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The mechanochemical bromination of a heterocyclic sulfoximine is studied by ex-and in-situ solid-state NMR spectroscopy. A clean and fast reaction is observed in a mixer mill, which can alternatively be induced either using the centrifugal pressure of magic-angle spinning or by solely magnetic stirring the solid entities.

This paper describes the preparation of a transparent glass‐ceramic from the SiO2‐K2O‐ZnO‐Al2O3‐TiO2 system containing a single crystalline phase, gahnite (ZnAl2O4). TiO2 was used as a nucleating agent for the heat‐induced precipitation of gahnite crystals of 5‐10 nm. The evolution of the ZnAl2O4 spinel structure through the gradual formation of Al‐O bonds was examined by infrared spectroscopy. The dark brown color of the transparent precursor glass and glass‐ceramic was eliminated using CeO2. The increase in transparency of the CeO2‐doped glass and glass‐ceramics was demonstrated by UV‐visible absorption spectroscopy. EPR measurements confirmed the presence of Ce3+ ions, indicating that CeO2 was effective in eliminating the brown color introduced by Ti3+ ions via oxidation to Ti+4. The hardness of the glass‐ceramic was 30% higher than that of the as‐prepared glasses. This work offers key guidelines to produce hard, transparent glass‐ceramics which may be potential candidates for a variety of technological applications, such as armor and display panels.

The structure of crystalline and amorphous materials in the sodium (Na) super-ionic conductor (NASICON) system Na1+xAlxGe2−x(PO4)3 with x = 0, 0.4 and 0.8 was investigated by combining (i) neutron and X-ray powder diffraction and pair-distribution function analysis with (ii) 27 Al and 31 P magic angle spinning (MAS) and 31 P/ 23 Na double-resonance nuclear magnetic resonance (NMR) spectroscopy. A Rietveld analysis of the powder diffraction patterns shows that the x = 0 and x = 0.4 compositions crystallize into space group type R 3 whereas the x = 0.8 composition crystallizes into space group type R 3c. For the as-prepared glass, the pair-distribution functions and 27 Al MAS NMR spectra show the formation of sub-octahedral Ge and Al centered units, which leads to the creation of non-bridging oxygen (NBO) atoms. The influence of these atoms on the ion mobility is discussed. When the as-prepared glass is relaxed by thermal annealing, there is an increase in the Ge and Al coordination numbers that leads to a decrease in the fraction of NBO atoms. A model is proposed for the x = 0 glass in which super-structural units containing octahedral Ge (6) and tetrahedral P (3) motifs are embedded in a matrix of tetrahedral Ge (4) units, where superscripts denote the number of bridging oxygen atoms. The super-structural units can grow in size by a reaction in which NBO atoms on the P (3) motifs are used to convert Ge (4) to Ge (6) units. The resultant P (4) motifs thereby provide the nucleation sites for crystal growth via a homogeneous nucleation mechanism.

This work reports structural and lithium-ion mobility studies in NASICON singleor multiple phase Li 1+x M x Ge 2−x (PO 4 ) 3 (M = Ga 3+ , Sc 3+ , Y 3+ ) glass-ceramics using solid-state NMR techniques, X-ray powder diffraction, and impedance spectroscopy. X-ray powder diffraction data show the successful incorporation of Ga 3+ and Sc 3+into the Ge 4+ octahedral sites of the NASICON structure at the levels of x = 0.5 and 0.4, respectively. The glass-to-crystal transition was further characterized by multinuclear NMR and electrical conductivity measurements. Among the studied samples, the gallium-containing glass-ceramic presented the highest DC conductivity, 1.1 × 10 −4 S/cm at room temperature, whereas for the Sc-containing samples, the maximum room temperature conductivity that could be reached was 4.8 × 10 −6 S/ cm. No indications of any substitution of Ge 4+ by Y 3+ could be found. K E Y W O R D S ionic conductivity, nuclear magnetic resonance, phosphates, structure How to cite this article: d'Anciães Almeida Silva I, Nieto-Muñoz AM, Rodrigues ACM, Eckert H. Structure and lithium-ion mobility in Li 1.5 M 0.5 Ge 1.5 (PO 4 ) 3 (M = Ga, Sc, Y) NASICON glass-ceramics. J Am Ceram Soc. 2020;103:4002-4012. https ://doi.

In recent years it was shown that mechanochemical strategies can be beneficial in directed conversions of organic compounds. Finding new reactions proved difficult, and due to the lack of mechanistic understanding of mechanochemical reaction events, respective efforts have mostly remained empirical. Spectroscopic techniques are crucial in shedding light on these questions. In this overview, the opportunities and challenges of solid‐state nuclear magnetic resonance (NMR) spectroscopy in the field of organic mechanochemistry are discussed. After a brief discussion of the basics of high‐resolution solid‐state NMR under magic‐angle spinning (MAS) conditions, seven opportunities for solid‐state NMR in the field of organic mechanochemistry are presented, ranging from ex‐situ approaches to structurally elucidate reaction products obtained by milling to the potential and limitations of in‐situ solid‐state NMR approaches. Particular strengths of solid‐state NMR, for instance in differentiating polymorphs, in NMR‐crystallographic structure‐determination protocols, or in detecting weak noncovalent interactions in molecular‐recognition events employing proton‐detected solid‐state NMR experiments at fast MAS frequencies, are discussed.This article is protected by copyright. All rights reserved

Mechanical forces, including compressive stresses as one of the most important consequences, have a significant impact on chemical reactions. Besides the preparative opportunities, mechanochemical conditions benefit from the absence of any organic solvent, the possibility of a significant synthetic acceleration and unique reaction pathways. Together with an accurate characterization of ball-milling products, the development of a deeper mechanistic understanding of the occurring transformations at a molecular level is critical for fully grasping the potential of organic mechanosynthesis. In this vein, we studied a bromination of a cyclic sulfoximine in a mixer mill and used solid-state nuclear magnetic resonance (NMR) spectroscopy for structural characterization of the reaction products. Magic-angle spinning (MAS) NMR was applied for elucidating the product mixtures taken from the milling jar without introducing any further post-processing on the sample-of-interest. Ex-situ 13C-detected NMR spectra of ball-milling products showed the formation of a rather crystalline solid phase with the regioselective bromination of the S-aryl group of the heterocycle in position 4. Completion is reached in less than 30 minutes as deduced from the NMR spectra. The bromination can also be achieved by magnetic stirring, but then, a longer reaction time is required. Mixing the solid educts in the NMR rotor allows to get in-situ insights into the reaction and enables the detection of a reaction intermediate. The pressure alone induced in the rotor by MAS is not sufficient to lead to full conversion and the reaction occurs on slower time scales than in the ball mill, which is crucial for analysing mixtures taken from the milling jar by solid-state NMR. Our data suggest that on top of centrifugal forces, an efficient mixing of the starting materials is required for reaching a complete reaction.

Glasses and glass-ceramics of composition Na 3+3x−y RE 1−x P y Si 3−y O 9 were synthesized using RE = Sc and Y, x = 0.4, and y = 0.0 and 0.3 to obtain multiple-phase glass-ceramics containing the highly conducting Na 5 RESi 4 O 12 (N5) phase. In addition, the two model compounds Na 5 ScSi 4 O 12 and Na 5 InSi 4 O 12 were synthesized. Samples were characterized at two distinct annealing stages using X-ray powder diffraction, electrical conductivity measurements, and multinuclear solid-state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The N5 phase is dominantly formed for Sc-containing glass-ceramics (both with y = 0.0 and 0.3) at crystallization temperatures above 900 • C. For the other glass-ceramics, the crystallized phases were dominantly Na 3 RESi 2 O 7 (N3), RE = Sc and Y, and Na 9 YSi 6 O 18 (N9) phases. 29 Si MAS-NMR peak assignments were done with the aid of 29 Si{ 45 Sc} rotational echo adiabatic passage double resonance (REAPDOR) experiments. 29 Si and 23 Na MAS-NMR spectra reveal complex phase compositions and local environment distributions, which could be largely assigned based on known semiempirical chemical shift correlations with average Si-O and Na-O bond distances. 31 P MAS and 31 P{ 45 Sc} REAPDOR NMR results suggest the presence of orthophosphate groups, arguing against the literature model of isostructural substitution of silicon by phosphorus in the N5 phase.