Recent Advances in Solid-State 25Mg NMR Spectroscopy

Billion‐Fold Enhancement in Sensitivity of Nuclear Magnetic Resonance Spectroscopy for Magnesium Ions in Solution

“…This may be considered to be an artifact of the current measurements, but could also be exploited as an internal chemical-shift reference, which gives a resonance conveniently far from the range where chemically and biochemically interesting resonances are observed; therefore, no serious overlap of signals will occur. The other resonance is then found in the same range as that observed for Mg 2 + -containing compounds in conventional NMR spectroscopy, [21] that is, within approximately 100 ppm of an 11 m MgCl 2 reference, presumably reflecting the coordination of the carboxylates of the ionic-liquid anion.…”

“…The difference in resonance frequency between the two signals corresponds to a chemical shift of approximately 1300 ppm, which is far beyond the usual range of chemical shifts of about 200 ppm observed for Mg 2 + -containing compounds when using conventional 25 Mg NMR spectros-copy. [21] However, it is well established that the Knight shift, owing to polarization of conduction electrons in metals, is typically of the order of 1000 ppm; it is also reported to range from 990 to 1750 ppm, specifically for 25 Mg in Mg metal as well as in alloys of Mg and Al. [22] This correlates well with the discussion concerning the loss of beam in the aluminum pipe, vide supra, indicating that a fraction of 31 Mg + is deposited in the aluminum.…”

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)

“…Consideration of the overestimation observed by Cahill et al (C Q calc = 1.225C Q exp À0.13 (in MHz)) brings the calculated C Q values into much closer agreement with experimental ones. [17,18] However, the 25 Mg isotropic chemical shift for the MgO 7 site also falls within the MgO 6 range, indicating that caution must be taken when assigning coordination number of MgO x sites based solely on the chemical shift. [17,18] However, the 25 Mg isotropic chemical shift for the MgO 7 site also falls within the MgO 6 range, indicating that caution must be taken when assigning coordination number of MgO x sites based solely on the chemical shift.…”

“…Calculations indicated that the second site although still an MgO 6 had a much larger quadrupolar interaction (~5 times greater) and needed a variable offset cumulative spectroscopy (VOCS) approach to detect it as a much broader underlying second resonance. [17,18] Hence there looks to be significant promise in developing 25 Mg solid-state NMR as a probe of local structure, such that extending the combination of experimental and computational data from well-defined local magnesium environments will further increase the confidence and utility of this approach. Simulations showed that the 25 Mg NMR parameters are able to distinguish between the different vacancy arrangements on the magnesium sites.…”

Coordination Networks Based on Boronate and Benzoxaborolate Ligands

“…Most of the crystalline structures mentioned above have been characterized using 25 Mg, 43 Ca and 87 Sr solid state NMR, as illustrated in Figure 10. Alkaline earth metals are very challenging for NMR, due to their low resonance frequency, low natural abundance, and/or large quadrupole moment, and their isotopic enrichment is costly [33][34][35]. Nevertheless, 25 Mg, 43 Ca, and 87 Sr NMR Figure 9.…”