Achieving high resolution dipolar NMR information without fast sample spinning: combining magic angle turning with dipolar based NMR methods.

In this article we present a new approach to high resolution NMR combining the concepts of magic angle hopping (MAH)/magic angle turning (MAT) and dipolar based NMR methods such as SEDOR, REDOR or cross polarization (CP). Employing aluminophosphates as model systems we demonstrate that No MAS needed (NOMAS) is capable of supplying high resolution dipolar information without the need of fast MAS.

Fast screening of solid electrolytes: a high throughput solid state NMR probe.

In this article we describe the construction of a high throughput solid state NMR probe for a fast and reliable determination of the NMR line width of a given nuclear species within a solid material. Since the NMR line width scales with the inverse of the mobility of the studied species and hence its ionic conductivity, this approach allows a fast screening of the material's promise as a solid electrolyte. The functionality of the approach is exemplified by the determination of the (7)Li-NMR line width of a set of 30 different liquid and solid Li-containing samples.

Al(22)Cl(20).12L (L = THF, THP): the first polyhedral aluminum chlorides.

Aluminum subhalides of the type Al(22)X(20).12L (X = Cl, Br; L = THF, THP) are the only known representatives of polyhedral aluminum subhalides and exhibit interesting multicenter bonding properties. Herein, we report on the synthesis and structural investigation of the first chlorides of this type. Additional investigations applying solid-state (27)Al NMR (MAS), XPS (of Al(4)Cp(4) and Al(22)X(20).12L), and quantum chemical calculations shed more light upon the structure of the molecules and possible Al modifications.

Structure of the fluorosulfite anion: rotational disorder of SO(2)F(-) in the alkali metal fluorosulfites and crystal structures of alpha- and beta-CsSO(2)F.

19F solid-state NMR spectra of the alkali metal fluorosulfites KSO(2)F, RbSO(2)F, alpha-CsSO(2)F, and beta-CsSO(2)F show that the fluorosulfite anion is subjected to dynamical disorder at room temperature. This disorder can be modeled by 120 degrees rotational jumps with respect to the C(3)-pseudoaxis of the anion. The exchange frequency of this disorder decreases with decreasing temperature. The calculated jump frequencies at room temperature are 5 x 10(5) Hz for KSO(2)F, 2 x 10(5) Hz for RbSO(2)F, 1 x 10(7) Hz for alpha-CsSO(2)F, and 5 x 10(5) Hz for beta-CsSO(2)F, respectively. The crystal structures of alpha- and beta-CsSO(2)F were determined for the first time (alpha: Pnma; Z = 4; a = 790.98(8), b = 666.07(7), c = 798.93(9) pm; T = 293 K. beta: R3m; Z = 3; a = 659.22(6), c = 800.50(4) pm; T = 293 K). X-ray single-crystal data of KSO(2)F, RbSO(2)F, and alpha-CsSO(2)F taken at various temperatures were refined using the disorder model developed from the NMR results. It is shown that it is impossible to obtain reliable structural parameters of the SO(2)F(-) ion by refinement of X-ray data as long as rotational disorder persists. The preference of an ordered structure increases with decreasing temperature. The degree of disorder remaining in alpha-CsSO(2)F at 93 K is small. The structural parameters of the fluorosulfite anion as obtained by a routine refinement of this phase (S-F, 169.0(2) pm; S-O, 147.8(1) pm) are the best lower (S-F) and upper (S-O) limits of the "true" bond lengths determined experimentally. They comply with the values obtained from quantum chemical calculations.

Magnetochirality-induced asymmetric synthesis.

Magnetochiral anisotropy, the combined effect of a collinear arrangement of a magnetic field B and the wave vector k of a light beam--as illustrated in the picture--has been proven to produce an enantiomeric excess in a chemical reaction, to make this effect a likely candidate for the origin of the homochirality of life.

13C-(27)Al TRAPDOR and REDOR experiments for the detection of (13)C-(27)Al dipolar interactions in solids.

We report (13)C-(27)Al double resonance experiments (REDOR and TRAPDOR) on several aluminum organic compounds with the aim of detecting (13)C-(27)Al dipolar couplings and distances in solids. The (13)C and (27)Al pulses are applied to the same probe channel because their resonance frequencies are in close proximity. The different possibilities of controlling the efficiency of the TRAPDOR approach (by varying the (27)Al RF amplitude and the MAS frequency) are investigated. The results indicate that TRAPDOR is superior to REDOR in resolving differences in (13)C-(27)Al distances when choosing the proper experimental conditions. Where known, the crystal structure data are in qualitative agreement with the distance information extracted from our experiments. The experiment should be very valuable in different fields of solid state chemistry, where the interaction of organic and inorganic sample fractions is of fundamental importance.

Double resonance experiments in a single resonance probe: detecting 23Na-51V dipolar interactions in sodium vanadates.

23Na-[51V] double resonance TRAPDOR experiments are presented on two different sodium vanadates. This is the first time that the heteronuclear dipolar interaction between nuclei, whose Larmor frequencies lie within a range of 0 to 3 MHz is detected in order to monitor connectivity and internuclear distance information in these systems.

1H-13C-27Al triple resonance transfer of populations in double resonance experiments for the detection of 13C-27Al dipolar interactions.

A 13C [1H] CPMAS [27Al] TRAPDOR NMR experiment is reported with the aim of detecting 13C-27Al proximities and distances in solids. The 13C and 27Al pulses are applied to the same probe channel, because their resonance frequencies lie extremely close to each other. The study of the heteronuclear dipolar interaction between these two nuclei, which are of fundamental importance in solid state science, is not possible with standard double resonance approaches. Results are presented for the model compound aluminum lactate. The 13C signals for the three lactate carbons show different magnitudes of the TRAPDOR effect, in excellent agreement with their mean Al-C distances, calculated from crystal structure data. The results illustrate the feasibility of this method for the study of systems where the interaction of organic and inorganic fractions is directing the structure (template/zeolite) or controlling the catalytic efficiency (organic reactant/catalytically active sites in zeolites or clays).

11B[27Al] and 27Al[11B] double resonance experiments on a glassy sodium aluminoborate.

Cross-polarization/magic-angle spinning (CP/MAS) and rotational echo double resonance (REDOR) experiments involving two half-integer quadrupolar nuclei, 11B and 27Al, are reported, to demonstrate boron-aluminum connectivities in a model aluminoborate glass. A detailed study of the spin-lock behavior of 11B and 27Al proves to be a prerequisite for successful CP/MAS experiments. Under MAS conditions, two distinct boron sites are observed, corresponding to tetrahedral BO4/2- sites (nuclear electric quadrupole coupling constant near 0.3 MHz) and trigonal BO3/2 sites (nuclear electric quadrupole coupling constant near 2.7 MHz). The BO4/2- sites are most successfully spin-locked in the adiabatic regime at high radio frequency (RF) field strengths, whereas for the BO3/2 sites optimum spin-lock conditions are achieved in the sudden regime (low RF field strengths). These differences can be exploited for spectral editing purposes in REDOR experiments. Using corresponding T1p filters, it becomes possible to measure individual REDOR dephasing curves for both types of boron sites. The results illustrate the possible utility of heteronuclear X-Y double resonance techniques in unravelling the intermediate range order in amorphous systems containing quadrupolar nuclei.

11B MAS NMR spectroscopy for characterizing the structure of glasses.

11B MAS NMR spectroscopy has been shown to deliver reliable parameters for the chemical shift and the quadrupole interaction in glasses if short excitation pulses, high-speed magic angle spinning and satellite transition spectroscopy are applied. It is possible, in particular, to separate the contributions for trigonal BO3 and tetrahedral BO4 units to determine the relative fractions of both, and to use the isotropic chemical shift values as a sensitive probe for the nearest and next nearest environments of the boron atoms. The potential of the method has been demonstrated for some borate and borosilicate glasses prepared by the alkoxide gel techniques.