidence for the realization of a spin liquid ground state in highly disordered Kitaev lattice.

2H NMR study on temperature-dependent water dynamics in amino-acid functionalized silica nanopores.

We prepare various amino-acid functionalized silica pores with diameters of ∼6 nm and study the temperature-dependent reorientation dynamics of water in these confinements. Specifically, we link basic Lys, neutral Ala, and acidic Glu to the inner surfaces and combine 2H nuclear magnetic resonance spin-lattice relaxation and line shape analyses to disentangle the rotational motions of the surfaces groups and the crystalline and liquid water fractions coexisting below partial freezing. Unlike the crystalline phase, the liquid phase shows reorientation dynamics, which strongly depends on the chemistry of the inner surfaces. The water reorientation is slowest for the Lys functionalization, followed by Ala and Glu and, finally, the native silica pores. In total, the rotational correlation times of water at the different surfaces vary by about two orders of magnitude, where this span is largely independent of the temperature in the range ∼200-250 K.