Local Structure of Nanoscopic Magnesium Hydroxide ­Fluorides Studied by Natural Abundance ²⁵Mg Solid State NMR Spectroscopy

Abstract

Along with X-ray diffraction measurements, 25 Mg solid state NMR experiments were performed in natural abundance at 9.4 T on crystalline and mechanically milled samples of MgO, Mg(OH) 2 , MgF 2 , and magnesium hydroxide fluorides Mg(OH) x F 2-x prepared on mechanochemical and sol-gel syntheses routes. In addition to single pulse and spin-echo sequences, both static 1 H-25 Mg CP and 19 F-25 Mg CP measurements allowed the registration of 25 Mg spectra in attractive 694 short measurement times. Although an assignment of different magnesium species in magnesium hydroxide fluorides is only hardly possible, position and line shapes of 25 Mg spectra of magnesium hydroxide fluorides reflect chemically reliable trends. All samples studied here show a sixfold fluorine, oxygen, or mixed fluorine / oxygen coordination of magnesium, also in highly disordered samples.

A Combined 25Mg Solid‐State NMR and Ab Initio DFT Approach to Probe the Local Structural Differences in Magnesium Acetate Phases Mg(CH3COO)2 ⋅ nH2O (n=0, 1, 4)

“…In the current study, multinuclear ( 1 H, 13 C, 25 Mg) solid-state NMR is reported for Mg(OAc) 2 · 4H 2 O, Mg(OAc) 2 · H 2 O and Mg(OAc) 2 with an emphasis on 25 Mg. The crystal structures based on single crystal work has been reported for these phases.…”

“…1 H MAS NMR spectra were recorded using a depth pulse sequence. 13 C and 1 H MAS NMR spectra (10 kHz MAS, 16.4 T) were run before and after the 25 Mg experiments and showed no phase change as a result of spinning the samples for lengthy periods, indicating that the water remains bound to the magnesium. 25 Mg solid-state NMR spectra were also obtained at 20.0 T on a Bruker Avance 850 MHz spectrometer operating at a Larmor frequency of 52.0 MHz.…”

“…[8,9] Both these studies [8,9] combined experimental and computational approaches, showing that the NMR parameters (usually both the chemical shift and quadrupolar) could be extracted and were sensitive to the local environment around magnesium. [13] 25 Mg solid-state NMR has proved effective in studying magnesium-containing MOFs. For enstatite (MgSiO 3 ), all three polymorphic forms contain two crystallographically-distinct magnesium sites, but MAS NMR spectra at both 14.1 and 20.0 T only showed a single site.…”

“…[12] Changes of magnesium coordination in nanoscopic magnesium hydroxide fluorides produced by different chemical routes could be readily followed by 25 Mg NMR. [13] 25 Mg solid-state NMR has proved effective in studying magnesium-containing MOFs. Examples include the effect of guest species on the magnesium environment in CPO-27, [14] probing the paraelectric-ferroelectric transition in [NH 4 ][Mg(HCOO) 3 ] [15] and demonstrating the unambiguous formation of five-coordinate magnesium centres in activated Mg 2 (dobpdc).…”

Theoretical study on the morphology of MgF2 nanocrystals at finite temperature and pressure

“…Sol-gel synthesized magnesium fluoride consists of agglomerated nanocrystals in the rutile structure, the surface properties of which can be controlled through changes in the synthetic conditions, e.g. temperature and partial pressure of hydrogen fluoride and water [6][7][8][9]. By now well established, this method has opened new possibilities for the production of high-surface, thus highly active, nanomaterial with tunable properties for heterogeneous catalysis applications.…”