Recent progress in solid-state nuclear magnetic resonance of half-integer spin low-γ quadrupolar nuclei applied to inorganic materials

An overview is presented of recent progress in the solid-state nuclear magnetic resonance (NMR) observation of low-γ nuclei, with a focus on applications to inorganic materials. The technological and methodological advances in the last 20 years, which have underpinned the increased accessibility of low-γ nuclei for study by solid-state NMR techniques, are summarised, including improvements in hardware, pulse sequences and associated computational methods (e.g., first principles calculations and spectral simulation). Some of the key initial observations from inorganic materials of these nuclei are highlighted along with some recent (most within the last 10 years) illustrations of their application to such materials. A summary of other recent reviews of the study of low-γ nuclei by solid-state NMR is provided so that a comprehensive understanding of what has been achieved to date is available.

Nano metal fluorides: small particles with great properties

The recently developed fluorolytic sol–gel route to metal fluorides opens a very broad range of both scientific and technical applications of the accessible high surface area metal fluorides, many of which have already been applied or tested. Specific chemical properties such as high Lewis acidity and physical properties such as high surface area, mesoporosity and nanosize as well as the possibility to apply metal fluorides on surfaces via a non-aqueous sol make the fluorolytic synthesis route a very versatile one. The scope of its scientific and technical use and the state of the art are presented.

A Combined 25 Mg Solid-State NMR and Ab Initio DFT Approach to Probe the Local Structural Differences in Magnesium Acetate Phases Mg(CH3 COO)2 ⋅ nH2 O (n=0, 1, 4)

Multinuclear (¹ H, ¹³ C, ²⁵ Mg) solid-state NMR data is reported for a series of magnesium acetate phases Mg(CH₃ COO)₂  ⋅ nH₂ O (n=0 (two polymorphs), 1, 4). The central focus here is ²⁵ Mg as this set of compounds provides an expanded range of local magnesium coordinations compared to what has previously been reported in the literature using NMR. These four compounds provide 10 distinct magnesium sites with varying NMR interaction parameters. One of the anhydrous crystal structures (α) has an MgO₇ site which is reported, to the best of our knowledge, for the first time. For those phases with a single crystal structure, a combination of magic angle spinning (MAS) NMR at high magnetic field (20 T) and first principles density functional theory (DFT) calculations demonstrates the value of including ²⁵ Mg in NMR crystallography approaches. For the second anhydrate phase (β), where no single crystal structure exists, the multinuclear NMR data clearly show the multiplicity of sites for the different elements, with ²⁵ Mg satellite transition (ST) MAS NMR revealing four inequivalent magnesium environments, which is new information constraining future refinement of the structure. This study highlights the sensitivity of ²⁵ Mg NMR to the local environment, an observation important for several sub-disciplines of chemistry where the structural chemistry of magnesium is likely to be crucial.

The non-aqueous fluorolytic sol-gel synthesis of nanoscaled metal fluorides

This review article focuses on the mechanism of the non-aqueous fluorolytic sol gel-synthesis of nanoscopic metal fluorides and hydroxide fluorides. Based on MAS-NMR, XRD, WAXS and SAXS investigations in combination with computational calculations, it is shown that a stepwise replacement of alkoxide by F-ions takes place resulting in the formation of a large variety of metal alkoxide fluoride clusters, some of them being isolated and structurally characterised. It is shown that these nanoscopic metal fluorides obtained via this new synthesis approach exhibit distinctly different properties compared with their classically prepared homologues. Thus, extremely strong solid Lewis acids are available which give access to new catalytic reactions with sometimes unexpectedly high conversion degrees and selectivity. Even more interestingly, metal hydroxide fluorides can be obtained via this synthesis route that are not accessible via any other approach for which the hydroxide to fluoride ratios can be adjusted over a wide range. Optically fully transparent sols obtained in this way can be used for the first time to manufacture antireflective coatings, corundum ceramics with drastically improved properties as well as novel metal fluoride based organic-inorganic composites. The properties of these new fluoride based materials are presented and discussed in context with the above mentioned new fields of application.

The effect of electron correlation on the adsorption of hydrogen fluoride and water on magnesium fluoride surfaces

Periodic DFT and local MP2 calculations elucidate the role of electron correlation in the adsorption of H₂O and HF on MgF₂ surfaces.