Wide-line Techniques Research Articles

Solid-state nuclear magnetic resonance of spin-9/2 nuclei 115 In and 209 Bi in functional inorganic complex oxides.

Indium and bismuth are technologically important elements, in particular as oxides for optoelectronic applications. 115 In and 209 Bi are both I = 9/2 nuclei with high natural abundances and moderately high frequencies but large nuclear electric quadrupole moments. Leveraging the quadrupolar interaction as a measure of local symmetry and polyhedral distortions for these nuclei could provide powerful insights on a range of applied materials. However, the absence of reported nuclear magnetic resonance (NMR) parameters on these nuclei, particularly in oxides, hinders their use by the broader materials community. In this contribution, solid-state 115 In and 209 Bi NMR of three recently discovered quaternary bismuth or indium oxides are reported, supported by density functional theory calculations, numerical simulations, diffraction and additional multinuclear (27 Al, 69,71 Ga, and 121 Sb) solid-state NMR measurements. The compounds LiIn2 SbO6 , BiAlTeO6 , and BiGaTeO6 are measured without special equipment at 9.4 T, demonstrating that wideline techniques such as the QCPMG pulse sequence and frequency-stepped acquisition can enable straightforward extraction of quadrupolar tensor information in I = 9/2 115 In and 209 Bi even in sites with large quadrupolar coupling constants. Relationships are described between the NMR observables and local site symmetry. These are amongst the first reports of the NMR parameters of 115 In, 121 Sb, and 209 Bi in oxides.

Wide Line Surface‐Enhanced Raman Scattering Mapping

AbstractSurface‐enhanced Raman spectroscopy (SERS)‐based molecular detection at extremely low concentrations often relies on mapping of a SERS substrate. This yields a large number (>1000) of SERS spectra that can improve the limit of detection; however, the signal collection time is a major constraint. In this work, a wide line (WL) laser focusing technique aimed at fast mapping of SERS substrates is presented. The WL technique enables acquisition of thousands of SERS spectra in a few seconds without missing any of the electromagnetic “hot spots” in the illuminated area. In addition, the SERS signal averaging across the line in the WL mode displays extremely high signal‐to‐noise ratios. The advantages of the WL technique for SERS‐based sensing are verified using different analyte molecules, that is, p‐coumaric acid and melamine. Results show that the limit of detection can be improved by one order of magnitude compared to results obtained using a commercial Raman microscope.

Determination of rotational symmetry elements in NMR crystallography

In this work we present a consistent set of NMR experiments including high-resolution as well as wideline techniques, which allow to determine crystallographic rotational symmetry elements in crystalline solids. 1D spectra acquired with fast sample spinning about the magic angle provide the number of crystallographically inequivalent nuclei. By making use of the anisotropic properties of the chemical shift interaction the sets of crystallographically equivalent nuclei can be divided into subgroups of magnetically equivalent spins by means of radio-frequency-driven spin-diffusion wide-line exchange experiments. Maximum information can be achieved from these experiments by a combination of time- and frequency-domain analyses. We could demonstrate that the number of subgroups is equal to the order of the rotational symmetry element in which the crystallographically equivalent nuclei are arranged. From the evolution of the polarisation transfer as a function of the mixing time distances of these spins can be estimated quite accurately. Furthermore, it is often possible to distinguish between rotation and rotoinversion axes. The potential of this strategy for ab initio structure determination is demonstrated on the crystal structure of triphenyl phosphite, where eighteen molecules are arranged in a R-centred trigonal unit cell.

Dynamics of an Amorphous Polymer by an Improved NMR Approach Based on the Simultaneous Analysis of 1H and 13C Relaxation Times

A new approach to extract quantitative dynamic information from NMR relaxation data of amorphous polymers is presented, consisting of the simultaneous fitting of 1H and 13C T1 vs temperature curves obtained at different frequencies by means of unified motional models. The reliability of the dynamic parameters obtained by this approach is substantially increased with respect to the single curve analysis because of the possibility of both investigating motions over a wide frequency range and combining relaxation times carrying either global (1H nuclei) or local (13C nuclei) dynamic information. Experimental data were obtained for an amorphous ethylene−propylene random copolymer over a wide temperature range above its glass-transition: 1H spin−lattice relaxation times were measured by wide-line techniques at four Larmor frequencies, while high-resolution MAS techniques were used to get 13C spin−lattice relaxation times at a single frequency. The experimental data were analyzed in terms of segmental main-cha...

B11NMR studies of the electronic and magnetic properties of LuRh4B4and GdRh4B4

The /sup 11/B NMR of two members of the (rare earth)Rh/sub 4/B/sub 4/ series of ternary metals has been examined using wide-line techniques on powdered samples at frequencies from 6--27 MHz and temperatures of 90--300 K. In LuRh/sub 4/B/sub 4/, satellite pairs (+-3/2 reversible +-/2 transitions) flank a narrow central resonance (+-1/2 bold-arrow-left-right minus-or-plus 1/2 transitions). From these quadrupolar satellites, we find e/sup 2/qQh=523 kHz and eta=0.37. The central transition has isotropic, K/sub iso/=+0.013%, and anisotropic, K/sub anis/=-0.124%, components to the Knight shift; the magnitude of K/sub iso/ as well as the residual linewidth are in agreement with our calculated values. The magnitude of K/sub anis/ is much larger than previously observed for /sup 11/B. The spectra are independent of temperature in the range 90--300 K, in contrast to the reported strong temperature dependence of the static susceptibility for this material. Magnetic interactions broaden the /sup 11/B NMR for GdRh/sub 4/B/sub 4/. Paramagnetic shifts for the central component of K/sub iso/=-0.263% and K/sub anis/=-0.56% are seen; the calculated interactions between the /sup 11/B nuclei and the Gd/sup 3 +/ magnetic moments are sufficient to account for both K/sub iso/ and K/sub anis/. From the observed satellite structure, we estimate e/supmore » 2/qQ/h=345 kHz, indicating that the electrostatic environment at the B sites is similar to that in LuRh/sub 4/B/sub 4/.« less

Deuterium lineshape study of tetrahedral jumps in solid hexamethylenetetramine

The reorientational motion of hexamethylenetetramine (HMT) in the solid has been studied by 2H NMR. Powder spectra were taken by wideline techniques in the temperature interval T = 368 to 448 K. The lineshape changes from the powder pattern of a rigid solid (fake diagram) to a narrow line, the total width of the spectrum being reduced from 250 to less than 1 kHz. For intermediate temperatures the lineshape consists of a superposition of a broad absorption and a narrow central component of virtually temperature-independent width. The data are analyzed in terms of a stochastic model of tetrahedral jumps. A simple computer program for the numerical calculation of the powder lineshape is described. The correlation times τ obtained from lineshape analysis, follow a simple Arrhenius plot with an activation energy ΔE = 70.2 ± 3 kJ/mol. Extrapolation to lower temperatures shows excellent agreement with the results of an earlier 14N relaxation study of Alexander and Tzalmona; the Arrhenius plot thus extends over at least five orders of magnitude from T ≈ 0.3 sec to τ ≈3 × 10 −6 sec.

Wideline NMR studies of ammonia intercalation complexes. II. TaS2(ND3) and TiS2 (ND3)

The 2D NMR of ND3 molecules in the intercalation complexes TaS2(ND3) and TiS2(ND3) has been studied at temperatures from 5–300 K by wideline techniques. The magnitude and temperature dependence of the observed electric quadrupolar coupling constant (e2qQ/h)eff provides information about the configuration of the intercalated ND3 molecules and their dynamics. The similarity of (e2qQ/h)eff to previously reported values for solid ND3 suggests that intercalation entails only small changes in molecular geometry or electronic configuration. The molecules exhibit several types of motion, including spinning about their threefold (C3) symmetry axis and a complex reorientation of that axis. The rates of these motions are reduced as the temperature is lowered, with reorientation falling to ∼106 s−1 near 140 K. C3 spinning persists at rates greater than 106 s−1 even at temperatures of 5 K. The quadrupole interaction does not vanish at high temperatures, ∼300 K, showing that reorientation of the C3 axis is not isotropic and the form of motion is deduced from the high temperature value of the coupling constant. A central component of the spectrum is observed at low temperatures and attributed to ND3 molecules residing near molecular vacancies in the layers. The present results are compared in detail with 1H observations in the ND3 analogues.

Magnetic relaxation of quadrupolar nuclei in nonaqueous electrolyte solutions

The NMR relaxation times of the quadrupolar nuclei 7Li, 23Na, 87Rb, and 133Cs in electrolyte solutions in methanol have been measured with pulse and wide-line techniques. In addition, 87Rb relaxation rates were obtained in solutions of RbF in ethanol, ethylene glycol, and formamide. The data were used to test an electrostatic relaxation theory in the limit of infinite dilution. The theory furnished the relaxation rates of the correct order of magnitude when the suitable model for the state of solvation is applied. With measurements on the concentration dependence of the relaxation rates, the electrostatic theory also allows calculation of the contribution to the relaxation rate due to ion-ion interaction.

Proton resonance in membrane model systems: Octyl ammonium chloride and potassium oleate in the oriented lamellar phase

The binary systems octyl ammonium chloride-water and potassium oleate-water were oriented in the lamellar phase between glass slides. Proton magnetic resonance at 100 MHz showed reasonably well resolved spectra for magnetic field orientations at the magic angle of 54°44′ with respect to the optical axis. At angles slightly deviating from the magic angle, dipolar broadening and an indication of a splitting of the methylene and methyl protons are observed. At 0 or 90° orientation, a well-defined doublet structure is observed by wide-line techniques. It is concluded that in both systems a section of the hydrocarbon chain with a length of 5–6 carbon atoms near the polar head group has a uniform degree of order, while the molecule as a whole shows a rapid rate of reorientation around the optical axis.

Nuclear magnetic relaxation and selective solvation of Rb+ in water-methanol mixtures

Relaxation times of Rb87 for the nuclear magnetic relaxation which is caused by quadrupolar interaction have been measured in solutions of RbF in water-methanol mixtures using the wide-line technique. The aim of this work was to investigate the environment of the Rb+ cation in going from pure water to pure methanol. The entirely different effect of the addition of methanol to wrater on the quadrupolar relaxation of the cation nucleus as compared to that on the anion nucleus is described. The explanation is given in terms of selective solvation of the cation, in such a manner that water molecules as neighbours are preferred.

Proton NMR and covalency parameters of ruthenium(III) hexaammine

The NMR signal of the ammine protons of the Ru(NH3)63+ ion was directly measured by a wide line technique at various temperatures. A non-Curie behavior of the paramagnetic chemical shift was observed and the ligand pseudocontact interaction suggested by Kurland and McGarvey was used for its interpretation. The contact hyperfine interaction with the ammine protons was found to be A = 5.9 MHz. The covalency parameter was calculated as λ = 0.33, but after allowing for cross-term spin densities it was reduced to 0.28. The NMR relaxation times are discussed in terms of the ruthenium proton distance and the electronic spin relaxation times of the Ru(NH3)63+ ion.